Status as of 6/29/2011

After a couple of attempts to begin recirculating the processed water, it appears all the piping leaks have been fixed.  They are now injecting a mix of processed water and fresh water into the Unit 1, 2, and 3 reactors for cooling. 

Construction of the structure around the Unit 1 reactor building has begun.  A construction crane is now in place for lifting a steel framework which is being preassembled offsite.  Panels of one millimeter-thick polyester fiber panes will be attached to the frame.  The structure will be about 162 feet high and is expected to be completed by late September.

Status as of 6/27/2011

Water from the water treatment plant was injected into the reactors for one and a half hours before the discovery of leaking pipes halted the recycle.  The original schedule had anticipated the recycling would be working by mid June.  An estimated 110,000 tons of water has collected in the basements and tunnels in the plant and 1850 tons has been processed.

Status as of 6/20/2011

The water treatment plant was started on Friday, but was stopped after 5 hours because a component reached its limit for radioactive contamination much faster than expected.  The contaminated water is to undergo three processes, the first separates the oil and water, the second reduces the radiation by absorbing the cesium, and the third removes the salt and other impurities.  The processed water will be stored and eventually used to cool the reactors.  The oil in the water is from the machinery which is in the basements of the flooded buildings.  The salt is from the seawater which was injected into the reactor for several days following the earthquake until a supply of fresh water could be obtained.  The cesium and other radioactive materials are from the damaged fuel and appeared to be at concentrations higher than TEPCO anticipated.  While it is expected that the water treatment plant will concentrate radioactive materials, they need to monitor the radiation level in order to avoid the problem of the ‘filter’ becoming too radioactive to be handled and disposed of properly.

The Unit 2 reactor building doors were opened to reduce the humidity in the building.  Efforts to cool the spent fuel pool apparently did not remedy the situation previously reported May 23.  The humidity was at 99%.  They want to reduce it to below 70% to create better working conditions.  

Question: What is the difference between a nuclear melt down and a melt through? What are the implications?

There is a bit of a difference in that a melt through is where the fuel melts through the lower core plate and through the lower head of the pressure vessel into the primary containment.  It makes clean up a bit more challenging.  There may be some additional releases to the environment.  However, there is nothing necessarily catastrophic about this problem.  It's a bit like the difference in a turbine explosion of having all the blades contained, or a few actually being ejected past the engine containment.  Either way, your day is going to suck.   This is not the nuclear equivalent of a disk explosion.

There is actually some benefit to having some melt through because the fuel is now spread out and you have a larger surface to volume ratio allowing more cooling potential of radio nuclide decay heat.   The fuel that falls to the bottom of containment is also under water and in contact with a huge heat sink.  Part of the trick to cooling the fuel is lots of wetted surface area.

See the diagram below.  The reactor pressure vessel (brown) is inside the primary containment (yellow).  Leaking out of the reactor vessel does not mean being released to the environment.  Assuming the primary containment is still substantially or completely intact, melting through the reactor vessel into the drywell should not cause much additional release to the environment.

The primary containment is protected from steam overpressure by venting into the Torus which is partially filled with cold water.  The steam released from the RV into containment during an accident is vented underwater in the torus and condenses reducing its volume and controlling pressure in the primary containment.

Status as of June 16, 2011

The water processing facility is undergoing final testing and could start operations by tomorrow.  After processing, the radioactivity in the water should be reduced between one-1000^th and one-10,000^th.  It will then be transferred to makeshift tanks at the plant and be used for cooling the fuel.  TEPCO estimates more than 110,000 tons of radioactive water has accumulated and will need to be processed.

TEPCO is also working on installing a system to clean the water in the intake bay.  It is pumping the water through zeolite to capture the radioactive cesium which has escaped into the bay.

Assembly of the framing which will support a polyester fabric for Unit 1 reactor building has begun.  The frame is 120 ft x 120 ft x 150 feet high.  After it is complete it will be lifted and placed over the damaged building then the fabric will be put into place.

Status as of June 8, 2011

Testing of components in the facility for processing the radioactive water has begun.  June 15 is the target date for it to begin operations.  The facility will remove the radioactive cesium and flocculate other radioactive substances with a capacity of 1200 tons/day.  The plant is collecting 500 tons/day from the constant injection of water into the reactors.  The current inventory of water for processing is 105,000 tons.  Without any additional water processing taking place, it will take over 100 days to process the water already collected.  Some of the processed water will be injected back into the reactor, but there will be a surplus of processed water which will need to be stored. 

Remote controlled equipment continues to be used to cleanup debris on the site.  The debris needs to be surveyed for radioactivity because when hydrogen explosions scattered contaminated materials from the reactor buildings.  There are guidelines for the disposal of radioactive materials which are based on the level and type of radioactivity which makes the cleanup effort more difficult.   

Status as of 6/2/2011

The water level in the Unit 2 and 3 tunnels is 28 cm and 24 cm from the top of the tunnel and rising.  They are considering using the basements of a couple of buildings for additional storage.  Earlier in the week Fukushima experienced a typhoon, so additional water entered into the damaged buildings.  The water processing facility is still a couple of weeks away from being ready.  Groundwater surveillances have been increased to determine whether any of the buildings are leaking radioactive water.

A heat exchanger has been installed for cooling the Unit 2 spent fuel pool.  The temperature of the pool is down to 58°C.  The lower temperature will reduce the humidity in the Unit 2 reactor which needed to be lowered to facilitate working within the building.

It was estimated that cleaning up Fukushima Daiichi and the surrounding area would cost $250 billion over 10 years.  The estimate included $54 billion for buying all the land within 12.4 miles of the plant.  This indicates the radioactive isotopes released from the plant have contaminated the land and people living in the area would receive levels of radiation in excess of allowable limits

Status as of 5/27/2011

After suspending pumping of water into the waste water storage facility, the water level in the storage facility dropped 4.8 cm in 20 hours.  TEPCO’s initial investigation did not identify where the radioactive water was leaking.  They have now reported finding the water in another building which is connected to the storage facility by an underground passage.  Currently the pumping of water out of buildings is suspended.

Status as of 5/24/2011

TEPCO analyzed the data and interviewed operators to put together the sequence of events after the March 11 earthquake. They have determined Unit 1 sustained a full meltdown and the molten mass is at the bottom of the reactor vessel.  Units 2 and 3 have damaged fuel and some fuel is melted down but there was always a sufficient level of water in the reactors to prevent a total meltdown.  This analysis is important because it affects the methods which will be employed for maintaining cooling and the subsequent removal of the highly radioactive fuel and materials in the reactor.

The pumping out of the Unit 2 and 3 reactor buildings will be suspended by the end of the week because the onsite storage capacity will be full.  The water processing facility is under construction and expected to be completed by mid-June.  Water continues to be injected into Units 1, 2, and 3.  No plans have been announced for how they will handle the additional water.

Status as of 4/23/2011

The Unit 2 reactor building is mostly intact and as a result the warm water in the spent fuel pool is causing high humidity inside, which is limiting the workers stay time.  TEPCO will be installing a heat exchanger to cool the Unit 2 spent fuel pool to improve working conditions prior to working on the reactor cooling system.

Work is beginning on to reinforce the Unit 4 spent fuel pool.  30 steel supports will be installed below the spent fuel pool.

The MegaFloat structure pictured in the April 20 update below is now moored at the site.  It will be used to store low level waste water.

Status as of 5/18/2011

Today’s status will summarize the work on all the Fukushima Daiichi Units.

The original plan to fill the reactor containment structures with water to a depth high enough to cover the fuel in the reactor vessels has been abandoned because of damage to the containment structures from the hydrogen explosions.  The new plan calls for circulating water from the reactor buildings or containment into the reactor vessel piping which will cool the fuel and then leak out of the reactor vessels to the reservoir of water they are tapping.  The new plan requires continuous pumping of water while the abandon plan required maintaining water level but would not need a continuous injection of water. 

The Unit 1, 2, and 3 reactors contain damaged and melted fuel.  Data is now available for Unit 1 which indicates extensive melting took place when power was lost and the water covering the fuel boiled off.  The cladding and fuel overheated causing it to burn, releasing hydrogen and creating a molten mass which flowed to the bottom of the reactor vessel.  The molten mass melted holes in welded seams at the bottom of the vessel.  The injection of water into the reactor vessel is keeping the molten mass cool.  Because the molten mass continues to produce heat from the radioactive isotopes, cooling will need to continue.  Water continues to be injected into the three reactors at rates between 1800 to 2700 gallons/hour.

Work has begun on the putting in the circulating water system for Unit 1.   They have started work on covering the damaged Unit 1 reactor building with construction fabric.  The reactor building basement is flooded with 12 feet of radioactive water. 

Four workers entered the Unit 2 reactor building for the first time since the earthquake.  They did a survey of the building to map the radiation levels in order to plan the next tasks.  The basement of the building and a piping tunnel are flooded.  

130 tons (34,000 gallons) were pumped out of the Unit 3 reactor building yesterday lowering the level about 0.5 inches.  There is about 56 inches of water remaining.  Water was found to be leaking into the ocean on Monday.  There was no status on whether the leak has been stopped. TEPCO has indicated the silt barrier for capturing some of the radioactive contaminants is not working.  They are continuing to use zeolite to absorb the cesium.

The hydrogen explosion in the Unit 4 reactor building has now been attributed to hydrogen from Unit 3 which entered the building via a common duct.  A video of the fuel in the Unit 4 spent fuel pool does not show the expected damage to the fuel which could have produced the amount of hydrogen needed to cause the explosion.  The water level in the Unit 4 spent fuel pool is being maintained by the injection of water every other day. 

Water is being pumped from the Units 5 and 6 buildings to makeshift tanks.  This water is not highly radioactive.

Status as of May 16, 2011

TEPCO has concluded that most of the fuel in the Unit 1 reactor is damaged.  The original estimate of 55% core damage was low based on the data now available.  The fuel is at the bottom of the reactor vessel and the heat from the molten mass melted holes through the bottom of the vessel at welded seams.  The damaged fuel is being cooled by the continuous water injection into the vessel and is being maintained below 100°C.  On Sunday the injection was increased from 8 to 10 tons/hour (2100 – 2600 gal/hr) to quantify the cooling affects.  The increased flow decreased the temperature of the fuel at the bottom of the vessel by 15° C.  The plan to submerge the fuel by filling the reactor containment has been scuttled because of the leaking water.  Two alternate plans are being considered.  Both will continue to inject water into the reactor vessel, but the first would circulate the water already in the reactor containment through a heat exchanger and then into the reactor.  The second would draw the water from the flooded reactor building which has accumulated over 12 feet of water in the basement.

Radioactivity in water samples from the inlet bay near Unit 3 are on the rise again indicating leakage from the plant.  Radioactive cesium was measured to be 2400 times above the allowable limits.  TEPCO also reported Iodine-131 in water samples taken near the Unit 2 intake at 2,100 times the legal limits.  We will be watching for an explanation of this sample because the radioactive iodine from the fuel should have decayed to negligible amounts since the March 11 earthquake shutdown the reactors.  

Status as of 5/12/2011

The flooding of the Unit 1 reactor containment has reached a level 3 feet below the bottom of the fuel in the reactor.  When the final 150 tons of water was added to cover the fuel, the level gauge did not show an increase.  TEPCO initially thought the level gauge was not reading properly, but has since seen a rise in the water level in the reactor building and determined the gauge to be working.  This water level is too low to provide the stable core cooling which was planned.  The Unit 1 reactor containment is leaking into the reactor building.  A revised plan is expected to be announced next week.  Work in the Unit 1 reactor building has been limited by high radiation levels which limits the time workers can spend on a task.  They have been using lead blankets for shielding between the radiation source and the worker, a standard industry practice.

Two days ago the water levels in the Unit 3 turbine building started to drop.  On Thursday they found the leak, water was flowing through an electric cable conduit into a pit which eventually flowed into the inlet bay.  The leak has been plugged.  The volume of highly radioactive water which was released was not reported.

Japan’s Prime Minister has called for the shutdown of the Hamaoko nuclear plant because it does not meet the current standards for earthquake and tsunami protection.  The plant will need to be brought up to the current standards before it can be restarted.  There are 5 units at the site, but the 2 oldest units have already been retired.  Unit 3 was already shutdown for maintenance.  Units 4 and 5 are now being shutdown.  This will create a electric deficit for the utility which owns the plant which will need to be addressed.

Status as of 5/9/2011

The air in the Unit 1 reactor building has been filtered enough to allow workers to enter the building with respirators rather than supplied air tanks.  TEPCO has posted a video which shows the air filtration system.  http://www.youtube.com/watch?v=6VtwFsKT93s   Radiation surveys are being taken to map out the radiation levels within the building.  The radiation levels will determine the time and precautions workers will take when working in an area.  One task for today is to calibrate the gauge which provides an indication of the reactor containment vessel water level.  They will be inspecting the conditions of pipes and valves which will be used for to cool the reactors with the cooling system being built.

A video of the Unit 4 SFP has also been released.  The video was taken with a submersible camera which was attached to the end of the boom which is injecting water into the pool .  It shows the debris which has settle on top of the fuel racks.  http://www.youtube.com/watch?v=qCY0xQRZ1UY  At 41 seconds, the bales on the top of the fuel assemblies are being videoed.  The surface temperature of the pool is about 81° C.

Status as of 5/5/2011

Workers entered the Unit 1 reactor building for the first time since March 11 when the tsunami and subsequent hydrogen explosion damaged the roof of the building.  The area they entered provides access to the pipes which inject water into the reactor.  The workers were setting up air filtering equipment and ducting to begin cleaning the contaminated air.  The workers were wearing air packs and protective clothing and were limited to working for 10 minutes before reaching radiation exposure limits.  Several teams were needed to complete the equipment installation.  The air will be filtered for several days to remove the particulates from the air in order to make the areas safer for the work of connecting heat exchangers to the pipes leading to the reactor.

Status as of 5/4/2011

Updates on evolutions within the plant are not being reported.  We can only assume they are continuing to pump water from the tunnels.

The radioactive cesium levels from the inlet bay at Daiichi are not trending down as expected.  Cesium levels should be trending down because of water dilution and the zeolite absorber placed in the bay last week.  The zeolite was expected to concentrate the cesium by absorbing it.  TEPCO will be lowering another canister of zeolite with a pump to circulate the water through the absorber in an attempt to capture more cesium.  The concentration of cesium may not be changing because contaminated water continues to be leak from the site.  Below is a picture of the inlet bay.  The silt fence installed to capture sediment can be seen floating across the bay.   

Inlet Bay (credit: TEPCO)

Status as of 5/1/2011

No gauges or instrumentation were built into the reactor containments to provide the water level for flooding the fuel so TEPCO has a plan to install a gauge.  An air filtering system is being installed in the Unit 1 reactor building to reduce airborne contamination.  This will make it safer and increase the stay time for workers.  Plans call for installing a water level gauge and a heat exchanger for removing the heat in the water.

Government officials are facing more protests about the situation.  In response to raising the allowable radiation level for children in the affected areas parents delivered a bag of contaminated soil to the parliament.  A top level advisor resigned in protest to the government actions.  A group of shareholders proposed a motion calling for TEPCO to close all its nuclear plants.  

Status as of 4/29/2011

The filling of the Unit 1 reactor containment continues at 10 tons per hour. 

Pumping of water out of the Unit 2 tunnel into the waste water treatment facility continues.  After 9 days of pumping the water level has dropped only 10 cm.  They have been working on fortifying the area around the waste water treatment facility in case another tsunami should strike because a large tsunami could breach the facility which would release the highly radioactive water.  The water levels in the Unit 3 and 4 tunnels have been rising.  The level in the Unit 3 tunnel rose 6 cm in 3 days. It doesn't look like they are getting ahead of the amount of water pooled in the buildings and tunnels. 

Status as of 4/27/2011

The water level in the Unit 1 reactor containment vessel has reached 18 feet deep.  It will need to reach 54 feet to cover the fuel in the reactor.  Robots are being used to inspect for seepage and leakage.  Plans call for increasing the flow from 6 tons/hour to 14 tons/hour.   

The city of Koriyama which is 30 miles from the site will be removing 1 inch of topsoil from schoolyards to remove contaminated soil in order to allow children to resume outdoor activities.  This is an example of how the radioactive releases from Daiichi impacts the lives outside of the restricted areas.

Status as of 4/26/2011

The highest priority work at Daiichi is the removal of highly radioactive water from of the Unit 2 tunnel and reactor building because it prevents access to equipment areas.  Pumping has been taking place around the clock, but the level in the Unit 2 tunnel has not dropped in the last few days.  The radiation levels prevent taking any action to identify and stop the additional water from entering the tunnel.  Meanwhile water levels in Unit 3 and 4 tunnels are rising and are close to reaching a level which will require removal, but there no storage tanks available.  TEPCO will need to resolve the water inventory problem.  Water is continuously being added to the Units 1, 2, and 3 reactors to cool the fuel and water is periodically injected into the Units 1, 2, 3, and 4 spent fuel pools.  The water is boiling off into steam, collecting in the reactor containment structure, collecting in a spent fuel pool, or leaking out into the tunnels and reactor buildings.  Somehow they need to identify, quantify, and resolve the how the water is leaking out.

When the hydrogen explosions destroyed the Unit 1, 3, and 4 reactor buildings, radioactive particles were released and spread across the Daiichi site.  TEPCO completed a test which proved a resin sprayed on the ground reduces the spread of contamination from wind and rain.  They will begin spraying the entire site using remotely operated equipment.

Status as of 4/25/2011

The Fukushima Daiichi site cleanup will take place overall several years so the systems for remediation are being designed to sustain potential earthquakes, tsunamis, and site blackouts.  Electric busses are being wired with redundant taps to the grid, equipment is being situated on higher ground, and structures will need to be capable of withstanding earthquakes.  The plan calls for separating the radioactive water based of the level of radioactivity.  The mega-float barge will be used for low level storage.  High level waste water will be filtered and cooled for recirculation into the reactors.

The plan for cooling the fuel in the reactors is to flood the reactor containment structure with enough water to cover the top of the fuel in the reactor vessel.  Below is a simplified diagram showing the reactor containment structure which is the light blue area shaped like a light bulb.  The current water level is estimated to be 18 feet which is below the reactor vessel.   Concerns about the ability of a flooded reactor containment structure to withstand an earthquake are being addressed.  Units 1 will be flooded first.  Unit 2 cannot be flooded until the containment leaks are repaired.

Additional information has been provided about the Unit 4 spent fuel pool structure.  Photos taken by a drone helicopter showed structural damage to the Unit 4 reactor building which has raised concerns about the integrity of the Unit 4 spent fuel pool.  In an effort to reduce the mass of water in the pool, the criteria for adding water has been changed to be temperature based in order to determine an equilibrium point between maintaining cooling and minimizing the amount of water.  A plan is being drawn up to install additional supports below the pool.

TEPCO released a radiation survey map of the site which will show progress of cleaning up the site.  They have found some highly radioactive concrete chunks which were scattered by the hydrogen explosions.  The radioactive debris is being placed in containers which will eventually be shipped to a radioactive waste site.

Status as of 4/21/2011

6 weeks after the people evacuated for the tsunami warning, the Japanese government is hardening it’s stance on entry into the evacuated area because residents have been making unauthorized forays to their homes.  This exposes them to radiation and raises the potential for spreading radioactive contamination.  Since many households evacuated for the tsunami with only the clothes on their back and will not be able to return for several months, the government is allowing one person from each household a trip to retrieve valuables and important documents.  The population in the 12 mile evacuation zone was 78,200.  The 12 to 18 mile zone population was 62,400. Prior to cleaning up the evacuation zone the Daiichi Units 1, 2, and 3 will need to be on a closed cooling loop and structures in place which contain the atmospheric releases otherwise they risk recontaminating the area.  Because the evacuation zone has been contaminated with isotopes such as cesium, cleanup will consist of surveying soil, excavated contaminated areas, and transporting it to special landfills.  The longer it takes to begin the cleanup, the deeper the radioactive isotopes will leach into the ground.

450 tons of water has been pumped from the Unit 2 tunnel into the waste water facility lowering the level in the tunnel by 3 cm.  Radioactive water has been collecting in a Unit 3 tunnel, rising several centimeters a day.  It will soon reach one meter below ground level.  Also rising water levels in the Unit 5 and 6 turbine buildings are being monitored but is thought to be ground water. 

A Japanese official reported they are looking for ways to shore up the structure below the Unit 4 spent fuel pool to prevent it from collapsing.  The structure may have been weakened from the earthquake and subsequent hydrogen explosions.  Based on the amount of water which has been injected into the pool, we suspect some leakage was occurring.  If aftershocks are weakening the structure and the additional weight of debris cause a massive leak to occur, the scenario of exposing the 1331 spent fuel assemblies to air would be a major setback for stabilizing and cleaning up Daiichi because of the resulting high radiation levels.

Status as of 4/20/2011

210 tons of water was pumped out of the Unit 2 tunnel at a rate of 10 tons/hr (2640 gal/hr).  They will monitor the pumping for leaks and add more pumps over the next few weeks because there are 25,000 tons to pump from the Unit 2 structures and an estimated total of 67,500 tons has collected in the buildings and tunnels of Units 1 through 6.  Areva has been contracted to build an onsite facility to cleanup the water with a target to begin operations in June.  Below is a picture of the Mega-Float structure which will be docked offshore and be used for additional water storage.  It was a public fishing park in Shimizu, Japan.

A remote controlled robot is being used for reconnaissance work inside the reactor buildings.  The robot is outfitted with radiation, temperature, and oxygen sensors, a video camera, and lights.  It has a mechanical arm which enables it to open doors and travels on treads.  It has encountered debris blocking pathways and high humidity fogging up the camera lens.  The information will be used for determining the equipment and precautions which will be needed for worker safety.  In areas of high radiation levels using robots will be essential.  On the plant site, they have been using remote controlled trucks outfitted with scoops to pick up and place debris  into containers.

One area of concern for RGA Labs is the continued reporting of I-131 being found in food and water samples.  The earthquake struck 40 days ago, the natural decay rate of I-131 has eliminated 97% of the isotope from the reactors.  All of the I-131 should not have been released and what has been released is spread over a large area, so they should not be measuring any significant levels of I-131.  If I-131 is still being produced and released into the atmosphere, then the nuclear fission of uranium is still taking place which would indicate the damaged fuel is in a configuration which is not responding to the water injection for cooling.  This is contrary to the measured data which shows the reactors are being cooled and are stable.

photo credit: Kyodo News

Status on 4/18/2011

TEPCO announced a plan to establish cooling and cover the buildings which would take 6 to 9 months.  The condition of the existing plant systems and the high radiation levels in the reactor buildings led to a decision to build a new facility which will cool and reprocess the water being injected into the reactors to establish a closed loop system.  Units 1 and 3 will be put on the new system first.  Unit 2 will first need to have the reactor containment patched before being placed on the cooling system.  The damaged buildings will be temporarily covered with construction tarps while design of a cement structure is developed.  Entry into the reactor buildings is dangerous because of the radiation levels.  A robot was sent into the Unit 1 and 3 reactor buildings which measured radiation levels which limit a human to a 4 to 5 hour stay time before reaching the maximum allowed annual dose.  The robot will be sent into Unit 2 today and where higher radiation levels are expected.

The level of contaminated water collecting in the Unit 2 tunnel rose a few centimeters over the weekend.  We did not see any reports of pumping to the condensers taking place.  Ground water sampling did not see any increase in radiation levels.  TEPCO is preparing the on site waste water treatment plant, which is normally used to cleanup non contaminated water for discharge into the ocean, for holding some of the highly contaminated water.  It provides and additional 30,000 tons (7.9 million gallons) of capacity.

The tens of thousands people evacuated from the area have been told it will be months before they can return to their homes.  Prior to their return the plant needs to be stable with no more radioactive releases and the contaminated grounds must be cleaned up. 
Below is a picture taken by a T-Hawk drone of Unit 4 showing the debris on spent fuel pool area which prevents knowing the water level in the pool.  The green structure is the bridge which spans the pool and is used for lifting the fuel assemblies.  Steam is being produced by the spent fuel.  (reference: http://cryptome.org/eyeball/daiichi-npp8/daiichi-photos8.htm)

Status on 4/15/2011

Precautions take precedence in the pumping out of the tunnels and Unit 2 reactor building.  They are checking for leaks and making sure the ad hoc pumping systems are capable of withstanding any subsequent aftershocks.  The most recent reports do not indicate whether anymore water has been pumped out of the tunnels since Wednesday.

Ground water samples have shown a 5 fold increase in Iodine-131 and a 57 fold increase in Cesium-134 concentration from a sample taken last week.  This is an indication that the leak from the Unit 2 tunnel which was stopped last week has found a flow path into the ground.  

Status on 4/14/2011

In the last week there have been a couple of earthquakes which exceeded 6.  The earthquake and subsequent tsunami warning stopped the reactor cooling and pumping work which highlighted the temporary nature of the systems providing cooling.  Since the prognosis is it will take several months to restore the closed cooling systems, work was done to upgrade the core cooling systems for unmanned operation.  The diesel generators were moved to higher grounds and electrical feeds were improved.  Fresh water continues to be injected into the Unit 1, 2, and 3 cores.  Periodically water is injected into the spent fuel pools to maintain level and cooling.

Recognizing the work and time which will be needed to secure and cleanup Daiichi led to the reclassification Daiichi from a level 5 to 7.  Three Mile Island is a level 5 accident and Chernobyl is a level 7 accident.  The total radioactivity released by Daiichi will not exceed Chernobyl but because the area around Daiichi has a greater population density the affect on the public is much greater.  Additional areas have been evacuated in the last week.

The pumping of water from the Unit 2 reactor building into the condenser was halted by the recent earthquakes but progress has been made.  About 900 of the estimated 6000 tons (1.6m gallons) have been pumped to the condenser.  They have seen the water level drop, but it is also rose overnight due to leaking of the core cooling injection water into the reactor building.

Some metal plates and sediment fences have been installed at the entrance to intake bay of the plant to reduce the amount of radioactivity which may be getting into the ocean.   Normally the intake bay’s flow is into the plant and is used for cooling.  The earthquake and tsunami took out the pumps which draw in the water.  The highly radioactive water leak which was stopped last week was flowing into the intake bay.  The reports on the ocean samples are not showing the decrease in radioactivity from dilution we would expect if there were no additional leakage is occurring from the site.

Status on 4/8/2011

413 cubic meters of nitrogen was injected into the Unit 1 reactor vessel raising the pressure 8 fold which confirms the vessel is intact.  More nitrogen will be added over the next few days.  Plans are being made to do the same for Units 2 and 3 but there are indications that these vessels are not holding pressure which changes the scenario for where the hydrogen could be collecting.

300 tons (~79,000 gallons) of contaminated water remains to be released which will get them a step closer to pumping out the reactor buildings and tunnels.  The plants configuration doesn’t allow them to pump directly from the reactor building to the empty storage tanks.  The water will be staged into the condenser, condensate storage tank, and suppression pool surge tank.

Status on 4/7/2011

The nitrogen injection into the Unit 1 reactor containment has started as a precaution to prevent a buildup of hydrogen and oxygen reaching an explosive concentration. 

The water level in the Unit 2 tunnel rose 5 centimeters in the last 24 hours which is probably a result of the plugging of the leak.  They will be monitoring the tunnel level because an additional 1 meter in the water level would overflow the tunnel.  There are 8000 tons (~2.1 million gallons) more radioactive water to release into the ocean from the storage tanks.  

Status on 4/6/2011

The leak of highly radioactive water through the crack in a cement wall has been stopped with the resin injection into the gravel.  TEPCO is monitoring for new leaks which may be caused by changing the flow path.  They are unable to isolate the pipe from which the water is flowing because of the high levels of radioactivity in the reactor building and they are not sure of how the water is entering into the pipe.  Monitoring of radiation levels in the ocean are ongoing so it is expected the measurements will begin to drop.  The leak was measured at 7 tons per hr which is 1850 gallons per hour. 

In the last week Japan has been engaging experts to assist in addressing the problems at Fukushima Daiichi.  Experts are concerned about salt deposits which may have formed from the sea water cooling.  The salt deposits could be restricting the flow of water in some areas of the reactor reducing the cooling effectiveness of the water.  Hydrogen is being produced from a reaction between the high energy radiation and water.  One of the actions about to take place is the injection of nitrogen into the Unit 1 reactor containment to address concerns about the hydrogen concentration reaching explosive levels. 

There is a recognition that the continuous injection of freshwater for cooling is producing too much highly contaminated water, but without another method for cooling it will continue.  

Status on 4/5/2011

The controlled release of 10,000 tons (which is 2.57 million gallons) of contaminated water has started.  The leak of highly radioactive water has been traced to a cracked pipe.  The water is finding its way through gravel then out a crack in a cement wall into the ocean.  TEPCO is injecting a resin into the gravel which has reduced the flow of water out the crack.  We are concerned that this approach may stop the water from flowing out the crack, but the water will find another path into the ground below the plant which would be a worse problem.  While releasing radioactivity into the ocean is bad, the dilution factor tremendously reduces the immediate problem.  The future problem will be whether the radioactive isotopes like Cesium-137 concentrate in the food chain.  Small fish have been caught with a Cesium-137 amount 5% over the acceptable limit, so fisheries have to suspend catching the sand lance.  Predator fish will consume the sand lance, which will concentrate the Cesium-137 in these larger fish.  With a 30 year half life, the Cesium-137 will be around for quit awhile. 

In an attempt to control the radioactive particles flowing from the plant, TEPCO is considering erecting silt barriers in the ocean.  

Status 4/4/2011

The situation at Fukushima now warrants allowing a release of contaminated water into the ocean which exceeds regulatory limits because it will free up space in the tanks for water which is more contaminated.  TEPCO has been granted permission to release 10,000 tons contaminated water which is being classified as low level contamination, but it exceeds the normal allowable level by 100 times.  Without a cooling system, the continuous injection of water for cooling into the Units 1, 2, and 3 reactors will continue to produce highly contaminated water.  Expect to see additional waivers granted as the inventories of water build up. 

A leak of highly contaminated water directly into the ocean from a pit near Unit 2 was found on April 2.  One report indicated the flow to be 7 tons per hour.  Two attempts were made to plug the leak by dumping plugging materials in a suspected tunnel.  Neither attempt worked.  They have determined the water was coming from multiple paths.  They are now attempting to capture the water which is leaking out by enclosing the pit into which it is spewing and plugging the multiple pathways from the water source.  As with other situations, this work is dangerous because they are dealing with very high levels of radiation.
There are also reports of samples from the ground water taken at the site showing radioactive materials. If this is true, radioactive contaminants in the water table creates a flow path which is very difficult to control. 

Analysis of Fukushima Daiichi

Ron Chin and Bob Abboud of RGA Labs have compiled this analysis of the events at Japan's nuclear plant based on information found on the web and newspaper articles as of March 16.


 
Analysis of the conditions at Japan's Fukushima Daiichi Plant following the earthquake and subsequent tsunami.

Link to daily status	Link to topics
Status on 3/16/2011	What keeps the radioactive materials inside?
Status on 3/18/2011	Is this like Chernobyl?
Status on 3/19/2011	How do iodine tablets protect me?
Status on 3/20/2011	Is there fuel meltdown?
Status on 3/21/2011	Radioactive release vs Exposure to a radioactive source
Status on 3/22/2011	Satellite photos of Fukushima Daiichi
Status on 3/23/2011	Measuring Radiation
Status on 3/25/2011	What happens to the radioactive contaminants?
Status on 3/28/2011	How is the decay heat being removed?
Status on 3/29/2011	Reports of Core Meltdown
Status on 3/30/2011
Status on 3/31/2011

 
Status 4/1/2011

It's been three weeks since Units 1, 2, and 3 shutdown from the earthquake. Once the Units shutdown, the production of iodine-131 should have stopped and the amount built up in the fuel should have begun decaying. Iodine-131 has a half life of 8 days, so after 16 days only 25% of the inventory should have remained, at 21 days there should be less than 20% of the original amount. But reports keep coming in about finding iodine-131 in samples taken further from the site and the amount in the ocean has increased. This indicates Daiichi is continuing to spew out the radioactive isotopes and there is a good possibility that the melted fuel is generating heat by going critical, thus producing more iodine.

Plans are underway to construct a storage pond, a storage tank and a water processing plant on the site to clean up the contaminated water. They hope to have the additional storage available in a couple of weeks and the processing plant running in a month. Meanwhile water continues to be added to the Unit 1, 2, and 3 reactors to keep the heat down and the spent fuel pools water inventories are being replenished on daily basis. Additional concrete pumping units are being brought in to provide a more controlled water injection into the spent fuel pools.


 
Status 3/31/2011

TEPCO has been pumping water from the condensers to other storage tanks to make space for pumping the flooded areas to the condensers. They are considering creating an artificial pond and bringing in an ocean tanker for additional storage. Until the pooled water can be removed work on restoring equipment is on hold. After the water is removed they will be dealing with highly contaminated areas which will be prone to become airborne when dirt and dust is kicked up.

They have determined a majority of the flooding in the trenches was deposited by the tsunami.

When the hydrogen exploded in the reactor buildings a large amount of radioactive contaminants were released into the atmosphere. The heavier dust and particles fell onto the plant grounds and are now being tracked and blown around thus spreading the radioactive materials. They feel the dust being blown around is the main source of the contaminants getting into the ocean. TEPCO will test spraying an adhesive resin onto the ground to contain the dust. If it works on the test area, they will spray it on all the contaminated areas.

Reports of Core Meltdown

Analysis of the radioactive isotopes being released and the data available from instrument within the reactor vessels and reactor containment are now indicating that fuel has melted. There are diverse opinions on how much has melted, where the molten mass resides, and how it is shaped. The worse case describes a large blob which has been going critical. Going critical means it is creating heat via nuclear fissions thus creating more contaminants. The best case is there are multiple smaller blobs which are hot from only the decay heat. TEPCO thinks it is in the form of smaller blobs which are at the bottom of reactor vessel. But the blobs are leaking out the penetrations which exist for the control rods. For a more detailed description of the meltdown see: http://spectrum.ieee.org/tech-talk/energy/nuclear/nuclear-engineer-says-theres-evidence-fuel-melted-through-reactor-pressure-vessel/?utm_source=techalert&utm_medium=email&utm_campaign=033111 .


 

 

 
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Writeup prior to March 31, 2011


 
The Fukushima Daiichi complex has six nuclear reactors. At the time of the earthquake three units (1, 2, & 3) were producing heat to generate electricity. The other three units (4, 5, & 6) were shutdown for refueling, a normal maintenance event.

When the earthquake occurred a blackout occurred at the plant causing Units 1, 2, and 3 to shutdown automatically. A shutdown stops the nuclear chain reaction which produces heat. A nuclear reactor requires electricity to operate its own safety equipment. Nuclear plants have diesel generators to provide backup power in the event of a power failure. The Daiichi has several diesel generators to provide backup power. When the tsunami hit the facility, it damaged the diesel fuel tanks thus resuming blackout conditions.

After a shutdown the fuel must cool. Despite stopping the nuclear chain reaction the radioactive isotopes continue to release heat, known as decay heat. Normally, there is cooling water available for circulating around the fuel to remove the decay heat. Reports of using sea water to remove the decay heat lead us to believe the water or associated piping was damaged by the tsunami beyond repair. Using seawater means they will not be able to produce power from that unit again, a sign that conditions required severe measures.

Fuel rods no longer usable for producing electricity are stored on site in spent fuel pools. The spent fuel pool is a large, steel lined, pool of water. There are seven spent fuel pools at Fukushima Daiichi. One common pool and six smaller pools associated with each unit. The amount of cooling each pool requires would depend upon the quantity of fuel assemblies in the pool and the amount of decay heat they are producing. Nuclear plants maintain 16 feet of water above the fuel rods.

What keeps the radioactive materials inside?

A nuclear reactor has multiple barriers to prevent the release of radioactive materials. The radioactive nuclear fuel, cylindrical pellets about 1 inch long and ½ inch in diameter, known as fuel pellets, are sealed into a zirconium metal tube about 12 feet long known as a fuel rod. This is the first barrier. A nuclear reactor contains tens of thousands fuel rods. The reactor vessel is a stainless steel lined canister with walls over 6 inches thick. It is about 14 feet wide and 25 feet high. This is the second barrier.

A concrete structure surrounds the reactor vessel. This is the third barrier which is known as the reactor containment. There is a large chamber below the reactor vessel for capturing steam called the suppression pool. The reactor building houses the reactor containment and the spent fuel pool. This is the fourth barrier.

When the plant lost backup power the decay heat from the fuel in Units 1, 2, and 3 boiled away the remaining water in the reactor vessel over a couple of hours. Without their normal pumps, the operators pumped seawater to cool the fuel with their fire system pumps. But by the time the seawater pumping began, the fuel pins had heated to temperatures exceeding 2000 C. When zirconium heats to 2000 C it disintegrates and rapidly oxidizes with the surrounding water releasing hydrogen. Hydrogen explosions clearly indicated that some of the fuel rods overheated. There are relief valves in the system which allowed the hydrogen to vent/escape into the reactor building which is why the initial explosion occurred in the reactor building. The radioactive fuel remained within the reactor vessel. Some small quantities of radioactive gases were released with the hydrogen, however they were. adequately mixed in the air to mitigate being a hazard.


 
Is this like Chernobyl?

This situation differs markedly from the last major nuclear emergency, Chernobyl. Then, a fire took place in the reactor during a nuclear chain reaction. The reactor building was the only barrier between the outside and the burning fuel. When fire destroyed the reactor building's roof fission products from the fuel were released into the atmosphere.

Wind carries the smallest particles for hundreds of miles, while the heavier particles drop to the ground closer to the plant, thus contaminating the immediate area around the plant. The area of contamination is dependent on the direction and speed of the wind for carrying the radioactive materials. The stronger the winds the further the contamination will spread. Only areas downwind from the site will be contaminated. .

Ordinarily a nuclear plant periodically releases pent up gas into the atmosphere through its vent stack. Before releasing the gas, the plant filters and removes particulates. While the gas may be radioactive, it has been mixed with enough air to make the radiation concentration less than what one would receive when taking a cross country airplane flight.


 
How do iodine tablets protect me?

Radioactive iodine can be one component in a gas release. In the event of a major release, such as Fukushima Daiichi, people who may be exposed to the fallout receive a potassium iodine tablet. This saturates the thyroid gland to prevent the body from accumulating radioactive iodine.


 
The first hydrogen explosion was in the Unit 1 reactor building on March 12 after venting the reactor vessel containment. The explosion created a small radioactive release which was measured to be 11 mrem/hr at the site boundary. The reactor building sustained some damage, but overall it continued to provide protection although the damage necessitated additional precautions and planning.

Lacking the normal ability to pump water to cool Unit 3, excessive heat damaged the fuel rods, which caused a hydrogen buildup in its containment vessel. Plant personnel had to pump seawater into Unit 3 to stop the damage. They also vented the containment vessel into the containment building. On March 13, however, a hydrogen explosion occurred in containment building which blew out a wall and ceiling. . The public was evacuated from the 12 mile radius around the plant.

The explosion in Unit 3 may have initiated a problem with the Unit 2 cooling system. The fuel boiled off all the water. Although they pumped seawater into the reactor to cool it down, the pressure buildup did not permit filling the reactor vessel more than halfway. The seawater boiled off. On March 14 the pressure buildup caused a hydrogen explosion in the reactor containment vessel. The explosion occurred because they did not detect a malfunctioning relief valve. The explosion, however, reduced the pressure, thus allowing the seawater to resume flowing into the reactor.

At this point onsite radiation readings were elevated throughout the site. Seven hundred-fifty non essential workers were evacuate leaving 50 to maintain the seawater cooling of Units 1, 2, and 3. Fukushima is using the industry guidelines for allowable exposure to radioactivity to guide the decisions on personnel evacuations.

On March 14, a fire, reportedly due to lubrication oil, broke out in the Unit 4 reactor building and took 140 minutes to extinguish. As this reactor was shutdown and fuel rods were still hot, we believe water in the spent fuel pool dropped to levels that could not keep the stored fuel rods cool. The water level dropped due to some of the pool water sloshing out during the earthquake Furthermore, on March 16, another fire began in the Unit 4 reactor building, which took two hours to extinguish. The announced plans to use helicopters to drop water confirmed to us the plant had problems maintaining the water inventory in the spent fuel pool.

Subsequent reports confirm there was a hydrogen explosion in the Unit 4 reactor building which caused the building damage. The hydrogen was from the fuel in the spent fuel pool heating up.


 
Is there fuel meltdown?

The only way to get water to fuel in Units 1, 2, and 3 is through existing piping. At this time there are five fire pumps injecting sea water into these three units. The company has provided estimated fuel damage to be 70% of the zirconium in Unit 1 has disintegrated and 33% in Unit 2. If one could look into the reactor vessel one would see the fuel pellets piled up around the base of the partial fuel assembly skeletons. One would not see is a molten mass of glowing uranium generating so much heat to melt through the vessel.

Fukushima Daiichi Status 3/18/2011

The Unit 1, 2, and 3 reactors are in a stable cooling mode with the sea water being pumped into the system.

The company has tried to check the rising temperature in the Unit 3 reactor building by dropping water from helicopters above and spraying water from fire trucks on the ground. The loss of water in the spent fuel pool has caused the emission of highly radioactive gamma rays into the atmosphere.


 
Radioactive release vs Exposure to a radioactive source.

The earlier radioactive releases consisted of gases which are diluted as they drift in the atmosphere. These gases do not give off high amounts of energy and over a short period of time lose a significant portion of their radioactivity. The radioactivity within the fuel is a high energy source which will maintain its energy for years. If you are in the line of sight with the fuel you will be getting radiation. The amount of radiation is reduced in three ways, distance, time, and shielding.

The current actions at Daiichi indicate the Unit 3 spent fuel has been uncovered so it is a major radiation problem. They are working on refilling the spent fuel pool to cover the fuel with water which is an excellent shield. The helicopter pilots were dropping water on the building without hovering to reduce the time they spent over the exposed fuel. The emergency crews spraying water into the building are probably positioned to use the shielding provided by the concrete structures to minimize the radiation level.

Below are some satellite photos of Daiichi taken since the earthquake. Figure 1 was taken shortly after the hydrogen explosion in Unit 3. Note the roof on Unit 1 is missing and the Unit 3 building is damaged and steam being emitted which indicates the water in the spent fuel pool is boiling off. Figure 2 was taken after the fires in Unit 4 were reported. The building is now damaged and open to the atmosphere indicating the fire was more than a lube oil fire.

Efforts are concentrated on getting water into the Unit 3 spent fuel pool. The fuel pools for Unit 4, 5, and 6 have risen above their normal temperatures but are still below boiling point. We hypothesize Unit 3 lost its water inventory so much faster than the other units because it has developed a leak.

Reports indicate diesel generators are supplying power to Units 5 and 6. Later today they plan to have power to Units 1 and 2 by tapping into the high voltage lines. They hope to have power to Units 3 and 4 in a couple of days. Having electric power will greatly alleviate using non conventional methods such as fire trucks and fire pumps to get water on the fuel.


 
Fukushima Daiichi Status 3/19/2011

The water injection into the Unit 3 reactor building successfully cooled the fuel pool as evidenced by a satellite photo which lacks the steam being emitted from the damaged building. The fire trucks will be used to spray water into the Unit 4 building.

Until power is restored and the normal cooling equipment can be used, it will be necessary to repeat water spraying to keep the spent fuel pool water from boiling off and exposing the fuel.

There are now reports of contaminated food stocks in the area around the plant. This would be caused by radioactive particulates which have been released from the explosions and buildings which are open to the atmosphere. In particular, some radioactive iodine has been measured in the affected zone.

Figure 1 Satellite photo from March 14 after explosions in Unit 1 & 3 reactor buildings

Source: http://isis-online.org/isis-reports/detail/satellite-image-shows-damage-to-reactor-buildings-at-fukushima-daiichi-comp/

 


Figure 2 Satellite photo from March 16, Unit 4 reactor building roof is also compromised

Source: http://isis-online.org/isis-reports/detail/new-satellite-image-of-fukushima-daiichi-nuclear-site-in-japan-from-march-1/


 
Fukushima Daiichi Status 3/20/2011

With electricity available to Units 5 and 6, the spent fuel pool cooling has been restored. So at this time Units 5 and 6 are in stable conditions.

Units 3 and 4 spent fuel pools continue to be sprayed by the fire trucks using seawater. Aerial reconnaissance indicates this is controlling temperatures in the spent fuel pools. They are working on getting power to Unit 4.

They are now unsure whether the Unit 3 reactor containment is damaged as earlier reported because it is holding pressure.

They have begun spraying the Unit 2 spent fuel pool with seawater from the fire trucks. The reactor continues to be cooled with seawater.

The Unit 1 reactor continues to be cooled with seawater. The spent fuel pool has not been sprayed yet.

It appears that they are close to having electricity connected to Units 1 and 2.


 
3/21/2011 Status

Getting electricity restored to each of the units is a first step. Electrical equipment which has been soaked from the seawater spraying is particularly susceptible to shorting out. Workers need to check out the pumps and motors prior to energizing them.

Unit 5 was on diesel generator power. It has now back on the normal AC power. Restoring Unit 6 to AC power is in progress. With AC power restored, these units are in a safe condition.

There were reports of grey smoke emanating from Unit 3 and later Unit 2. We suspect some smoke was from equipment which caught on fire when Unit 2 electricity was restored and the smoke followed a path out of the Unit 3 reactor building.

When electricity is available, they are working on getting the control room ventilation systems working. The control room contains all the switches and indicators needed to operate the unit. When the plant lost power and the hydrogen explosions occurred, one of the consequences was the control rooms were evacuated because the ventilation systems could not filter the radioactive contaminants. Plus without power they could not do much. Getting back into the control rooms will be helpful in assessing the condition of the unit.


 
Measuring radiation

Some media sources are quoting radiation doses in mrem and some are using microsieverts. The dose is the amount of energy which would be absorbed by human tissue. The higher the dose the more likely it will cause cellular damage. This damage could destroy a living cell or cause changes to the DNA. But there are acceptable amounts of radiation.

Mrem (millirem) and µSv (microsievert) are measures of radiation dose. There are 1000 mrem in a rem. rem is the customary unit in America. The international standard uses sievert.

    1 mrem = 10 µSv

Some examples of radiation doses encountered by the general public:

Airplane flight	0.01 to 1 mrem depending on length and sunspot activity
Chest X-ray	6 mrem
Mammogram	70 mrem
Dental X-ray	9 mrem
EPA Cleanup standard	15 mrem/year (amount of radiation if at the site for a full year)
Avg Dose to human-made sources in a year	66 mrem

 
Status 3/22/2011

A crane with a boom has been setup to replace the spraying of seawater into the Unit 4 spent fuel pool. This equipment will produce less seawater runoff. Unit 3 continues to receive periodic spray downs to maintain temperature and levels.

The spray downs have been used to keep the spent fuel pool temperatures under control, but produce runoff. Several samples of seawater were taken from the ocean around the plant and found to contain elevated levels of radioactive Iodine and Cesium. Japanese officials indicate the elevated levels are still considered safe for someone consuming the average amount of water ever day for a full year. The ocean around the plant could have become contaminated by the runoff and the atmospheric releases.

The smoke seen coming from Unit 2 has subsided. The smoke from Unit 3 has changed from gray to white. No information has been provided as to the source.

AC power has been restored to Units 2, 4, 5, and 6.

Status 3/23/2011

AC Power is available to all units. But checking out the equipment before energizing it is taking time. They are restoring equipment based on a prioritized list. If a piece of equipment checks out it is energized, if it cannot be energized they determine whether to replace it or go to the next item on the list. They have restored lighting to the Unit 3 and 4 control room.

A plant status published by the Japanese Atomic Industrial Forum indicates "possibly damaged" for the Units 3 and 4 spent fuel pool. This is the first time we have seen a report recognizing the possibility of spent fuel pools are leaking, something we have suspected for awhile. Because some fuel rods in these pools are damaged, the continued replenishing of the water in these pools can be carrying off the radioactive contaminants from inside the fuel rods thus spreading the contamination.

Status 3/25/2011

On March 24 workers in Unit 3 crossed a flooded area. The water was deeper than the height of their boots resulting in their feet getting soaked. The water was contaminated with radioactive particles from the fuel causing the workers feet to be exposed to high levels of radiation. Their feet were washed but they had already been exposed to levels of radiation which caused burns.

Because the contaminants were from the fuel, there have been some concerns that this indicates the Unit 3 reactor vessel has been breached. We think it is more likely the contaminants are from the damaged fuel in the leaking spent fuel pool.


 
Status 3/28/2011

Experts were expressing concern about salt deposits building up on the fuel assemblies in the reactor which would prevent cooling from taking place. The US provided some barges of freshwater. The freshwater is now being injected into the reactors to cool the fuel. Now the concern is the contaminated water in the lower levels of the turbine building where pieces of equipment needed to establish normal cooling reside. The contaminated water prevents workers from safely entering the areas. The inventory of radioactive contaminants in the water is being used to determine the where the source of the water. Initial reports that it was a reactor was based on an incorrect measurement which identified a short lived iodine isotope in the water.

What happens to the radioactive contaminants?

When the reactors shutdown on March 11 from the earthquake, the nuclear chain reactions stopped, establishing a baseline inventory of radioactive isotopes in each fuel assembly. Each radioactive isotope has its own half life. The half life is the time it takes for only 50% of the baseline amount to remain. The shorter half lives are measured in seconds, the longer are measured in years. It takes 6 half lives to reduce the amount of a radioactive isotope to less than 1% of the baseline inventory. The isotope is changing because radioactivity is the emission of a subatomic particle or energy which results in a change in the inventory of neutrons, protons, and electrons in the atom. The radioactive emission can create a stable atom (i.e. the new atom does not emit radioactivity) or another radioactive isotope with a different half life. But all the chains eventually end up with as a stable atom.

Iodine-131 has been measured in Tokyo's water, crops around in the plant, and in the sea water. Since March 11, Daiichi has not produced any more. This isotope of Iodine has a half life of 8.1 days, so as of Sunday March 27 there were 2 half life periods which results in only 25% of the baseline amounts remains. If Iodine-131 is ingested, the body first replenishes thyroid gland with the iodine and allows any surplus to be excreted as waste.

Caesium-137 is another isotope which is being monitored. It has a half life of 30.1 years. So it will be around for decades. The concern about caesium is it will enter the food chain by accumulating in fruits and vegetables. When food with caesium is ingested the body will remove it through sweat or urine.

The amount of radioactive contaminated water which needs to be removed is a challenge. Normally the water could be processed through demineralizer tanks which would concentrate the contaminants, but result in clean water. But most likely these plant systems have been damaged. Daiichi is pumping the water into the condenser, a chamber which normally collects water and steam after it has been used to turn the turbine generators.


 
Status 3/29/2011

There has been a shift in actions being taken at Daiichi. Starting with the 3 workers getting contaminated by radioactive water on March 24, there appears to be a greater emphasis placed on the containment of the radionuclides which have been released from the damaged fuel.

In addition to the water collecting in the lower levels of the reactor buildings, contaminated water has now been found in trenches used for electric cable and piping which run under the site grounds. A trench which is 12 feet high, 9 feet wide and 228 feet long yielded a 100 rem/hr water sample. They are trying to determine the source of the contaminated water. Workers are putting sandbags around the trenches to contain any water which may overflow.

There are not enough tanks and places to which the contaminated water can be pumped.

The pumping of freshwater into the reactors to maintain cooling has been reduced by over 50% in an effort to reduce a source of the water. This will cause the reactors to heat up. But the control rooms are now inhabited again, so the temperatures are being monitored.

The reports of plutonium being found in samples taken from the ground on the site confirm the contents of the damaged fuel rods have been released to the atmosphere. The plutonium is a danger if it is ingested because it will be retained in the body emitting radiation.


 
Status 3/30/2011

Work at the plant centered on pumping the water from flooded areas. Pumping water from the Unit 1 reactor building into the condenser was suspended when the condenser became filled to capacity leaving about 8 inches of water in the building. Plans to pump water into the Unit 2 and 3 condensers were not executed because the condensers were already filled with water. Water will be transferred to other storage available storage tanks.

Freshwater is now being pumped to the Unit 1, 2 and 3 reactors using diesel generator driven electric pumps rather than the fire truck pumps.

How is the decay heat being removed?

Daiichi is working on keeping the fuel in Units 1, 2, and 3 reactors cool and the spent fuel in Units 1, 2, 3, and 4 pools cool by adding water to replenish the water being turned to steam by the hot fuel rods. Under normal conditions the steam is not released to the atmosphere. In the reactors and spent fuel pools decay heat normally heats up water which is run into a heat exchanger. The heat exchanger cools the water which has been in contact with the fuel without exposing it to the atmosphere. This is called a closed loop system. As an additional layer of protection the heated water from the heat exchanger is fed into another heat exchanger for cooling. The second heat exchanger system is cooled to the atmosphere.

From the information we have seen, Units 5 and 6 are being cooled in the normal mode.

Units 1, 2, and 3 do not have any of the heat exchangers working so water is either turning into steam or is collecting in the systems. In the reactor vessels the water level is about half way covering the fuel. As the steam pressure in the vessels builds up it is released into the reactor containment where it eventually condenses and collects in the suppression chamber. In the case of Unit 2, the reactor containment was damaged and the steam is able to enter the reactor building which is open to the atmosphere via a panel which has been removed on the side of the building. For Units 1 and 3 the reactor containments are able to maintain pressure. But without any heat removal systems for cooling the steam is building up and we hypothesize is venting to the reactor buildings which have been destroyed by explosions.

The spent fuel pools normally are cooled by the Residual Heat Removal (RHR) system and are not allowed to boil. The Unit 1, 2, 3, and 4 spent fuel pools are boiling off the water and water is being sprayed or injected to replace the lost inventory.

Until the cooling systems are available, TEPCO will need to find the balance between injecting water for cooling and causing more contaminated water to collect throughout the plant. Eventually they must stop the steam from being vented to the atmosphere without filtration because it is releasing radioactive contaminants.