ML19282A633

LER 79-002/03L-0 on 790127:operation in Degraded Mode Resulted from Repairs to Seat of Buffer Helium Purge Valve. Bypass of Buffer Helium Dryer Caused by Leakage Past Valve Seat Insert of Velan Model P-33876-N/78R Valve

ML19282A633
Person / Time
Site:	Fort Saint Vrain
Issue date:	02/26/1979
From:	Gahm J PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19282A631	List: ML19282A630 ML19282A633
References
LER-79-002-03L, NUDOCS 7903050226
Download: ML19282A633 (6)

Text

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REPORT DATE: Feb rua ry 26, 1979 REPORTABLE OCCURRENCE 79-02 ISSUE 0 OCCURRENCE DATE: Janua ry 27, 1979 Pare 1 of 5 FORT ST. VRAIN NUCLEAR GENERATING STAIION PUBLIC SERVICE COMPANY OF COLOPaD0 P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT No. 50-267/ 79-02/03-L-0 Preliminary IDENTIFICATION OF OCCURRENCE:

On January 27, 1979, operation in a degraded mode of LCO 4.2.10 and LCO 4.2.11 resulted during repairs to the seat of a buffer helium dryer purge valve.

Operation in a degraded mode of LCO 4.2.10 again occurred on January 27, 1979, and January 30, 1979, during the return to power operation.

These events are reportable per Fort S t. Vrain Technical Specification AC

7. 5. 2 (b) 2.

EVENT DES CRIPTION :

At about 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> on January 27, 1979, Operations personnel observed that leakage past the seat of a buffer helium dryer purge valve had developed.

The buffer helium dryer was bypassed and a reduction in reactor power from 62% to 41% was begun in anticipation of an increase in the primary coolant mois ture and oxidant concentrations (refer to Figure 1, Point ([) . By 1700 Hours , Point ([) , the oxidant concentration had risen to 10.0 volume pa:ts per million (10.0 vpm) . Although reactor power was being reduced at that time, the core average outlet temperature did not decrease below 1,200*F un-til about 1815 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.906075e-4 months <br />. Therefore, operation in a degraded mode of LCO 4.2.10 resulted.

While repairs were being made to the purge valve, the primary coolant moisture concentration continued to increase. By 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br />, the reactor dew point exceeded the limits of LCO 4.2.11, Figure 4.2.11-1. Reactor power was further reduced to 32% to decrease the core average outlet temperature. The primary coolant moisture concentration returned to within the specifications of LCO , 4.2.11 at 0200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> on January 28, 1979.

At 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> on January 28, 1979, reactor power was increased to 42% to aid in removal of moisture from the reactor core graphite. This power level was maintained until the moisture concentration could be reduced.

The total oxidant and moisture concentration had decreased to 15.0 vpm and 6.6 vpm, respectively, by 0800 hours0.00926 days <br />0.222 hours <br />0.00132 weeks <br />3.044e-4 months <br /> on January 29, 1979. Because as much moisture as possible had been removed for the existing plant conditions, reac-tor power was increased to 60% and the core average outlet temperature again exceeded 1,200*F (Point (3)).

790305D M

~

REPORTABLE OCCURRENCE 79-02 ISSUE 0 Page 2 of 5 EVENT LESCRIPTION (continued):

The increase in the primary coolant temperature caused residual moisture to be removed f rom the core graphite and an increase in the total oxidant concentra-tion to about 25 vpm. Because this concentration persisted, the reactor power was again reduced to 42% at 2040 hours0.0236 days <br />0.567 hours <br />0.00337 weeks <br />7.7622e-4 months <br /> (Point ( } ). The core average outlet temperature was again less than 1,200*F by 2125{ hours.

On January 30,1979, at 0800 hours0.00926 days <br />0.222 hours <br />0.00132 weeks <br />3.044e-4 months <br />, reactor power was raised to 60% while the oxidant concentration was at 10.8 vpm and on a downward trend (Point (3)).

At 1338 hours0.0155 days <br />0.372 hours <br />0.00221 weeks <br />5.09109e-4 months <br /> (Point ([) ), while performing electrical maintenance, a voltage transient caused a reactor scram. No further degraded mode operations of LCO 4.2.10 or LCO 4.2.11 have occurred to date.

CAUSE DESCRIPTION:

Normally, dry helium from the buffer helium dryer is supplied to the circula-tor upper journal bearing seals at a pressure slightly higher than primary coolant pressure. By design, approximately half of the buffer helium enters the PCRV, and the other half is returned to the buffer helium dryer where mois-ture picked up from the journal bearing water cavities is removed.

When the buffer helium dryer purge valve developed seat leakage it was neces-sary to bypass the dryer to perform repairs. When the dryer is bypassed, some moist buf fer helium can enter the PCRV via the circulator seals resulting in an increase in the primary coolant moisture and oxidant concentrations.

The cause of the purge valve seat leakage was a cracked seat insert. The in-sert was replaced in kind and the buffer helium dryer returned to normal opera-tion.

The cause for the failure o f the disc insert has not been determined. This is the third occurrence of this type since December 24, 1978, (reference Re-portable Occurrence Report No. 50-2 67/ 78-39/03-L-0) .

CORRECTIVE ACTION:

For the event of January 27, 1979, reactor power was reduced to 32% to decrease the core average outlet tempera ture. Buffer helium supply and return flows to the circulators were approximately equalized to reduce the amount of mois-ture introduced into the PCRV via the circulator upper journal bearing seals.

>bnitoring of the primary coolant moisture concentration was increased to 10 minute intervals. The faulty valve was repaired and the buffer helium dryer returned to service.

The core average outlet temperature was maintained below 1,200*F while the purification system removed the oxidant impurities. Reactor power was not increased until the moisture concentration had been reduced as much as pos-sible for the plant conditions.

~ REPORTA3LE OCCURRENCE 79-02 ISSUE O Page 3 o f 5 CORRECTIVE ACTION (continued):

inserts has not The reason for the recent failures of the purge valve seatResults of an investigation yet been determined.

included in a final supplement to this report.

REPORTABLE OCCURRENCE 79-02 ISSUE 0

, Page 4 of 5

, 40 From a Maximum

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O 1200 0000 0000 0000 0000 1/27 1/25 1/29 1/30 1/31 DATE /TDIE

REPORTABLE OCCURRENCE 79-02 ISSUE O Page 5 of 5 Prepared by:

Charles H. Fuller Technical Services Technician Reviewed by: f / ,p

. W. Gahm Technical Services Supervisor Reviewed by: -

Frank M. >bthie Operations >bnager Approveo by: Ot SL6% u u.q 2ht Don Warembourg (j

/

bbnager, Nuclear Production

(7 77)

LICENSEE EVENT RFPORT

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REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h o 2 On January 27, 1979, operation in a degraded mode of LCO 4.2.10 and LC.' 4.2.11 re- l o 3 suited during repairs to the seat of a buf fer helium purge valve. Operation in a l o 4 degraded node of LCO 4.2.10 occurred on January 29 and January 30, 1979, during the l o 3 l return to power operation. These conditions are reportable per Fo rt S t. Vrain Tech- l o s lnical Specification AC 7.5.2(b)2. I o 7 I l o s 1 I 7 8 9 80 SYSTEM CAUSE CAUSE COMP. VA LV E CODE CODE SURCODE COMPONENT CODE SU8 CODE SUBCODE 7

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18 19 20 SEQU E N TI AL OCCURRENCE REPORT REVISION

, EVENT YEAR R EPORT No. CODE TYPE NO.

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-l 23 lo l0 12 l 24 26 l/

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40 43 44 CAUSE DESCRIPTION AND CORRECTIVE ACT;ONS i o [ Leakage past the valve seat insert of Velan Model P-33876-N/78R valve required bv- l

[i [i l l pass of buf fer helium dryer. Third failure of this type. Refer to RO 78-39/03-L-0.

, , l Investigation into cause of problem will be reported in final suprlement to this i 3 l report.

i i4 1 7 4 3 80 ST S  % POWER OTHER STATUS ISCOV RY DISCOVERY DESCRIPTION i s E l@ l0 l6 2l@l N/A l A l@l Operator Observation l ACTIVITY CONTENT RELEASED OF RELEASE AMOUNT OF ACTIVITY LOCATION OF RELEASE W lZ @ l Zl@ N/A l N/A l 7 d 9 10 tt 44 45 80 PERSONNEL EXPOSURES NUMBER TYPE DESCRIPTION s i 7 l0 0l0l@lZl@l "N/A S l

,E nSONNE L iNJ ES NUYBER DESCRIPTION 7

1 a 8 9 l0l0l0l@l 11 12 N/A 80 l

LOSS OF OR DAMAGE TO FACILITY TYPE DESCRIPTION L'

7 9d 9Izl@l 10 N/A 30 PUBLICITY NRC USE ONLY

• 2 o ISSU Nl E l D@ N/AOESCRIPTION l llllll ll l lll}

NAME OF PREPARER M

/W/d -

J. w. cahm PHONE:

< 3E3)785-2253 j