SCC Tests In SCW Environment

Supercritical water cooled reactor is one of the potential next generation nuclear power plant concepts. The supercritical water (SCW) environment is typically ultrapure water as the solubility of the ionic species is low. The operation temperature and pressure are typically 550°C – 650°C and 25 MPa– 35 MPa, respectively.

There are several references related to the construction material SCC phenomena studies. Most of the tests are SSRT where as less crack growth rate tests or fracture mechanical tests have been performed. As the operation environment is rather difficult, it is understandable that the irradiation effect on the SCC and CF has not been studied extensively.

Cormet has designed and built a recirculation loop and an HT HP testing cell with a loading device for the University of Birmingham. The instrument operation parameters are 650°C temperature and 300 bar pressure.

The testing cell has been equipped with a metallic window that allows the exposure of the tensile specimen to the proton or the neutron beam. The ion beam energy reduces strongly in SCW media. Therefore, the distance between the metallic window and the tensile specimen must be minimised. The instrument has designed and built a window construction that allows the moving of the window close to the specimen even in the presence of high temperature and high pressure.

The loading device capacity is 25 kN as it has been designed for regular 4 mm and 6 mm diameter round tensile specimens and ½” CT specimens. Additionally, the Customer wants to operate the instrument with SSJ flat tensile specimens with 1.2 mm specimen width and 1 mm thickness. Cormet has designed electrically isolating specimen holders for this specimen. It is a challenge to test these specimens as the load related to the UST is about 500 N. It is obvious that the 25 kN loading device capacity is too high for the SSJ specimens but we could perform reasonable SSRT tests with them in an SCW environment (650°C / 296 bar). The optimal maximum loading device capacity would be 1 kN – 2 kN for such tests.

There are no electrochemical tools available as the low conductivity of the SCW makes those tests really difficult. However, Operator can use the recirculation loop adjustable dissolved oxygen controlling functionality as a “chemical potentiostat”.