Abstract

Throughout the years, various reports and training manuals on CANada Deuterium Uranium (CANDU) reactors have mentioned that the CANDU lattice is overmoderated. Overmoderation is not always defined in such documents but often appears associated with the positive void reactivity of the CANDU lattice. Some documents refer, logically, to overmoderation as meaning that the lattice pitch is larger than the pitch that maximizes the infinite-lattice multiplication constant but do not demonstrate this is the case for CANDU. We demonstrate that in fact, the CANDU lattice is undermoderated; that is, the current 28.575-cm lattice pitch is smaller than the pitch for which the infinite-lattice multiplication constant reaches its maximum. We hypothesize that the misconception of CANDU overmoderation may have originated from attributing the CANDU positive void reactivity to too much moderator by incorrectly equating the effect of losing heavy water coolant with the effect of losing heavy water moderator.

摘要

多年来，关于加拿大氘铀 (CANDU) 反应堆的各种报告和培训手册都提到 CANDU 晶格过度减速。在此类文件中并不总是定义过度节制，但经常出现与 CANDU 晶格的正空隙反应性相关联。一些文件在逻辑上将过度调节称为晶格间距大于使无限晶格倍增常数最大化的间距，但并未证明 CANDU 是这种情况。我们证明，事实上，CANDU 格子是欠节制的；也就是说，当前的 28.575 厘米晶格间距小于无限晶格倍增常数达到最大值的间距。