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 life-time 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 corre-spondingly 76, 54 and 27 ppm). Resistance to brittle frac-ture depending on hydrogen concentration was evaluated. Leak before break analysis was carried out ac-cording to requirements of RBMK 1500 regulatory docu- 11 ments. 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 de-terministic analyses have confirmed that the fuel channels (TMO-1) fulfil the LBB requirements.