Attenuation of atomic displacement damage in the heavy reflector of the PERLE experiment and application to EPR

Attenuation of neutron and photon-induced irradiation damage in pressurized water reactor pressure vessels

“…[1], [3] show that the attenuation of DPA is different from the recommended formula of the US Nuclear Regulatory Commission (NRC) regulatory guide 1.99 revision 2 [8], based on neutron fluence above 1 MeV [8]. Our recent work [5] points out that the neutron fluence above 0.5 MeV is quite representative of DPA in the SS heavy reflector from the point of view of attenuation. Moreover, the 0.5 MeV threshold is the Eastern European Standard [7].…”

“…All Tripoli-4.10 Monte Carlo simulations are based on the JEFF-3.1.1 evaluated pointwise nuclear data library [12]. The accuracy of Tripoli-4 simulations of the PERLE core and heavy reflector with JEFF-3.1.1 was validated against experimental measurements on reactivity [5], [11], [13], pin-by-pin power distribution [11], neutron and photon doses in the SS heavy reflector [11], [13]. The neutron and photon spectra used for calculating DPA rates in the RPV are the volumeaverages in the hollow cylinders for z-axis from the bottom to the top of fuel pins.…”

“…As explained in Ref. [5], the DPA rates presented in this paper are calculated by folding the neutron and photon flux spectra from Tripoli-4.10 simulations with the corresponding neutron and photon-induced damage cross sections. By analogy to the attenuation of flux density in a 1-D approximation, our previous work [5] proposed a simple formula for describing the neutron-induced DPA rate versus the penetration in steel reflector as:…”

“…In the heavy reflector, due to the important albedo of thermal neutrons from the external moderator, the thermal neutron radiative capture reaction rate is an important source of photon production [5]. In the vicinity of the RPV outer surface, because there are only negligible backscattered thermal neutrons (as illustrated in Figure 2), the photon-induced DPA can be simplified as:…”

“…Ref. [3] points out that a simple exponential form cannot fit the shape of attenuation of neutron-induced DPA in stainless steel (SS) RPVs, whereas our previous paper [5] shows that the exponential form is quite suitable to describe the attenuation of neutron-induced DPA rates in the SS heavy reflector. Since the neutron and photon (called also as gamma-ray) spectra in a RPV are quite different to those in a SS heavy reflector (details are presented in Section 3), this paper investigates the attenuation of neutron and photon-induced DPA in RPVs with and without a 22 cm thick SS heavy reflector surrounding the core, using Tripoli-4 ® [6] Monte Carlo simulation.…”