Boron chemistry during transportation in the high temperature region of a boiling water reactor under severe accident conditions

Abstract

ABSTRACT Boron (B) chemistry during transportation at temperatures above 400 K was experimentally investigated to evaluate the transport behavior of control rod material B during a severe accident (SA) of a boiling water reactor while considering effects of B on cesium (Cs) and iodine (I) behavior. The heating test on B2O3 specimens was conducted at 1150 K in a steam atmosphere using the dedicated experimental apparatus named the TeRRa reproducing release and transportation of B in an SA. New findings on B chemistry in the high-temperature region emerged. A large amount of released B2O3 vapor was deposited above 1000 K by condensation on stainless steel (SS). The B deposits and/or vapors significantly reacted with SS above 1000 K, forming 2FeO · FeBO3 The experimental data indicate that a large amount of released B from a degraded BWR control blade in an SA remains in the high-temperature region like a Reactor Pressure Vessel (RPV). These results and thermodynamic considerations suggest the presence of B deposits in the high-temperature region decrease the amount of Cs vapors transported from an RPV. This is attributed to the possible formation of low volatile compounds like CsBO2 from the reaction of B deposits and Cs vapors.