Pipe break testing of primary loop piping similar to Department of Energy's New Production Reactor-Heavy Water Reactor

Oak Ridge National Laboratory is completing a major task for the Department of Energy in the demonstration that the primary piping of the New Production Heavy Water Reactor (NPR-HWR), with its relatively moderate temperature and pressure, should not suffer an instantaneous Double-Ended-Guillotine-Break (DEGB) under design basis loadings and conditions. The approach to showing the improbability of an instantaneous DEGB for HWR primary piping required a major facility (Pipe Impact Test Facility, PITF) to apply all possible design loads, including an equivalent major earthquake (called the SSE earthquake). The facility was designed and built at ORNL in six months. The test article, a 20 ft long 16 in. diameter at SCH-40 pipe of stainless steel 316L material was fabricated to exacting standards and inspections following the nuclear industry standard practices. A flaw was machined and fatigued into the pipe at a butt weld as an initial condition. The flaw/crack was sized to be beyond the worst-case flaw that HWR piping could see in 60 years of service -- if all leak detection systems and if all crack inspection systems failed to notice the flaw's existence. Since October 1991, the test article has been subjected to considerable overloadings. The pipe has been impacted over 40 times at levels equal and well beyond the SSE loadings. In additions over 300,000 fatigue cycles, and three purposeful static overloads have been applied in order to extend the flaw to establish the data necessary to confirm fracture mechanics theories, and, more importantly, to simply demonstrate that an instantaneous DEGB is highly improbable for the relatively moderate energy system