ML19256E292
| ML19256E292 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 10/22/1979 |
| From: | Eisenhut D Office of Nuclear Reactor Regulation |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| TAC-42410, NUDOCS 7911020060 | |
| Download: ML19256E292 (20) | |
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NUCLEAR REGULATORY COMMISSION
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October 2,1979 Docket No. 50-336 Mr. W. G. Counsil, Vice-President Nuclear Engineering & Operations Northeast Nuclear Energy Company P. O. Box 270 Hartford, Connecticut 06101
Dear Mr. Counsil:
SUBJECT:
NRC REQUIREMENTS FOR AUXILIARY FEEDWATER SYSTEMS AT MILLSTONE NUCLEAR POWER STATION UNIT 2 The purpose of this letter is to advise you of our requirement.s for the auxiliary feedwater systems at thr subject facility. These requirements were identified during the course of the NRR Siletins and Orders Task Force review of operating reactors in light of the accident at Three Mile Island, Unit 2.
Enclosure I to this letter identifies each of the requircments applicable to the subject facility. These requirements are of two types, (1) generic requirements applicable to most Combustion Engineering-designed operating plants, and (2) plant-specific requirements applicable only to the subject facility. Enclosure 2 contains a generic request for additional information regarding auxiliary feedwater system flow requirements.
The designs and procedures of the subject facility should be evaluated against the applicable requirements specified in Enclosure 1 to determine the degree to which the facility currently conforms to these requirements.
The results of this evaluation and an associated schedule and commitment for implementation of required changes or actions shculd be provided for NRC staff review within thirty days of receipt of this letter. Also, this schedule should indicate your date for submittal of information such as design changes, procedure changes or Technical Specification changes to be provided for staff review.
You may also provide your response to the items in Enclosure 2 at that time.
In addition to the requirements identified in this letter, other requirements which may be applicable to the subject facility are expected to be generated by the Bulletins and Orders Task Force. Such requirements are those resulting from our review of the loss-of-feedwater event and the small break loss-of-coolant acc-ident as described in the Combustion Engineering report CEN-ll4-P (Amendment 1-P) 1257
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W. G. Counsil entitled, " Review of Small Break Transients in Combustion Engineering Nuclear Steam Supply. Systems." Our specific concerns include systems reliability (other than the auxiliary feedwater system), analyses, guidelines and procedures for operators, and operator training.
We plan to identify, in separate correspondence, the requirements resulting from the additional items from the Bulletins and Orders Task Force ieview.
Sincerely, e U+Y TE:=re Darrell G. Eisenhut, Acting Director Division of Operating Reactors Office of Nuclear Reactor Regulation
Enclosures:
As stated cc w/ enclosures:
See next page
i Northeast Nuclear Energy Company CC:
William H. Cuddy, Esquire Day, Berry & Howard Counselors at Lav One Constitution Plaza Hartford, Connecticut 06103 Waterford Pu'lic Library o
Rope Ferry Road,' Route 156 Waterford, Connecticut 06385 flortheast Nuclear Energy Company ATTN:
Superintendent flillstone Plant Post Office Box 128 Uaterford, Connecticut 06385 Northeast Utilities Service Company ATTN: Mr. James R. Himmelwright Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut 06101 Anthony Z. Roisman, Esq.
Natural Resources Defense Council 917 15th Street, N.W.
Washington, D.C.
20005 Mr. John T. Shedlosky Nuclear Regulatory Commission, Region I Office of Inspection and Enforcement 631 Park Avenue King of Prussia, Pennsylvania 19406
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ENCLOSURE 1 X.5 (CE)
MILLSTONE 2 AUXILIARY FEEDWATER SYSTEM X.5.1
System Description
X.5.1.1 Configuration and Overt 11 Design The auxiliary feedwater system (AFWS) is designed to supply water to the steam generators (SG) for reactor coolant system decay heat removal when the main feedwater system is not available.
It is also used for plant startups and shutdowns below the pcser level where the main feeddater system is not required.
The AFWS is shown in simplified form on Figure 1.
The system consists of a steam turbine-driven pump having a 600 gpm capacity, and two motor-driven pumps each bsving a 300 gpm capacity.
The steam supply to the turbine is obtained from a common line connected to lines coming from each of two steam generators. The AFWS is normally aligned as indicated on Figure 1, the motor-driven pumps supplying No. 1 SG and the turbine driven pump supplying No. 2 SG.
A condensate storage tank (CST) of 250,000 gallons capacity is the primary' source of water for the AFWS, and the pro.ary water storage tank (PWST) of 150,000 gallons capacity is the secondary source. Another back-up source consists of two'250,000 gallon fire storage water tanks.
In addition, a connection to the city water supply exists which can be used to provide AFW for an extended period of time, if 12C,7, 9 h) required.
2 The AFWS is manually actuated from the control room.
The pumps and appropriate valves can be controlled from t.1e control room and from the remote shutdown panel.
X.5.1.2 Component Desigt. Classification The pumps, motors and piping associated with the AFWS are designed to seismic Category I requirements.
The CST is not designed to seismic Category I requirements; however, a seismic Category I missile barrier surrounds the CST.
This barrier will contain the water in the event of a CST tank failure.
X.5.1.3 Power Sources The motor-driven pumps are supplied from separate Class lE emergency buses. All motor operated valves (MOVs) associated with the AFWS are powered from the 480V AC emergency buses and fail as-is.
Steam generator level instrumentation, AFWS pump breaker and valve controls are powered from their associated Class 1E emergency buses.
Although the AFWS instruments and associated wiring are not Class 1E, they are powered from Class 1E emergency buses.
The steam for the turbine-driven pump is received from the main steam system via a series of valves as shown in Figure 1.
Steam is intro-duc d to the turbine via a normally closed motor operated steam idmission valve, and steam flow is regulated by a turbine throttle valve in series with the admission vi' 0
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3 X.5.1.4 Instrumentation and Control X.5.1.4.1 Controls The AFWS can be controlled from either of two control stations, one at the main control room;the other at the remote shutdown panel.
X.5.1.4.2 Information Available to the Operator The following indications are available, except as indicated, at both control stations:
1.
SG level 2.
Pump turbine RPM (control room only) 3.
Pump motor current (control room only) 4.
MOV valve positions 5.
Pump motor breaker position 6.
CST level 7.
DWST level (control room only) 8.
Auxiliary feed flow 9.
Pump' discharge pressure The following alarms annunciate at both control stations:
1.
CST low level 2.
SG low level X.5.1.4.3 Initiating Signals for Automatic Operation Not applicable since AFW is manually initiated.
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4 X. 5.1. 5 Testing The systems are tested monthly in accordance with plant Technical Specification requirements.
In addition to the periodic testing, the systems are retested in the recirculation mode in accordance with the surveillance tests subsequent to performing maintenance.
The systems are tested using the recirculating lines, at which time discharge pressures and pump motor currents are monitored.
In addition, valve positions are verified monthly.
The licensee uses t':e system routinely during startup and shutdown thus verifying valve positions.
X.5.1.f Technical Specifications The Limiting Condition For Operation (LCO) for the system is 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> upon a failure of one of the AFWS trains (e.g., a pump motor failure).
If the affected AFWS train is not restored within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, the unit must be brought to a hot shutdown in the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
A review of the Technical Specifications indicated that these speci-fications cover LCOs and periodic surveillance testing consistent with current Standard Technical Specifications.
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5 X.S.2 Reliability Evaluation Results X.S.2.1 Dominant Failure Modes Failure modes of the AFWS were assessed for three loss of main feedwater initiating events.
The dominant failure modes for each transient type are discussed below.
Loss of Main Feedwater (LOFW) with Offsite Power Available The dominant failure mode of the AFWS for this transient is failure of the operator to n.anually actuate the system.
Upon the loss of main feedwater, the licensee estimates that the operator has 15 to 45 minutes, depending on the initiating transient, to actuate the AFWS before the steam generators would boil dry.
Because of this time restriction, failure to perform the required actuation prior to boiling the SG dry has been assessed to be the dominant failure mode for this transient.
LDW With Only Onsite AC Pcuer Available This transient is very similar to the transient discussed above, except that the offsite AC power system is not available.
Additional failure modes related to the onsite AC power system were considered; however, these did not have a significant impact on the dominant failure mode.
As such, the dominant failure mode discussed above (i.e., failure of the operator to actuate the AFWS) is also dominant for this transient.
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6 LOFW with Only DC Power Available For this event no AC power (onsite or offsite)'is available; therefore, the AFWS is reduced to the steam-driven pump train.
Failures which can fail this train include hardware failures of the pump or valves, maintenance outages, and human errors.
The dominant failure mode for this event is failure of the operator to manually open two normally closed valves (the steam admission valve and the AFW discharge valve) in the turbine-driven train within the aforementioned 15 to 45 minutes.after the demand.
The valves are AC motor-operated and are normally powered from offsite power or from the diesel generators on loss of offsite AC power.
Since neither of these power sources is available during this event, local manual opening of the valves is required.
X.5.2.2 Principal Dependencies The most significant dependency found in this evaluation is the dependence on operator action to actuate the AFWS on demand.
The second significant dependency found is the dependence on AC power to actuate certain portions of the steam-driven puinp train of the AFWS.
This dependency is the dominant contributor to AFWS unavail-ability upon the total loss of AC power.
Location dependencies, such as component proximity to high energy lines, were considered but do not appear to be significant.
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7 X.5.3 Recommendations The short-term recommendations (both generic, denoted by GS, and plant-specific) identified in this section represent actions to improve AFW system availability that should be implemented by January 1, 1980, or as soon thereafter as is practicable.
In general, they involve upgrading of Technical Specific'tions or establishing procedures to avoid r mitigate potential system or operator failures.
The long-term recommendations (both generic, denoted by GL, and plant-specific) identified in this section involve system design evaluations and/or modifications to improve AFW system reliability and represent actions that should be implemented by January 1,1981, or as soon thereafter as is practicable.
X. 5. 3.1 Short-Term 1.
Recommendation GS Emergency procedures for transferring to alternate sources of AFW supply should be available to the plant operators.
These procedures shou 1 include criteria to inform the operator when, and in what order, the transfer to alternate water sources should take place.
The following cases should be covered by the procedures:
The case in which the primary water supply is not initially available.
The procedures for this case should include any operator actions required to protect the AFW system pumps against self-damage before water flow is initiated; and, q[
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The case in which the primary water supply is being depleted.
The procedure for this case should provide for transfer to the alternate water sources prior to draining of the pri.iary water supply.
2.
Recommendation GS The plant should be capable of providing the required AFW flow for at least two hours from one AFW pump train independent of any alternating current power sou-e.
If manual AFW system initiation or flow control is required follow-ing a complete loss of alternating currert power, emergency procedures should be established for manually initiating and
. controlling the system under these conditions.
Since the water for cooling of the lube oil for the curbine-driven pump bearings may be dependent on alternating current power, design or procedural changes shall be made to eliminate this dependency as soon as practicable.
Until this is done, the emergency procedures should provide for an individual to be stationed at the turbine-driven pump in the event of the loss of all alter-nating current power to monitor pump bearing and/or lube oil temperatures.
If necessary, this operator would operate the turbine-driven pump in an on-off mode until alternating current power is restored.
Adequate lichting powered by direct current power sources and communications at local stations should also be provided it manual initiation and control of the AFW system is needed.
(See Recommendation GL-3 for the longer-term resolu-1 tion of this concern.)
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Recommendation GS The licensee should confirm flow path availability of an AFW system flow train that has been out of service to perform period 1c testing or maintenance as follows:
Procedures should be implemented to require an operator to determine that the AFW system valves S properly aligned and a second operator to indepenc 11tly verify that the valves are properly aligned.
1..t.icensee should propose Technical Specifications to assure that prior to plant startup following an extended cold shutdown, a flow test would be performed to verify the normal flow path from the primary AFW system water source to the steam generators.
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test should be conducted with AFW system valves in their normal alignment.
4.
Recommendation GS The licensee should install a sysr.em to autu.natically initiate AFW system f 'ow.
For the short-term, this system need not b3 safety grade however, it should meet the criteria listed below, which are similar to Item 2.1.7a of NUREG-0578.
For the longer term, the automatic initiation signals and circuits should be upgraded to meet safety grade requirements as indicated in Recommendation GL-1.
The design should provide for the automatic initiation of the auxiliary feedwater system flow.
The automatic initiation signals and circuits should be designed so that a single failure will not result in the loss of auxiliary feedwater system funct in.
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10 Testability of the initiating signals and circuits should be a feature of the design.
The initiating signals and circuits should be powered from the margency buses.
Manual crpability to intiate the auxiliary feedwater system from the control room should be retained and should be implemented so that a single failure in the manual circuits will not result in the loss of system function.
The alternating current motor-driven pumps and valves in the auxiliary feedwater system should be included in the automatic actuation (simultaneous and/or sequential) of the loads to the emergency buses.
The automatic initiation signals and circuits should be designed so that their failure will not result in the loss of manual capability to intiate the AFW system from the control room.
X.5.3.2 Additional Short-Term Recommendations The following additional short-term recommendations resulted from the staff's Lessons Learr.ed Task Force review and the Bulletins and Orders Task Force review of AFW systems at Babcock & Wilcox-designad operating plants subsequent to our review of the AFW system designs at W-and C-E-ddsigned operating plants. They have not been examined
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11 1.
Recommendation - The licensee should provide redundant level indications and 1cs level alarms in the control room for the AFW syste.
"ater supply to allow the operator to anticipate tt-a water or transfer to an alternate water sur.
.at a low pump suction pressure condition from occurring.
The low level alarm setpoint thould allow at least 20 mi1utes for operator action, assuming that the largest capacity AFW pump is operating.
2.
Recommendation - The licensee should perform a 72-hour endurance test on all AFW system pumps, if such a test or continuous period of operation has not been accomplished to date.
Following the 72-hour pump run, the pumps should be shut down and cooled down and then restarted and run for one hour.
Test acceptance criteria should include demonstaating that the pumps remain within design limits with respect to bearing / bearing oil temperatures and vibration and that pump room ambient conditions (temperature, numidity) do not exceed environmental qualifica-tion limits for safety-related equipment in the room.
3.
Recommendation - The licensee should implement the following requirements as specified 1:y Item 2.1.7.b on page A-32 of NUREG-0578:
" Safety grade indication of auxill sry feedwater flow to each steam generator shouid be provided in the control
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12 "The auxiliary feedwater flow instrument channels should be powered from the emergency buses consistent with satisfying the emergency power diversity requirements for the auxiliary feedwater system set forth in Auxiliary Systems Branch Technicrl Position 10-1 of the Standard Review Plan, Section 10.4.9."
4.
Recommendation - Licensees with plants which require local manual realignment of valves to conduct periodic tests on one AFW system train, and there is only one remaining AFW train availab % for operation should propose Technical Specifications to provide that a dedicated individual who is in communication with the control room be stationed at the manual valves.
Upon instruction from the control roon, this operator would realign the valves in the AFW system train from the test mode to i*s operational alignment.
X.5.3.3 Long-Term Long-term recommendations for improving the system are as follows:
1.
Recommendation - GL Licensees with plants having a manual starting AFW system should install a system to automatically initiate the AFW system flow.
This system and associated auto-matic initiation signals should be designed and installed to meet safety grade requirements.
Manual AFW system start and control capability should be retained with manual start serving q0
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as backup to automatic AFW system initiation.
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Recommendation - GL At least one AFW system pump and its associated flow path and essential instrumentation should automatically initiate AFW system flow and be capable of being independently of any alternating current power source for at least two hours.
Conversion of direct power to alternating current is acceptable.
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ENCWSURE 2 BASIS FDR AUXILIARY MATER SYSTEM FwW REQUIREMDTIS As a result of scent staff reviews of operating plant auxiliary feedwater systers (AEWS), the staff concludes that the design bases and criteria provided by licensees for establishing ATdS requirements for f1w to the steam generator (s) to assure ade-quate mroval of reactor decay heat are not ull defined or documented.
We require that you provide the follcwing AT4S flow design basis infon:'ation as appli-cable to the design basis transients and accident conditions for your plant.
Identify the plant transient and accident conditions considered in estab-1.
a.
lishing AIVS ficw requirerents, including the following events:
- 1) Icss of Main Feed (LTM)
- 2) D Td w/ loss of offsite AC power
- 3) LTW w/lcss of offsite and onsite AC power 14 ) Plant cooldown
- 5) Turbine trip with and without bypass
- 6) Main steam isolaticn valve closure
- 7) Main' feed line break
- 8) Main steam line bmak
- 9) Small break LOCA
- 10) Other transient er accident conditiens not listed above.
b.
Describe the plant protection acceptance criteria and cormsponding techni-cal bases used for each initiating event identified above. The acceptance criteria should address plant lirits such as:
- Maxinrn RCS pressure (PORV cr safety valve actuatien)
- Fuel temperature er darage lirits (DNB, PCI, raximum fuel cennal temperate
- RCS cooling rate lirit to avoid excessive coolant shrinkage
- Mininrn steam generator level to assure sufficient steam generator heat tra".E fer. surface to remove decay. heat and/cr cooldown the primary system.
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Describe the analyses and assumptions and corresponding technical justification used with plant conditions considered in 1.a. above including:
Maxim:m reactor power (including instn: ment errer allowance) at the time of a.
the initiating transient er accident.
b.
Tire delay frun initiating event to reactor trip.
Plant parameter (s) which initiates AWS flew and time delay between initiat-c.
ing event and introduction of AWS flow into steam generator (s).
d.
Minimum steam generater water level when initiating event occurs, Initial steam generator water inventory and depletion rate before and after e.
AWS ficw conmences - identify reactor decay heat rete used.
f.
Maximum pressure at which steam is released from steam generator (s) and against which the /*.W pump must develop sufficient head.
g.
Mini =n nurber of steam generators that must receive /G1 flow, e.g.,1 of 2, 2 cf 47 RC ficw condition - centinued operation of RC pumps er natural cirralation.
h.
- i. Maximum AW inlet te :perature,
- j. Following 'a postulated steam or feed line break, tim delay assumed to isolate break and direct AW flow to intact steam generator (s). AW pt :p ficw capacity allowance to acccccdate the time delay and raintain minirun steam generator water level. Also identify credit taken for pri;rary system heat re. oval due to blewdown.
k.
Volume and maxi;=ra temperature of water in min feed lines between steam generator (s) and A?dS connection to rain feed line.
1.
Operating condition of steam generater norral blowdcun follcwing initiating event.
Prirary ani secondary system water and metal sensible heat used for ccoldown m.
and AFd ficw sizing.
n.
Ti e at hot standby and time to cooldown RCS to FHR (cr SCS) system cut Q> i in te= erature to sine A2d water source inventcry.
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Verify that the AW pt=ps in your plant will supply the necessary flow to the steam generator (s) as deterrdned by iters 1 and 2 above considerire a single failure. Identify the cargin in sizing the pump ficw to allow for pug recir-culation ficw, seal leakage and pump wear.
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