Ageing assessment of RBMK-1500 fuel channel in case of delayed hydride cracking

Abstract

This paper presents the ageing assessment of RBMK-1500 fuel channel TMO-1. One of the factors determining remaining lifetime of Zr-2.5% Nb fuel channel (FC) is the amount of hydrogen dissolved during corrosion process. When the concentration of hydrogen exceeds the terminal solid solubility limit zirconium hydrides are precipitated. As a result decreases resistance to brittle fracture and form necessary conditions for delayed hydride cracking (DHC). The experimental investigations were performed to estimate DHC rates in RBMK TMO-1 pressure tubes. During the tests in average DHC values were determined at 283, 250 and 144 °C (with hydrogen concentrations correspondingly 76, 54 and 27 ppm). Resistance to brittle fracture depending on hydrogen concentration was evaluated. Leak before break analysis was carried out according to requirements of RBMK 1500 regulatory documents. J-integral and crack opening were calculated with finite element method. Critical crack length was calculated using R6 and J-integral methods. Coolant flow rate through the postulated crack was estimated using SQUIRT software. The results of experimental investigations and deterministic analyses have confirmed that the fuel channels (TMO-1) fulfil the LBB requirements.