ML19345E989
| ML19345E989 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 01/30/1981 |
| From: | Bailey K, Jackie Cook BECHTEL GROUP, INC., 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, 11173, MCAR-43, NUDOCS 8102060488 | |
| Download: ML19345E989 (6) | |
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Geaeret owes. 194S West Parnett Acad, Jeckson, MI 49201 + (517) 788 0453 k
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~1 Mr J G Keppler, Regicnal Directer N
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Office cf Inspectica and Enforce =ent 2
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US Nuclear Regulatory Cc=nissica M
Region III 799 Recsevelt Ecad Glen Ellyn, IL 60137 MIDIXiD FRCJECT -
DOCKr NCS 50-329, 50-330 CCMFCNE*'T CCOLI:'G WATER DEIG:I FILE:
0.h.9.h3 UFI:
73*1C"01, 10111(S) SERIAL:
11173 Feference: J W Cook letter to J G Keppler; Same Subject; Serial 10053; Dated Nove ber 7, 1950 The referenced letter was an interi= 50.55(e) report, as is this letter, concerning the effect of a failure of a ncnessential pertion of the ec penent cooling water (CCW) en the essential (safety-related) portion of the CCW.
The attach =ent to this letter provides the status of actiens to be taken conce ning this ite=.
Another repert, either interi= or final, vill be sent en er bercre March 31, 1961.
at~a O Att JLV/1r
Attachment:
MCAR-L3, Interim Report 2, Cenpenent Cooling Water System Susceptibility to Loss-of-Ceolant Accident-Induced Failures, dated January 20, 1981 CC: Director of Office of Inspecticn & Enforce =ent Att: Mr Victor Stello, USNRC (1$)
Director,' Office of Management Information & Prcgram Centrol, USNRC (1)
RJCock, NRC Resident Inspector - Midland Plant (1) l i
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2 Serial 11173 CC: C3echheefer, ASL3 Panel GALinenberger, ASL3 Panel FPCcvan, ASL3 Fanel AS&L Appeal Fanel D! Cherry, Esq MSinclair CRStephens, US:iEC WPaten, Esq, US'IRC FJKelly, Esq, Attorney General S!iFree=an, Esq, Asst Attorney General Graylor, Esq, Asst Attorney General
'n~rS!arshall GJMerritt, Esq, T?iK&J Great Lakes QA Mana6ers l
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Attachment to Serial 11173
SUBJECT:
MCAR 43 (issued 10/10/80)
Component Cooling Water System Susceptibility to Loss-of-Coolant Accident-Induced Failures INTERIM REPORT 2 DATE:
January 20, 1981 PROJECT:
Consumers Power Company Midland Plant Units 1 and 2 Bechtel Job 7220 Introduction This raport describes the interim status of project activities concern-ing conponent cooling water (CCU) 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 CCU pump trains supply cooling water to the associated high pressure injection (IIPI) makeup pump lube oil coolers, reactor building spray pump, decay hcat removal (Dl!R) pump ceal coolers, and DHR hea t exchangers following a LOCA; and to safety-related fuci pool heat exchacgers, 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 CCL' pump trains have a valve closing time of 60 to 75 seconds, exclusive of delay in the control signal to activate them. Each CCU pump train has a CCU surge tank with a total capacity of 1,000 gallons and a nominal minimum operating level of 300 gallons, with a nonseismic makeup from the demineralized water storage and transfer system.
Nonscismic CCW piping to the reactor coolant pump motor coolers, letdown coolers, and control rod drive mechanism in the reactor building may not be adequately protected from LOCA-induced failotes such as jet impinge-ment or pipe whip. Other CCU piping to the radwaste evaporator condenser in the auxiliary building is not designed as Seismic Category I.
There-fore, the piping may not retain its integrity under LOCA-induced failures or during a seismic event.
MCAR 43 Interin Report 2 January 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 urge (IT-73A) low-low level signal will trip its associated CCW pump,4P-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 CCU system. This scenario is analogous for each CCW train in both units.
If an energency 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.
41th a pipe break in a line not specifically designed to withstand the pos tula ted seismic event, the operating CCW surge tank 1cvel 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, 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 b5 inadequate.
An ECCAS signal would restart the tripped CCW pump, which could result in loss of CCW flow and pump cavitation because of low npsh availability. The standby CCW train is postulated to be
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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 are supplied by a common safety-related portion of the piping including the common non-safety-related heat loads by motor-operated valves IMO-1610A and B (2MO-1710A and B) and IM0-1623A and B (2MO-1723A and B).
During a pipe break due to a LOCA-induced failure or seismic event along with a loss of of fsite power, the motor-operated butterfly valves (for Unit 1, IMO-1685A and B and IMO-1687), which are powered from a non-Class lE
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power source, do not receive an isolation signal and nay fail to close.
l With a low point in the nonseismic portion of the ruptured pipe, the CCW l
pipes to and from the fuel pool heat exchanger may be drained. The net ef fect is that capability to provide CCW to the spent fuel pool heat exchanger is lost. Closing the common safety grade valves, !!Ol685A cnd B and IMO-1687, raestablishes the CCW pressure boundary to the spent j
fuel pool heat exchanger.
Filling and venting of that pipe may be.
required prior to establishing CCW flow to the fuel pool heat exchangers.
Potential Safety Implications
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The design deficiency has no ef fect on the normal safe operation of the pla nt.
However, following a LOCA, CCW capability is required to trans-l fer heat from the DilR heat exchangers within approximately 22 minutes, i
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MCAR 43 Interim Reporg 2 January 20, 1981 Page 3 and from the DilR pump seal coolers, reactor building spray pump seal coolers, and llPI makeup pump lube oil coolers within approximately 30 minutes.
It cannot be ensured that these requirements 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 containment air coolers to remove heat is not affected by this scenario.
With total loss of CCW to the fuel pool heat exchangers fron both units, the fuel pool water tenperature will increase at a rate of 8.7F/hr and the water will start boiling within a minimum 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 seismic event and a CCW system pipe rupture occur simultaneously in both units.
Because the current design is a significant deficiency in final design, as approved and released for construction, such that the 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, the design deficiency is reportable under 10 CFR 50.55(e).
Correct 1ve Actio3 Correc,tive action has been initiated to ensure that the CCW system surge tank Icvel is maintained (to ensure an adequate npsh for safe operation of the CCW pumps) and that the design conforms to the design basis stated in the final safety analysis report (FSAR). The surge capacity will be increased from 1,000 gallons to at least 2,500 gallons; the size of the pipe connecting the CCW surge tank to the CCW punp suction may be increased to preclude cavitation at the CCW pump suction during an event resulting in significant vater loss rates from the CCW system.
Faster motor operators with a closure time of approximately 5 seconds will replace the existing motor operators on 16-and 18-inch butterfly valves IMO-1610A and B (2M0-1710A and B) and IMO-1623A and B (2HO-1723A and B) to isolate safety-related CCW pump trains from the nonsafety-related CCW loads. This will ensure the availability of at least one CCW train following a LOCA nad/or a seismic event concurrent with a single active failure.
The fuci pool heat exchanters are located on the common safety grade portion which also servr.s the common nonsafety-related heat loads. The motor-operated butterfly valves serve to 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 (2M0-1785A and B) and IMO-1687 (2M0-1787). These valves receive non-Class IE power and can be closed manually, either locally or
MCAR 43 interin Feport 2 o
January 20, 1981 Page 4 remotely from the notor control center or control roon.
With loss of offsite power, these valves may remain open.
Operator action can be initiated with sufficient time available to close the failed-as-is valves nanually, and to establish CCW flow to the fuel pool heat exchangerJ by adding service water (SW) makeup hose connections near the CCW piping to and f rom the fuel pool heat exchangers to refill the drained portion of the CCW piping. One hose station from each SW train (A and B) in the auxiliary building will be provided. Approxir.ately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> could be rquired to refill this part of the systen 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 />, nanual action is consi-dered adequate to reinstate CCW to the spent fuel pool ecoling systen.
Because the above corrective actions will ensure that the design conforms to the design bases stated in the FSAR, further high-energy line break analysis and seismic analysis of the nonscismic CCW systen piping under question will not be pursued as a resolution of the design deficiency.
Incidental benefits gained fron seismically analyzing and supporting nonseismic CCW system piping for reasons other than resolution of this discrepancy will be acknowledged in inplementation of corrective action.
It has been determined, af ter reviewing other systems, that sinilar problems would not occur in other systens because the CCW systen is the only closed-loop, dual-purpose system serving both safety-related and non-safety-related loads in the Midland plant.
Design implementation of the above corrective action is proceeding.
Additional details of the design implementation and scheduling information will be provided in the next report.
Investigation of the cause of the deficiency is s till underway. The results of this investigation will be discussed in the next report, which will be provided by >bech 20, 1981.
Prepared by fv D. I?. L M ~
Approved by
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