Moderator temperature effect on reactivity in light water moderated experimental reactors

The moderator temperature coefficient of reactivity has been measured in a U-233 fuelled plate type light water moderated reactor (KAMINI). Using neut ron cross sections based on WIMS library, lattice homogenization code SMAXY and 3D core calculation code COMESH the moderator temperature coefficient of reactivity is predicted very well (within 0.6 pcm per degrees C). For U- 235 and Pu-239 fuelled KRITZ experiments also, moderator temperature coeffi cients of reactivity have been predicted and compared with Studsvik results using lattice code MURLI and 2D core calculations. Our predictions of the moderator temperature coefficient of reactivity is fairly good for these co res. For U-233 fuelled KAMINI, the close agreement on moderator temperature coefficient of reactivity was not found using more recent U-233 cross-sect ions derived from ENDF/B-N (WIMKAL). By comparing the a (capture to fission ratio) of U-233 at low energies between WIMS and ENDF/B-IV and VI, the bet ter comparison with WIMS is attributed to the flatter a behavior with energ y. There appears to be a need for measurement of a of U-233 below 0.1 eV. ( C) 2000 Elsevier Science Ltd. All rights reserved.