ML20004F827
| ML20004F827 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 04/23/1981 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Crane P PACIFIC GAS & ELECTRIC CO. |
| Shared Package | |
| ML20004F826 | List: |
| References | |
| NUDOCS 8106220481 | |
| Download: ML20004F827 (1) | |
Text
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UNITE] STATES -
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REGION V 1900 N. CALIFORNIA BOULEVARD e<
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,,,a WALNUT CRE3K. CALIFORNIA 94006 April 23, 1981 Docket f;o. 50-133 Pacific Gas and Electric Cor pany l
P. O. Bov. 7442 San Francisco, California 94106 Attention: Mr. Philip A. Crane, Jr.
Assistant General Counsel l
Gentlemen:
i The enclosed information notice provides early notification of an event that may have safety significance. Accordingly, you should review the information notice for possible applicability to your facility.
No specific action or response is requested at this time; however, contingent upon the results of further staff evaluation, a bulletin or a l
circular recomending or requesting specific licensee actions may be L
issued.
If you have any questions regarding this matter, clease contact l
the Director of the appropriate NRC Regional Office.
l Sincerely, i
l
\\V Lil M R. H. Engel E N
Director l
Enclosure:
l IE Information Notice No. 81-16 cc w/ enclosure:
i J. D. Shiffer, PG&E W. Raymond, PG&E E. Weeks, PG&E, Humboldt Bay l
i 81062204/4
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SSills flo. : 6835 Accession Fo.:
8103300372 If4 81-16 UflITED STATES flVCLEAR REGULATORY COMMISSI0ft 0FFICE OF IflSPECTI0ft Af4D EllFORCEMEflT WASHI!iGT0fl. D.C.
20555 April 23, 1981 IE IrlF0P.MATI0ft fl0TICE fl0. 81-16: C0flTROL R0D DRIVE SYSTEM MALFUtlCTI0flS Descriotion of Circumstances:
Continued flRC evaluation of BWR control rod drive (CRD) systems operating experience has identified several operating events which highlight the need for timely ooerator action if certain CRD system nalfunctions occur during specific modes of reactor operation.
In each event, operator action was taken when needed and scram capability was maintained at all times. However, if timely operator action were not taken (or if other circumstances existed) scram capability might have been degraded.
This notice is provided to inform reactor operators ci these events and re-emphasize the reliance on timely operator action (IER 80-17 Supplement 4. Confirmatory Order dated October 2, 1980, and Safety Evaluation Report dated December 1,1980.)
On February 24, 1981, at Brunswick Unit 2, the reactor was manually scrafhmed from 1.5% power af ter the group 4 control rods had received three scram signals.
(Group 4 contains 33 control rods and is one of four control rod grouos.)
The first scram signal for group 4 occurred when surveillance testing caused a trip of RPS "B" channel. Reactor power decreased from 7". to 1.5% and the RPS "B" trip was resec by the operator. Another grouo 4 scram signal, received when an intermediate range monitor (IRh) drifted upscale, was reset by the onerator. A third scram signal, received when the IRf1 drif ted upscale again, caused the operator to initiate a manual scran.
Subsequent investi-gation revealed that a relay contact (K14c) in groun 4 RPS "A" had failed open. Thus, group a rods received a scram signal each time RPS "B" was tripped.
We note that rod group scrams of this type have been previously addressed by the flRC (December 1,1980 Safet/ Evaluation Reoort pages 22-24).
For plants like Brunswick with good communication between the SDV and instrument volume (IV), operator action is not needed to maintain scram capability.
- However, for those BURS with poor communication between the SDV and IV, CRD seal leakage from the scrammed control rods (with open scram outlet valves) could potentially result in filling the SDV before level switches in the IV initiate an automatic scram.
In this case, timely operator action is needed to prevent a temporary loss of scram capability.
Indications are available to alert the operator to scrammed CRDs and accumulation of water in the SDV.
These indications include control rod position indication, rod drif t indication (with annunciator), high level in SDV (with annunciator), high level in IV (with rod block and annunci-ator), and change in reactor power with attendant indications. With current
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equipment and requirements (IEB 80-17 and Confirmatory Orders) we expect the operator would initiate a manual scram while sufficient capacity remains in the SDV.
Ifl 81-16 April 23, 1981 Page 2 of 2 Two other cperating events involved operator action following CRD system rulfunctions not related to SDV perfonnance. At Brunswick 1 on August 27, ItB0, both CRD pumps became inoperable due to low suction pressure caused by hi <h pressure drop across the suction filter coincident with low level in the coidensate storage tank.
In accordance with procedures the operator manually scranned the reactor which was in startup, subcritical with some control rods not fully inserted, and at approxiriately 5 osig pressure. At Oyster Creek on flovember 30, 1980, operability of both CRD pumps was challenged by seal eter piping leaks on each pump. This condition was detected and corrected by operators during routine power operation. There was no direct threat to loss of scram capability in this event since the reactor was cressurized, however, this event is of interest since similar failures affected both pumps. Scra:n capability was maintained at all times dur'ng both events.
Evaluation of these two events and possible CRD system failure modes show the l
need for operator action to maintain scram capability. Under conditions of reactor low pressure, such as those encountered during startup, control rod scram capability could be lost in an event in which complete failure of CRD hydraulic flow occurred simultaneously with gross leakage from the scram accumulators. The CRD pumps maintain the pressure on the accumulators and prcvide motive force for single rod drive operations.
Failure of CRD hydraulic flow can be caused by (1) inoperability of both CRD pumps caused by power failure; (2) plugging of CRD pump suc* ion strainers; (3) lack of an adeouate condensate storage tank supply; or (4) ather failures in the CRD hydraulic system. Scram capability under these conditions is designed to be provided by l
the scram accumulators. Extensive deterioration of the accumulator charging l
line check valves could cause a sufficient number of accumulators to discharge I
dnd result in a loss of scram capability if the operator does not take appro-l priate action.
In the event of such multiple failures, reactor shutdown would have to be accomplished by use of the liquid control system.
This information is provided as a notification of a possibly significant matter that is still under review by the flRC staff.
In case the continuing flRC review finds that specific licensee actions would be appropriate, a bulletin or circular may be issued.
In the interim, we expect that licensees will review this information for applicability to their facilities paying particular attention to their coerating procedures.
The operating procedures l
should include specific actions (i.e., initiation of full scram) to be taken by the operator in resoonse to a scram of a portion of the control rods.
Procedures should also include the reouired response (i.e., again to initiate a scram) on recognition of loss of operability of both CRD pumps especially during the initial stages of plant startup whe'n reactor pressure is insuffi-cient to accomplish a scram.
It is noted that current licensing requirements, as reflected in BWR Standard Technical Specifications, include surveillance testing at least once every eigh+aen months to check the leak tightness of the scram accumulators to hold pressure for at least 20 minutes.
flo written response to this information is reouf red.
If you need additional information regarding this matter, please contact the Director of the appro-priate flRC Regional Office.
Attachment:
Recently issued IE InfJrmation flotices
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Attachment IN 81-16 April 23, 1981 RECENTLY ISSUED IE If! FORMATION NOTICES t
i.1 ormation Date of f
Notice No.
Subject Issue Issued to 81-15 Degradation of Automatic 4/22/81 All power reactor ECCS Actuation Capability facilities with an by Isolation of Instrument OL or CP Lines 81-14 Potential Overstress of 4/17/81 All oower reactor Shaf ts on Fisher Series facilities with an 9200 Butterfly Valves OL with Expandable T Rings 81-13 Jammed Source Rack ir; 4/14/81-Specified Irradiator Gamma Irradiator licensees 81-12 Guidance on Order Issued 3/31/81 All BWR facilities January 9,1981 Regarding with an OL or CP Automatic Control Rod Insertion on Low Control Air Pressure 81-11 Alternate Rod Insertion 3/30/81 All BWR facilities for BUR Scram Represents with an OL or CP a Potential Path for loss of Primary Coolant 81-10 Inadvertant Containment 3/25/81 All power reactor Spray Due to Personnel facilities with an Error OL or CP 81-09 Degradation of Residual 3/26/81 All power reactor Heat Removal (RHR) System facilities with an OL or CP 81-08 Repetitive Failures of 3/20/81 All oower reactor Limitorque Operator SNB-4 facilities with an Motor-to-Shaf t Key OL or CP 81-07 Potential Problem ws h 3/16/81 All power reactor Water-Soluble Purge Dam facilities with an Materials Used During OL or CP Inert Gas Welding 81-06 Failure of ITE Model 3/11/81 All power reactor K-600 Circuit Breaker facilities with an OL or CP OL = Operating Licenses CP. = Construction Permits
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