Dynamic fracture mechanics analysis of hydrogen embrittlement of Zr-2.5 Nb pressure tube

This paper describes the dynamic fracture behavior of heat treated Zr-2.5 Nb pressure tube which is used for the Prototype Heavy Water Reactor 'FUGEN' that is under construction by the Power Reactor and Nuclear Fuel Development Corporation. Hydrogen is picked up by the reactor pressure tube from the water coolant. The hydrogen concentrates in regions with stress concentration and the regions become very brittle. Therefore, in designing structures and safety systems, the effects of stress on hydrogen density and hydrogen concentration must be taken into consideration. When a local fracture initiates in a brittle region it must be arrested in order to prevent unstable fracture of the pressure tube. Four experiments have been done in order to clarify the dynamic fracture behaviors of the pressure tubes. The experiments are: (1) a leak before rupture experiment using tube specimens with a part-through-crack under internal repeated pressure, (2) a dynamic fracture toughness experiment using drop weight equipment at temperature to 3000C, (3) a crack arrest experiment using a double cantilever tube specimen under wedge force, and (4) a hydrogen enrichment and concentration experiment with the specimen subjected to various stresses. The test results are discussed systematically from the view of dynamic fracture mechanics. (Auth.)