ML20005H097
| ML20005H097 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 01/16/1990 |
| From: | Hairston W GEORGIA POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 90-001, HL-921, NUDOCS 9001240138 | |
| Download: ML20005H097 (5) | |
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N January 16, 1990 U.S. Nuclear Regulatory Commission i
ATTN: Document Control-Desk Washington, D.C.
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PLANT HATCH - UNIT 2 NRC DOCKET 50-366 OPERATING LICENSE NPF-5 SPECIAL REPORT'90-001 DRYWELL HIGH RANGE POST-ACCIDENT RADIATION MONITOR DECLARED IN0PERABLE Gentlemen:
o In accordance with the requirements of the Unit 2 Technical I
Specifications >. Section 6.9.2 and Table 3.3.6.4-1, Georgia Power Company is submitting the enclosed special report concerning an event where one t
channel of the Unit 2 drywell high range radiation instrumentation was inoperable longer than seven_ days. This event occurred at Plant _ Hatch
~ Unit'2.
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Sincerely, i
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L W. G. Hairston, III L
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Enclosure:
SR 50-366/1990-001 c:
(See next page.)
1 632-9001240138 900116
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L Georgialbwer A U.S. Nuclear Regulatory Comission January 16, 1990 Page Two c:
Georaia Power Comoany L-Mr. H. C. Nix, General Manager - Nuclear Plant
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Mr. J. D. Heidt, Manager Engineering and Licensing - Hatch GO-NORMS U.S. Nuclear Reaulatory Comission. Washinaton. D.C.
h Mr. L. P. Crocker, Licensing Project Manager - Hatch f
. U.S. Nuclear Reaulatory Comission. Reaion 11 b
Mr. S. D. Ebneter, Regional Administrator P
Mr. J. E. Menning, Senior Resident Inspector - Hatch l
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i ENCLOSURE b
PLANT HATCH - UNIT 2 NRC DOCKET 50-366 OPERATING LICENSE NPF-5 P
SPECIAL REPORT 2-90-001 DRYWELL HIGH RANGE POST-ACCIDENT RADIATION MONITOR DECLARED INOPERABLE A.
REQUIREMENT FOR REPORT
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This report is required per Unit 2 Technical Specifications Table 3. 3 '. 6. 4-1 note (b) because one channel of the Drywell High Range' Radiation Instrumentation-was inoperable for greater than seven days.
Specifically, item 12 of Table 3.3.6.4-1 requires that two channels of instrumentation be operable while the unit is in the Run mode.
Footnote of Table 3.3.6.4-1 requires that a Special Report be submitted (b) to the NRC in the event that one of the required channels is inoperable for-a period greater than seven days.
B.
UNIT STATUS AT TIME OF EVENT On 1/2/90, Unit 2 was in the Run mode at an approximate power level of 2436 MWt (approximately 100 per cent of rated thermal power).
C.. DESCRIPTION OF EVENT On 1/2/90,at approximately 1700 CST, Drywell High Range Radiation
- Monitor, 2011-K621B, was declared inoperable due to spiking, and Limiting Condition for Operation 2-90-003 was initiated.
Licensed operations personnel had previously noted that the monitor had been spiking intermittently and that the monitor had tripped.
The cause of the trip and spiking could not be determined during preliminary investigations.
It was noted that the "A" channel of the Drywell High Range Radiation Monitoring System, 2011-K621A, had not been spiking and had been exhibiting a nominal reading of approximately 10 R/hr.
Consequently, monitor 2D11-621B was declared inoperable.
At the time the monitor was declared inoperable, the pre-planned alternate method for monitoring drywell radiation was implemented as required by footnote (b) of Unit 2 Technical Specifications Table 3.3.6.4-1.
This method uses the post luss-of-coolant-accident (Post-LOCA) Normal Range Drywell Radiation monitors. These monitors were verified operable at approximately 1700 CST and every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter.
Maintenance Work Order (MWO) 2-90-0019 was initiated to investigate the phenomenon.
Under this MWO the proper connection and function of cables leading from the monitor to the detector were verified as described below. The high voltage cable connectors as well as the L
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' ENCLOSURE (Continued)
SPECIAL REPORT 2-90-001 DRYWELL HIGH RANGE POST-ACCIDENT-RADIATION MONITOR DECLARED INOPERABLE signal cable connectors were first cleaned and then replaced with new connectors.
To verify _the continuity and integrity of the coaxial signal cable, a Time Domain Reflector (TDR) test was performed. The o
w, TDR test'showed that no circuit discontinuities existed in the cables and connectors between the monitor (located in the Main Control Room) and 'the detectors (located in the drywell).
Also, the monitor was calibrated successfully in accordance with procedure 57CP-Dil-009-2S, "Victoreen Model 876 Radiation Monitor." This testing showed that the monitor and cabling were operating properly at the time the TDR test was performed and that the source of the problem was most likely in the drywell which is inaccessible during power operation.
Since further y'
testing 'and repair required.a' unit outage and drywell entry, the monitor could not be returned to operable status within the seven day
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r time limit.
On 1/9/90, at approximately 1700 CST, seven days after the monitor was declared ' inopera)le, it-had not been returned to operable status.
Therefore, this Special Report is required.
On 1/12/90 at a) proximately 1610 CDT, ten days after the monitor was declared inopera)1e, the Unit 2 reactor scrammed on a Group 1 isolation due to a sensed loss of condenser vacuum (LER 50-366/1990-001). During this forced outage, maintenance personnel entered the drywell, identified the cause of the instrument spiking and repaired a damaged cable. connector at the detector.
The drywell high range radiation monitor. 2D11-K621B was returned to operable status on 1/14/90.
D.
CAUSE OF EVENT r
1.
The root cause of this event is component damage.
Instruments and 1
Control (l&C) personnel investigating the erratic operation (spiking) l of the monitor discovered a damaged cable connector at the detector.
The damaged connector resulted in upward surges in the detector current l
_ producing the intermittent high instrument reading.
The cable L
connector was most likely damaged inadvertently during the recently completed Unit 2 refueling outage.
E.
ANALYSIS OF EVENT The post-accident monitoring instrumentation, of which monitor 2D11-621B is a part, ensures that sufficient information is available k
on selected plant parameters to monitor and assess important variables following an accident. This device monitors radiation levels in the 3(
drywell and is one of two totally separate and redundant instruments in the Drywell High Range Radiation Monitoring system. Monitor 2D11-K621A 1s the other instrument in the system.
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EhcLOSURE (Continued) t DRYWELL HIGH RANGE POST-ACCIDENT
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RADIATION MONITOR DECLARED INOPERABLE i
L Additionally, the pre-planned alternate method of monitoring drywell radiatior. levels was initiated immediately upon declaring 2D11-K621B i
The alternate method consists of using the four k
post-LOCA gamma radiation monitors 2Dll-K622A, B, C, and D.
These four monitors are completely separate from 2011-k621A and B.
Therefore, problems in one. monitoring system will not prevent the other monitoring
. system from operating properly. ' Furthermore, the four post-LOCA gamma radiation. monitors are separated into. two subsystems, using two detectors per subsystem and receiving 120 VAC power from separate power supplies.
This ensures a highly reliable system where, if a single failure were to occur, two monitors would still be operable.
Based on the above information, it is concluded that this event had no adverse impact on nuclear safety. This analysis is applicable to all power levels.
F.
CORRECTIVE. ACTIONS Corrective actions for this event include:
l 1.
Declaring Drywell High Range Radiation Monitor 2D11-K621B inoperable and. initiating LC0 2-90-003.
- 2.. Implementing the pre-planned alternate method for monitoring l
drywell radiation.
3.
Completing a root cause investigation.
4.
Repairing. the damaged connector to the detector, calibrating, and
-functionally testing the monitor, l
Drywell high range radiation monitor 2011-K6218 was returned to service on 1/14/90 and LC0 2-90-003 has been terminated.
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