Cross-sectional TEM and X-ray examination of radiation-induced stress relaxation of peened stainless steel surfaces

• Published in: Journal of nuclear materials Vol. 336; no. 2; pp. 314 - 322
• Main Authors: Sencer, B.H., Was, G.S., Yuya, H., Isobe, Y., Sagisaka, M., Garner, F.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2005; Elsevier
• Subjects: Applied sciences; Controled nuclear fusion plants; DEFORMATION; DISLOCATIONS; ELECTROPOLISHING; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Fuels; HELIUM; Installations for energy generation and conversion: thermal and electrical energy; IRRADIATION; LIFETIME; LINE BROADENING; MATERIALS SCIENCE; MICROSTRUCTURE; MODIFICATIONS; NEUTRONS; Nuclear fuels; PROTONS; RELAXATION; STAINLESS STEELS; STRESS RELAXATION; STRESSES; TARGETS; S0500; E0300; P1400; R0200; X0100; R0300; Surface layer; X ray; Helium; Cross section (collision); Transients; Nuclear reactor; Lifetime; Boiling water reactor; Stainless steel; Proton irradiation; Neutron irradiation; Microstructure; Residual stress; Reactor core
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2004.10.120

Neutron irradiation-induced relaxation was emulated using proton irradiation in order to determine the expected amount of stress relaxation in the peened surface layer of a BWR core shroud during its 40 year lifetime. Samples of 304 SS were shot peened to induce a compressive residual stress, and then irradiated with 3.2 MeV protons at 288 °C to four dose levels spanning 0.1–2.0 dpa. One set of specimens was as-peened and a second was pre-injected with 25 appm He. Depth-dependent measurements of internal stress were conducted using successive steps of X-ray line broadening measurement and electropolishing. Results showed that the compressive stress state was progressively relaxed, but was maintained at some level for the majority of the 2 dpa target dose. Helium pre-injection did not significantly affect the relaxation, but the magnitude of thermally-induced relaxation was somewhat greater, although it was observed to be largely a transient, saturable process. A new cross-section technique was developed that allows multiple observations to be made in one specimen at all depths, both in and beyond the peen-damaged range. The as-peened microstructure varies strongly with depth, consisting of deformation twins and dense dislocation networks. The radiation-induced relaxation on the microstructural level was expressed primarily in modification and reduction of the dislocation structure. A comparison was made between the proton-induced relaxation of internal stresses and predictions based on neutron-induced relaxation of externally-applied stresses. The relatively good agreement indicates that proton irradiation is a valid emulation of neutron irradiation for this application.