French Researchers: Lower Bound Estimates of Atmospheric Release of Iodine, Cesium from Fukushima "about 5 to 10 times less than the Chernobyl atmospheric releases"

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, D05122, 16 PP., 2012 (Received 27 September 2011; accepted 23 January 2012; published 9 March 2012)

Estimation of errors in the inverse modeling of accidental release of atmospheric pollutant: Application to the reconstruction of the cesium-137 and iodine-131 source terms from the Fukushima Daiichi power plant

Victor Winiarek

CEREA, École des Ponts ParisTech–EDF R&D, Université Paris-Est, Marne la Vallée, France

INRIA Rocquencourt Research Centre, Paris, France

Marc Bocquet

CEREA, École des Ponts ParisTech–EDF R&D, Université Paris-Est, Marne la Vallée, France

INRIA Rocquencourt Research Centre, Paris, France

Olivier Saunier

Institute of Radiation Protection and Nuclear Safety, Fontenay-aux-Roses, France

Anne Mathieu

Institute of Radiation Protection and Nuclear Safety, Fontenay-aux-Roses, France


A major difficulty when inverting the source term of an atmospheric tracer dispersion problem is the estimation of the prior errors: those of the atmospheric transport model, those ascribed to the representativity of the measurements, those that are instrumental, and those attached to the prior knowledge on the variables one seeks to retrieve. In the case of an accidental release of pollutant, the reconstructed source is sensitive to these assumptions. This sensitivity makes the quality of the retrieval dependent on the methods used to model and estimate the prior errors of the inverse modeling scheme. We propose to use an estimation method for the errors' amplitude based on the maximum likelihood principle. Under semi-Gaussian assumptions, it takes into account, without approximation, the positivity assumption on the source. We apply the method to the estimation of the Fukushima Daiichi source term using activity concentrations in the air. The results are compared to an L-curve estimation technique and to Desroziers's scheme. The total reconstructed activities significantly depend on the chosen method. Because of the poor observability of the Fukushima Daiichi emissions, these methods provide lower bounds for cesium-137 and iodine-131 reconstructed activities. These lower bound estimates, 1.2 × 10^16 Bq for cesium-137, with an estimated standard deviation range of 15%–20%, and 1.9 − 3.8 × 10^17 Bq for iodine-131, with an estimated standard deviation range of 5%–10%, are of the same order of magnitude as those provided by the Japanese Nuclear and Industrial Safety Agency and about 5 to 10 times less than the Chernobyl atmospheric releases.

=======================================================

Researchers at CEREA created the simulation map of cesium-137 deposition across the Pacific Ocean last year.

Tweet