ML20090G478

Special Rept:On 920302,meteorological Tower Differential Air Temp Instrumentation Declared Inoperable to Facilitate Troubleshooting Re Discrepancy in Meteorological Data. Missing Ducting Tube from Aspirator Installed

ML20090G478
Person / Time
Site:	Clinton
Issue date:	03/06/1992
From:	Spangenberg F ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
U-601946, NUDOCS 9203120255
Download: ML20090G478 (3)

Text

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• libnois Power Company

- Chnton Power StaSon P.O Box 678 Chnton, IL 61727 Te!217 935 8881 ILLIN#4IS u.601946 P(s M R t30-92co3-Os>tP 8E.110 March 6, 1992 10CFR50.36 Docket No. 50-461 u, 2. 1k .4 Nuclear Regulatory Commission Washington, D.C. 20555 Subj ect: Special Report: Inoperability of the Meteorological Tower Differential Air Temperature Instrumentation at Clinton 10wer Station (CPS)

Dear Sir:

CPS Technical Specification 3.3.7.3, Action "a", requires that inoperabilities of meteorological monitoring instruments: ;rt channels for more than 7 days be reported to the Commission vf1.is 10 days pursuant to Technical Specification 6.9.2, SPECIAL RCPORTS. From Febrna v 18, 1992 until February 25, 1992, the 10-meter to 60 meter differential air temperature instrumentation was declared inoperable.

This SPECIAL REPORT is being submitted in accordance with the CPS Technical Specifications to provide information regarding the cause of the malfunction and plans for restoring the instrumentation to OPERABLE status.

Cause of Malfunction On January 9,1992 it was discovered that a discrepancy existed botseen the meteorological data provided in the CPS Updated Safety Analysis -

Report (USAR) and recent data reported by CPS. Specifically, the baseline site meteorological data recorded at the meteorological tower between 1972 and 1977 and documented in the USAR yielded Pasquill Stability Class frequencies significantly different than the data

' provided by CPS in the 1990 Annua 1LRadiological~ Environmental Monitoring Report. Condition Report 1-92-01-006 was written to document this discrepancy and initiate an evaluation of the problem'.

Preliminary indications were that the "A" Stability Class was '

predominant when solar radiation incident on the 10-meter temperature sensor was at a maximum (i.e. during sunny periods). This pbenomenon has occurred even on days when atmospheric turbulence was less than what would be expected for "A" conditions. Based on the USAR, "A" Stability Class conditions should oct:ur approximately 4.4% 'of the time; however, i '

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,. , Page 2.of 3 the 1990 CPS meteorological data indicated the "A" stability class occurred 32.4% of the time. A review of all past CPS Annual Radiological Environmental Monitoring Reports (1987-present) indicated that this condition has existed since 1987. Ilowever, the current instrumentation was installed following removal of the instrumentation previously used to obtain the CPS baseline meteorological data and it is not known if the condition existed prior to 1987. Immediate action taken as a result of the condition report included development of an interim plan for correct determination of the existing stability class utilizing alternate methods. This would ensure that appropriate protective action guidelines are utilized in the event of an accident at CPS.

Personnel who utilize atmospheric stability class data to determine offsite doses were informed of this issue and alerted to the meteorological conditions under which the atmospheric stability class determination would be questionable. Until the identified problem was carrected, th a "' 4.nd.tviduals were directed to verify any stalility class determinations on sunny days by using an alternate method. The alternato methods are identified in Emergency Plan Implementing Procedure (EPIP) f RA-01, " Manual Radiological Dose Assessment."

The initial evaluation by Engineering indicated that the 10 meter temperature probe was being affected by sunshine and thus was providing inaccurate temperature indications (i.e. too high). This in turn was providing inaccurate differential temperature values resulting in the high frequency of "A" stability class occurrence. Maintenance Work Request (MWR) D15996 was written to perform troubleshooting on the 10 -

meter temperature sensor to determine the cause of the incorrect differential temperature indications.

Control and Instrumentation personnel began troubleshooting on March 2, 1992 in accordance with MWR D15996. They determined there was a problem with the aspirator on the mounting arm _at the 10 meter elevation of the meteorological tower. The aspirator draws air across the temperature and dewpoint sensors to provide for high heat transfer from the ambient air to the sensing element, while at-the same time affording maximum protection from incoming short-wave solar radiation and outgoing long-wave radiation. Tne 10 meter mountin6_ arm was removed from the metiorological tower to facilitate troubleshooting, thus making the 10-meter temperature and dewpoint sensors-inoperable, as well'as the differential temperature instrumentation. Measurements performed for the existing configuration indicated no airflow over the sensors. It was discovered that a ducting tube was missing from the. aspirator which resulted in the observed lack of airflow over the sensors.

Discussions with the vendor indicated that the missing ducting tube (a rigid plastic hose on the downstream side of the fan) is important to the operation of the aspirator. The. ducting tube directs air out of the unit to the discharge duct, and if the tube is missing, air may be getting lost in the output housing. The vendor provided dimensions for the tube and one was manufactured onsite and installed on March 3, 1992. After installation of the missing ducting tube, proper airflow was observed over the temperature sensors.

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. Plans for Restoration On March 4, 1992, further data was obtained in accordance with MVR D15996 to verify that the problem had been corrected. At 0131 hours0.00152 days <br />0.0364 hours <br />2.166005e-4 weeks <br />4.98455e-5 months <br /> on March 6 ,

1992, the meteorological tower 10 ineter temperature and differential temperature instrumentation was declared operable. l E

Illinois Power is currently evaluating the impact of the differential  ;#

temperature instrumentation problem on the previous Annual-Radiological Environmental Monitoring Reports. A determination will be made as to whether the previously reported data should be corrected or annotated.

Radiation Protection will establish administrative methods to ensure that [I future Pasquill Stability Clasm frequencies are in agreement with the CPS baseline meteorological data.

Sincerely yours, C. ] w F..A. Spa genbe ., III ,

Manager, L cens. g and E fety TAB /alh cc: NRC Clinton Licensing Project Manager NRC Resident Office Regional Administrator, Region III, USNRC Illinois Department of Nuclear Safety

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