IR 05000237/1981035
| ML17194A443 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 01/18/1982 |
| From: | Burton R, Connaughton K, Holzmer M, Peschel J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML17194A442 | List: |
| References | |
| 50-237-81-35, 50-249-81-27, NUDOCS 8202020463 | |
| Download: ML17194A443 (8) | |
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U.S. NUCLEAR REGULATORY COMMISSION
REGION III
Report No. 50-237/81-35; 50-249/81-27 Docket No. 50-237; 50-249 License No. DPR-19; DPR-25 Licensee:
Commonwealth Edison Company P. 0. Box 767 Chicago, IL 60690 Facility Name:
Dresden Nuclear Power Station, Units 2 and 3 Inspection At:
Dresden Site, Morris, IL Inspection,c::;:~:~ October 23 -
Inspectors: ;y./~
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K: Co~~a~£ht~-,
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December 8, 1981 R. Burton CfnJ~ef
~:::~:~t Programs Section Approved By:
Inspection Summary
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Inspection on October 23 - December 8, 1981 (Report No. 50-237/81-35; 50-249/81-27)
Areas Inspected:
Special safety inspection of Unit 2/3 and,Unit 3 Diesel Generator Cooling Water Pump (DGCWP) inoperabilit The inspection in-volved 116 inspector-hours onsite qy four NRC inspectors.*
Results:
No items of noncompliance or deviations were identified during the inspectio.
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DETAILS Persons Contacted
- D. Scott, Station Superintendent D. Farrar, Administrative Services & Support Assistant Superintendent
'1{R. Ragan, Operations Assistant Superintendent M. Wright, Unit 3 Operating Engineer J. Eeriigenberg, Maintenanc'e As.sistant Superintendent
- J. Brunner, Technical Staff Supervisor R. Meadows, Maintenance Staff R. Rybak, Systems Group Leader J. Bitel, Assistant to the Manager) Station Nuclear Engineering Department
R. Kolflat, Reliability & Design Specialist C. Reed, Vice President The inspectors also interviewed several other licensee employees including Shift Engineers, Shift Foremen, Equipment Operators, and Technician *Denotes those present at the exit interview on December 23, 198.
Events of October 23, Novembe'r.19, and December 1, 1981 On October 23, November 19, and December 1, 1981, the Dresden Station experienced events concerning the Unit 2/3 and Unit 3 Diesel Generator Cooling Water Pumps (DGCWP).
The following description of these events is based upon the statements of equipment operators and their trainees, shift supervisory personnel, information provided-by the licensee and plant computer alarm type printout Events of October 23, 1981 While conducting surveillance tests on October 23, 1981, Dresden Station experienced trips of both the Unit 2/3 and the Unit 3 Diesel Generators (DG). * The cause of the trips is attributed to insufficient c6oling water flow to the diesel heat exchangers (HX), resulting in High Engine Temperature protective trip At approximately 0217, DOS 6609-1, a monthly DG surveillance test was commenced on the Unit 2/3 D The diesel was started normally from the control room while the Equipment Operators (EO) were in the Unit 2/3 DG.roo After taking initial log readings, the EO's left the roo At approximately 0224, the Unit 2/3 DG tripped on High Engine Temperatur The Diesel Generator Cooling Water. Pump (DGCWP) tripped when the DG tripped, as per desig The EO's returned to the room, followed by two
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Shift Foreme Although no personnel involved can recall start-ing the pump, plant alarm typer shows that the Unit 2/3 DGCWP started at about 022 The pump was then manually cycled several times in order to determine the nature of the proble Cooling water pressure at the DGHX remained abnormally lo The DGCWP was then secure The two shift foremen then proceeded to the Crib House in order to examine the pum Using radio communications, the foremen, who suspected air.binding, directed the cycling of the pump twice more, during which time the pump was vente No air was observed to issue from either of the two *vent paths which share a 1/2 inch tap on the pump discharge pip The pump discharge pressure gage and motor bearing lubrication line also share this ta The foremen observed low pump discharge pressure, low vent flow, abnormally low levels of pump.noise and vibrations, and an abnormally warm motor stator_ cooling lin This line is supplied by another tap on the pump discharge pip The formen also re-ported that valve line ups were visually checked and found to be prope Since the 2/3 pump can be supplied power from either unit, the supply was switched from Unit 2 power to Unit 3 power in an effort to ~ee if the low cooling water flow was caused by an electrical proble The pump was cycled again, but HX pressure
.remained lo The power supply was returned to normal, and the Unit 2/3 DGCWP was declared inoperabl At approximately 0500, DOS 6600-1 was commenced on the Unit 3 D Indications of insufficient cooling water flow were observed in the DG room and reported by the EO's, and a DG shutdown was commenced by the control room operators at about 040 A few seconds later, the diesel tripped on High Engine Temperatur The Unit 3 DGCWP tripped with the diesel as per desig The Shift Foremen and Shift Engineer proceeded to the DGCWP while the EO's remained in the DG room; radio communications were used to coordinate their effort The Unit 3 DGCwP was cycled
- several times during which time, the pump was vente No air was observed during venting, and the pump performance was essentially the same as for the Unit 2/3 DGCW Valve line ups
. again were checked and found to be prope At about 0417, immediately after one of the pump starts, the Shift Foremen and the Shift Engineer heard coil.side:i::'able noise from the Unit 3 DGCWP and observed pump discharge pressure to increas In the DG room, the EO's observed DGHX pressure return to norma The pump was cycled several more times without inciden A hot restart of the Unit 3 DG was.then conducted, and the DGCWP :ang
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DG functioned normall '
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.. _ The Unit 2/3 DGCWP was then tested, found to op~rate satisfactorily and returned to servic DOS 6600-1 was completed on the Unit 3, Unit 2/3, and Unit 2 Diesel Generators at 0535, 0703 and OQ37 a.m. respectivel The licensee had not exceeded a limiting condition for operation, and all DGCWP's were operable in accordance with Technical Specification Due to the unusual nature of the event, the licensee agreed to conduct DOS 6601-1 on the Unit 2/3 and Unit 3 DGCWP's for seven days while investigating.the even Event of November 19, 1981 At about 0453 during a surveillance test of the Unit 3 DG,
. the diesel tripped on High Engine Tempera tu.r The cooling
. water pump was cycled twice, during which time the. pump was vente The B-man who vented the pump, observed what he con-sidered to be an air and water mixture issuing from the vent path (the discharge pressure gauge test connection isolation valve) for about five minute The Unit 3 DGCwP was declared inoperable and the Unit 3 DG was removed from servic Dresden Unit 3 then operated under a Technial Specification limiting condition for operation while the event was investigate On November 20, 1981, a Confirmation of Action Letter (CAL) was issued to Commonwealth Edison Company concerning the operability of the Unit 3 DGCW The CAL is attached to this report (Attach-
.ment 1).
The Region III staff issued the letter following the November 19, 1981, event in order to provide adequate assurance that onsite emergency power would be available in the event of an accident, while the licensee continued to investigate the cause of the DG cooling water insufficiencie A broken check valve on the discharge of the Unit 3 DGCWP was found and replaced on November 23, 198 The valve disk had broken free of the pivot arm and was lodged in the discharge side of the valve, restricting nearly all flo On November 25, 1981, a second CAL was issued to Commonwealth Edison Company superseding the letter of November 20, 198 This CAL allowed the Unit 3 DGCWP to be declared operable provided that normal surveillances were performed satisfactorily, and additional assurances of operability were give The CAL is provided as an attachment to this report (Attachment 2).
The Region III staff felt that while a possible reason for inadequate cooling water flow had been identified, the licensee had not adequately explained the observed events of October 23 and November 19, 198 Additional assurances of operability were therefore re-queste The CAL also stipulated that these additional conditions
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would remain in effect unti.l the licensee provided tile* Region III office, in writing, "either a description of circumstances that, with a high degree of credibility, accounts for the observed behavior of the Unit 2/3 and Unit 3.Diesel Generator Cooling Water Pumps during the event of October 23; 1981, and the observed behavior of the Unit 3 Diesel Generator Cooling Water Pump during the event of November 19, 1981" or"...
alternate assurances that the probability of a similar event occurring has been significantly reduced and this matter is concurre.d in by this office." Event of December 1, 1981 On December 1, 1981, the Unit 2/3 DGCWP exhibited a slow decrease in indicated discharge pressure accompanied by increasing noise and vibrations levels at the pum This decrease in indicated pressure and the increase in noise and vibration levels were later determined, through visual inspection, testing, and deter-mination of actual bearing clearance to be caused by excessive wear of the DGCWP bearing Since the discharge pressure gauge and the motor bearing cooling water supply line share.a common tap on the pump discharge, the gauge respond.ed to changes. in bearing cooling water flo This same tap also provides the two vent paths for the pump:
the discharge pressure gauge test connection and the blowdown line for the Y-strainer in line with the bearing cooling water suppl It was believed that bearing wear may have been accelerated by frequent venting of the pump while it was running as required by the previous two CAL' The pump was replaced, due to the long turn-around time for repair, and on December 2, 1981, a CAL was issued ammending the November 25, 1981, CAL by providing relief from the frequent pump venting operation The CAL is provided as an attachment to this report (Attachment 3).
During the pump replacement, the licensee inspected the Unit 2/3 DGCWP discharge check valve and found it to be broke As was the case with the Unit 3 pump discharge check valve, the disk had broken free of the pivot ar In the instance of the Unit 2/3 pump, however, the disk had not lodged into the body of the valve, but was free to rriove in any direction within the valve bod.
NRC Actions An inspection team was dispatched to the site on October 23, 1981, to begin to determine the adequacy of the licensee's response to the initial even Due to the licensee's inability to identify th~
cause of the event to the inspector's satisfaction, the licensee agreed to run surveillances on the pumps daily to verify operabilit This team returned to the site on October 27, 1981, to gather addi-tional informatio In a telephone call between the Plant Superin-tendent and Region Staff on October 28, 1981, the licensee was
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requested to increase th~ intensity of their investigation into the even On October 30, 1981, Region, III upper management was briefed by the inspector Since the initial data had a number of inconsistencies, it was decided that an investigator should be assigned and that sworn statements would be taken to ensure that the information received had a greater level of reliabilit During the next four weeks, seven site visits were made during which eight sworn statements were take The statements are provided as an attachment to this report (Attachment 4).
Additional technical data was gathered as information became availabl In addition, site visits and conference calls with the licensee's plant and corporate staffs were made to gather information and in connection with the CAL's described in paragraph.
Licensee Actions The discharge check valves for the *unit 2/3 and Unit 3 DGCWP's were replace Although the Unit 2 diesel had functioned properly through-out the foregoing events, the discharge check valve for the Unit 2 DGCWP was inspected, found to be broken, and replace In the case of the number 2 DGCWP discharge theck valve, the pivot arm remained attached to the valve disc, but was broken at the hinge to the valve bod The Unit 2/3 DGCWP was replaced following thebearing failur Instrumentation changes for the cooling water systems for all three diesels are planne An additional pressure gauge on the discharge volute of each DGCWP has been installe The licensee will also provide a more accurate indication of system flow than presently exists when an engineering study is complete Procedural reviews have resulted in changes to plant procedures which will help to lower the probability of air leakage into the DGCWP' s or i.nadvertent shutting of pump suction valve In addition, motor bearing tolerances for the DGCWP's which are checked annually will be recorded for trend analysis purpose The electrical supply and control systems have been extensively tested in an effort to determine that the DGCWP's operated properl No negative results were f9und, however, the pump motor electrical overload devices were changed so that they will reset automatically instead of manuall The computer alarm input connection from the U3 supply breaker of the U2/3 DGCWP was inspected, found to be loose, and tightene The faulty indication was noticed due to its effect on the computer alarm typer printouts during testing, but had no significant effect on the events of October 23 and November 19, 1981, since the U2/3 DGCWP is normally powered from the U2 supply breake Numerous tests were conducted to determine the cause of the malfunc-tion, including:
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.....d system tests to verify or deny the possibility of air binding or suction blockag tests to determine normal indication.
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a test to deny the possibility of P1:1lllP runout.*
radiography of valves in the cooling water syste Pump operability t'ests wen~ conducted througP.out as. needed to provide additional assurance that the systems would operate properly if called upo The licensee also conducted interviews with plant personnel, and pro-vided a written explanation of the events as required by the Confirma-tion of Action Lette The licensee's explanation of the events was reviewed and accepted by the Region III staf The licensee was verbally released from the requirements of the December 2, 1981, Confirmation of Action Letter in a telephone conversation between Mr. R. Knop of our staff and Mr. D. Scott, the Plant Manager, on December 24, 198 * Conclusions The licensee has demonstrated to the satisfaction of the Region III staff that the cause of the events of October 23 and November 19,
. 1981, was defective check valves in the discharge of each pum The licensee has stated and the RIII office has concurred that the unexplained start of the U 2/3 DGCWP at 0228 on October 23, 1981, was most likely due to a manual switch operation which no operator can recal This conclusion was reached after detailed circuit analysis and questioning of the operators by both the licensee and RIII personnel, and after circuit tests and wiring inspections by the licensee to verify that the circuit operated as designe The licensee also stated that the apparent air/water mixture which was reported to have issued from the discharge pressure gauge test connection valve of the U3 DGCWP on November 19, 1981, was due to the atomizing effect that can occur by partially opening the valve (gate valve).
This explanation wa.s found to be acceptable to the RIII staff, members of which have personally observed this atomizing effec The statement of Equipment Operator /13 (Attachment 4), has incon-sistencies concerning switch manipulatio This matter has not been acceptably addressed by the licensee and is considered an unresolved item requiring further review (50-237/81-35-01; 50-249)81-27-01).
The event of October 23, 1981, occurred with the Unit 3 DGCWP lined up to take a suction on the same bay as the Unit 2/3 DGCWP through a crosstie piping arrangemen The valve lineups were performed using approved.procedures and have been conducted many times in
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the operational history of Dresden Statio The same capability for common suction is also available through valve manipulation for the Unit 2 and Unit 2/3 DGCWP's.
. The ~rosstie arrangement utilizes sections of common piping. It appears that a single passive failure of a pipe or valve could render two diesel generators inoperabl Th~ inspectors are concerned that this capability may be co~trari to General Design Criterion 17 of 10 CFR 50," Appendix A, and *is considered an unresolved item which has been referred to Headquarters for further review (50-237/81-35-02; 50-249/81-27-02). Unresolved Items Unresolved items are matters about which more info.rmation is required in order to ascertain whether they are ac~eptable items, Items of Noncompliance, or Deviation Unresolved items disclosed during the inspection are discussed in Paragraph.
Exit Interview The inspectors met with licensee representatives denoted in ~aragraph
.1 at the conclusion of the inspection on December 23, 198 The inspectors summarized the purpose and the scope of the inspection
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and the finding Additional information was gathered on December 29, 198 The purpose, scope and findings were discussed with the Technical Staff Supervisor who acted as directed by the Plant Manager.
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