Evaluation of neutron irradiation-induced displacement damage in heat pipe reactor

Abstract

• Neutron irradiation-induced displacement damage in a 5 MW HPR is evaluated. • 91 maximum DPA is obtained for the SS316 monolith after a reactivity-determined cycle length. • The more than 4% swelling of the monolith leads the refueling to be difficult. • The maximum neutron irradiation dose in the Al 2 O 3 reflector is beyond available experimental data. • Two factors are proposed to convert the fast neutron fluences into DPA for Al 2 O 3 . The present work evaluates the neutron irradiation-induced displacement damage in a 5 MWth Heat Pipe Reactor (HPR) based on the latest released ENDF/B-VIII.0 nuclear reaction data library. The evaluations are performed for the SS316 monolith in the reactor core and the inner surface of the radial Al 2 O 3 reflector, the two individual parts suffering the highest neutron irradiation. At the end of the fuel cycle length, i.e., after 90 years of full-power operation, the global maximum neutron irradiation damage in the SS316 monolith is about 91 Displacements per Atom (DPA). The corresponding more than 4% volume swelling makes the refueling difficult, even though the allowed 200 DPA in other fast neutron reactors implies two potential cycles for the HPR by considering the mechanical behaviors of SS316. In the Al 2 O 3 reflector, the maximum neutron irradiation dose ( Φ E > 0.1 M e V = 3.3 × 10 22 c m - 2 and Φ E > 1 M e V = 6.4 × 10 21 c m - 2 fast neutron fluence) is beyond the available observed data. Further experiments should be performed to study the behavior of Al 2 O 3 in the HPR reflector after more than 63 years of full-power operation. For this purpose, two factors are proposed to convert the fast neutron fluences into DPA with certain specific values for the threshold displacement energy of Al and O in Al 2 O 3 because they are still not well recognized.