Pool scrubbing in unit 1 of fukushima daiichi

Abstract

Under the frame of OECD/BSAF and ARC-F projects, CIEMAT estimated that around 40% of the Cesium initial inventory in the reactor core and nearly 60% of the Iodine one of the Unit 1 of Fukushima Daiichi, got absorbed in the suppression pool. CIEMAT has critically reviewed the bases of the MELCOR pool scrubbing module, including the major assumptions and approximations underneath, under the prevailing conditions in Unit 1 of Fukushima Daiichi during fission product scrubbing. The results have shown that most fission product mass is retained in the water nearby the injection point as a consequence of diffusiophoresis and inertial mechanisms. However, some of the approximations underneath the corresponding models have been found to be questionable and some new formulations have been considered and implemented within the stand-alone SPARC-90 code, which is the basis of the MELCOR models for pool scrubbing. In particular, a model capable of describing the scrubbing effect of jet injection has been implemented. This work presents better-fitted models for the scenario and, after implementing them into the SPARC-90 code, the resulting moderate quantitative impact on the accident scenario of Unit1 in Fukushima Daiichi, has been discussed to be well within the uncertainty range associated to the original code estimates. However, updating of MELCOR concerned models for fission products trapping in pools is highly recommended for physical consistency.