Abstract: [Background] In reactor core, recoil protons produced by fission neutrons may interact with coolant of the primary circuit and produce radioactive nuclides through reactions ¹⁶O(p,α)¹³N, ¹⁸O(p,n)¹⁸F and ¹¹B(p,n)¹¹C. Positrons emitted by the radioactive nuclides, ¹³N, ¹⁸F and ¹¹C, etc., can be detected by coincidence measurement, hence the leakage of the reactor coolant inferred. However, calculation of the source terms of the nuclear reactor core are mainly based on solving the point burn-up equation or simulation of the reactivity based on Monte Carlo method, lacking the capability to simulate (p,α) and (p,n) reactions for protons at 0~20 MeV. [Purpose] This study aims to simulate the production of source terms generated by protons for the reactors of Qinshan's second nuclear plant. [Methods] Full reactor core of the reactor was modeled in GEANT4. Source sampling description based on general particle source (GPS) was achieved in consideration of radial and axial power distributions of the reactor core. G4-NONU was developed using C++ for neutron transportation to realize the function of NONU card in MCNP (Monte Carlo N Particle Transport Code) by modifying the fission model in GEANT4. Energy spectrum of recoil protons in water of the primary circuit was calculated, so were the reactivities of ¹⁶O(p,α)¹³N, ¹⁸O(p,n) ¹⁸F and ¹¹B(p,n)¹¹C. Eventually, concentrations and activities of ¹³N, ¹⁸F and ¹¹C of the primary circuit were computed. [Results and Conclusion] Methods for description of source terms for pressurized water reactor in GEANT4 were established and nuclear reactor problems involving charged particles can be simulated by self developed G4-NONU, which is an enrichment of the simulations tool for nuclear reactor.

Key words: GEANT4 simulation, Pressurized water reactor, Charged particles, Source terms of the primary circuit