Pressure tube failure - Pickering NGS unit 2

A pressure tube failure occurred after 342 days of continuous operation of Pickering NGS, Unit 2 and a lifetime capacity factor from 1971 December to 1983 December of 80.8 percent. The failure was a result of unexpectedly high levels of deuterium in the Zircaloy-2 bulk metal and contact between the pressure tube and calandria tube for a period of seven to ten years. The deuterium level in zirconium-niobium pressure tubes is significantly lower than in Zircaloy-2. The zirconium-niobium pressure tubes are expected to achieve the design life of 30 years. The G16 pressure tube failure demonstrated that: the calandria tube that surrounded the pressure tube can withstand full heat transport system pressure, thereby minimizing the consequences of such a failure; the fuel channel end fitting design severely restricted leakage out of the reactor; properly trained operators can deal with a pressure tube failure without invoking the special saftey systems. These special safety systems are designed to automatically shutdown the reactor, provide additional cooling to the fuel and contain any radioactivity released. Design and operating analyses have confirmed that pressure tube failures such as occurred 1983 August 1 present no public safety nor worker safety concerns. Work to retube Units 1 and 2 is underway with a preliminary start up schedule of the middle of 1986 and 1987 respectively