A principal component in plant life extension is assuring that the reactor pressure vessel can withstand a pressurized thermal shock during re-cooling after a LOCA. Under the intense radiation fields present in the reactor core, pressure vessels become embrittled because of the development of a fine defect microstructure, which includes small Cu-rich precipitates, nanovoids, and dislocation loops which are invisible to most detection techniques.

At Penn State, we are working on a non-destructive evaluation method for measuring these small defect clusters, based on Positron Annihilation Lifetime Spectroscopy. In this method, we correlate the positron lifetime in the solid with the type and amount of specific defects and defect clusters in the material. The objective is to show that there is a correlation between specific positron annihilation spectra and decreases in fracture toughness, as measured by the Charpy test. Results so far have indicated that the technique can differentiate between different levels of cold-work in the material, and between neutron damage (up to 10¹⁷ n.cm^-2) and cold-work. The technique was also shown to be sensitive to neutron damage annealing. Current research is extending these results to higher fluences and higher temperatures. We expect eventually to correlate our results to fracture toughness.

Researchers: S.E.Cumblidge, G.L.Catchen and A.T.Motta.

Funding: FERMI Project