Status May 21, 2012
Work has just begun on the cover for the Unit 4 building. To date only the Unit 1 cover has been
erected. The Unit 3 and 4 covers were
awaiting completion of debris removal before proceeding.
Fukushima has multiple potential disasters which can lead to
releasing radiation if another large earthquake/tsunami should hit in the next
few years. The Unit 4 building sustained
substantial structural damage and the fuel pool has the largest inventory of
fuel assemblies. The pool received
external cooling from the fire hoses during the first months after the
earthquake. One of the first actions
after gaining access to the area was to shore up the fuel pool with 30 steel
supports. They continue to filter the
water in the spent fuel pool to remove the salt water introduced to the system.
The challenge of remediating all the damage at Fukushima
requires untested solutions. There are 3
reactors with damaged fuel which has leaked out of the reactor vessel into the
drywell. In 2 cases the drywell appears to be damaged, so the highly
radioactive molten mass cannot be shielded via flooding. The Unit 3 building is still open to the
elements and debris needs to be removed.
Also, there is fuel in each of the 3 associated spent fuel pools. Plans are being formulated on how the damaged
reactor vessels can be accessed in order to remove the damaged fuel. They will also need to gain access to the
area below the reactor vessel to remove the fuel which melted through the
vessel. This is a procedure which has
never been performed or planned.
They are storing a huge volume of highly radioactive water
containing cesium and strontium in temporary tanks on site. The water is being cleaned and recirculated for
cooling, but the pumping and piping systems were quickly assembled and are
prone to break downs and leaks. If a leak occurs the risk of runoff into the ocean is high. Since
the buildings are not sealed the inventory of water continues to increase when it rains. The basements of several buildings are
flooded with contaminated water.
Removing the fuel from the Unit 4 pool requires substantial
infrastructure repairs. A 100 ton
crane is needed to lift the fuel storage casks used for removing the fuel, but they still need to clear the debris which sits on
top of the fuel. The debris includes the
crane which would normally be used to place the fuel into the storage casks. The support systems for evacuating water from
the cask after loading are probably damaged because wiring and motors have been
water logged.
The plan and work to cleanup Fukushima will take decades to
complete. The risk of a large earthquake
and tsunami incurring substantial damage and releasing radioactivity into the
environment will be there all the time.
