HTGR Knowledge Base

Conference Article: Safety research on iodine plate-out during postulated HTGR core heat up events

Barsell, A.W.; Chawla, O.P.; Hoot, C.G. (General Atomic Co., San Diego, CA (USA))

Abstract

In support of probabilistic risk assessment (PRA) studies on the high-temperature gas-cooled reactor (HTGR), an experimental program was conducted for iodine plateout on HTGR primary circuit metals during core heatup conditions. Metal iodine formation and adsorption characteristics were measured primarily for mild steel and to a limited extent for Incoloy 800 and other alloys. Pseudoisopiestic tests indicated quantitative formation of less volatile and water soluble iodides, FeI2 or CrI2, during core heatup conditions. The rate of formation of FeI2 was limited by mass transfer at temperatures above 5700K and was proportional to the partial pressure of iodine. The rate of iodide formation on chrome-nickel alloys appeared to be temperature sensitive, indicating slower reaction kinetics. The iodides preferentially plated out on surfaces at 520 to 620 K. Plateout tests were also performed for FeI2 in helium carrier gas flowing over mild steel or quartz surfaces over which a temperature gradient was maintained. PADLOC computer program correlations of the plateout profile based on the FeI2 vapor pressure assumed in the PRA studies were in fair agreement. The temperature at which most of the plateout occurred was from 620 to 700 K, depending on the partial pressure of the FeI2 tested.

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key words: adsorption; deposition; fission products; heating; htgr type reactors; incoloy 800; iodine; p codes; primary coolant circuits; radionuclide migration; reactor materials; steels; alloys; carbon additions; chromium alloys; computer codes; cooling systems; elements; gas cooled reactors; graphite moderated reactors; halogens; heat resisting alloys; incoloy alloys; iron alloys; iron base alloys; isotopes; nickel alloys; radioactive materials; reactor components; reactor cooling systems; reactors; transition element alloys
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:94-99