In-situ measurement of void swelling of austenitic steels used in PWR core internals

Full text: Void swelling of austenitic core internal components has been identified as an issue by the U.S.N.R.C. that must be addressed prior to extension of a power plant license from 40 to 60 years. The vulnerable components are the baffle-former assembly, especially at reentrant corners. Swelling has been observed in some PWR components and a number of studies have shown that in some local areas the swelling might be rather large. The major issues associated with void swelling are component distortion and especially void-induced embrittlement at swelling levels on the order of ∼10%. WWER of Soviet design will also be subject to void swelling, especially in the baffle ring. This paper shows that swelling induces significant and measurable changes in important physical properties such as density, electrical and thermal resistivity, elastic moduli and ultrasonic velocity. These changes can be measured nondestructively under water within the core using remote probes. The results of several proof-of-principle studies have shown that it is feasible to measure swelling within the core of a PWR reactor. The studies have used both non-radioactive surrogate specimens and highly irradiated steels with significant levels of neutron-induced swelling