Radiation-induced stress relaxation in high temperature water of type 316L stainless steel evaluated by neutron diffraction

Abstract

RadiationWeld beads on plate specimens made of type 316L stainless steel were neutron-irradiated up to about 2.5 Â 10 25 n/m 2 (E > 1 MeV) at 561 K in the Japan Material Testing Reactor (JMTR). Residual stresses of the specimens were measured by the neutron diffraction method, and the radiation-induced stress relaxation was evaluated. The values of r x residual stress (transverse to the weld bead) and r y residual stress (longitudinal to the weld bead) decreased with increasing neutron dose. The tendency of the stress relaxation was almost the same as previously published data, which were obtained for type 304 stainless steel. From this result, it was considered that there was no steel type dependence on radiation-induced stress relaxation. The neutron irradiation dose dependence of the stress relaxation was examined using an equation derived from the irradiation creep equation. The coefficient of the stress relaxation equation was obtained, and the value was 1.4 (Â10 À6 /MPa/dpa). This value was smaller than that of nickel alloy.

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

“…Understanding on irradiation creep has obtained mainly from data at temperatures higher than 400 • C [278] and experimental data at LWR-relevant temperatures (280-370 • C) are scarce [279,280]. Recently data on irradiation creep and stress relaxation at temperatures around 300 • C have been accumulated by MTR irradiation experiments in the last decade [281][282][283][284][285][286][287]. Figure 22 shows the data of irradiation stress relaxation in type 304 and 316L SSs at 288 • C [280][281][282][283][284].…”

Crack growth rate in core shroud horizontal welds using two models for a BWR

“…The stress intensity factor, the crack growth rate and the crack depth through-wall to core shroud were determined using the actual size and distribution of the cracks and the combination of weld residual stress distribution presented in Fig. 5 [3], applying a 30% relaxation to residual stress distribution that had been measured in unirradiated welded stainless steels according with information in BWRVIP-14NP-A and [12].…”

“…Under constant displacement conditions (e.g., for weld residual stresses), radiation produces substantial stress relaxation for a neutron fluence above of 5 Â 10 24 n/m 2 (E > 1 Mev), which is an important factor in understanding and predicting the behavior of core component [10,12].…”

“…Weld residual stress magnitude is expected to decrease as a result of relaxation caused by irradiation-induced [10,12].…”

“…Experiments performed by Ishiyama et al [12] on weld beads on plate specimens made of type 316L stainless steel neutron irradiated from 5.3 Â 10 24 n/m 2 to 2.5 Â 10 25 n/m 2 (E > 1 Mev) at 288°C concluded that, residual tension stresses decreased with increasing neutron dose and proposed an equation to quantify percentage of radiation-induced stress relaxation.…”