12 research outputs found
Estimation of marine source-term following Fukushima Dai-ichi accident
International audienceCs 134 Cs 131 I Environmental half time a b s t r a c t Contamination of the marine environment following the accident in the Fukushima Dai-ichi nuclear power plant represented the most important artificial radioactive release flux into the sea ever known. The radioactive marine pollution came from atmospheric fallout onto the ocean, direct release of contaminated water from the plant and transport of radioactive pollution from leaching through contaminated soil. In the immediate vicinity of the plant (less than 500 m), the seawater concentrations reached 68 000 Bq.L À1 for 134 Cs and 137 Cs, and exceeded 100 000 Bq.L À1 for 131 I in early April. Due to the accidental context of the releases, it is difficult to estimate the total amount of radionuclides introduced into seawater from data obtained in the plant. An evaluation is proposed here, based on measurements performed in seawater for monitoring purposes. Quantities of 137 Cs in seawater in a 50-km area around the plant were calculated from interpolation of seawater measurements. The environmental halftime of seawater in this area is deduced from the time-evolution of these quantities. This halftime appeared constant at about 7 days for 137 Cs. These data allowed estimation of the amount of principal marine inputs and their evolution in time: a total of 27 PBq (12 PBqe41 PBq) of 137 Cs was estimated up to July 18. Even though this main release may be followed by residual inputs from the plant, river runoff and leakage from deposited sediments, it represents the principal source-term that must be accounted for future studies of the consequences of the accident on marine systems. The 137 Cs from Fukushima will remain detectable for several years throughout the North Pacific, and 137 Cs/ 134 Cs ratio will be a tracer for future studies
Consequences of radioactive releases into the sea resulting from the accident at the Fukushima Dai-ichi nuclear power plant - Evolution of expert investigation according to the data available
The accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in March 2011 led to
an unprecedented direct input of artificial radioactivity into the marine environment. The
Institute for Radioprotection and Nuclear Safety was requested by the French authorities
to investigate the radioecological impact of this input, in particular the potential
contamination of products of marine origin used for human consumption. This article
describes the close link between the responses provided and the availability of the data,
as well as their nature and ability to meet the requirements of expert investigation.
These responses were needed: (i) to evaluate the inputs of radionuclides into the marine
environment, (ii) to understand their dispersion in seawater, and (iii) to estimate their
transfer to the biota and sediments. Three phases can be distinguished which characterise
these processes during the accident and post-accident periods. The first phase corresponds
to an emergency phase during which no measurements were available on samples from the
marine environment. It involved the formulation of hypotheses based solely on the
expertise of the Institute for Radioprotection and Nuclear Safety. The second phase
started when the Japanese authorities provided measurements of the concentrations of
radionuclides in seawater. Although these data were not yet adapted to addressing the
problems of radioecology, the scenarios could then be refined and the estimates developed
in more detail. During the third phase, the accumulation of data over the course of time
made it possible to study the phenomena in an appropriate way. The chronology of the
events shows that it is essential to have (i) significant measurements of concentration
from samples collected in the various matrices of the marine environment, regularly
updated and sufficiently well-documented, (ii) samples of seawater collected at the
earliest opportunity as close as possible to the damaged site to characterise the source
term, and (iii) a numerical tool allowing rapid modelling of the dispersion of
radionuclides in seawater, as well as their transfer to sediments and the biota,
ultimately for the purpose of estimating the dose to humans