ML20248L172
| ML20248L172 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 06/02/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20248L166 | List: |
| References | |
| NUDOCS 9806100475 | |
| Download: ML20248L172 (8) | |
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30S86-0001 os...../
SAEETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
1 RELATED TO AMENDMENT NO. 211 TO FACILITY OPERATING LICENSE DPR-57 AND AMENDMENT NO.152 TO FACILITY OPERATING LICENSE NPF-5 SOUTHERN NUCLEAR OPERATING COMPANY. INC.. ET AL.
EDWIN 1. HATCH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-321 AND 50-366
1.0 INTRODUCTION
By "HL-5366, Application for Amends to Licenses DPR-57 & NPF-5,revising Requirements for Power Sources to Valves Associated W/Low Pressure Coolant Injection (LPCI) Mode of [[system" contains a listed "[" character as part of the property label and has therefore been classified as invalid. (RHR) Sys.Proprietary Encl NEDC-32720,withheld|letter dated May 30,1997]], as supplemented April 1,1998, Southern Nuclear Operating Company, Inc. (Southern Nuclear), et al. (the licensee) proposed license amendments to change the Technical Specifications (TS) for the Edwin !. Hatch Nuclear Plant, Jnits 1 and 2.
The proposed changes would revise the requirements for power sources to valves associated w:th the low pressure coolant injection (LPCI) mode of the residual heat removal (RHR) system.
The affected valves are the LPCI injection valves, the LPCI pump minimum flow valves, and the reactor racirentation pump suction and dischargq valves. The power supply to the Unit 1 reactor core wlation coolant (RCIC) steam suppiy isolation valve ns also being changed. The April 1,1998, submittal provided clarifying information that did not change the scope of the May 30,1997, app'ication and the initial proposed no significant hazards consideration determination.
2.0 EVALUATION Currently, the LPCI inverters supply uninteruptable 600 V ac power supply to these valves. This
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is accomplished by inverting 250 V de power from tnt station service batteries to 600 V ac power and supplying it to the LPCI velves. The licensee has proposed to power Unit 1 LPCI motor-operated valves (MOVs) from Unit 2 Class 1E busses backed by the Unit 2 diesel generators (DGs) and the Unit 2 LPCI MOVs from Unit 1 Class 1E busses backed by Unit 1 DGs. Also, the licensee proposed TS charges, which resulted from the design moddication of the power supplies to the LPCI MOVs. Changes are proposed to TS Surveillance Requirements (SRs) 3.5.1.5 and 3.8.1.19; Limiting Conditions for Operation (LCOs) 3.8.1, 3.8.2, and 3.8.4; and Required Action 3.8.1. These sections of de TS establish requirements for power supplies to the valve load centers. Operability of the affected valves is required for LPCI system operability.
2.1 System Description
The LPCI mode of RHR is one of the emergency core cooling system (ECCS) subsystems required to inject water into the reactor vessel in the event of a loss-of-coolant accident (LOCA).
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L ' The LPCI system design consists of two trains, each having two pumps and a common flow
, path from the suppression pool to the reactor vessel. The LPCI mode of the RHR system, along with the core spray system, is designed to establish and maintain adequate core cooling following a LOCA. The LPC: mode of RHR is automatically initiated upon receipt of a high drywell pressure or a Level 1 low reactor water level signal. The MOVs required to function automatically for LPCI injection during a LOCA are the reactor recircula'. ion pump discharge valves, the LPCI injection valves, and the RHR minimum flow valves. These valves sre referred to as the LPCI MOVs. The recirculation pump discharge MOVs automatically close to allow LPCI reflooding, and the LPCI injection MOVs automatically open to inject water into the vessel.when reactor pressure decreases to a pPset pressure permissive value during the LOCA.
- The onsite electrict. distribution system consists of three safety related busses for each unit that provide two redundant divisions of normal offsite and emergency onsite power. In the event of a loss of offsite power (LOOP), two of the three busses are provided emergency power by dedicated DGs. The third bus is backed by another DG, referred to as the swing DG, which can power the third bus of either Unit 1 or Unit 2. During normal operation, the operator assigne the swing DG to one unit. However, in the case of a LOCA signal, the swing DG automatically transfers to tne LOCA unit.
Currently, the LPCl MOV load centers are normally supplied by power sources independent of Division I and Division ll emergency ac power that supplies the remainder of the RHR system.
I During normal operation, the LPCI inverters supply uninteruptable 600 V ac motive power for the LPCI MOVs. This is accomplished by inverting 250 V de power from the station service bat:eries (which are backed by a charger) to 600 V ac power and supplying it to the LPCI MOV
' load centers. Other loads are also powered from the LPCI MOV load centers but are not required to respond automatically during a LOCA event. Altemate power for the LPCI MOV load centers is currently supplied f om the respective Divisien i or Division 11600V emergency ac sources (DGs) of the same unit. These attemate power sources are used only during maintenance activities requiring an inverter outage or during forced outage of the inverters.
2.2 Proposed Changes to the LPCI MOV Load Centers' Power Supply Under the proposed modification, the LPCI inverters will be retired from service. The Unit i LPCI MCV load centers will now receive power from the corresponding Unit 2 Division I and Division ll ac power sources, which use the dedicated Unit 2 DGs for backup power in the event of rap LOOP. Also, attemate power for one, but not both simultaneously, of the Unit 1 LPCI MOV load centers is available from an attemate Unit 1600V bus. This attemate source of power to one of the LPCI MOV load centers is available during any piant condition. The altamate buis truceives backup power from swing DG 1B during:
LOOP events on Unit 1 only.
Tota: LOOP events without a concurrent LOCA when the swing OG 1 B selector switch is aligned to Unit 1.
~ Total LOOP events with a concurrent Unit 1 LOCA.
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4 This attemate bus can also be used to power one of the LPCI MOV load centers while the respective Unit 2 dedicated DG is out of service.
The proposed TS changes are similar for both units, the following discussion addresses Unit 1
. changes only. The only difference in the proposed modification between Unit 1 and Unit 2 is, for Unit 1 only, the electrical power supply source for the RCIC steam supply valve will be changed to power this valve from the same source as the Unit 1 Division ll LPCI valve load center.
2.3 Proposed Technical Specification Changes Surveillance Requirement (SR) 3.5.1.5, requiring operability demonstrations for the Unit 1 LPCI inverters is deleted. Operability of the proposed normal power supply for the LPCI MOV load centers is demonstrated by SR 3.8.1.19 when Unit 1 is operating and SR 3.8.2.2 when Unit 1 is either shutdown or in the refueling mode.
LCOs 3.8.1.f and 3.8.1.g, which specify the ac sources required for plant operation, are added as new requirements which reflect the new power sources for the LPCI MOV load centers.
' LCO 3.8.1.f requires that two DGs be available that are capable of supplying power to the two Unit 1 LPCI MOV load centers required to be operable per LCO 3.5.1. That is, any combination of the Unit 2 DGs and the swing DG can be used. New LCO 3.8.1.g requires that each Unit 1 LPCI MOV load center be supplied with offsite power via either the Unit 2 Class 1E system or the altc.nate Unit 1 Class 1E bus.
Required Action 3.8.1.C is revised to clarify that only one Unit 2 DG is required to support standby gas treatment system operation as stated in LCO 3.8.1.c. This change also provides a required action should one of the Unit 2 DGs required to support operation of a LPCI MOV load center become inoperable. The Condition becomes inapplicable when the affected LPCI MOV load center is realigncd to the altemate ocwer source backed by the swing DG 18.
Required Action 3.0.1.G will be added to specify the Unit i requirements when all DGs required for LPCI MOV load centers are out of service; i.e., the Unit 2 DGs and the swing DG. Adding Required Action G renames current Required Actions G and H to Required Actions H and I.
This change also adds Condition G to the list of entry conditions for revised Condition H.
SR 3.8.1.19 will be revised to delete Unit 2 SRs 3.8.1.11 and 3.8.1.18 from the list of Unh 2 SRs not applicable to Unit 1, therefore making them applicable. SR 3.8.1.19 defines the requirements for the Unit 2 ac power sources that are also applicable to Unit 1. The proposed change makes Unit 2 SR 3.8.1.11, verification that specified DG trips arc bypassed on emergency starts, ar.d Unit 2 SR 3.8.1.18, verification of simultaneous starting capability,
. applicable to Unit 1. These requirements are appropriate for Unit 1, concurrent with a Unit 2 LOOP, and are acceptable.
LCOs 3.8.2.e and 3.8.2.f will be added to require new operable power sources for the LPCI MOV load centers during shutdown. LCO 3.8.2.e requires offsite power and the associated Unit 2 or attemate Unit 1 power systems to be available to a required unit LPCI MOV load
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, ~ center. LCO 3.8.2.f requires that either one of the Unit 2 DGs or the swing DG be operable.
The operable DG is capable of supplying power to suoport the appropriate Unit 1 LPCI MOV load center if th&t LPCI train is required per LCO 3.5.2, "ECCS-Shutdown."
LCO 3.8.4.c will be revised to delete reference to Unit 2 equipment, since both Unit 1 and Unit 2 equipment are powered by Unit 2 DGs. Unit 2 DG dc power is required to operate the Unit 2 DGs and the Unit 2 distribution system, which are required to operate the unit LPCI MOV load centers.
l The proposed TS changes reflect the retirement of the LPCI inverters whose current design function is to provide power to certain LPCI MOVs independent of Unit 1 ac power supplies, which power the remainder of the RHR system. The Unit 1 LPCI MOV load centers will now be powered from Unit 2 Class 1E busses so that a Unit 1 ac power supply failure canMt incapacitate an entire LPCI train. The proposed configuration also allows one LPCI MOV load 1
center to be powered from an altomate Unit 1 bus backed by the swing DG 18. Also, the proposed chrnges eliminate a section of TS that is no longer applicable to Unit 1, and add requirements specifying that appropriate power supplies from Unit 2 be available to the Unit 1 LPCI MOVload centers.
The licensee has also proposed charges to the Unit 1 electrical power supply source for the RCIC steam supply valve for compliance with Appendix R design requirements. This is applicable to Unit 1 only. The RCIC steam supply valve for Unit 1 will be powered from the Unit 2 Division 11 DG. This change will. maintain the original design and the ECCS system performance requirements. Based on the preceding discussion, the staff finds this change to be acceptable.
The licensee performed a detailed single-failure modes and effects analysis to support the proposed modification. The design basis criteria for the plant's onsite poor supplies (the DGs) are the simultaneous occurrence of an LOOP on either one or both units, and any other accident on one unit. The single fa!!ure analysis considers the occurrence of a postulated accident on either Unit 1 or Unit 2, and verifies that an adequate combination of ECCS equipment (combination of RHR and/or core spray subsystems)is available. The analysis considers postulated accidents with the following power source configurations for the LPCI MOVload centers:
Both Unit i load centers connectea to the Unit 2 power supplies.
One Unit i load center connected to its Unit 2 power supply and the other load center connected to the altemate supply, a Unit 1 bus backed by swing DG 1B.
The single failure analysis also censiders the case where the proposed modification is complete and the Unit 1 LPCI MOV load centers are supplied power per the proposed configuration, but the proposed modification fer Unit 2 is not complete and the Unit 2 LPCI MOV load centers are supplied power per the existing configuration with the inverters in service.
A summary of the results of the single failure modes and effects analysis results are presented in the following cases:
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,. 1.
in the case of an LOOP on Unit 1, Unit 2 offsite power is available for the LPCI MOV load centers, and the Unit 1 DGs automatically start to power the remainder of the RHR system. The swing DG starts on an LOOP signal from either unit and automatically aligns to power the LOOP unit. Therefore, if one of the LPCI MOV load centers is on the sitemate supply, it will be powered by the DG through the Unit 1 altomate bus.
2.
In the case of simultaneous LOOP and LOCA on Unit 1, the power supply configurations listed in Case 1 above exist.
3.
In the case of an LOCA on Unit 1 and an LOOP on Unit 2, the Unit 2 DGs and the swing DG automatically start in it's normal power supply configu,Wion, the Unit 2 DGs provide power to the assceisted Unit 1 LPCI MOV load centers. Should one of the Unit 1 LPCI MOV load centers be on the altemate power supply Unit 1 bus, it will be powered by the offsite power system. The swing DG automatically aligns to the Unit 2 altemate bus because of the LOOP in that unit.
4.
In the case of an LOOP on both units, all five DGs start automatically. In the normal power configuration, the Unit 2 dedicated DGs power the respective Unit 1 LPCI MOV load canters and the Unit 1 DGs power the remainder of the RHR system. The operator chooses the unit to which DG 1B is aligned to power, if one of the unit LPCI MOV load centerst is on the altemate supply, it will be aligned to the Unit i attemate bus. The Unit 1 Atemate bus may not be powered, depending upon which unit the swing DG is aligned to power. However, an adequate amount of LPCI equipment is available to accomplish required safety functions, if needed.
5.
In the case of a concurrent LOOP on both units and a LOCA on Unit 1, all five DGs start, and the swing DG automatically aligns to power the LOCA unit. Therefore, in the normal power supply configuration, the LPCI MOV load centers are powered from the Unit 2 DG, and the Unit 1 DGs power the remainder of the RHR system. Should one'of the Unit 1 LPCI M0V load centers be aligned to the attemate Unit 1 bus backed by the swing DG, power is available because the swing DG automatically aligns to the LOCA unit, in this case Unit 1.
With this proposed change, appropriate new LCOs are added to the plant TS to ensure that if an LPCI subsystem is required to perform its safety function during normal power or shutdown operation, the appropriate powe,r supplies to operate the valves are available.
As sta' < earJer, in the current configuration, the LPCI MOV load centert have an uninterupMw power supply provided from the station service batteries. However, for the proposed modification, power may be unavailable to the LPCI MOV load centers for 12 seconds because of the DG start time. The licensee states that its new LOCA analysis conservatively assumes 21 secon# for DG start. Therefore, the 12-second delay in power supply to the LPCI
' MOV load centers is bounded by the assumptior;a of its revised LOCA analysis because the first signal to initiate motion of a valve connected to an LPCI MOV load center does not occur
' until approximately 20 seconds after s postulated accident. This is because it takes approximately 20 seconds to depressurize to the pressure permissive setpoints for the LPC!
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j 6-injection valves and the recirculation discharge valves. Therefore, power is avaliable to the LPCI MOV load canters when needed, and the 12-second delay associated with a DG startup does not affect the function of the valves associated with the LPCI MOV load centers during a postulated accident The licensee claims that the change from the inverters to the Unit 2 ac power for the LPCI valves, with the ability to power the valves from an altamate ac source backed by the swing DG 18, maintains the original design and ECCS system performance i
requirements.
All new devices added, as a result of this modification, to the motor control center and main contro' room control panel and locally mounted transfer switch and manual disconnect switches will be safety-related. Seismic and environmental qualification of the new devices will be in accordance with the Hatch Final Safety Analysis Report requirements.
l This modification utilizes some of the existing spare circuits and adds new circuits in existing and new raceways. The physical separation between the redundant divisions will be maintained in accordance with Hatch separation criteria. Fuses and/or flexible metal conduits and SILTEMP tape are provided as separation devices where clearance between the redundant division circuits are less than adequate.
The staff was concemed about the use of SILTEMP as a separation device and fuses to provide isolation between non-Class 1E and Class 1E devices. The licensee stated that the
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Class.1E fuses are used in annunciation circuits. The annunciation circuits are non-Class 1E and provide an alarm in the main control room when Class 1E power feeder fuse (s) opens. The power fuses are installed in the feeder circuits. Each power fuse has a status monitoring device, a Bussmann KAZ, which operates an output contact, a micro switch, when the power fuse opens. The KAZ device is a current operated actuator, which is wired in parallel with the main fuse. When the main fuse is blown, current higher than 10 amps will flow through the KAZ device actuator, which will release a pin to operate a micro switch mounted separately on the fuse block. There is no physical connection between the fuse and the micro switch. The micro switch is connected to the non-Class 1E alarm circuit through 1 amp Class 1E control fuses, which are wired in series with the micro switch contac'. This wiring configuration provides the required isolation and limits the impact of the energy flow on the Class 1E components during a fault in the non-Class 1E alarm circuits. The control fuse will blow to isolate the non-Class 1E circuit and will prevent the Class 1E circuit from degradation. Based on the above, the staff finds the use of the fuse as an bolation device in this configuration to be acceptable.
In the proposed modification, SILTEMP tape is used in the LPCI valve manual transfer switches where flexible conduits will be used for routing power and control cables. In addition, a metal barrier is provided to maintain separation between Division I rnd Division ll control wiring terminal blocks. The SILTEMP tape will be used if necessary, as a conservative measure to cover the exposed portion of the conductor between the flexible mr'1llic conduit and termination point for the conductor. The staff finds the use of SILTEMP tape in this manner to be acceptable.
The staff was also concemed that the proposed modification 'of adding Unit 1 LPCI MOV load centers on Unit 2 DGs may impact DG loading and the degraded voltage relay setpoints.. The
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.[G',4-J licensee stated that a load of 27.7 kW for each Division I and Divisior. l; Unit 2 DG is added for Unit 1 LPCI MOVs during a LOCA on Unit 1 and an LOOP on Unit 2. Although, the MOV load is a transient load, which is expected during the initial couple of minutes of the event, it is ac%d
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as a steady state load in the DG loading calculation for conservative purposes. When the.
Unit 1 LPCI MOVs operate automatically during the first 2 minutes, the total joads on the respective Division DGs are as follows: DG 2A-262g.52 kW, DG 2C-2600.58 kW, DG 1 B
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- (swing)-2535.89. The loads tabulated above are within the rating of each of the DGs.
Similarly, for Unit 2 LPCI modification, loads of 27.84 kW and 28.31 kW for Division I and Division 11, respectively, are added on Unit 1 DGs for Unit 2 LPCI MOVs during a LOCA on Unit 2 and LOOP on Unit 1. When Unit 2 LPCI MOVs operate automatically during the first two minutes, the total load on DG 1 A is 3036.52 kW, DG 1C is 3073.23 kW, and DG 1B is
' 1996.89 kW. The loads tabulated above are within the rating of each of the DGs.
The licensee stated that the preceding calculations for Unit 1 and Unit 2 are conservative because, under the preceding pos'.ulated scenario for each unit, the core spray pumps are not loaded.
The degraded gnd voltage analysis was raviewed and updated to reflect the load cha; ses due to the proposed LPCI inverter modification. The LPCI MOV terminal voltages are calculated 1
based on the assumed worst case scenario of sparing unit auxiliary transformer 1 A and loading the 4.16 kV busses 1C.1D 1E,1F, and 1G on SAT 1D, with the grid at the scheduled minimal voltage of 101.3 percent of 230 kV. Voltages at the motor terminals of all MOVs were found 1
acceptable with the exception of two MOVs,2B~,1-F031A and B. Voltages at MOVs 2831-F031 A and B were slightly less than desired under the postu!ated worst case scenario.
In order to improve voltage at the MOV terminals, the outboard portion of the existing feeder cables (3/C #9 AWG) for MOVs 2831-FO31 A and B will be replaced with 3/C #6 AWG cables as part of this modification. The replacement will provide adequate voltage at the LPCI MOV terminal when starting with normal or alternate power feeds. Therefore, the effect of adding LPCI MOVs on the 4.16 kV Class 1E busses is minimal and no changes to the degraded grid relay setpoint will be necessary.
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Based on the staff's review of the information provided by the licensee, the staff concludes that the proposed chan0e for LPCI MOVs power supfy from the inverters to the opposite unit's DGs as the source of power plus the ability to power the valves from an altemate ac source backed by the swing DG will provide more reliable power than the current source of power by the inverters, which have proven te be unreliable over the past years and have developed maintenance problems (t'ased on the licensee's experience with the inverters). Further, this I
change in power supply for the LPCI MOVs does not alter the function or mode of operation of
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the LPCI valves. Although the power to the valves will be de!ayed for 12 seconds because of the DG start time, the delay does not affect the function of the valves during a postulated
. accident because it takes approximately 20 seconds to depressurize the vessel to the pressure
~ ermissive setpoints for the LPCI MOVs. Therefore, the power is availatale te the LPCI MOVs p
when needed. Additiontly, the licensee has added appropriate TS changes for the proposed change to ensure that if an LPCI subsystem is required to perform its safety function during L
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.w normal power or shutdown reperation, the appropriate power supplies to operate the valves are available. Therefore, the staff finds the proposed modification and the corresponding TS changes to be acceptable.
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3.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Georgia State omcial was notifed of the proposed issuance of the amendments. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
- The amendments change a requirement with respect to the installation or use of facility
. components located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements. The NRC staff has determined that the amendments involve no significant increase irl the amounts, and no significant change in the types, of any effluents that may te released offsite, and that there is no significant increase in individual or cumulative riccupational radiation exposure. The Commission has praviously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (62 FR 38139 dated July 16,1997). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
5.0 CONCLUc;lQN The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that tne health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the l
Commission's regulations, and (3) the issuance of the amendments will not be inimical to the
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common defense and security or to the health and safety of the public.
PrincipalContributor: O. Chopra Date:
June 2,1998
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