Application of the Reconstituted Subsize Specimens for Assessment of Irradiation Embrittlement of RPV Steels

摘要

The actual values of the weld metal characteristics required for determination of the RPV lifetime, that is the ductile-to-brittle transition temperature (DBTT) in the unirradiated condition (T_(ko)), the phosphorus and copper contents (that are known to affect the radiation stability of steel), were not measured during manufacturing of old VVER-440 reactors. The small samples (templets) were cut out of the inside surface of the old Russian VVER-440 reactor pressure vessels (RPV) to assess the actual condition of the RPV material before and after post-irradiation annealing and after re-irradiation. Calculations have shown that it is not admissible to cut out samples of the size appropriate for machining of fullsize Charpy specimens necessary to comply with Russian Guide for determination of RPV steel DBTT. An application of subsize specimens for estimation of irradiation embrittlement of RPV steel was substantiated. In order to substantiate application of reconstituted subsize specimens made from broken subsize specimens for assessment of irradiation embrittlement of RPV materials, the correlation dependencies between the DBTT values of reconstituted and standard subsize specimens were developed. With this aim reconstitution of broken 5x5x27.5 mm specimens was performed by the stud-welding method. Both unirradiated and irradiated to high fluence steels were used in this program. The influence of reconstitution on the correlation dependence of DBTT for standard fullsize and subsize impact specimens was studied. Irradiation and re-irradiation kinetics of RPV steels were studied using subsize specimens machined from templets of operating units.