ML20246F388

RO 12:on 881227,concentrations of I-131 & Xe-133 Discovered in Reactor Pool Water.Caused by B&W Element 204 Releasing Fission Products.B&W Contacted to Review Mfg Process.Air Samples Will Be Taken Above Pool on Monthly Basis

ML20246F388
Person / Time
Site:	University of Michigan
Issue date:	05/03/1989
From:	Fleming R MICHIGAN, UNIV. OF, ANN ARBOR, MI
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
12, NUDOCS 8905120220
Download: ML20246F388 (3)

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!=. - Nuclear Reactor Laboratory

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The University of Michigan

. . Ford Nuclear Reactor Phoenix Memorial Laboratory 2301 Bonisteel Boulevard 1 Ann Arbor, Michigan 48109-2100 (313) 764-6220 May 3, 1989 Docket 50-2

' License R-28 United States Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. '20555 Reportable Occurrence No. 12 Release of Fission products from the Ford Nuclear Reactor Gentlemen:

ThisLletter.is a follow-up concerning our Reportable Occurrence No. 12-submitted on January 16,.1989.

Summary of Initial Fission Product Detection A fifteen minute analysis taken on December 27, 1988, after the reactor had been shutdown for five days, showed the following concentrations, in the reactor pool water, of the fission products,. iodine-131 and xenon-133:

I131 2.76x10-6 microcurie /ml Xe133 1. 3 9x10- 5 microcurie /ml The reactor was brought to full power on January 4, 1989.

A fifteen minute analysis of pool water sampled on that day showed no iodine-131. Xenon-133 concentration was about 25% of that measured December 27, 1988.' High background activity associated with reactor operation may have prevented detection of low concentrations of iodine-131. The pool water sample drawn on January 4, 1989 was analyzed again after five days of decay.

Iodine-131 was detected in the five-day analysis. It ic possible that iodine-131 was present in pool water before December 27, 1988. Background activity may have been too high to permit its detection in fifteen-minute analyses, and the iodine-131 could have decayed below detectable levels by the time our routine two-week analyses were performed.

We reanalyzed pool water data for the preceding year, this time looking for xenon-133 peaks. We had not previously looked for xenon-133 as a fission product indicator. We found low levels of xenon-133 in pool water back to October, 1988, but none earlier than that.

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, May 3, 1989 i

An analysis of water in the facility's radioactive  ;

liquid retention tanks was performed. All liquids from the reactor facility are dumped into the retention tanks and analyzed .

prior to' discharge into the Ann Arbor sewer system. Between f December 27, 1988 and January 4, 1989, a pool water demineralized i was recharged. The recharge water was discharged into the .,

retention tanks.' The following concentrations of iodine-131 and cesium-137 were found:

l 1131 9.44x10-8 microcurie /ml Cs137 3.04x10-8 microcurie /ml l In an attempt to confirm the release of fission products, air samples were taken at several locations above the surface of the reactor pool on-January 5, 1988. Analysis of a high volume sample

.taken.directly over the reactor core showed very small, but detectable quantities of rubidium-88 (daughter of krypton-88) and cesium-138 (daughter of xenon-138). Representative concentrations were:

Rb88 2. 3 5x10- 10 microcurie /ml-of air Cs138 4.47x10-11 microcurie /ml of air Corrective Action Fuel elements were removed from the core one at a time and were replaced ^by other elements. When the reactor was returned to power, air samples and pool water samples were taken to determine if removal of a particular element reduced or eliminated fission t

product generation. Using this technique, one element was found to be releasing fission products, our element number 204. The element was first installed in the reactor core on April 27,-1987.

The element was manufactured by Babcock and Wilcox.

After removal of element 204, fission product activity in the reactor pool water dropped below detectable levels. We performed additional tests of every other element in the core to verify that a minute leak did not exist in another element. The reactor was operated in natural circulation at a power of 80 kilowatts to promote upward water flow through the elements. Maximum natural circulation power is 100 kilowatts. A liquid sipping tube was placed directly over each element in turn. Water from above each element was pumped through an ion exchange resin column to collect and concentrate any fission product ions. No fission products were detected using this technique. In addition, a 500 milliliter sample of water was drawn from above each element. pc'assium iodide carrier and silver nitrate were mixed into each ample to '

precipitate fission product iodine in the form of silver iodide.

None was detected.

i As the result of thewe tests, it was concluded that fuel element 204 was the single source of fission product releases. The page 2 1 1

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(. United States Nuclear Regulatory Commission May 3, 1989 manufacturer has'been contacted to review its manufacturing process. While in the core, element 204 was always surrounded by J other elements. It was never in-a position, such as along the Jperimeter of the core, where it could have been damaged by experimental devices or routine operations evolutions.

Procedural' Changes Our regular pool-water analyses were conducted fifteen minutes and two weeks after sampling. The two-week analysis has been replaced by a one-week analysis. In'seven days, the source of high background, sodium-24, has decayed away, but relatively short-lived fission products such as iodine-131 are still detectable. Based on past analyses, fission products that were detectable after one week had decayed below detectable levels after~two weeks.

During the search for the leaking fuel element, we found that xenon-133 was a significantly more sensitive fission product indicator than iodine-131. Consequently, xenon-133 was added to our analysis library. Molybdenum-99 also was added to provide a strong indicator of particulate releases.

On.a monthly basis, air samples will be taken above the reactor pool. Particulate filters will be used to trap fission product daughters, rubidium-88 and cesium-138. A charcoal filter will be used to trap any fission product iodine.

Sincerely,

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Ronald F. Fleming Director xc: Dr. Linda S. Wilson, Vice President for Research John Jones, Director, Radiation Control Service Ken Schatzle, Director, OSEH Director, Region III, United States Nuclear Regulatory Commission Safety Review Committee Members i

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