HTGR Knowledge Base

Conference Article: Fission product behaviour in the Peach Bottom and Fort St. Vrain HTGRs

Hanson, D.L.; Baldwin, N.L.; Strong, D.E. (General Atomic Co., San Diego, CA (USA))

Abstract

Actual operating data from the Peach Bottom (PB) and Fort St. Vrain (FSV) High-Temperature Gas-Cooled Reactors (HTGRs) have been compared with code predictions to assess the validity of the methods used to predict the behaviour of fission products in the primary coolant circuit. For both reactors the measured circuit activities were significantly below design values, and the observations generally verify the codes used for large HTGR design. The PB primary circuit after seven years of operation was exceptionally clean. A fuel element purge system virtually eliminated the release of fission gases into the primary coolant circuit. Extensive examinations at end-of-life revealed that only Cs and trace amounts of Sr had plated out in the circuit. Their plateout distributions were in excellent agreement with PAD code predictions. Most of the deposited activity was associated with carbonaceous surface films which resulted from occasional small inleakages of lubricating oil. Primary circuit activities in FSV during the first cycle were also very low. Noble gas activity was about 1% of the design limit. And the circulating iodines were at least one order of magnitude below the limit, although the measurement uncertainties are significant. The plateout per pass of the iodine isotopes increased with decreasing half-life (the value for I-131 is about 1% per pass) as predicted with the PADLOC code. Gamma scanning of two helium circulators indicated very low plateout activities. Iodine-131 was the principal fission product observed, along with small amounts of Cs-134, Cs-137, and Ba/La-140.

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key words: comparative evaluations; computer calculations; fission products; p codes; peach bottom-1 reactor; primary coolant circuits; radionuclide migration; testing; vrain reactor; computer codes; cooling systems; enriched uranium reactors; gas cooled reactors; graphite moderated reactors; helium cooled reactors; htgr type reactors; power reactors; radioactive materials; reactor components; reactor cooling systems; reactors; thermal reactors
Reference:
Specialists meeting on coolant chemistry, plate-out and decontamination in gas-cooled reactors Juelich, Federal Republic of Germany 2-4 December 1980
International Atomic Energy Agency, Vienna (Austria)
IWGGCR--2, pp:49-54