Preliminary neutronics analysis of the hydrogen leakage effect on yttrium hydride moderated heat pipe cooled microreactor

Among the various metal hydrides, yttrium hydride exhibits remarkable thermal stability and maintains a relatively high hydrogen atom density at high temperatures, making it a popular choice in microreactors. When the temperature of yttrium hydride exceeds 870 °C, the hydrogen atom density decreases with increasing temperature, which would result in a series of changes in the microreactor parameters. This study uses the RMC code with the ENDF/B-VIII cross section database to investigate the effect of the reduction in hydrogen atom density on the neutronics parameters of the microreactor in response to high temperatures. The results show that the initial k eff decreases with increasing yttrium hydride temperature and the time for critical operation of the microreactor is reduced. The worth of reactivity control increases with temperature, whether it be the control drums or the control rod. The decrease in density of hydrogen atoms at high temperatures results in a further negative temperature reactivity coefficient. The results presented in this paper will serve as a valuable reference for the design and analysis of the yttrium hydride moderated microreactor.