IR 05000295/1982001
| ML20042A386 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 02/19/1982 |
| From: | Connaughton K, Connaughton K, Gildner M, Peschel J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML20042A377 | List: |
| References | |
| 50-295-82-01, 50-295-82-1, 50-304-82-01, 50-304-82-1, NUDOCS 8203230378 | |
| Download: ML20042A386 (6) | |
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U.S. NUCLEAR REGULATORY COMMISSION
REGION III
Report No. 50-295/82-01(DETP); 50-304/82-01(DETP)
Docket No. 50-295; 50-304 License No. DPR-39, DPR-48 Licensee: Commonwealth Edison Company Post Office Box 767 Chicago, IL 60690 Facility Name: Zion Nuclear Power Station, Units 1 and 2 Inspection At: Zion site, Zion, IL Inspection Conducted: December 11, 12, 18, 1981 and January 7, 1982 f?,5l.
NR wr Inspectors:
K. A. Connaug ton
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. L. Gildn
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Approved By:
M. Peschel, Acting Chief 8//9/72.
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anagement Programs Section Inspection Summary Inspection on December 11 12, 18, 1981 and January 7, 1982 (Report No. 50-295/82-01(DETP) '0-304/82-01(DETP))
Areas Inspected: Special inspection to review failure of 2B auxiliary feedwater pump on December 6, 1981 (LER 50-304/81-31) and failures of 2B and 2C auxiliary feedwater pumps on December 11, 1981 (LER 50-304/81-33).
The review consisted of interviews with operating, maintenance, technical staff and Station Nuclear Engineering Department personnel, examinations of the shift log and computer alarm typer printouts, review of test pro-cedures, witnessing of tests, and review of test results. The inspection included 27 inspector-hours onsite by two NRC inspectors.
Results: No items of noncompliance were identified during the inspection.
l 8203230378 820304 PDR ADOCK 05000295 G
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DETAILS 1.
Persons Contacted K. Graesser, Zion Station Superintendent
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W. Kurth, Master Instrument Mechanic E. Campbell, Electrical Group Leader l
A. Amaroso, Technical Staff-
- E. Fuerst, Operating Assistant Superinteudent
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P. Budoulle, Operating Engineer A. Miose, Zion Technical Staff Supervisor
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- G. Plim1, Administrative and-Technical Support Services Assistant Superintendent
- Denotes those attending exit meeting on January 7, 1982.
In addition to those identified above, the inspectors contacted oper-
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ating, maintenance, technical staff, and Station Nuclear Engineering Department (SNED) personnel.
2.
Event Descriptions
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a.
Failure of 2B Auxiliary Feedwater Pump to Auto Start on Low Low Steam Generator Level on December 6,1981 (LER 50-304/81-31)
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On December 6, 1981, following a Unit 2 reactor trip from 89%
power, the 2B motor driven auxiliary feedwater pump apparently
auto started in response to low low steam generator level and then, almost immediately, tripped on low suction pressure. 'The operators did not witness the 2B auxiliary feedwater pump start and immediate trip, but merely observed that it was not running.
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The alarm associated with the low suction pressure trip was apparently cleared without having been noted. Hence the 2B auxiliary feedwater pump failure was characterized by the licensee as a " failure to auto start." The 2C motor driven auxiliary feedwater pump also auto started, and ran acceptably.
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Upon noticing that the 2B auxiliary feedwater pump was not
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running, operators manually started the 2B auxiliary feedwater
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pump and it ran acceptably.
b.
Failure of both the 2B and 2C Auxiliary Feedwater Pumps.to Auto Start on Low Low Steam Generator Level on December -11,1981 l
(LER 50-304/81-33)
I On December 11, 1981, Zion, Unit 2 tripped due to an electrical fault in the main generator. The trip resulted in low low steam generator levels and auto start signals 'to the 2B and 2C motor-l driven auxiliary feedwater pumps. The pumps started and tripped almost immediately on low suction pressure. Subsequently, a
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reactor operator attempted to manually restart the pumps. The 2B auxiliary feedwater pump started as required when the operator i
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placed the control switch in the "close" position. The operator placed the 2C auxiliary feedwater pump control switch in the
"close" position and the 2C pump failed to start. The operator then moved the 2C auxiliary feedwater pump control switch to the
" reset" or " trip" position and then again tried to manually restart the pump by placing the switch in the "close" position.
The 2C auxiliary feedwater pump again failed to start. The operator then'placed the control switch in'" pull-to-lock."
Approximately four minutes later, the operator removed the contro. switch'from the pull-to-lock position in order to demonstrate the manual start failure to a fellow operator and the pump auto-started.
-At the time of the event, the 2A turbine-driven auxiliary feedwater pump was out of service. The 2B and 2C motor-driven auxiliary feedwater pumps were aligned in a split-discharge header configuration, i.e., each pump feeding the steam genera-tors through physically separate discharge piping.
On December 11, 1981, a Confirmation of Action Letter (CAL) was issued to Commonwealth Edison Company concerning Auxiliary Feed-water Pump Operability at Zion Station. The CAL is attached to this report. The Region III staff issued the letter following the December 11, 1981, event in order to provide adequate assurance, prior to Zion Unit 2 leaving the shutdown condition, that the Auxiliary Feedwater Pumps would start and run when called upon.
3.
Licensee Actions --Investigative and Corrective a
Event of December 6, 1981 (LER 50-304/81-31)
On December 6, 1981, the licensee performed ESF actuation logic testing which included auto starts of the 2B and 2C motor driven auxiliary feedwater pumps on simulated low low steam generator level. These auto starts were performed, by procedure, one pump at a time. Both pumps performed acceptably and testing was successfully completed. The licensee also inspected the 2B auxiliary feedwater pump breaker and found no abnormalities.
Unable to determine the cause of the 2B auxiliary feedwater pump
" failure to auto start" and after demonstrating actuation logic and pump performance to be acceptable, the licensee returned the pump to service, b.
Event of December 11, 1981 (LER 50-304/81-38)
Between December 11 and 18, 1981, investigations and extensive testing were conducted by the licensee to determine the causes of the low suction pressure trips of auxiliary feedwater pumps 2B and 2C and subsequent failure of the 2C auxiliary feedwater pump to manually start. The following was revealed:
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Low suction pressure trip switches were properly calibrated
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with as-found trip settings well within tolerances.
(2) While in the split-discharge header configuration, and discharges throttled for rated flow, simultaneous starts of the 2B and-2C auxiliary feedwater pumps cause sections of the suction line near the pump to sustain a temporary pressure reduction, thus causing a reverse flow in the sensing lines of
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the low suction pressure switch. The sensed suction pressure momentarily drops (about.8-1.0 seconds in duration) below the low-suction pressure switches' trip setpoints.
In the case of a single auxiliary feedwater pump start, the sensed suction pressure momentarily drops to near the low suction pressure trip setpoint.
(3) Control circuits affected by modifications M22-1/2-80-24 (Modifications to monitor neutral contact continuity status of Westinghouse W-2 control switches) behave in the following manner:
Following an auto start and subsequent auto trip (such as low suction pressure on Aux. FW pumps), if the auto start
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signal persists and the trip resets, the component may not restart, as per design, when the control switch is moved from the neutral or " auto" position to the "close" position.
If the control switch is moved from " neutral" position to the "close" position rapidly enough, there is insufficient time between the " break" of the neutral (auto start) contacts and the "make" of the close contacts for current in the lock-out relay coil (Y) of the supply breaker to decay sufficiently to allow the breaker to reset as per design. The breaker must reset in order to reclose upon demand. During the event, the 2B auxiliary feedwater pump started manually because the operator manipulated the control switch slowly enough to allow breaker reset.
Corrective action taken and corrective action planned by the licensee includes the following:
(1) The licensee has modified the 2B and 2C auxiliary feedwater pump control circuits such that the low suction pressure condition must remain below the low suction pressure trip setpoint for greater than 2.5 seconds. This modification will prevent low-suction pressure trips of the motor-driven auxiliary feedwater pumps due to momentary drops in sensed suction pressure following simultaneous starts of the motor driven auxiliary feedwater pumps while.in the split-discharge header configuration.
After completion of the modification installation and testing, the licensee was released from the conditions of the December 11, 1981, Confirmation of Action Letter during-4-
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a telephone conversation between Messrs. J. Peschel and E. Fuerst on December 20, 1981.
The licensee has already acquired parts and obtained approval for performing this modification on the Unit 1 motor-driven auxiliary feedwater pumps at the next scheduled outage or within the LCO time limitations (7 days) for operating with the 1A turbine-driven auxiliary feedwater pump out of service and one motor driven auxilliary feedwater pump assumed inoper-able, whichever occurs first. Testing will be performed to verify that this fix is applicable to the unit 1 auxiliary feedwater systems.
(3) The licensee is currently planning to correct the breaker reset problem by an additional modification to affected control circuits. As an interim measure, the licensee has issued Standing Order Number 0149 to alert operators to this potential problem and to instruct them to go to the
"close" position slowly in order to assure essential safety systems will respond properly.
4.
Discussion and Findings At the time of both events the 2A turbine driven auxiliary feedwater pump was out of service for maintenance.
When the 2A auxiliary feedwater pump is available, it is lined up to discharge through one of the two separate discharge headers, while the 2B and 2C motor driven auxiliary feedwater pumps both discharge through the other discharge header.
Currently, when the turbine driven auxiliary feedwater pump is not available, the motor-driven pumps are realigned, by procedure, to different discharge headers, thereby maintaining two distinctly separate trains for auxiliary feedwater supply. This practice was established by Revision 8 to Surveilance Procedure PT-7 in September of 1979. Prior to this procedure revision, the 2B and 2C motor driven auxiliary feedwater pumps shared a common discharge header, whether or not the 2A turbine driven auxiliary feedwater pump was available.
Auxiliary feedwater system preoperational testing, auxiliary feedwater pump performance testing, and auxiliary feedwater pump actuation logic testing did not include simultaneous starting of the 2B and 2C motor driven auxiliary feedwater pumps, while lined up in the split discharge header configuration. Furthermore, based on discussions with operating personnel, neither Units 1 nor 2 have experienced loss of main feedwater or a reactor trip from appreciable power levels and associated
>w low steam generator level conditions while their respective motor driven auxiliary feedwater pumps were lined up in the split-discharge header arrangement, prior to December 6,1981. The licensee, therefore, did not realize the potential for the occurrence of auxiliary feedwater pump low suction pressure trips under these peculiar circumstances.
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On January 13, 1982, NRC and Westinghouse Nuclear Corporation repre-sentatives met to discuss potential generic concerns, resulting from the modification to control circuits to monitor neutral contact continuity of Westinghouse W-2 type control switches described in Westinghouse NSD Technical Bulletin, NSD 80-09, and endorsed by IE Bulletin No. 80-20.
It had been determined that the subject modification accounted for the breaker reset failures during manual start attempts of the 2B auxiliary feedwater pump on December 11, 1981, at Zion Station.
Based on this discussion, it was concluded that this effect on control circuit performance was of minimal safety significance, since auto-start capability was unimpaired, and slow deliberate control switch manipulation precluded failure of the breaker to reset. Further, this effect appeared to be peculiar to Zion's Sargent and Lundy control circuit design.
(0 pen) Unresolved Item (50-295/82-01-01; 50-304/82-01-01): The inspector tried to ascertain whether or not Revision 8 to surveillance test Procedure PT-7, which incorporated provisions for realigning the 2B and 2C auxiliary feedwater discharges to separate headers, had received appropriate review.
The licensee was unable to produce documentation of the required onsite review. The licensee is currently trying to locate such documentation.
(0 pen) Unresolved Item (50-295/82-01-02; 50-304/82-01-02): The licensee is planning to install modifications to affected control circuits on each unit during the next scheduled refueling outages, which will result in the elimination of hold up paths which exist when the control switches are in the " trip" position and an auto start signal is present. Breaker reset will then be accomplished, as in other control circuit designs, by moving the control switches to the " trip" position. A low suction pressure trip time delay interlock will also be added to the IB and 1C auxiliary feedwater pump control circuits. This item will remain open until these modifications are installed and satisfactorily tested.
5.
Unresolved Items Unresolved Items are matters about which more information is required in order to ascertain whether they are acceptable items, Items of Noncompliance, or Deviations.
Unresolved Items disclosed during the inspection are discussed in Paragraph 4.
6.
Exit Interview The inspectors met with licensee representatives denoted in Paragraph I at the conclusion of the inspection on January 7, 1982. The inspectors summarized the purpose and the scope of the inspection and the findings.
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