Mechanical Property Changes in Reactor Vessel Materials Thermally Aged for 209 000 H at 260°C

Abstract

Surveillance materials consisting of a SA-508 Class 2 forging, a Mn–Mo–Ni Linde 80 submerged-arc weld, and an SA-533, Grade B, Class 1, correlation monitor material were thermally aged on a commercial reactor pressure vessel. The materials were exposed to a thermal environment of 260°C for 209000h. This temperature is below the range (minimum of 370°C) where the effects of long-term thermal aging are typically considered relevant. Charpy impact, master curve transition temperature, upper-shelf fracture toughness, and tensile testing were conducted to evaluate the long-term thermal aging changes in material properties. Small changes in the impact properties were observed for all the materials, but were generally within the 95 % confidence bounds for typical Charpy data. Upper-shelf energy also showed small variations, but a general decrease for all materials was not seen. Fracture toughness testing at the upper shelf indicated that the upper-shelf toughness had increased, however the data is scattered. Master curve T0 testing in the transition region showed little change in the forging and plate results; however an improvement in the transition temperature of the weld metal was measured.

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“…Because of its location, the surveillance material was considered to have negligible neutron fluence exposure which was experimentally verified. The bulk compositions of these alloys and the change in mechanical properties during extended aging treatments are given in Table 2 [53]. Small changes in the impact properties were observed, but were generally within the 95% confidence bounds for typical Charpy data [53].…”

“…The bulk compositions of these alloys and the change in mechanical properties during extended aging treatments are given in Table 2 [53]. Small changes in the impact properties were observed, but were generally within the 95% confidence bounds for typical Charpy data [53]. Uppershelf energy showed small variations.…”

“…Uppershelf energy showed small variations. Master curve T 0 testing in the transition region showed little change in the forging and plate and a small improvement in the weld [53].…”

“…In these experiments, the thermal aging specimen boxes were attached to the service support structure on top of the reactor vessel head [Oconee Nuclear Station, Unit 3 (ONS3)] and are located under the head insulation. In this study, a SA-533 grade B class 1 plate B (HSST-02, A1195-1), SA-508 class 2 forging A (ANK 191) and a submerged arc weld B-Mn-Mo-Ni weld wire/Linde 80 flux (WF-209-1) were placed on the reactor vessel heads before startup and were removed from ONS-3 after an exposure time of either 93 000 or 103 000 and 209 000 h ($24 years) at a temperature of $260°C [53]. The exact exposure time for each set of materials was difficult to determine because of the time allowance for reactor heatup, cooldown and hot standby.…”

“…Note the enrichment of manganese in the precipitate and the nickel and manganese enrichments at the precipitate-matrix interface. Material courtesy Gunawardane and Hall of AREVA[53].…”