Quality assurance for HTR fuels

Quality Assurance (QA) for a nuclear fuel is no different from that for any other complex manufacturing process and product. However, such fuel cannot be functionally tested before use even though the consequences of a failure - e.g. lack of electricity production - are particularly costly. Risk assessment may be used to define the confidence level required and this will normally imply a ''three-legged stool'' approach to QA, the three equally vital supporting areas being validated manufacture, Quality Control and Quality Audit. In HTR fuel, primary fission product containment is achieved on a microscale by the use of carbon and silicon carbide coating barriers, pyrolytically deposited on actinide materials in the form of small spherical kernels. The coated particles are dispersed in a graphite matrix and used either as spherical balls in a pebble-bed reactor or carried as cylindrical fuel bodies in hexagonal fuel elements of a prismatic HTR. This paper reviews the QA information which has been published for HTR fuels. Over the last four years the subject has benefited from the Dragon Project having organized an international working party for discussion of QA for HTR fuels. It is important to form strong linkages at the outset between Design, Manufacture, Quality and Performance to establish the specification. The specification, derived from two main types of requirement, functional and safety, is the result of an iterative process working back from the final product aided by a Quality Factor classification. For each manufacturing step along this chain a series of input-output relationships is defined, and it is shown, with examples, how Quality Control is applied throughout as a mixture of input, in-process and output controls. The emphasis is on the primary importance of getting the product right first time. It is concluded that general experience with HTR fuel is good and the next phase of work must be mainly concerned with large-scale validation under non-accelerated operating conditions. (author)