A Comparison Between French Surveillance Program Results and Predictions of Irradiation Embrittlement

Abstract

At the beginning of 1986, thirty-two 900-MWe and four 1300-MWe nuclear power stations were in service in France. A regulatory surveillance program is in progress concerning the base metal, weld metal, and heat affected zones of every nuclear pressure vessel; a reference metal sample is also present in each reactor. This surveillance program was implemented largely in accordance with U.S. rules. The specifications for the core shell forgings in MnNiMo low alloy steel and the associated welds require low contents in embrittling elements such as copper and phosphorus. The results presented here concern materials containing less than 0.08 wt% Cu and 0.011 wt% P, except for the welds of the first six reactor vessels, which have 0.13 wt% Cu and 0.019 wt% P maximum. The main aim is to obtain the RTNDT shift from Charpy-V tests, in relation to the fluence measured from fissile and activation dosimeters. Tensile, compact, and three-point bend specimens are also included in the capsules. Results for the first capsules removed after up to four years of operation, corresponding to fluences (E > 1 MeV) less than 1.5 × 1019 n · cm−2 (2.9 × 10−2 dpa), are presented and evaluated. The mean and upper values of the RTNDT shift are about 20 and 40°C, respectively, and there is no significant difference between parent metal and weld. A new formula to predict embrittlement has been derived from test reactor experiments, because of the strict limits on the residual element contents in French materials when compared with materials for which other formulae have been established. The surveillance program results are discussed and compared with the predictions of these formulae.

Reactor pressure vessel embrittlement: Insights from neural network modelling

“…In addition to the experimental programme, significant efforts have been made in order to develop a better understanding of these phenomena. These have approached the problem by incorporating physical understanding into existing models [10,11], by developing a model on sound reasoning and fitting the resulting parameters to data [12,13], or by developing a model using solely modelling and simulation [14]. The preference for physical understanding over empiricism is fundamental in reducing risk and is reflected in the considerable research undertaken by the industry.…”

60th Anniversary of electricity production from light water reactors: Historical review of the contribution of materials science to the safety of the pressure vessel

“…According to the country and the approach used to establish them, those methods are also called "embrittlement trend curves", "embrittlement prediction curves", "dose damage relationships" [163]. The first ones were set up from the mid-1970s [164,165], and they mostly relied on analysis of results obtained after irradiation in MTRs. Then, with the aging of the nuclear fleets, the setting up of subsequent methods or revisions of existing ones have been done by taking into account only or mostly results produced in the framework of RPV surveillance programs (e.g., [166]).…”

The development of radiation embrittlement models for US power reactor pressure vessel steels

“…The development of new embrittlement prediction equations [13,14] stems from a series of studies on radiation embrittlement models, such as Guthrie's model [15], the model of Odette et al [16], Fisher and Buswell's model [17], Lowe and Pegram's model [18], the French model [19], and several other parameter studies on the PR-EDB. Although the copper-precipitation model, in addition to the matrix damage model, has been extremely successful in explaining many aspects of irradiation embrittlement, it is becoming increasingly evident that other elements also contribute to the embrittlement of RPV steel, such as Ni, P, Mn, Mo, and S. Theoretically, all the impurities in low-alloy steel are candidates for inclusion in the modeling.…”