Development of facility for in-situ observation during slow strain rate test for irradiated materials

Irradiation assisted stress corrosion cracking (IASCC) is a degradation phenomenon caused by synergy of neutron radiation, aqueous environment and stress on in-core materials, and it is an important issue in accordance with increase of aged light water reactors (LWRs). Isolating crack initiation stage from crack growth stage is very useful for the evaluation of the IASCC behavior. Hence facility for in-situ observation during slow strain rate test (SSRT) for irradiated material was developed. The facility for in-situ observation has been installed in Waste safety testing facility (WASTEF) located in Tokai research establishment. The facility consists of a test machine installed in a hot cell, a water circulation system with pressurized high temperature water loop and control unit installed at operation room. Main specification of the facility is as follows; Maximum load capacity 20 kN; Cross head speed range 10-7 mm/min∼10 mm/min; Maximum test temperature 573 K (300degC); Maximum test pressure 10MPa; Water supply rate 0.03m3/h (30 l/h, constant); Controllable range of dissolved oxygen (DO) 10 ppb∼32ppm; Controllable range of dissolved hydrogen (DH) 10 ppb∼2.8ppm; Monitoring of water chemistry DO, DH, conductivity, pH; Other specifications in-situ observation and recording during SSRT, injection of hydrogen peroxide into autoclave; As performance demonstrations of the facility, tensile test with in-situ observation and SSRT without observation were carried out using unirradiated type 304 stainless steel in 561 K water at 9 MPa. The following were confirmed from the results. (author)