TEMPERATURE COEFFICIENT OF REACTIVITY OF CALDER HALL TYPE REACTOR

Abstract

As the conversion ratio of the fuel is comparatively high for the Calder Hall type reactor, about 0.8, considerable amounts of Pu/sup 239/ are built up in a relatively short irradiation time. As Pu/sup 239/ has a large resonance absorption for the neutron energy of about 0.3 ev, the reaction rate of Pu/sup 239/ increases as the temperature increases, in contrast with the reaction rates of U/sup 235/ and U/sup 238/ which show the opposite tendency. Though the temperature coefficient of reactivity is negative for fresh fuel, it changes to positive as the exposure proceeds and Pu/sup 239/ is accumulated. The moderator temperature coefficient becomes zero at an irradiation of about 150Mwd/ton, and exceeds +10/sup -4/ deg C at about 2,000 Mwd/ton. The fuel temperature coefficient is almost constant, about - 1.7 x 10/sup -5// deg C, throughout the exposure. The fuel temperature coefficient is a prompt one, and the moderator temperature coefficient shows the delayed property owing to the large heat capacity of the graphite. Consequently, the negative fuel temperature coefficient is effective at first, although the over-all temperature coefficient is positive at high exposure, and the operation of the reactor is not so difficult essentially. A calculation ofmore » these changes of the temperature coefficient of reactivity is presented and an investigation on the effect of the increases of enrichment of U/sup 235/ on the temperature coefficient is presented. (auth)« less

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