An Evaluation of Through-Thickness Changes in Primary Damage Production in Commercial Reactor Pressure Vessels

Abstract

An extensive database of atomic displacement cascades in iron has been developed using the method of molecular dynamics (MD). More than 300 simulations have been completed at 100K with energies between 0.1 and 100 keV. This encompasses nearly all energies relevant to fission reactor irradiation environments since a 100 keV MD cascade corresponds to the average iron cascade following a collision with a 5.1 MeV neutron. Extensive statistical analysis of the database has determined representative average values for several primary damage parameters: the total number of surviving point defects, the fraction of the surviving point defects contained in clusters formed during cascade cooling, and a measure of the size distribution of the in-cascade point defect clusters. The cascade energy dependence of the MD-based primary damage parameters has been used to obtain spectrum-averaged defect production cross sections for typical fission reactor neutron energy spectra as a function of depth through the reactor pressure vessel. The attenuation of the spectrum-averaged cross sections for total point defect survival and the fraction of either interstitials or vacancies in clusters are quite similar to that for the NRT dpa. However, the cross sections derived to account for the energy dependence of the point defect cluster size distributions exhibit a potentially significant variation through the vessel. The production rate of large interstitial clusters decreases more rapidly than dpa whereas the production of large vacancy clusters is slower than dpa.

Current understanding of radiation-induced degradation in light water reactor structural materials

“…Reliability of such estimations has been examined using irradiation defect production calculations and mechanical property tests on decommissioned pressure vessels [139]. For example, molecular dynamics calculations of freely migrating point defects with a neutron transport calculation through pressure vessel steels revealed that the dpa attenuation trend was suitable to predict the attenuation of damage production [140]. Data from the decommissioned French PWR Chooz A pressure vessel demonstrated that the change in measured transition temperature shift was in agreement with the trend of the predicted shift assuming a dependence of (fluence) 0.48 [141].…”

INCAS: an analytical model to describe displacement cascades

“…• a 'short-term irradiation' module treats the neutron spectrum to provide the PKA spectrum (with the code SPECMIN 4 [27,28]). Then, using this spectrum as source term, INCAS gives the induced sub-cascade spectrum (number of sub-cascades versus their dissipated energy).…”

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

“…( 2) obtained from the least square fitting is numerically different from the value of Σ '() in Eq. (1). Therefore, the difference between the fittings from Eqs.…”

“…However, Refs. [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.…”

“…Due to the slowing down and absorption of neutrons in RPV, the DPA attenuates with increasing penetration in RPV. Stoller and Greenwood [1] investigated the neutron-induced DPA in different penetrations in RPV using both the standard Norgett-Robinson-Torrens (NRT) formula [2] and Molecular Dynamics (MD) simulations. Carew and Hu [3] studied the radial and axial dependence of neutroninduced DPA in RPV.…”