French version : 9 July 2013
English translation : 7 August 2013

Fukushima Daiichi nuclear accidentManagement of contaminated water from the damaged
reactors
Situation as of end June 2013This document is based on publicly available information on the situation of the Fukushima Daiichi nuclear power plant.

I.

General context: a build-up and a continuous influx of water in thebuildings

The natural phenomena that led to the accident that affected TEPCO’s Fukushima Daiichi nuclear
power plant on March 11th, 2011 also led to flooding of the site leading to an accumulation of waterin the basements of the power plant buildings. Furthermore, since the accident, the water used tocool the damaged cores of the reactors has been flowing into the basements of the buildings from
where it is pumped in order to be re-used, after treatment, to cool the reactors. As things stand,more than 350 m3 of water is entering the basements on a daily basis. This water circulates in thereactor vessel, the confinement vessel and the torus, and cools the degraded nuclear fuel. It picks
up radioactivity, particularly by leaching of the most mobile elements still contained in the corium.
In this respect, although uranium and transuranian elements have very limited solubility, certain
fission or activation products are more easily dispersible in water (caesium, strontium, antimony,tritium, etc.). TEPCO thus reports a caesium 137 activity of the order of several GBq/m3 in thewater that has accumulated in the basements of unit 1 and 2 “turbine” buildings. The dose rates insome of the building basements, due in particular to the presence of contaminated water but also
to the reactor circuits installed in these basements (such as the torus), can reach one Gray perhour.
Furthermore, water from the groundwater is penetrating the basements, thereby contributing to
the increase of amount of accumulated water. TEPCO is maintaining the level of water in thebasements slightly below the groundwater level, which limits the transfer of contamination but
favours the influx of water. However, this slight difference limits the flow, which has neverthelessbeen evaluated at several hundreds of m3 a day. Finally, rainwater also contributes to the build-upof water in the buildings.
Since the water contained in the basements of the buildings is contaminated and since theamount of water entering them is very considerable (currently estimated to be at least 700 m3 aday, taking the cooling water and the influx of natural water together), its treatment andstorage have become important challenges, since the first weeks following the accident, asregards regaining full control of the facilities in order to limit releases into the environment.
The importance of these challenges only increases as time goes by as the accumulated wateramount has now reached several hundreds of thousands of m3.

II.

Water treatment

Treating the water has two objectives: desalination and the removal of radionuclides.
- Desalinisation of the water is necessary: the wave that submerged the site when the accident
occurred was composed of seawater, and TEPCO also injected seawater into the reactors to coolthem for several days following the accident. A reverse osmosis process was developed and put inplace very quickly a few months after the accident.

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It should be recalled that TEPCO also had to desalinate the water of the spent fuel storage pools ofreactors 2, 3 and 4, into which seawater was also injected. This operation is currently completed.
- As with desalination, TEPCO also quickly implemented an initial method for removing
radionuclides. It has called on external contractors, notably French, whose expertise enabled
operational equipment to be made available a few months after the accident. These measures allow
partial removal of the radioelements contained in the treated water.
TEPCO then launched the development of a second system enabling a complementarytreatment, which it has called a “multi-nuclides removal equipment” (the ALPS facility). Thissystem comprises three equivalent sub-systems, each with a unit treatment capacity of 250 m3/day.
The hot testing began in the second quarter of 2013 and are still on-going. TEPCO envisages the fullscale operation of this water treatment system in the course of the second half of 2013.
According to TEPCO, the order of magnitude of the volume of water treated since the accident issome 700,000 m3.
The figure below gives a synthetic view of the complete treatment chain of water from theFukushima Daiichi reactor zones following commissioning of all the various systems.

Source TEPCO – General block diagram of the routing of water accumulated in Fukushima Dai-ichi
TEPCO is regularly improving the water treatment equipment in order to take into account thelessons that have been learned from various incidents that have occurred, e.g. by increasing thenumber of pumps to improve reliability, replacing flexible piping by rigid piping in order to reduce
the risks of leakage or modifying the control of valves in order to be able to control them remotely.
Finally, the design of the ALPS system takes account in particular of the difficulties encounteredwith current treatment systems: installation of leak detectors and a retention system surrounding
the facility, insulation of equipment to protect them from freezing, use of rigid pipes, specifictraining of operators, etc. TEPCO is also carrying out long term tests in order to detect potential
defects. As an illustration, some defects have been recently identified on a tank welding.

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Water storage

Water treatment is only the first step in the management of the water that has accumulated on
the site. In fact, firstly the removal of radionuclides is still only partial, as mentioned above and,secondly, even when all of the systems have been in operation, it would be necessary for TEPCO toobtain authorisations to release the treated water, which would still contain residual radioactivity.
In the meantime, TEPCO has to store increasing volumes of water. At the end of March 2013,
TEPCO thus announced a storage capacity of 325,000 m3 with an objective of 450,000 m3 by mid2013 and, beyond that, a capacity of some 700,000 m3 by mid-2015.
TEPCO has put in place various types of storage facilities, as shown in the image below, which also
indicates the location of the treatment systems.

Source TEPCO (January 2013) – Location of accumulated water storage zones in Fukushima Daiichi
Once again, the particularly difficult context has meant that TEPCO has not been able to install andoperate these water storage facilities without encountering problems of leak tightness from time totime, such as the leak that recently affected the underground reservoirs in April 2013.
IRSN points out that, notwithstanding the difficulties of storing the accumulated water, its
treatment generates waste, such as sludge containing extracted radionuclides, the managementof which constitutes a major challenge, not only in terms of safe long term storage but also
subsequent conditioning. TEPCO has already defined actions in this respect. For example, what are
known as “high integrity” containers are planned for the waste from the ALPS facility and aresearch programme is scheduled. Whatever the case, the information available concerning thesesubjects remains less detailed than information relative to less pressing issues.

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