Fracture Toughness Evaluation of Zr-2.5Nb Pressure Tubes Manufactured Employing Double Forging for PHWR700

Effect of direction of approach of test temperature on fracture toughness of Zr–2.5Nb pressure tube material

“…Being brittle, the presence of substantial quantities of hydrides can cause embrittlement of the host matrix resulting in loss of ductility, impact and fracture toughness. Both impact and fracture toughness of this alloy shows strong influence of hydrides below 150 1C [8][9][10] and above 150 1C, the influence of hydrides on impact [8] and fracture toughness [9,10] is insignificant.…”

“…However, it was also pointed out that the gross tensile ductility of this alloy is reportedly unaffected by temperature(s) up to 300 1C [12,13] and the hydride of this alloy reportedly fails in brittle manner up to 400 1C [14]. The increase in temperature will result in partial dissolution of hydrides, and hence the degree of hydride embrittlement (HE) can be expected to reduce with the reduction in hydride volume fraction with increase in temperature.…”

Influence of loading rate and hydrogen content on fracture toughness of Zr-2.5Nb pressure tube material

“…The critical crack-length (CCL) values for the catastrophic failure of the pressure tube under PHWR operating conditions were computed by matching the crack-driving force (CDF) modified by Folias factor (M) to the crack-growth resistance of the material. This was achieved by using J max values as crack-growth resistance of the material and by following an iterative method [8,9]. The aforementioned fracture toughness parameters were determined as a function of the hydrogen content and pulling rate in the temperature range of 25e300 C. For metallography, the specimens were sectioned along the radialecircumferential (RC) and the axial-radial (AR) planes of the pressure tube.…”

“…To meet LBB criteria, the critical crack length (CCL) causing catastrophic failure of the pressure tube should be sufficiently large. The CCL is calculated using fracture toughness parameters mainly J max [8,9] and tangency criteria [9,11]. There is no data available in literature showing the effect of loading rate on the fracture toughness of the Zr-2.5Nb pressure tube material.…”

“…There is no data available in literature showing the effect of loading rate on the fracture toughness of the Zr-2.5Nb pressure tube material. A greater concern is the effect of the loading rate on the fracture toughness of hydrided pressure tube materials because they show typical S curve behaviour with a lower shelf energy level one fourth of the un-hydrided material [9,10] furthermore, the loading rate may shift S curve into higher temperatures. This may lead to lower CCL at operating temperature or an increase in safe temperatures at which pressure tubes can be kept in pressurised conditions during reactor shut down.…”