ML20099B623

Special Rept:On 920623,discovered Lower than Normal Chart Recorder Indication on Stack Radiation Monitor Gas Channel. Caused by Pieces of Sheet Metal Impacting Kinetic Probe. Tygon Tubing Connection Replaced W/Solid Tubing

ML20099B623
Person / Time
Site:	University of Missouri-Columbia
Issue date:	07/20/1992
From:	Meyer W MISSOURI, UNIV. OF, COLUMBIA, MO
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 9207310249
Download: ML20099B623 (4)

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't, Research Reactor Facility Reseech Park Columbia Mfswun 65211 UNIVERSITY OF MISSOURl-COLUMBIA "jp3(3[4@2 July 20,1992 Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Station P1-137 Washington, DC 20555 -

Reference:

Docket No. 50-186 University of Missouri License R-103

Subject:

Report as required by Technical Specification 6.1.h(2) concerning reactor operation with unreliable monitoring of the reactor facility stack effluent.

Introduction:

The reactor was operated from 1558 June 22,1992, to 1519 June 23,1992, with unreliable radiation monitoring of the exhaust stack efiluent as ccquired by Technical Specification 3.4.a. Several pieces of sheet metal used as bending vanes in the exhaust ventilation system were found to have broken loose, impacting the isokinetic sampling probe for the stock radiation monitor and causing it to become disconnected from the stack monitor sampling (suction)line. With the stack radiation monitor disconnected from the isokinetic sampling probe, the reactor control room stack monitor indications required by Technical Specification 3.4.a. were not reliable representations of exhaust stack effluent.

Descrintion:

At approximately 1415 on June 23,1992, the Reactor Shiit Supervisor requested that the Health Physics Group investigate the cause oflower than normal chart recorder indication on the stack radiation monitor gas channel.

The gas channel chart recorder was indicating the low count rate normally observed when the reactor is shutdown (approx. 30-40 counts / min). Tha

,- 'rticulate channel was indicating in its normal range and the iodine channel rder indication was slightly lower than the normal range observed when the Oreictor operates at 10 MW.

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Page 2 A Health Physicist, assisted by an Electronics Technician, performed an electronic and source calibration check of the stack monitor gas channel and found it to be operating normally. Further investigation by the Health Physicist revealed that the isokinetic probe was disconnected from the stack radiation monitor sampling line. At 1519 the isokinetic probe was reconnected to the sampling line and the gas channel indication immediately rose to the expected level.

Further investigation was made of t' isokinetic probe and sampling line to determine why the probe had disconnected from the stack monitor sampling line. j This investigation revealed that several large pieces of sheet metal were caught or the isokinetic probe, turning the probe 90' from its desired orientation. The reactor was shutdown at 1621 on June 23,1992, in order to determine the source of

-the loose sheet metal pieces and to remove them from the exhaust plenum.

The sheet metal pieces were found to be flow bending vanes used in an exhaust system transition piece. This sheet metal had travelled through the exhaust ducting several feet before impacting the ischinetic probe. These loose

' pieces were removed and the exhaust ducting and remaining bending vanes were inspected. The remaining bending vanes were determined to be adequately secured within the exhaust duct transition piece. The isokSetic probe was

. removed and inspected. Several small dings were removea from the isokinetic probe and the ptobe was reinstalled. The exhaust ventilation system and the stack radiation monitoring system were tested and found to be operating normally. The reactor was refueled and returned to operation at 2227 on June 23, 1992.

- Analysis:

The objective of Technical Specification 3.4.a. Reactor Instrumentation is to ensure that sufficient reliable information is presented to the reactor operators to assure safe operation of the reactor. Technical Specification 3.4.a. states "the -

reactor shall not be operated unless the instrument channels listed are operable."

The stack radiation monitor is one of the five instrument channels listed in

Technical Specification 3.4.a. as required for Mode I (10 MW) operation. A for.tnote to the stack radiation monitor requirement states the: " . . . monitor may be p! aced out of service for up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for calibration and maintenance. During this out of service time, no experimental or maintenance activities will be conducted which could likely result in the release of unknown quantities of airborne radioactivity."'

The longest period that the stack radiation monitor is believed to have been providing unreliaHe information is from 1558 on June 22 to 1519 on June 23,1992.

Review of stack radiation monitor charts the day of June 22, with the reactor shutdown for scheduled maintenance activities, show the normal response to hot

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director of Nuclear Reactor Regulation July 20,1992 - .l Page 3 j 3

cell activities scheduled that day. Reactor Operators, as part of the Reactor Pre- I Startup Checks, exercise the exhaust system fans shortly before startup to test alarms and the ability of the backup exhaust fan to start upon loss of the rtmning fan. This testing of the two exhaust fann suses a lapper plate to shift within the

- ducting and creates significant air flow transients within the ducting. It is '

believed the bending vanes broke loose during these fan shifts and travel!id several feet through the ducting before impacting the isokinetic probe, turning it 90* and causing the probe to be disconnected from the stack monitor sampling line.' .This sampling line and the base of the isokinetic probe is made of 3/4 inch

. diameter copper tubing. The connection between the two was thick-walled tygca tubing.

Reactor operations, laboratory work, hot cell activities, and pneumatic tube irradiaP.ans for the period ofinadequate monitoring were reviewed to determine whether there had been any unusual situations which might huve resulted in release of unknown quantities of airborne radioactivity. No unusual activities were found to have occurred during ti,is time period. Containment nir co centrations were continuously monitored by the air plcaum radiation mcnitors during the time ofinadequate stack monitoring. These monitors indicated no' unusual airbo ne radioactivity during this time. The primary

system fission product monitor was in continuous operation during this time and indicated'no unusual activity in the primary system. The Alpha 6 air monitor was continuously monitoring the air exhaust fin.n the Alpha laboratory during .

this time and indicated no Lbnormai readings.

g The stack monitor filters (particui 3. and charcoal) which had been i

installed and sampling since June 10,1992, at 0943, were pulled for analysis at 1755 on June 23. During this time frame, we'were also running, for evaluaticn purposes, the new digital radiation monitoring system (NMC model RAK-22ABIB-P/6) which was monitoring the exhaust system effluent through a separate isokinetic probe situated about six feet downstream of the current stack monitor isokinetic probe. This new isokinetic probe was not affected by the loose p;eces of

- sheet metal. The new monitor had been placed on line for testing at 0856 on June 19,1992. This system was being run to test new electronic components, but a new isotopic calibration had not yet been performed. This monitor's filters (particulate and charcoal) were also pulled for analysis at 1800 on June 23,1992. On June 24,

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1992, the historical data for the new monitor's gas channel was retrieved and calibration for the gas channel was checked using Argon-41. This historical data showed no abnormally high indications.

n All analyses and review of activities showed the stack gas, particulate and iodine activities to be normal and within Technical Specification limits during the

- time the primary source of stack monitoring was inadequate. It is concluded from this review of MURR activities and the analysis of alternate sources of

j. -airborne efiluent information that no abnormal release of radionuclides occurred -

L during the time ofinadequate stack monitoring.

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Director of Nuclear Reactor Regulation July 20,1992 Page 4 Corrective Actions:

The immediate corrective action was to reconnect the isokinetic probe to the stack radiation monCor sampling line. Upon discovery that several pieces of sheet metal were impacting the isokinetic probe, the reactor was shutdown so that the loose pieces of sheet metal could be removed ano tac isokinetic probe could be inspected for damage. The exhaust ducting was inspected to ensure that no additional pieces of sheet metal were likely to come loose.

The tygon tubing connection between the stach monitor sampling line and the isokinetic probe was replaced by solid tubing with compression fittings during maintenance activities July 13,1992.

The MURR engineering staff evaluation of the exhaust ducting indicated that no similar event is likely. However, to be conservative, the exhaust plenum transition piece that contains the bending vanes is being scheduled for replacement.

Licensed operators and Health Physics personnel discovered this problem while performing an investigation of unusually low readings on the stack monitor. After reviewing their actions and relating the circumstances of this event to all licensed personnel and Health Physics personnel, the importance was stressed ofinitiating investigations of unusually low readings on the stack monitor charts in a more timely fashion.

Sincerely, b #

b Walter A. Meyer, Jr.

Reactor Mar.ager ENDORSEMENT:

Reviewed and Approved j k4/ / /p J. Charles McKibbon Associate Director WAM:bjb A @b 2

- n. - m p RY puBuc 5TATi & N:SSGRI i - NOTA xc: Regional Adnu. ms. trator, NRC, Region III a emy Reactor Advisory Conunittee nv canssa m on. icoss Reactor Safety Subcommittee

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