Feasibility of zero temperature coefficient core with highly diluted fuel and graphite moderator

The feasibility of the special core of which temperature coefficient is almost zero over wide temperature range and becomes negative at very high temperature is shown in the present study. To avoid the effect of the power density distribution which causes temperature distribution in the core, homogenous core is assumed in this study. The graphite is adopted as the moderator from its small neutron absorption. The fuel is highly diluted to make the thermal neutron flux peak high and to make epithermal and fast neutron flux low. If the plutonium and Er-167 are mixed in this core properly, it is possible to make the core temperature coefficient almost constant between 300 and 900K and to make it suddenly negative above 900K. The proper density of plutonium and Er-167 depends on the neutron leakage from the core and the moderation ratio of the core. The moderation ratio shows an optimum value around 6000 for the sample case. If this zero temperature coefficient core is used for experimental reactor, new type of experiments may be performed. The application to pulse reactors may be one of the interesting applications.