Abstract
When the reactor was in the subcritical state, the criticality safety of the core was monitored by the source range detector which was placed out of the core. According to the “Initial Loading Test for Pressurized Water Reactor of Nuclear Power Plant” (NB/T 20434-2017RK), the recommended value of count rate of the detector was larger than 0.5 cps. But during loading and other subcritical reactor conditions, the number of neutrons in the core is relatively low, causing that the count rate of the ex-core source range detectors could not reach 0.5 cps. Thus, secondary neutron source was placed in the following cycle of reactor to increase the neutron count rate of the ex-core source range detectors to 0.5 cps to meet the standard. In fact, the use of secondary neutron sources raises a number of problems, such as: 1) the production of radioactive and other tritium from secondary neutron sources, the total production of which is a limiting criterion for the construction of nuclear power plants; 2) the increased procurement costs of secondary neutron sources; and 3) the vulnerability to damage due to the long presence of secondary neutron sources in the core, increase the radioactivity level of the primary circuit. Because of the use of low leakage loading fuel management in HPR-1000, the spent fuel assemblies were placed closer to the source range detector and generated more neutrons, it is possible for the ex-core source range detectors to meet the counting requirement of 0.5 cps regardless of whether the core is in the subcritical state. This paper studied the removal of secondary neutron source in HPR-1000. The neutron source intensity of spent fuel assemblies and neutron count rate in fuel loading process were calculated in a conservative method with three dimension monte carlo code. The calculated results had shown that the removal of secondary neutron source in HPR-1000 satisfies safety requirements.
