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Conference Article: The measurement of burn-up level in HTR-10

Abstract

Without shutting down the HTR-10, each fuel ball unloaded from the core must be measured. Judgment is made whether the desired burn-up level is reached. A fuel ball should be reloaded into the core when its burn-up level is less than 72,000MWD/tu. Since the measurement of burn-up level for a ball containing 0.9g 235U at most must be nondestructive, a gamma spectroscopy method with high-resolution for the fission product 137Cs is typically chosen. However, because the HTR-10 is not provided with any kind of external calibrating source, it is impossible to achieve the goal that the accuracy of measurement is up to 2% by the above method. The method measuring burn-up levels without external source uses the ratio of 134Cs to 137Cs and gets bogged down in something unusual that both successful and failed examples have alternated in publications.

The inner calibrating method is proposed in the paper. It is necessary to solve the following problems: a). The simple relationship between 134Cs/137Cs and burn-up level is held only in a specified range, but not for a spent ball. b). The migration must be ignored. c) How to deal with the neutron spectrum within HTR-10? The paper also introduces such useful method as neutron spectrum correction, picking out the graphite balls and extraction of The measurement of burn-up level in HTR-10 137Cs from ? spectra of reactor.

The appropriate instrumentation that discriminates out the spent fuel balls and picks out the graphite balls is described.

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Reference:

Proceedings of the Conference on High Temperature Reactors, Petten, NL, April 22-24, 2002
Organized by HTR-TN in cooperation with the European Nucler Society (ENS) and the IAEA

International Atomic Energy Agency, Vienna (Austria)

HTR-2002, pp:1-5