On the Composition and Structure of Nanoprecipitates in Irradiated Pressure Vessel Steels

Abstract

Nanoscale Cu rich precipitates (CRPs) are widely believed to be the dominant hardening feature resulting in severe embrittlement in irradiated reactor pressure vessel (RPV) steels. However, this view has recently been challenged by interpretations of atom probe field ion microscopy (APFIM) measurements that describe the dominant nanofeatures as dilute solute atmospheres (DSAs). The practical impact of these differing views is very significant. This work compares and contrasts the CRP versus DSA descriptions to a wide variety of pertinent data. Mechanical property trends as well as small angle neutron scattering (SANS) and field emission scanning transmission electron microscopy (FEGSTEM) measurements support the presence of CRPs. CRPs are also consistent with the fundamental thermodynamic and kinetic laws. However, standard theory cannot provide the atomic level resolution needed to fully understand the nanofeatures. Therefore, a new Lattice Monte Carlo (LMC) atomistic method is used to simulate the complex chemical structures of the CRPs. The LMC method unifies the SANS/FEGSTEM and APFIM data within a well founded physical framework.

Simulation of radiation damage in Fe alloys: an object kinetic Monte Carlo approach

“…In particular, the strict requirement of allowing only single point defects to migrate seems to be, at first glance, the only way of keeping some residual damage in the box at the end of the ageing, despite the evidence of cluster motion from MD simulations [21,[56][57][58][59][60]. Since damage is known to accumulate in Fe alloys under irradiation [1][2][3][4][5][43][44][45][46][47][48][49][50]84], this suggests that trapping mechanisms, either explicit (addition of traps in set B), or implicit (sets A and C) are fundamental for a correct prediction of radiation effects in these alloys. In the present section we propose a selection of simulations of irradiation experiments in pure Fe and Fe-Cu, aimed demonstrating that, provided that traps are introduced and with a choice of other parameters based mostly on MD simulation results, it is possible to obtain physically acceptable results from OKMC simulations, within the assumptions described in Section 2.…”

“…Low alloy ferritic steels are structural materials for the pressure vessels of light water reactors and are long known to undergo severe embrittlement under neutron irradiation during operation [1][2][3][4][5]. The microscopic mechanisms responsible for this effect are nowadays qualitatively fairly well understood in terms of matrix damage accumulation, radiation-enhanced copper precipitation and, to a lesser extent, grain boundary segregation [2,3].…”

“…doi:10.1016/j.jnucmat.2004.07.037 [3], while a number of significant uncertainties remain. Copper-rich precipitates are known to appear in the form of a relatively high density of ultrafine (<2 nm) particles, whose composition (Ni, Mn and particularly Fe content) and morphology (clouds or full precipitates) is still being debated [4][5][6]. The matrix damage component is generally interpreted as a collection of point defect clusters, such as self-interstitial atom (SIA) loops and nanovoids, although their exact nature, in combination and interaction with solute atoms, remains elusive [3].…”

Understanding of copper precipitation under electron or ion irradiations in FeCu0.1wt% ferritic alloy by combination of experiments and modelling

“…Hardening and embrittlement of the vessel steel under neutron irradiation are one of the limitations of the lifetime of such reactors. It is well established that the degradation of the mechanical properties of vessel steel under irradiation is in relationship with the formation of a high number density (>10 23 m À3 ) of very fine ($2 nm in diameter) solute clusters [1][2][3][4][5][6][7][8][9][10][11][12]. These clusters are enriched in one solute known to be in super-saturation [13,14] in iron at the temperature of irradiation (300°C) -the copper -and also in some under saturated solutes in iron [15]: manganese, nickel, silicon and phosphorus.…”

Roadmap for Nondestructive Evaluation of Reactor Pressure Vessel Research and Development by the Light Water Reactor Sustainability Program

“…The TTS implications of LBP and transformation of CRPs to Mn-Ni-Si dominated features are increasing TTS with increasing neutron fluence, results not predicted by models based on surveillance data at relatively low fluences. References [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] were used variously for much of the preceding discussion.…”