French version : 10 July 2013
English translation : 7 August 2013

Fukushima Daiichi nuclear accident
Contamination of the ground between the damaged reactors
and the Pacific Ocean

This document is based on publicly available information on the situation of the Fukushima Daiichi nuclear power plant.

One of the major challenges faced by TEPCO following the Fukushima Daiichi accident has been
dealing with the contaminated water1 present on the site. In fact, cooling the cores of the damaged
reactors requires the continuous injection of water into the reactors; this water then flows into thebasements of the buildings, from where it is collected before being treated and reused for coolingthe cores. Influx of water into these building basements from the groundwater and from rainfall,
which is in addition to the influx of cooling water, means that the amount of water that need tobe recovered daily and then treated is very considerable (currently at least 700 m3 a day). In
addition to this water present in the building basements, there is the water contained in certain
services galleries of the site, in storage areas (before and after treatment), in treatment facilities,and in the connecting circuits between these various areas and equipment, the total length of which
is nearly 4 kilometres.
The amount of contaminated water on the site is currently estimated at several hundreds ofthousands of m3. The considerable volume and number of zones and equipment concerned (theconfinement characteristics of which are highly variable) mean there are high risks of leakage,as various events that have occurred in April 2013 have demonstrated. Potential locations forleaks are thus highly diverse, ranging from the pipes and storage facilities that are dispersed on thesite to service galleries and the buried parts of buildings. Whatever the case, while leakages fromover ground pipes and tanks are relatively easy to detect, particularly visually, the detection ofleakages from underground areas requires surveillance of the groundwater. Borings are also being
sunk for this purpose.
In particular, the presence of contaminated water in the basements of the reactor buildings andtheir associated turbine buildings presents a risk of pollution of the groundwater. In order tolimit the transfer of contamination into the groundwater, TEPCO is maintaining the water level inthese buildings slightly below the groundwater level. In addition, it is verifying that this potential
contamination does not reach the ocean; in particular, it is carrying out checks of radionuclide
levels in ocean water immediately downstream of these buildings and on the groundwater in borings
situated between the site buildings and the ocean.
Over the last few weeks, the presence of high activity levels (around 500 000 Bq/l in tritiumand 1000 Bq/l in strontium) in a hole located between reactor 1 and reactor 2 has led TEPCO tosink additional borings to try to pinpoint the source of the leak, and to reinforce its ocean watercontrols. The figure below shows the control points, particularly the zone marked N°1, the southernpart of which comprises two borings showing high radioactivity.

1For more information, see the note on the management of contaminated water from the reactors published jointly on
IRSN’s website.

TEPCO’s main hypothesis is that the contaminated water was able to infiltrate into the ground in
April 2011 when galleries located near to the aforementioned borings were flooded.

Source TEPCO – Surveillance points of the risk of contamination of the ocean
The controls carried out since the discovery of this increase in the radioactivity of the ground water
did not highlight any significant evolution of the activity of water in the ocean.
On the other hand, on the 9 July 2013, TEPCO measured caesium 134 and 137 levels ofrespectively 11,000 and 22,000 Bq/l in a boring in zone N°1, levels close to those measured theday beforehand but showing a very sharp increase compared to the first measurements made inthis boring.
Following these events, TEPCO has decided to undertake important work to reinforce the leaktightness of the ground in zone N°1 by the injection of sealing products along the bank situatedbetween reactors 1 and 2. The works should start in early August 2013.

Source TEPCO – Schematic diagram of chemical injections into the ground2

The origin of the significant rise in the radioactivity concentration measured in drilling on the edgeof ocean
The origin of the increase in the radioactivity concentration measured in the borings at theocean’s edge cannot be linked to a precise cause given the information currently available; infact, it could be explained by the event mentioned above, which occurred in April 2011. However, itcould also be due to a leak that affected, in the early phase following the accident, the basements
or galleries of the buildings, which were flooded by contaminated water. Depending on the natureof the ground, the migration of the groundwater contamination could have reached only recently
the zone mentioned above. Nevertheless, since the migration of caesium in the ground is muchslower than that of strontium or tritium, a multiple origin is also possible. The origin of the caesium
pollution should however be close to the incriminated zone, given its slow migration speed;
moreover, it is also possible that the origin of this pollution has now dried up. If this is the case, thecontamination levels should increase, and then level off before decreasing again. TEPCO’s
investigations into this event should provide more precise information on this subject.
Whatever the case, the fact remains that the actions underway to create a first barrier between
the ocean and the groundwater should be able only to limit contamination of the ocean. In thisrespect, besides the sealing of the soils by injection as indicated above, the construction of aleak tight screen between the site facilities and the ocean is continuing (expected to becompleted by mid-2014). This type of screen does not however enable all risks of contamination of
the ocean to be entirely averted if it is not complemented by pumping of the groundwater. In fact,
leak tightness is never total and a risk exists of the screen being by-passed because of thecontinuous influx of groundwater. On the other hand, this pumping increases the need for watertreatment and storage capacities, further increasing the complexity of the overall management of
the contaminated water on the site.
In addition, it should be noted that the lessons learned from the Chernobyl accident show that, inthe years following such an accident, a few thousandth of caesium deposited in the terrestrial
environment migrate annually due to soil erosion and run-off, towards the ocean in the presentcase. Furthermore, it should be recalled that caesium 137 discharges into the atmosphere and theocean due to the accident of March 2011 have been estimated respectively at around 60 and
27 PBq. Due to the leaching of deposits in the environment following the accident (deposits
estimated at around 2 PBq), the ocean is still receiving important amounts of radioactivity(estimated at several TBq/year). Given the values observed in the ground water, radioactive
contamination of the ocean by the site should remain limited with regard to this overallterrestrial influx, in light of the measures taken, and the potential ecological impacts may
remain localised to the immediate vicinity of the power plant due to the important dilution
capacity of the ocean.

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