Criticality studies of a natural uranium fueled, light water cooled, heavy water moderated nuclear reactor part-II: effect of moderator properties

The effects of increase in D/sub 2/O moderator height, moderator channel width and H/sub 2/O as an impurity in D/sub 2/O moderator on K/sub eff/ in natural uranium fuelled, light water cooled, heavy water moderated and graphite reflected system have been studied using computer codes WIMS-D/4 and CITATION. Core containing 192 standard fuel rods with one central thimble and 85 cm thick annular graphite reflector was analyzed. The analysis using transport theory lattice code WIMS-D/4 has shown that NRX and CIR reactors were under moderated systems. The analysis has shown that total excess reactivity in clean cold core is 44.283 mk and it achieves criticality at a moderator height of 185 cm. The presence of H/sub 2/O as an impurity in D/sub 2/O moderator has strong negative effect on k/sub eff/. (author)