HYDROGEN GENERATION DURING CLADDING COOLANT INTERACTIONS UNDER REACTIVITY INITIATED ACCIDENT CONDITIONS/

Hydrogen generation in chemical reaction of Zircaloy cladding with coo lant water under reactivity initiated accident conditions (RIAs) has b een studied with the in-pile experiments in the Nuclear Safety Researc h Reactor (NSRR). PWR type segmented fuel rods were subjected to pulse irradiation to simulate the power excursion of an RIA. Transient meas urements of the void fraction with a densimeter developed for the in-p ile experiment detected prompt generation of hydrogen with an increase in cladding surface temperature. The hydrogen generation ceases in th e initial 4 seconds of the power excursion even in the experiments res ulting in the melting of the fuel cladding and severe damage. The tota l amount of hydrogen generated during the power burst was estimated by integration of the densimeter data and also by metallographic examina tions of the oxidized cladding. The total amount of hydrogen produced increased with an elevation in the maximum temperature of the cladding surface, and the hydrogen generation was intensified as a function of damage to the fuel cladding. The applicability of the PRECIP-II code to the analysis of hydrogen generation under an RIA condition was also examined.