ML20137G450
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M DOW CHEMICAL U.S.A.
March 24, 1981 MICHIGAN DIVISloN MIDLAND, MICHIGAN 48640
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j/y /4 The U. S. Nuclear Regulatory Commission j
Region III 799 Roosevelt Road Glen Ellyn, Illinois 60137 This communication is to report the condition of a Continuou's Air Particulate Monitor (CAM) which could have resulted in a violation of the Technical Specifications and which can exist also at other facilities using similar equipment.
On December 31, 1979 the D TRI Reactor facility installed an Eberline Co. Model AMS-3 Beta Conti uous Air Monitor as replacement of the original Technical Measurement Corporation Continuous Air Monitor, used since the commissioning of the reactor in 1967.
The new unit was tested by the manufacturer and installed without modifi-cation. The alarm set point was selected based on the experience and custom of the old unit with the aid of a reference source. The system
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appeared to operate satisfactorily throughout the time period January 1980 to March 1981. The checkout procedure in force for testing the continuous air monitor, a slight modification of the procedure used with the original unit to accommodate the differences in design, was carried out, as part of the daily reactor checkout, every working day since installation. This procedure included: filter change, recording of instrument reading before and af ter the filter change, test of the alarm set level and annunciators with the use of a check source, and marking the attained level on the recorder chart.
Since early 1980 it was noticed that the difference in radiation levels indicated before and af ter filter change decreased gradually. Collected dust was, however, noticed on the filter every day. It was assumed that local air particulate emissions were being reduced and, therefore, this reduction in dust collection by the CAM was not surprising.
During a recent walk-through, as part of the operators' training program, it was noticed that the "0"-ring seal of the filter holder did not seat properly, even when the lock-in mechanism, set by the manufacturer, was actuated and in its operating position. This condition resulted in a partial bypass of the filter for the air sucked into the instrument by the air-moving pump downstream of the filter.
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The U. S. Nuclear Regulatory Commission Glen Ellyn, Illinois 60137 March 24, 1981 Further investigation revealed the following conditions:
1.
The filter is only partially in place when the filter-in lock is activated. In this position the "0"-ring seal is not seated properly and provides only a marginal seal of the air passage.
2.
A new properly lubricated "0"-ring can provide a seal in the marginal position. A "used" "0"-ring, which has been damaged by being positioned in the marginal position regularly and over a considerable amount of time, will not provide a seal, but permit part of the air to bypass the filter.
3.
If only part of the air passing through the pump (and the rotometer of the instrument) is actually filtered, only a fraction of the air par-ticulates in the pumped volume is retained by the filter. This results in the collection of less material and thus in a reduced sensitivity of the instrument in terms of signal per radioactivity in the pumped air.
4.
The alarm point for tge unit under discussion was placed at 4000 cpm, equivalent to 8 x 10- microcuries per milliliter of air. This set point is at 2.5% of the alarm level identified by regulatory require-ments for the air in the reactor room.
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The partitioning of the air stream is estimated to have permitted not more than 90% of the pumped air volume to bypass the filter.
For this case the signal from the instrument was only 10% of the signal expected, and an alarm would have resulted only if the intended alarm setting had been exceeded ten-fold.
We interpret these findings as follows:
The Dow TRIGA Reactor facility license R-108, requires that a continuous air monitor be in operation inside the reactor room whenever the reactor is in operation. This condition was met; i.e. the instrument was able to indicate increased radioactive particulate levels in the reactor-room air.
The alarm icvels, according to the Technical Specifications, are to be set by the Reactor Supervisor within the limits permitted by 10CFR20.
Although the intended alarm levels, which were set by the Reactor Supervisor, and verified daily, could have been exceeded during the time interval without causing an alarm, the actual levels, at which the instrument would have triggered the alarm, still remained within the limits set by 10CFR20. Therefore, no violation of the Technical Specifications was incurred.
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The U. S. Nuclear Regulatory Commission Glen Ellyn, Illinois 60137 March 24, 1981 The following remedial action has been taken:
The filter-in lock has been adjusted so that it cannot be closed unless the filter holder is pronerly seated.
The vacuum-relief valve has been relocated to behind the rotometer so that the latter can only measure air that passes through the filter and the filter-bypass leak.
The new checkout procedure, approved by the Reactor Operations Committee, provides for momentary plugging of the air intake and measuring of any bypass air with the rotometer.
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.N'N L. W. Rampy J. M. Macki
- Chairman, Chairman, Radiation Saf ety Committee Reactor Operations Committee i
1803 Building 1602 Building kf L_