Research on Obtaining Fast Neutron Spectrum through Radiation Testing of Fuel Rods for Fast Reactor in Thermal Reactor

Based on China’s High Flux Engineering Test Reactor (HFETR), research has been conducted on the neutron spectrum modification method and physical characteristics of fast reactor fuel rods. This study analyzed the effects of various neutron screen materials and multiple fuel pin irradiation devices on spectrum modification during fuel irradiation, as well as the changes in neutron screen characteristics and their influence on the reactor’s performance. Single-assembly calculations were performed using the MCNP code, and two materials (boron carbide and europium oxide) were selected from four candidate neutron screen absorber materials, while cadmium and hafnium were excluded due to their suboptimal spectrum modification results. After comparing absorbers of varying thickness, we found that a thickness of 0.3 mm or above achieved effective spectrum modification. When placed in the reactor’s central channel, device A exhibited a higher fuel rod linear power density and a relatively small negative reactivity, while device B displayed a lower fuel rod linear power density and a greater negative reactivity. Considering the impact of burnup on the absorbers under conditions accounting only for fuel and absorber material burnup, we determined that the lifetime of absorber in device A was less than 100 days, while the effective lifetime of boron carbide in device B ranged from 300 to 500 days, and europium oxide had an effective lifetime of 500 to 700 days. This paper preliminarily proposes a feasible spectrum modification scheme, demonstrating that the modification method can meet the requirements for conducting fast reactor fuel irradiation tests in a thermal-spectrum research reactor.