ML20084S878

Ro:On 710507,primary Sys Leak Discovered Due to Failure of Temporary Differential Pressure Transmitter on Primary Coolant Pump D.Caused by Failure of Head Bolts Allowing Head to Pull Away from Ctr Plate.Transmitter Removed

ML20084S878
Person / Time
Site:	Palisades
Issue date:	05/18/1971
From:	Haueter R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8306200046
Download: ML20084S878 (3)

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ce'nerai onTh. 2,2 west u,cn.g.n Avenue. anc w.on. u.cn.g n 492oi . Area Code S17 7 88 OSSO May 18, 1971 Dr. Peter A. Morris, Director Re: Docket 50-255 Division of Reactor Licensing License No DPR-20 United States Atomic Energy Commission Washington, DC 20545

Dear Dr. Morris:

Att: Mr. D. J. Skovholt This letter is written to apprise you of a primary system leak caused by temporary test instrumentation installed to measure the flow rates of the "D" primary coolant pump at the Palisades Plant.

The normal primary loop flow rate is measured by sensing the pressure drop across each of the two steam generators. To allow calibration of permanent instruments, temporary instruments were installed to measure the differential pressure across each of the four pumps.

One of these temporarily installed instruments, a Barton Model 332 differential pressure transmitter installed across the "D" primary coolant pump, failed on May 7,1971 and allowed a loss of primary greater tht @ coolant 0 gps [.' Thetocontainment the containmentfilled with atmosphere steam making at a rate ofg/]

visibility very~ limited. The leak was located after approximately _

two hours and the damaged instrumdht isolatedFThV rsactor was f goc >pf I suberitical during the entire incident with refueling concentration r of boron in the primary coolant system.

Sequence of Events The plant was nearing the completion of the post-core-loading precritical testing program with the primary coolant system at normal hot standby pressure and temperature (2100 psi, 532 F).

0600 - The pressurizer level dipped and the two standby charging pumps "B" and "C" started giving maximum charging rates.

The operator noted that pressurizer level was recovering slowly.

The "C" pump shut down due to increasing pressurizer level after -

y several minutes of operation.

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Dr. Peter A. Morris O 2 May 18, 1971 0613 - The auxiliary operator was contacted on the PA sys-tem and instructed to check out the charging system.

0615 - The Shift Supervisor entered the containment build-ing and entered the doorway near the base of the north steam generator.

The "C" and "D" primary coolant pumps were both in operation and the "D" pump was completely enveloped in steam. The supervisor left the area, phoned the control room and instructed the operator to: 1) shut down the "C" and "D" primary coolant pumps, 2) close letdown valve, 3) stop the blending of boric acid to fill SIRW tank, and 4) line the charging pump suction to the SIRW tank. Maximum cooling was initiated for No 1 and No 4 containment air coolers to condense steam in "A" steam generator cavity.

0630 - The "B" primary coolant pump was returned to service.

The spray valve on the "B" primary coolant loop was opened vide for the cooldown.

0640 - Commenced bypassing steam to the condenser to cool down the primary system.

5 0655 - Opened 480 V breaker to the pressurizer heater trans-former to prevent possible water damage. The breakers are located in room below the leak area.

0700 - Shift Supervisor and Combustion Engineering Site Manager entered the containment building and traveled to elevation of 649 Visibility continued to be near zero in "D" pump area due to steam.

0725 - Containment cooling was increased by placing con-tainment coolers No 2 and No 3 in full operation to minimize the humidity. Containment temperature continued to hold at 90 -100 F.

0820 - The Shift Supervisor and Combustion Engineering Site Manager entered "D" pump area from the 590 elevation and were able to see the pressure differential transmitter blowing steam. The instru-ment was isolated and the leak stopped.

Letdown flow was reestablished and the primary coolant system cooldown stopped. At this point, the system pressure was 1900 psia and the loop-pressurizer temperature difference was 1800 F.

Cause of Incident TVo of the four head bolts (size 3/8") failed on the Model 224 differential pressure bellows unit allowing the head to pull away from the center plate of the bellows unit. This allowed water at l

p- ,

Dr. Peter A. ris 3.

May 18, 1971 i

full system pressure of 2100 psia to escape. One of the two steel I cadium plated bolts appeared to be oxidized and brown in color in i the break area indicating it may have failed prior to this incident, while the second bolt was bright in the break area. The cause of this failure is not definitely known at this time. It is felt that the failure of the bolt that was oxidized and brown in color contri-buted to the failure of the second bolt.

Corrective Action The defective transmitter has been removed. A search was made to determine if permanent plant instrument channels utilized this identical Model 332 differential pressure transmitter.

A total of fifteen similar units were found to be installed in the reactor protective system. A replacement program is already in progress for these units, due to an earlier problem with the range springs. The Barton Model 295 transmitter units have been ordered to replace the presently installed Barton Model 332. The head assembly on the ordered units is held together with twelve bolts. This replace-  ;

ment program is scheduled to be completed prior to the start of the power test program.

Conclusions We conclude the replacement of the Model 332 differential pressure transmitter with a Model 295 unit will eliminate the possi-bility of similar failures occurring in the future. A review of equipment operation and operator actions during the incident indicated all systems functioned as designed and operator actions were correct ,

and timely. '

Yours very truly, Robert L. Haueter (Signed)

RBS/jes Robert L. Haueter Electric Production Superintendent - Nuclear CC: BHGrier Div of Compl USAEC i

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