ML20125D373

Submits 30-day Written Rept Re Detection of Trace Levels of Fission Product Activity in Pit Water & Surrounding Areas of Mark F Reactor.Increased Surveillance Will Continue Until Next Scheduled Reactor Shutdown Planned on 921223

ML20125D373
Person / Time
Site:	General Atomics
Issue date:	12/09/1992
From:	Asmussen K GENERAL ATOMICS (FORMERLY GA TECHNOLOGIES, INC./GENER
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
67-1997, NUDOCS 9212150145
Download: ML20125D373 (9)

Text

v CENERAL ATOMIC 3 \

67-1997 December 9,1992 Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

Docket No. 50-163; Reactor Facility License No. R-67: Detection of Trace Levels of Fission Product Activity Gentlemen:

On Tuesday, November 10,1992, General Atomics (GA) notified Mr. Alexander Adams, Jr., Senior Project Manager, Non-Power Reactors and Decommissioning Project Directorate, and NRC Region V, that extremely low levels of fission product activity were detected in the pit water and air surrounding GA's Mark F reactor. The levels detected were well below the maximum permissible concentrations 1MPC) for unrestricted release of the radionuclides; in fact, low enough to be considered "not present" as defined by 10 CFR 20, Appendix B, Footnote 5.

This 30-day written wrt is being submitted in accordance with the applicable license, as amended.

The effluent data from air and water samples that have been taken show that the detected fission product activities are not only well within MPC concentrations, but their trend and levels i

show that the likely source of this activity is " tramp uranium" rather than damaged clad on one or more fuel elements.

This letter presents the sequence of events that led to the discovery of fission products and the results of the increased monitoring efforts above those which are routinely carried out.

Sequence of Events i

The GA Mark F reactor is currently in an around-the-clock operating mode to perform in-pile irradiations on direct conversion (thermionic) devices. Beginning late in October 1992, a meteorological inversion layer was present in the San Diego area resulting in a noticeable increase in the background radiation levels detected on all monitors around the G A facility. On the 25th of October, these levels were high enough to cause the Mark F continuous air monitor (CAM) to signal an alert at 10,000 CPM (the scram is set at 50,000 CPM). To monitor the source of this increased activity, the filter paper that collects particulates in the air that is sampled by the CAM was removed twice and a gamma ray spectral analysis performed. At this l time, no fission products were cetected on any of the filter papers. Operation of the reactor continued with a general trend showing increases in background levels during the night hours followed by a decrease in levels during the day hours (see attact ' ctartup charts for typical change in activity - Attachment 1).

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S 1 3550 GEN $RAL ATOM!CS COURT, SAN DIEGO. CA 92121-1194 PO BOX 85808. SAN OfEGO, CA 9218& 9784 (619t 455 3000

U.S. Nuclear Regulatory Commission December 9,1992 67 1997 Page 2 On Monday, November 9, results of a gamma spectral analysis of a pool water sample, taken for the routine quarterly monitoring program, indicated the presence of very low levels of the fission product Xe-133. Subsequently, another sample was taken the following morning to look for typical isotope signatures that can be expected to be present from short lived fission product activity, in addition to the activation products normally present in the pool water. This analysis indicated low levels of fission products, as shown in Table 1.

l Table 1.

Mark F Pit Water Activity Levels 10 NOV 92 Radionuclide T 1/2 Activity (min) ( Ci/ml)

Rb-89 15.1 2.4 x 10-5 Kr-88D 18 (7) 3.1 x 10-5

! Ba-139 82.9 1.9 x 10-5 Cs-138 32.2 5.1 x 10-5 Xe-133 - 138 17 to 5.3d 1.4 x 104 l

Notably, no iodines or Cs-137 were deteved in the water.

The Reactor Safety Committee and Health Physics were notified of the detection of fission products in the pool water. As a precautionary measure, the TRIGA emergency air samples were turned on in the afternoon of the 9th of November to detect any potential airborne l activity outside the restricted area. On the following day the filter papers were removed and analyzed. No detectable radioactivity from any fission products was observed. With the concurrence of the Safety Committee, reactor opattions have continued while an exnanded surveillance program was implemented to monitor the fission product radioactiiity levels in the

! air and water.

! Filter papeis from the CAM, Mark F reactor room, and exhaust stack were also removed and analyzed. Trace levels of fission products were detected on the filter papers shown in l Figures 1 through 3 (as fraction of MPC). The primary signatures were from Rb-89, Ba-139 and Cs-138.

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U.S. Nuclear Regulatory Commission December 9,1992 67-1997 Page 3 l

l Summary of Radioactivity Levels and Personnel Expewn While the measured radioactivity on the CAM and in the reactor room showed detectable levels of short lived fission product isotopes, the airborne concentrations have remained well  ;

below MPC levels for controlled areas. For example, the concentration of the most prevalent isotope, Rb-89, was always detected at levels less than 0.006 of MPC, with the sum of ratios of detected fission products remaining less than 0.011 of MPC. In addition, these levels were measured in the air immediately above and around the reactor pool, which can be expected to be the location (s) of the highest concentration. As a result of further dilution in the reactor-room, the airborne concentrations elsewhere in the reactor room confinement can be expected to be further reduced.

The measured fission product activity in the reactor room stack was always less than 0.12 of the MPC for unrestricted areas. Whea a dilution factor of 2 90 for the GA site boundary is taken into account, the concentration of any airborne fission product activity at the site beundary ,vould not be measurable. In fact, an emergency sampler located on the roof of the reactor building, adjacent to the stack vent, showed no detxtable activity.

4 The radiation levels in the reactor and control rooms, have continued to be at normal levels, as evidenced by the area monitor readings. Sim%ly, the internal radiation exposure of personnel from invivo body counting performed during this period showed normal results. This is to be expected because of the extremely low levels of airborne activity as well as the short half lives of the airborne radin isotopes, j Actions and Analysis Upon detection of trace levels of fission product activity in the water and air sampl_es, the Physicist-in-Charge instituted a monitoring progiam involving increased frequencies at which -

water and air samples were analyzed. As a result, the particulate activity on the CAM and air sampler above the reactor tank were removed and analyzed-on alternaie days, and the stack sempler as well as the pit water sampled once a week. - The spectral analysis was carried out such that all short-lived activities could be detected and quantified.- Results of these analyses are shown in Figures 1 through 4.

Using Rb-89 activity as an indicator, it appears that equilibrium levels were never

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established, in addition to the fact that airbome activities are at trace levels for all isotopes. ' The source of the detected fission products therefore, appears to be a possible recurrence of the

" tramp uranium" problem previously encountered with the R-67 facility during the 1978-1980- <

period, rather than a clad failure on one or more fuel elements. -While a potential clad failure could not be ruled out, the level and trend of fission product activity since the activity was first

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U.S. Nuclear Regulatory Commission December 9,1992 67-1997 Page 4 I detected point away from such a failure being the source of the detected fission products.

Further, no new fuel has been added to the core since April,1992 and no fission products have been detected in the routine analyses of the air and water samples in the April-November time period. A new fueled experiment (thermionic device) was installed in-core in late September, 1992, but the fact that the fuel is doubly contained points away from this device being the source of the fission products.

GA will continue the increased surveillance as outlined in this report, until the next scheduled reactor shutewn on December 23,1992. The level of fission product activity will again be monitored after reactor startup on January 5,1993, at which time the necessity and level of increased surveillance wil! be reconsidered.

If you have any questions concerning this letter, please contact Dr. Junaid Razvi at (619) 455-2441, or me at (619) 455-2823.

Very truly yours,

~

Keith E. Asmussen, Director Licensing, Safety and Nuclear Compliance KEA:shs

Enclosures:

Attachment 1 l

Figures 1-4 l

cc: Mr. Alerander Adams, Jr., Sr. Project Manager, Non-Power Reactors and Decommissioning Project Directorate, Division of Operating Reactor Support, Office of Nuclear Reactor Regulation.

Mr. Phillip Qualls, NRC Region V.

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