Fukushima Nuclear Power plantsFukushima I 1 BWR-3 26.3.71 LowEnrU in operationFukushima I 2 BWR-4 18.7.74 LowEnrU in operationFukushima I 3 BWR-4 27.3.76 LowEnrU/MOX in operationFukushima I 4 BWR-4 12.10.78Fukushima I 5 BWR-4 18.4.78Fukushima I 6 BWR-5 24.10.79

Nuclear Power in Japan

55 reactors = 47,361 MWe (c 49,405 MWe gross)

BWR Reactor

BWR Reactor

PWR Reactor

Cooling systems BWR-3 reactor

Fukushima accident sequence of events

• Explosion of reactor 1 building At 15:36 JST on 12 March 2011 + Seawater used for cooling Reactorunit 2 Same controlled initial shutdown as the other units. Diesel generators and other systems failed whenthe tsunami overran the plant. + Cooling problems at unit 2 + Explosion in reactor 2 building 15 Marchin unit 2,Spent fuel pool40 tonnes of sea water was added to the spent fuel pool on 20 March. Thetemperature in the spent fuel pool was 53 ｰC as of 22 March 11:00 JST. + Reactor unit 3 Unlike the otherfive reactor units, reactor 3 runs on mixed uranium and plutonium oxide, or MOX fuel, making it potentiallymore dangerous in an incident due to the neutronic effects of plutonium on the reactor, the very long half-life of plutonium's radioactivity, and the carcinogenic effect in the event of release to the environment.

• + Units 3 and 4 have a shared control room. + Cooling problems at unit 3. 13 March 2011, theemergency cooling system of Unit 3 had failed, malfunctioning.+ Explosion of reactor 3 building At 12:33JST on 13 March 2011, +Spent fuel pool reactor 3 building + Ongoing Emissions Reactor unit 4 At thetime of the earthquake unit 4 had been shut down for a scheduled periodic inspection since 30 November2010. All 548 fuel rods had been transferred in December 2010 from the reactor to the spent fuel pool onan upper floor of the reactor building where they were held in racks containing boron to damp down anynuclear reaction. The pool is used to store rods for some time after removal from the reactor and nowcontains 1,479 rods. Recently active fuel rods produce more decay heat than older ones. At 04:00 JST onMonday 14 March, water in the pool had reached a temperature of 84 C compared to a normal value of 40-50 C. IAEA was advised that the temperature value remained 84 C at 19:00 JST on 15 March, but as of 18March, no further information was reported.+ Explosion of reactor 4 building At 06:00 JST on 15 March,+ Possibility of criticality in the spent fuel pool Reactor units 5 and 6. Both reactors were off line at thetime the earthquake struck (reactor 5 had been shut down on 3 January 2011 and reactor 6 on 14 August2010), although they were still fueled, unlike reactor 4 where the fuel rods had been removed prior to theearthquake. Government spokesman Edano stated on 15 March that reactors 5 and 6 were being closelymonitored, as cooling processes were not functioning well. At 09:16 JST the removal of roof panels fromreactor buildings 5 and 6 was being considered in order to allow any hydrogen build-up to escape. At 21:00on 15 March, water levels in unit 5 were reported to be 2 m above fuel rods, but were falling at a rate of8 cm per hour. On 17 March, Unit 6 was reported to have operational diesel-generated power and this wasto be used to power pumps in unit 5 to run the Make up Water Condensate System (MUWC) to supplymore water.Preparations were made to inject water into the reactor Central fuel storage areas. Used fuelassemblies taken from reactors are initially stored for at least 18 months in the pools adjacent to theirreactors. They can then be transferred to the central fuel storage pond. This contains 6375 fuelassemblies and was reported 'secured' with a temperature of 55 ｰC. After further cooling, fuel can betransferred to dry cask storage, which has shown no signs of abnormalities. On 21 March temperatures inthe fuel pond had risen a little to 61 ｰC and water was sprayed over the pool.

Sequence of accident at Fukushima plant• Tsunami wave 14 m (earlier TEPCO said 7.5 m) - Plant

designed for 5.7 m

The French nuclear authority and the Finnish nuclear authority estimate the unfolding crisisat Fukushima to be a Level 6 on the INES. On May 23rd accident level is estimated 7.

Previous serious nuclear accidents- Kyshtym (URSS) disaster (1957, INES 6)- Three Mile Island accident (1979, INES 5)- Chernobyl disaster (1986, INES 7)