Quality control of PHWR fuel tube closure welds

PHWR fuel bundle has 19 elements, each of about half a metre long enclosing natural uranium dioxide pellets; all the 19 elements being attached to the end plates of the two ends. The design of the bundle lends itself for mass production due to simplistic manufacturing route. Each element containing UO pellets is hermetically sealed at both ends with zircaloy end plates. Considering the large number of elements to be welded and due to the wall thickness being thin, resistance welding is being successfully employed. This process is considered critical and quality control check on this should give assurance with high level of confidence. Due to the complex nature of the shape and the thickness, a reliable and quick NDT method has not so far been identified and practised. Statistical method of control has been found to be very effective in maintaining the integrity of the welds. This paper describes the statistical method adopted with sampling plan for achieving good reliability. (author). 2 refs., 8 figs., 1 tab