Assessment of the Integrity of KANUPP Fuel Channels

Abstract

The KANUPP reactor first produced power in 1972. In 1983 one of the fuel channels, G12 was difficult to refuel due to the South end fitting being retracted relative to the adjacent channels. In November 1993, eight fuel channels were inspected non-destructively for defects. The dimensions and shape of the pressure tubes were measured, and channel G12 was removed for examination and testing at the Chalk River Laboratories. Examination of channel G12 showed that the South end calandria tube rolled joint had been leaking moderator heavy water into the annulus. The inborad bearing was completely corroded away which resulted in the South end fitting seizing in the debris. The Inconel X750 garter springs were both completely broken into small rings due to Stress Corrosion Cracking (SCC) in acids produced by radiolysis of the moderator heavy water. The inspection of the eight fuel channels did not reveal any serious defects. The length and diameter changes in the pressure tubes were both small. The deuterium ingress had been low with the result that the hydrogen isotope concentration of the pressure tubes was below Terminal Solid Solubility (TSS) even close to the end fittings. Irradiation had increased the strength and reduced the ductility and fracture toughness of the tubes and the Delayed Hydride Cracking (DHC) properties were similar to irradiated cold worked Zr-23% pressure tubes. The examination and testing showed that the KANUPP pressure tubes are all probably in good condition and fit for several more years service.