Control Rods Reactivity Worth Measurement in a Mixed Core Heavy Water Zero Power Reactor (HWZPR)

Systems related to reactivity control in a heavy water zero power reactor (HWZPR) consist of safety rod, control rod, emergency dump, and water level measurement and regulation systems. The control rod reactivity worth and safety rods should, therefore, meet the necessary safety criteria. The safety rods are used to shutdown the reactor through rapid falls in the emergency of the reactor and for a normal shutting down condition. According to the safety criteria, the equivalent rod reactivity worth must be appreciably greater than the maximum excess of reactivity which occurs in a reactor. The main applications of the control rods are to control the power rising period and the transition from subcritical to supercritical states. According to the safety guide for a HWZPR when a reactor is close to the critical state, the reactivity insertion rate should not exceed 2×10-4 (∆k/k)/s and the reactivity worth of each control rod should be less than 0.2% ∆k/k to ensure the safety of the reactor operation. According to the obtained calculational and experimental results, these conditions are satisfied for HWZPR. By changing the reactor fuel from natural metal uranium to mixed fuel (natural metal uranium fuel and natural oxide uranium), the control rod reactivity worth is measured and according to the obtained results, the control rod reactivity worth can meet the above provisions.