CANDU-Specific Severe Core Damage Accident Experiments in Support of Level 2PSA

摘要

This paper describes progress made in CANDU severe core damage accident experiments conducted with a singlernchannel of one-fifth scale containing twelve simulated fuel bundles in an inert atmosphere. The geometry of the referencernfuel channel considered in this study is a pressure tube-calandria tube composite, with the pressure tube ballooned intorncircumferential contact with the calandria tube. The tests are conducted to develop a better understanding of the behaviour ofrna CANDU fuel channel array when the CANDU reactor core undergoes a postulated, low probability severe core damagernaccident. The data are required to ensure that the core damage models used in MAAP CANDU code are adequate. MAAPrnCANDU code is used to calculate the progression of a severe core damage accident in a CANDU reactor to support Level 2rnProbabilistic Safety Assessment (PSA) activities.rnExperimental results from this study showed the development of time-dependent sag when the reference channelrntemperature exceeds 800rn℃, thus suggesting that creep is the mode of channel deformation. Significant localized wallrnthinning and high longitudinal strain localization were observed at the bundle junctions along the bottom-side of the channel,rnat a distance one to two bundles away from the channel mid-point. Thus the debris formed by this mechanism is expected tornbe two to three bundles long. A creep-assisted deformation mechanism is proposed to support the findings. The experimentsrnshowed that the end-load applied by the channel during heat-up and during cool-down is small. Scaling up the data showedrnthat the forces are not sufficient to pull a full-size CANDU channel out from the end-fitting. Therefore, it may be possible tornpump coolant into the channel for accident management, without inducing failure of the channel during the early stages of thernsag phenomena prior to the development of significant wall-thinning at the bundle junctions.