Core stability tracking of the KKB BWR in recent years

The core inventories of a number of BWRs are currently experiencing gradual transitions from 8 × 8 lattice fuel to SVEA fuel. One of them is the KKB (Brunsbüttel) BWR. In this reactor, as in many others in Germany, core stability tests have been conducted on a regular basis for many years, following an established and well-defined procedure.The test experience which has been acquired from the KKB core over recent years shows that, as its inventory of 8 × 8 lattice fuel was gradually replaced by SVEA fuel, the core stability improved progressively.The paper comments on the stability tests which were conducted in the KKB plant over the time period concerned, and discusses the observed stability trend in the light of the operational characteristics of the core on the various test occasions.