ML20058K809
| ML20058K809 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 07/02/1974 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| UE-263-74-02, UE-263-74-2, NUDOCS 9102140432 | |
| Download: ML20058K809 (2) | |
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Regulatory Docket File MW NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401 l
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.ci Mr. J F O' Leary, Director "C'iiT Directorate of Licensing
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Office of Regulation a.
C U S Atomic Energy Commission Washington, D. C.
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UNUSUAL EVENT REPORT TO THE AEC j
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l Recombiner Outlet Hydrogen Analyzer Low Sample Flow Trip 1.
Report Number: UE 263/74-2
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I 2A. Report Date: July 2, 1974 2B.
Event Date: June 9, 1974
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Facility: Monticello Nuclear Generating Plant (DPR-22)
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Monticello, Minnesota 55362
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4.
Identification of Event:
This report concerns the discovery of a single failure mode which could l
result in inoperability of the recombiner train outlet hydrogen analyzers.
5.
Conditions Prior tc the Event:
Routine Startuo Operation - Plant startup was in progress with operational testing of the modified off-gas holdup system being conducted. Reactor power was approximately 3% and reactor pressure approximately 300 psig.
6.
Description of Event:
On June 9, 1974, a plant startup was in progress with the B recombiner train in operation. hhile investigating an instrument problem associated with the recombiner train inlet flow control loop, the train was inadvertently tripped.
CONC HIQ1 annunciator was then received, however The TRAIN B - OUTLET H2 the hydrogen analyzer remote indicators in the control room indicated normal concentration (~1/2% hydrogen). The B recombiner train was then restarted and a test engineer was sent to the recombiner building to check the hydrogen analyzers and determine the cause of the annunciator. The three B recombiner train hydrogen analyzers were found to be tripped on low sample flow (which initiates the OUTLET H2 CONC HIGi annunciation). The A recombiner train was immediately placed in operation and the B train was shutdown. Subsequent investigation revealed that the low flow shutdown of all three analyzers was caused by an accumulation of moisture in the common sample line.
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7.
Designation of Apparent Cause of the Event:
Desien - The recombiner train trip logic did not include a trip input from low sample flow shutdown of the hydrogen analyzers. At the time the system was designed, a comon low flow trip of all three hydrogen analyzers on a recombiner train was considered to be a highly improbable event.
8.
Analysis of Event:
The purpose of the recombiner train outlet hydrogen analyzers is to monitor the hydrogen concentration in the off-gas leaving the recombiner and to trip the recombiner train in the event that high hydrogen concentration (2%) is detected. This action is designed to prevent an explosive hydrogen mixture from reaching the compressed gas storage system. Since the compressed gas storage system had never been placed in operation prior to the event, it did not affect the health and safety of the public.
9.
Corrective Action:
The recombiner train trip logic has been modified to include trip inputs from hydrogen analyzer low sample flow. Also, moisture separators have been added to the sample lines to reduce the possibility of water plugging the sample lines.
10.
Failure Data:
There were no equipment failures associated with the event.
t O My L 0 Mayer, PE Director of Nuclear Support Services ID4/mm cc: J G Keppler G Charnoff Minnesota Pollution Control Agency Attn: E A Pryzina
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