2 juillet 2012

Accident at the FUKUSHIMA DAI-ICHI nuclear power plant
Assessment of the situation in June 2012
This document is based on information publicly available concerning the situation at the Fukushima Dai-ichi power plant.

I.

BackgroundThe earthquake of magnitude 9 that occurred on 11 March 2011, 80 km east of the island of Honshu
in Japan, and the tsunami that followed, severely affected Japanese territory in the region ofTohoku, with major consequences for the population and infrastructures.
In devastating the site of the Fukushima Dai-ichi nuclear power plant (NPP), these natural events
led to the core meltdowns in three nuclear reactors 1 and the loss of cooling in several spent fuelstorage pools. Explosions also occurred in the buildings of reactors 1 to 4 due to production ofhydrogen during fuel deterioration. Very important radioactive releases into the environment
occurred. The accident was classified at level 7 on the INES scale.

II.

State of the facilities- Cores of reactors 1, 2 and 3
From the outset, the information available about the accident led IRSN to conclude that fuel fromthe three reactors had partially melted as a result of the loss of cooling. Although there was noclear evidence to suggest there had been significant rupture in the core vessels after corium wasprobably transferred to the bottom of the vessels, IRSN considered the integrity of the vessels andthe containment structure to be no longer guaranteed.
Analyses conducted by TEPCO have since concluded that:-for reactor n°1, total meltdown of the core and rupture of the core vessel has occurred,with corium spreading into the bottom of the containment structure;-for reactors n°2 and n°3, significant deterioration of the cores has occurred, with thepossibility of significant transfer of corium to the bottom of the vessel and a slight flow of
this corium to the bottom of the containment structure.

- Spent fuel storage pools
The information available (video monitoring of the interior of the pools and measurements of watercontamination) supports the hypothesis that there was no significant deterioration of the spent fuelstored.
However, material fell into the pools of reactors n°1, n°3 and n°4 following the explosions, which
will complicate the extraction of the spent fuel present in the pools.

1Reactor n°4 has been unloaded and reactors n°5 and n°6 have been placed in a safe shutdown

state.
1III.

Current status of the facilities

Reactors n°1, n°2 and n°3 are being cooled by injection of fresh water (approximately 10m3/hr).
TEPCO reported at the end of 2011 that a “cold shutdown” situation had been achieved (aninappropriate term given the status of the reactors) with a water temperature in the reactors below
100°C.
This limits water evaporation and thus reduces releases into the environment by containment leaks.
In this respect, the temperature currently measured by TEPCO at the measuring points in thereactors is between 30 and 60 ° C. Furthermore, TEPCO has provided information on the water levelin the reactor containment buildings; this water level would be 2 meters, 0.6 meter and 5 metersrespectively for reactor n°1, reactor n°2 and reactor n°3.
In addition, nitrogen is injected into the containment vessels of the reactors to maintain inerting
and thus avoid any risk of hydrogen explosion.
The storage pools of the six reactors and the site storage pool are now cooled in a closed circuit. Inaddition, TEPCO has carried out work to improve the civil engineering of the reactor n°4 pool aspart of its plan to regain control of the facilities.
In order to stabilise the status of the facilities, TEPCO has established redundant equipment andelectrical backup systems to maintain cooling of the facilities and ensure nitrogen inerting of thereactor containment buildings. In addition, some equipment has been installed in elevated areas
and anti-tsunami protection has been established at the site boundary. Finally, monitoring of crucial
parameters is ensured (water temperature, hydrogen level in the containment systems, waterlevels, etc.). IRSN acknowledges that TEPCO has implemented considerable resources in order toregain control of the facilities and reiterates that these actions should be maintained in the longterm, considering the time necessary to dismantle the facilities.
Various events have been encountered over time (rise in xenon level, outage or drift in temperature
measurements, leaks from water circuits, temporary loss of cooling in pools, of nitrogen inerting orof retransmission of real-time information to accurately monitor the status of the facilities etc.)
which, given the information available, have not revealed a significant variation in the status of thefacilities. IRSN stresses however that these factors confirm the need to maintain vigilant as tothe behaviour of the facilities, in a context that is still difficult due to limited accessibility andthe uncertain reliability of the monitoring methods. In any event, the activities conducted by
TEPCO in the facilities will inevitably lead to the discovery of new factors.
In recent months, TEPCO also started many visits and additional specific inspections of the reactors(visits of buildings by robots, control of the state of reactor n°4 building ...). TEPCO hopes this way
to be able to define better its action plan for decommissioning, but also to be able to ensure thatthe facilities are likely to resist a possible new major earthquake. IRSN stresses that these
inspections may also contribute to a better understanding of the accident of March 2011
through a better understanding of the real consequences on the materials.

IV.

Present radioactive releases

In light of the available information, diffuse releases continue (lower than about ten MBq ofcaesium/hr, according to TEPCO), but they are not comparable to those that occurred in mid-March2011.
TEPCO continues its activities aiming to control these diffuse releases, in particular:-by covering the reactor buildings with walls fixed on a metal framework (done for reactorn°1);-

by sealing off some underground technical installations and installing an underground wall
between the site and the ocean (in progress);-by treating the water present in the lower parts of the buildings. After treatment, thiswater is re-used for the cooling of the reactor;2-V.

by covering the bottom of the ocean, in the "port" of the site, with concrete slabs, inorder to mitigate the spreading of contaminated deposits.

Plan to regain control of the facilities

TEPCO considers that the first phases of regaining control of the facility have been completed,inasmuch as cooling is provided for the reactors and the pools, with a low water temperature
maintained in the facilities, and residual releases are at low levels. Cleanup activities on the site
are continuing, in particular to allow future work.
The action plan chosen by TEPCO now includes three major steps:- the first is to start the removal of the fuel in the pools of reactors 1 to 4, with a target of
2 years. To date, TEPCO plans to start in late 2013 the recovery of fuel in the reactor
pool 4, the most heavily loaded in fuel with high residual power;- the second undertakes the removal of the deteriorated fuel from reactors 1 to 3, with atarget of 10 years;- the last will lead to the complete dismantling of the facilities, with a target of 30 to 40years.
This action plan is combined with a significant research and development programme to specify andorganise the procedures to be carried out, which are major in scale and without precedent.
Without questioning the consistency of this action plan, IRSN stresses that the deadlines announced
can only be considered as approximately and that major, in-depth operations will have to beundertaken to establish the actual status of the facilities. IRSN notes, however, the importance ofthe resources deployed by TEPCO to accommodate the schedule announced. To date, theprogress seems in line with the overall schedule.

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