ML20003E449
| ML20003E449 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 03/31/1981 |
| From: | Jackie Cook CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, 11529, NUDOCS 8104030486 | |
| Download: ML20003E449 (7) | |
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General offices: 1945 West Parnell Road, Jackson, MI 49201 * (517) 788-0453 30-06 g3 March 31, 1981 g
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Mr J 3 Keppler, Regional Director s
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N:rcy, MIDL/diD PROJECT DCCKrr NOS 50-329 AND 50-330 COMP 0HE'iT COOLING WATER DESIG:I FILE:
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73*10*01, 10lll(S) SERIAL:
11529
Reference:
J W Cook letters to J G Keppler, Sant. 'ubj ect :
- 1) Serial 10053, dated :Iovember 7, 1980
- 2) Serial 11173, dated January 30, 1981 The referenced letters are interis 50 55'se) reports. This letter is the final 50 55(e) report concerning the effect of a failure of a nonessential portion of the component cooling water (CCW) on the essential (safety related) portion of the CCW.
A description of the discrepancy, probable cause and completed part corrective action are docicented in the enclosure to this letter. There is no need for precess corrective action for reasons which are discussed in the enclosure.
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Enclosure:
MCAR k3, Final Report,.varch 20,1981 "Cc=ponent Cooling water System Susceptibility to Loss-of-Coolant Accident-Induced Failu es" CC:
Director of Office of Inspection and Enfo. :enent Att Mr Victor Stello, USiRC (15)
Director, Office of Management Information & Progran Control, US:iRC (1)
RJCook, USNRC Resident Inspector Midland :iuclear Phnt (1) 8104030 6 S
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GALinenberger, ASL3 Panel
-revcvan, u+-r.e pane, AS&L Appeal Panel
'C'4herry, Esq MSinclair CEStephens, USNEC
- T?aten, Esq, US'iRC a
FJ elly, Esq, Attorney General SHFrea-an, Esq, Asst Attorney General G7 aylor, Esq, Ass: Attorney General
- 'EMarshall a
' GJMerritt, - Esq, THKLJ
Enclosure to Bechtel Associates Professional Corporation $rg 529 025C00
SUBJECT:
MCAR 43 (issued 10/10/80)
Component Cooling Water System Suscertibility to Loss-of-Coolant Accident-Induced Failures FINAL REPORT DATE:
March 20,1981 PROJECT:
Consumers Power Company Midland Plant Units I and 2 Bechtel Job 7220 Introduction This final report describes the project activities concerning component cooling water (CCW) system susceptibility to loss-of-coolant accident (LOCA)-induced failures.
Description of Deficiency The Midland Units 1 and 2 CCW system is a dual purpose system serving
- both safety and nonsafety-related equipment.
For each unit, redundant CCW pump trains supply cooling water to the associated high pressure injection (HPI) makeup pump lube oil coolers, reactor building spray pump, decay heat removal (DHR) pump seal coolers, and DHR heat exchangers following a LOCA; and to safety-related fuel pool heat exchangers, and other nonsafety-related heat exchangers during normal power operation.
The nonsafety-related loads and fuel pool heat exchangers are supplied by either CCW train during normal power operation while the redundant CCW pump train is on standby.
The 16-and 18-inch motor-operated butterfly valves isolating nonsafety-related loads from the CCW pump trains have a valve closing time of 60 to 75 seconds, exclusive of delay in the control signal to activate them.
Each CCW pump train has a CCW rurge tank with a total capacity of 1,000 gallons and a ncminal minimum operating level of 300 gallons, with a nonseismic makeup from the demineralized water storage and transfer syste=.
Nonseismic CCW piping to the reactor coolant pu=p motor coolers, letdown coolers, and control rod drive mechanism in the reactor building may not be adequately protected from LOCA-induced failures such as jet impinge-ment or pipe whip.
Other CCW piping to the radwaste evaporator condenser in the auxiliary building is not designed as Seismic Category 1.
There-fore, the piping may not retain its integrity under LOCA-induced failures or during a seismic event.
a
Bechtel Associates Professional Corporatir MCAR 43 Final Reoort a000 March 20, 1981 Page 2 If a pipe break were to occur in CCW piping because of LOCA-induced failures or a seismic event where the line is not specifically designed to withstand such an event and its consequences, the CCW surge tank level would drop.
For Unit 1, CCW train A, the CCW surge tank (IT-73A) low-low level signal will trip its associated CCW pump (IP-73A) and initiate closure of its associated motor-operated safety-related loop isolation valves (IM-1610A and IMO-1623A) isolating all nonessential components and fuel pool heat exchangers from the CCW system.
This scenario is analogous for each CCW train in both units.
If an emergency core cooling actuation signal (ECCAS) occurs, the CCW surge tank low-low level trip signal to the CCW pump will be bypassed, the CCW pump will start, and the safety-related loop isolation valves will close.
With a pipe break in a line not specifically designed to withstand the postulated seismic event, the operating CCW surge tank level could drop to the low-low level setpoint and closure of the safety-related loop isolation valves would then be initiated.
However, because of the slow (60 to 75 seconds) closure time of the isolation valves and because of potentially high CCW velume loss flowrates, enough water could be lost from the CCW system before the valves completely close so that the net positive suction head (npsh) available to the CCW pump would be inade-quate. An ECCAS signal would restart the tripped CCW pump, which could result in loss of~CCW flow and pump cavitation because of low upsh availability.
The standby CCW train is postulated to be unavailable because of a concurrent single active component failure.
Thus, the unit would have lost CCW heat transfer capability.
One fuel pool heat exchanger train is connected to the CCW system of each unit. The CCW to fuel pool heat exchangers is supplied by a j
common safety-related portion of the piping including the common non-safety-related heat loads connected by motor-operated valves IMO-1610A and B (2M0-1710A and B) and IMO-1623A and B (2MO-1723A and B) to either CCW pu=p trains.
During a pipe break due to a LOCA-induced failure or seismic event along with a loss of offsite power, the motor-operated butterfly valves (for Unit 1, IMO-1685A and B and IMO-1687), which are powered from a non-Class IE power source, do not receive an isolation j
signal and may fail to close. With a low point in the nonseismic portion l
of the ruptured pipe, the CCW pipes to and from the fuel pool heat exchanger may be drained.
The net effect is that capability to provide l
CCW to the spent fuel pool heat exchanger is lost.
Closing the common safety grade valves, IMO-1685A, B and IMO-1687, reestablishes the CCW i
pressure boundary to the spent fuel pool heat exchanger.
Filling and l
venting of that pipe may be required prior to reestablishing CCW flow to the fuel pool heat exchangers.
. Summary of Investigation of the Causes of the Deficiency While conducting the investigation, only one principal factor contri-buting to the deficiency was identified.
The sizing of the 1,000 gallon CCW surge tank was 'ased on an allowance for volumetric changes in the
Bechtel Associates Professional Corporation MCAR 43 Final Report 025000 March 20, 1981 Page 3 total CCW inventory due to te=perature variations from 40 to 200F.
The original design criteria did not include a LOCA-induced pipe failure or a failure of nonseismic piping due to a seismic event in the CCW syste=
concurrent with a single active failure and loss of offsite power.
The original tank has volu=e available to tolerate s=all leakage from the system.
Potential Safety Implications The design deficiency has no effect on the normal safe operation of the plant. However, following a LOCA, CCW capability is required to trans-fer heat from the DHR heat exchangers within approxi=ately 22 minutes, and from the DHR pump seal coolers, reactor building spray pu=p seal coolers, and HPI makeup pump lube oil coolers within approximately 30 minutes.
It cannot be ensured that these require =ents allow suffi-cient time following a LOCA to restore the level in the surge tank and restore flow to required components.
The capability of the engineered safety features pumps to operate without cooling water has not been evaluated.
The capability of the contain=ent air coolers to remove heat is not affected by this scenario.
With total loss of CCW to the fuel pool heat exchangers from both units, the fuel pool water te=perature will increase at a rate of 8.7F/hr and the water will start boiling within a mini =um of 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />.
This condi-tion can occur only when a seis=ic event and a CCW system pipe rupture occur simultaneously in both units.
The current design does not conform to the criteria and bases stated in the safety analysis report and could have an adverse impact on plant safety throughout the expected life of the plant.
Because of this deficiency, the current design does not meet final design require =ents for approval and release for construction.
The design deficiency is reportable under 10 CFR 50.55(e).
Corrective Action Corrective action has been taken to ensure that the CCW system surge l
tank level is maintained (to provide the required npsh for safe operation of the CCW pu=ps) and that the design confor=s to the design basis stated in the final safety analysis report (FSAR).
The surge tank capacity is increased from 1,000 gallons to approxi=ately 3,000 gallons; the size of the pipe connecting the CCW surge tank 'e9 the CCW pu=p suction is increased to preclude cavitation at the CCW pump suction during an event resulting in significant water loss rates fro = the CCW system.
The nor=al =inimus CCW surge tank inventory will be increased to a value which will permit detection and isolation of any non-Seis=ic Category I or LOCA induced piping syste= break while retaining level in the CCW surge tank that provides the required npsh.
Faster =otor operators which provide a valve closure ti=e of approxi=ately 5 seconds will replace the existing =ctor operators on 16-and 18-inch-butterfly
Bechtel Associates ProfessionalCorporation
This will ensure the availability of at least one CCW train following a LOCA and/or a seismic event concurrent with a single active failure.
The fuel pool heat exchcagers are located on the co= mon safety-grade portion which also serves the common nonsafety-related heat loads.
The motor-operated butterfly valves which isolate common nonsafety-related loads (e.g., letdown coolers, reactor coolant pump motor coolers, con-trol rod drive mechanisms, and radwaste evaporator condenser) from a common safety-related load (e.g., fuel pool heat exchangers) are IMO-1685A and B (2MO-1785A and B) and IMO-1687 (2MO-1787).
These valves receive non-Class IE power and can be closed manually, either locally or remotely from the motor control center or control room.
These valves will also be closed on a CCW surge tank low-level signal.
With loss of offsite power, these valves may re=ain open. Operator action can be initiated with sufficient time available to close the failed-as-is valves manually, and to establish CCW flow to the fuel pool heat ex-changers by adding service water (SW) =akeup hose connections near the CCW piping to and from the fuel pool heat exchangers to refill the drained portion of the CCW piping. A permanent provision is cade on each safety-related SW train (A and B) in the auxiliary building for e=ergency connection from the SW to the CCW system.
Two corresponding
. connections per unit are provided downstream of the 16-inch butterfly valves IMO-1623A and B (2MO-1723A and B) for refilling the drained portion of CCW piping. Approxi=ately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> could be required to refill this part of the system and reestablish CCW flow to the fuel pool heat exchangers if completely drained.
Because the spent fuel pool will not boil for at least 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />, manual action is considered adequate to reinstate CCW to the spent fuel pool cooling system.
Because the above corrective actions ensure that the design conforms to the design bases stated in the FSAR, further high-energy line break analysis and seismic analysis. of the nonseismic CCW syste= piping under question are not pursued as a resolution of the design deficiency.
Incidental benefits ~ gained from seismically analyzing and supporting t
nonseismic CCW syste= piping for reasons other than resolution of this discrepancy are acknowledged in i=plenentation of corrective action.
it has been' determined, af ter reviewing other systems for Midland plant, that similar problems would not occur in other systems because the CCW system is the only closed-loop dual purpose syste: serving both safety-related and~nonsafety-related loads in the ?Udland plant.
All Midland
' project system design engineers in the cechanical, nuclear systems, and control systems' groups will be sent a copy of this report along with an instruction noting that it is necessary to consider the effects of a failure of Seismic and non-Seismic Category 1 piping if induced by a
Bechtel Associates ProfessionalCorporation
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h[nalNeport 000 March 20, 1981 Page 5 LOCA or by failure of non-Seismic Category I piping due to a seismic event concurrent with a single active failure and loss of offsite power.
Design for this corrective action is proceeding. Drawing change notices issued on March 7,1981, show the changes to be i=plemented on Piping and Instrument Diagrams 7220-M '.16, Sheets 1A, IB, 2B; 7220-M-417, Sheets IA, IB, 2B; 7220-M-419A; and 7220-M-419B.
Control and electrical design modifications to implement this corrective action are underway.
The FSAR will be revised to include the description of the changes and operation of the system by the June 1981 amendment.
The schedule for implementation of these design changes and other work remaining to complete the CCW system is being shown on a project prcduction schedule which includes design, procurement, and conferuction activities.
At an appropriate time, the project production schedule will be superseded by a system completion punchlist.
All required design changes will be implemented before fuel load.
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