The water that was used for cooling the reactors and
fuel storage pools accumulated in the lower levels of the
reactor buildings and turbine halls. The total amount of
water by May 2011 was estimated by TEPCO as being
100,000 tons. One fraction of this highly contaminated
water flowed into the Pacific Ocean uncontrolled during
that early period. As a consequence, the concentrations
of iodine and cesium isotopes in the seawater increased.
To estimate the contamination of the seawater, TEPCO
and MEXT performed nuclide-specific measurements