Reactivity temperature coefficient evaluation of uranium zirconium hydride fuel element in power reactor

An in-core fuel management code package for uranium zirconium hydride power reactor, which is developed on the basis of the assembly lattice code TPFAP and the core calculating code BMFGD for LWR, is firstly introduced in this paper. The inherent safety of the U–ZrHx element which is mainly caused by the high prompt negative temperature coefficient is then evaluated, because the weight percentage of uranium, fuel rod radius and fuel temperature of U–ZrHx element will be different in power reactor from those in research reactor, and these changes may make obvious effect on the prompt negative temperature coefficient. The influence of weight percentage of uranium, fuel rod radius, fuel temperature, content of hydrogen and additional poison on prompt negative temperature coefficient for uranium zirconium hydride element are calculated respectively in this paper, and then the results are analyzed theoretically. The study shows that the absolute value of prompt negative temperature coefficient reduces observably along with the increasing of Uranium weight percentage from 10 wt% in research reactor to maximum 45 wt% in power reactor. Smaller radius, higher operating temperature and longer core life make little effect on the prompt negative temperature coefficient in the condition of high weight percentage of U. Additional poison erbium in fuel makes prompt negative temperature coefficient much more negative. Anyway, high prompt negative temperature coefficient can be achieved for U–ZrHx power reactor with higher weight percentage of U, smaller radius and Er poison, in other words, the characteristics of inherent safety of U–ZrHx core can be retained at power reactors.