ML20086C461

Resubmits 910919 Proposed Amend to Hazards Summary Rept, Based on Reevaluation of Radiological Hazards Associated W/ Release of Argon-41 from Reactor Facility

ML20086C461
Person / Time
Site:	U.S. Geological Survey
Issue date:	11/13/1991
From:	Danni Smith INTERIOR, DEPT. OF, GEOLOGICAL SURVEY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9111220205
Download: ML20086C461 (3)

Text

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GEOLOGICAL SURVEY assummuumummus BOX 25046 ' M.S. 97 3 T "'s DENVER FEDERAL CENTER DENVER, COLORADO 80225 IN REPEY REFER To:

DRANCH OF GEOCHEMISTRY .

November 13, 1991 i

l Docket 50-274

, _U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Sirs:

A recent re-evaluation of the radiological hazards associated with the production and release of Argon-41 from the U.S.

Geological Survey's 1000 kW Mark I TRIGA reactor facility (docket

50-274) has resulted in information that we would like to have l incorporated into our Hazards Summary Report. The argon analyses l were submitted to you in letters dated August 7, 1991 and l September 19, 1991. We are submitting the attached pages as a proposed amendment to the Hazards Summary Report. The pages are to replace the existing pages 8-2 and 8-3 of the report.

fm Sincerely,/

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David B. Smith Reactor Administrator l

Copy w/ attach:

i Mr. A. Bill Beach

l. Region IV

! Nuclear Regulatory Commission I 611 Ryan Plaza Drive, Suite 1000 f Arlington, TX 76011 L

USGS, Tim DeBey hkb e

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d - . = . A ~a 8-2 insert' ion of a fuel element into the core while the reactor is op'erating_at a steady-state power that the maximum reactivity that could be introduced in a single action would be $1.13. Since_ step additions of reactivity greater than this value are made on a routine basis when the~ reactor is pulsed, the addition of_one fuel element (or even two or three)_into_the critical. reactor core would present no hazard.

8.2. PRODUCTION AND RELEASE OF RADIOACTIVE GASES 8.2.1. Experimental Facilities In the TRIGA Mark I reactor installation, the pneumatic transfer tube, and the rotary specimen rack contain air. In addition,_the main reactor room is of course also filled with air that is in contact with the reactor pool. Of the radioisotopes produced in these air _ cavities, argon-41 is the most significant with respect to hazards and nitrogen-16 is considerably less significant.

At prolonged 1000-kw operation with no air exchange, the argan-41 activity in the pneumatic trcnsfer tube is 4 mC1, and in-the rotary specimen rack it is 860 mci. A measurable argon-41 release from the rotary specimen rack and reactor pool water occurs during normal'1000-kw operation. The release of argon-41 from the reactor pool water is discussed in Section 8.2.2.

Release of argon-41 into the reacter room is evaluated by representing'the room as a hemisphere of 550 cm radius. This

.results in a whole body dose from argon-4? that is a factor of 33 less.than the dose received by an infinite radius hemisphorical cloud, as assumed in 10 CFR 20 Appendix B. Therefore, the values of Appendix B do not directly correspond to the radiological hazard presented by'the argon-41 dispersed in the reactor room.

Operational data shows that a typical argon -41 concentration

.in the reactor room during 1000-kw operation is 4.35 x 10 4 ucl/ml.

A typical stay time in this environment of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> per week could give a whole body dose of about 16.5 mrem per calendar quarter.

Therefore, if a person remained in the reactor room for 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> per week under the same conditions, a quarterly whole body dose of about 82.5 mrem would result. These doses are well within the limitations of 10 CFR 20. Routine releases of argon-41 # rom reactor operation do not present a significant radiological hazard to the staff.

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8-3

~ Accidental flooding of an air-filled 9xperimental cavity could* release larger quantities of argon-41 into the reactor room.

Fl'ooding of the rotary specimen rack could result in the acute release of 860. mci into the reactor room. instantaneously. If the room ventilation system is operating normally, this activity will remain in the room for about 12 minutes. The maximum argon-41 concentration in the room would be 2.46 x 104 uCi/ml, assuming uniform mixing. Using the finite hemisphere cloud approximation, this discharge of 860 mci into the reactor room would give a whole body dose of about 17.9 mrem to a person positioned in the center of the room.

Comparing this accident with the release of 10 Ci of cobalt-60 equivalent activity discussed in Section 8.3, an accidental release of 10 Ci of argon-41 would give a whole. body dose of about 208 mrem. All of these doses are well below the occupational limits of 10 CFR 20.

The routine exposure of personnel in unrestricted areas from argon-41 releases is evaluated by assuming a person is standing next to the reactor building wall, at a distance of 8 meters from the release point.- An annual release of 25 Ci uf argon-41 would give a whole body dose of less than 17 mrem per year to a person near the building wall. The acute release of 3 Ci of argon-41 would give a whole body dose of about 2 mrem to a person standing near the reactor building wall.

In summary, the argon-41 produced in the reactor cavities is not a significant hazard to operating personnel or the general public.

8.2.2 Release of Arcon-41 from Reactor Water Aargon-41 activity in .the reactor pool water resul ts from irradiation of the air dissolved in the water.

The following calculations were performed to evaluate the rate of argon-41 escaping from the reactor pool water into the reactor room. The calculations show that the argon-41 decays while in the water, and most of the radiation is safely absorbed in the water. The changes in argon-41 concentration in the reactor, in the i

pool water external to the reacto , and in the air of the reactor room are given by dN V =V3N o -N (v + V do tA V)+N v g

(1)

-p r--, -+- ,-c y v