Modeling of fuel performance and metallic fission product release behaviorduring HTTR normal operating conditions

The computer codes PANAMA and FRESCO developed at the Research Center Julic h have been used for the prediction of fuel performance and fission product release behavior during the normal operation of the Japanese High-Temperat ure Engineering Test Reactor, HTTR. Basis for the calculations was the so-c alled 'Standard HTTR Operation Plan' with a nominal operation time of 660 e fpd including a 110 efpd period with enhanced fuel temperatures. Fuel perfo rmance model calculations with the PANAMA code have shown that for the temp erature distribution given, only a small additional failure fraction is exp ected. The diffusive release of metallic fission products from the fuel occ urs mainly from the central core layers with the maximum temperatures where as there is little contribution from the upper layer. Silver most easily es capes the fuel. The release data for strontium and cesium also reveal a sig nificant fraction to originate from still intact particles. The comparison with the calculations obtained with the JAERI models has shown a good agree ment for the release from the coated particles. (C) 2001 Elsevier Science B .V. All rights reserved.