ML20211C371
| ML20211C371 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 09/15/1997 |
| From: | Sorenson J NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9709260169 | |
| Download: ML20211C371 (6) | |
Text
Northern States Power Company 1717 Wakonado Dr. E.
Welch. MN 55009 Telephone 612-388-1121 September 15,1997 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50 306 DPR-60 Technical Specification Interpretation for Auxiliary Feedwater System Operability Durina Movement into Different Plant Conditions
References:
1.
Letter dated February 13,1997, from Stephen E. Quinn, Vice President, Consolidated Edison Company of New York, Inc. to the U.S. NuclEur Regulatory Commission, subject, " Indian Point Technical Specification Interpretation".
2.
Letter dated May 23,1997, from Jefferey F. Harold, Project Manager, NRC Office of Nuclear Reactor Regulation, to Stephen E. Quir.n, Vice President, Consolidated Edison Company, subject, " Manual vs. automatic operation as it relates to auxiliary feedwater operability at Indian Point Nuclear Generating Unit No. 2 (TAC No. M98056)".
NSP requests an interpretation of the Prairie Island Technical Specifications with respect to operability of the Prairie Island auxiliary feedwater system when the auxiliary feeowater pump selector switches are in the manual or shutdown auto position and the pump discharge valves are throttled. Recent review of Technical Specifications for verbatim compliance identified TS.3.4.B.1 and Table TS.3.5-2B requirements which may not be compatible with normal plant startup and shutdown procedures and thus would place the plant in non-compliance with the Technical Specifications. Three issues have been identified with respect to operability: 1) does throttling of the pump discharge valves make the valves inoperable under the requirements of TS.3.4.B.17; 2) does placement of the auxiliary feedwater pJmp selector switches in shutdown auto in MODE 2 when both main feedwater pumps are not operating violate the intent of Table TS.3.5-2B, Functional Unit 7.d.?; and 3) are the requirements of Table TS.3.5-28 violated during the transition period when y'
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USNRC 9/15/97 Page 2 of 6 the auxiliary feedwater pump sebctor switches are in shutdown auto and one of the main feedwater pumps is operating? Each of these issues is examined separately beloW.
As background information, the auxiliary feedwater pumps selector switches have three positions, AUTO, MANUAL, and SHUTDOWN AUTO. When the selector switch is in the AUTO position, all Technical Specifications required by Table TS.3.5-:'8 requiring automatic start functions are enabled for the auxiliary feeowater pump. In the MANUAL position the auxiliary feedwater pump can be started or stopped by placing the associated pump control switch in the START or STOP positions, respectively. In the MANUAL position, no automatic auxiliary feedwater pump start functions will apply to the pump. The SHUTDOWN AUTO position enables all Technicel Specification automatic start functions on the auxiliary foodwater pumps except the automatic start for loss of both main feadwater pumps.
During startup and shutdown operation when there is a low feed demand, the normal method for providing steam generator feedwater is by using the motor drive-auxiliary feedwater pump. This is required because at low power levels, extended operation of the main feedwater pumps in the recirculation mode would cause damage to the main feedwater pumps due to heating and vibration of the pumps.
In general, NSP does not believe that the NRC STAFF or the authors of these Technical Specifications intended a narrow interpretation of the Technical Specifications such that plant startup or shut down would require non-compliance with the Technical Specifications. The Technical Specification requirements are written to ensure safe operation of the plant and protect the health and safety of the public Certainly the Technical Specifications were noi intended to allow the plant to operate at full power without provision for safe startup or shutdown. Technical Specifications are developed to assure safe plant operation and are also intended to be encompass normal plant evolutions, such as startup or shut down, to assure the plant will remain safe during these evolutions.
- 1) Does throttling of the pump discharge valves make the valves inoperable under the requirements of TS.3.4.8.1.7 Auxiliary feedwater system Technical Specifications, TS.3.4.B.1.a and b roquire all four plant auxiliary feedwater pumps to be operable for two unit operation or the turbine driven auxiliary feedwater pump associated with the operating reactor and a motor driven auxiliary feedwater pump operable for single unit operation whenever the unit is critical or the RCS average temperature exceeds 350 *F. TS.3.4.B.1.c requires all valves and piping associated with the suxiliary feedwater pumps to t,a operable whenever the unit is critical or the RCS average temperature exceeds 350
'F. This specification makes an exception that 'during STARTUP OPERATION necessary changes may be made in motor-operai9d valve position". During normal plant startup and shutdown operations, the auxiliary feedwater pump discharge
USNRC 9/15/97 Page 3 of 6 valves are throttled to control steam generator levels. This raises operability questions similar to the issue addressed in References 1 and 2, namely, are the auxiliary feedwater pump discharge valves operable when they are throttled, particularly during shutdown operations? Thus verbatim compliance with the wording of TS.3.4.B.1 may not allow the plant to be started up or shutdown unless the plant is operated in non-compliance with the Technical Specifications, in Reference 1, the operators of Indian Point 2 proposed that the auxiliary feedwater pumps should be considered operable when they are in service even though the pump selector switches are in MANUAL The NRC STAFF concurred with this position in Reference 2. Likewise, NSP further proposes that the auxiliary feedwater pump discharge valves are also operable when they are throttled and under direct administrative control in accordance with the requirements of TS.3.4.B.1.c during plant startup and shutdown operations. Clearly, the intent of TS.3.4.B.1.c is that the auxiliary feedwater system is allowed to operate during plant startup. Thus, NSP concitdes that the auxiliary feedwater system is operable under these conditions during plant startup operations. Also, during plant shutdown operations the auxiliary feedwater system should be considered operable since auxiliary feedwater operations during plant shutdown are functionally the same as during startup. In both operations, one or both of the auxiliary feedwater pumps is operating with the discharge valves throttled to control flow to the steam generators, in both startup and shutdown operations the discharge valves are under direct administrative control in accordance with the provisions of TS.3.4.B.1.c.
It appears to NSP that TS.3.4.B.1.c was intended to address all operations in MODE 2, although for lack of a more general term when the Technical Specifications were originally developed, the term 'STARTUP OPERATION" was used. The Technical Specifications were certainly not intended to require plant operation in a manner which will challenge plant operators or equipment.
Thus NSP proposes to interpret the Technical Specifications such that the auxiliary feedwt.ter pump discharge valves are operable during plant startup and shutdown operations when they are throttled under direct administrative control in accordance with the provisions of TS.3.4.B.1.c.
- 2) Does plecement of the auxiliary feedwater pump selector switches in shutdown auto in MODE 2 when both main feedwater pumps are not operating violate the intent of Table TS.3.5-2B, Functional Unit 7.d.7 As a unit is started up, it is necessary to place the auxiliary feedwater system in operation to facilitate the startup operations. Prairie Island Technical Specifications Table TS.3.5-28 requires the auxiliary feedwater system to automatically start for some initiating events during MODE 3 and all initiating events during MODE 2.
Since plant conditions do not allow operation of a main feedwater pump until the wactor power approaches 2%, the auxiliary feedwater pump SHUTDOWN AUTO
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switch l osition is provided. This enables all automatic starts of the auxiliary feedwater system except for the automatic start associated with the loss of both main feedwater pumps. Likewise when the unit is shutdown, as the plant cower level approaches 2%, plant conditions no longer support continued operation of the main feedwater pumps. The auxiliary feedwater pump switches are placed in SHUTDOWN AUTO and the main feedwater pumps are tripped.
Table TS.3.5 28, Functional Unit 7.d requires the auxiliary feedwater pump automatic start function associated with the trip of both main feedwater pumps to be functional during MODE 2. NSP proposes that this should be interpreted to mean the auxiliary feedwater pump automatic start function associated with the loss of both main feedwater pumps is required to be operable only when the main feedwater pumps are operating. Requiring this automatic start function to be operable when the main feedwater pumps are purposely secured would not serve a useful function. Under these conditions the auxiliary feedwater pumps necessary to maintain steam generators' level are already operating and the heat loads are sufficiently low that operators have sufficient time to respond to a complete loss of the auxiliary feedwater system. Furthermore, this interpretation is consistent with the Prairie istand USAR which states:
The following signals AUTOMATICALLY start the pumps motors and open the steam admission control valve to the turbine pumps:
b.
Trip of both main feedwater pumps (bypassed during startup and shutdown operation).
Operating with both auxiliary feedwater pump selector switches in AUTO during plant startup and shutdown operations would satisfy the Technical Specification requirements, however th!s is not a safe, prudent manner to operate the plant.
During startup and shutdown operations it is difficult to properly maintain system temperaturos with both auxiliary feedwater pumps operating. This would especially cause problems during low power physics testing. In MODE 2 at power levels significantly below 2%, luth auxillery feedwater pumps would be operating if the 1
pump selector switches are in the AUTO position because both main feedwater pumps are secured. Due to the low demand for feedwater, one or both auxiliary feedwater pumps would have to be operated in the recirculation mode. Operation of the auxiliary feodwater pumps in the recirculation mode for extended time periods will damage the pumps. Also, operation of the turbine driven pump during startup will slew down the plant heatup rate due to the pump pulling steam out of the steam generators.
Thus, NSP proposes that Technical Specifications Table TS.3.5-2B Functional Unit i
7.d. requirements for MODE 2 be interpreted to only require automatic auxiliary I
feedwater pump start on loss of both main feedwater pumps when one or both main feedwater pumps are required for operation in MODE 2.
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- 3) Are the requirements of Table TS.3.5-2B violated during the transition period in MODE 2 when the auxiliary feodwater pump selector switches are in shutdown auto and one of the main feedwater pumps is operating?
Safe, prudent operation of the plao! requires placement of the auxiliary feedwater pump selector switches in SHUTDOWN AUTO during plant startup and shutdown.
An unavoidable consequence is that for some brief period of time the pump switch will be in SHUTDOWN AUTO while a main feedwater pump is operating. During startup operations, as the plant approaches 2% power the motor driven auxiliary feedwater pump is operating and both pump selector switches are in SHUTDOWN AUTO. The first main feedwater pump is started and once stable operation is confirmed, the motor driven auxiliary feedwater pump selector switch is briefly placed in MANUAL, the pump control switch is turned to STOP to secure the pump and then the auxiliary feedwater pump selector switch is set on AUTO. Likewiso during plant shutdown, once the plant is below 2% power one auxiliary feedwater pump selector switch is momentarily turned to MANUAL, the pump is started and then the switch is placed in the SHUTDOWN AUTO position and the other auxiliary feedwater pump selector switch is placed in SHUTDOWN AUTO. Then the last operating main feedwater pump is secured.
During both startup and shutdown evolutions the auxiliary feedwater pump selector switches are temporarily in SHUTDOWN AUTO or MANUAL while a main feedwater pump is operating. NSP proposes to interpret this an operable condition within the requirements of TS.3.4.B.1 and Table TS.3.5-2B, Functional Unit 7.d since the motor driven pump is operating and therefore operable. If the main feedwater pump were to trip during this short timc oeriod, the motor driven auxiliary feedwater pump would continue to operate and supply water to the steam generators. Since the demand for feedwater is very low under these plant conditions, even if the motor driven auxiliary feedwater pump tripped, the operators would have sufficient time to start the turbine driven auxiliary feedwater pump. In the very unlikely event operators did not start the turbine driven auxiliary feedwater pump, it would automatically start due to low steam generator level.
Thus, NSP proposes to interpret the auxiliary feedwater pumps to be operable within the requirements of Table TS.3.5-28, Functional Unit 7.d. for the brief period of time when the auxiliary feedwater pumps are operating in SHUTDOWN AUTO or MANUAL while the main feedwater pumps are operating, it is also understood that in order for the plant to comply with the Technical Specification requirements and perform normal safe plant evo!utions that the auxiliary feedwater pump selector switches require momentary placement in the MANUAL position. These switch placements only last a few seconds for each switch manipulation during which time the probability of an accident requiring automatic start of the pumps is extremely unlikely. Once the selector switch position is
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,.Pbge B of 6 returne*d to AUTO or SHUTDOWN AUTO, the pump will start and an accident will be mitigated with minimal impact due to the momentary delay caused by switch misposition. Thus, NSP Goes not consider normal starting and stopping of the auxiliary feedwater pumps in support of Technical Specification requirements and normal plant evolutions to be in non-compliance with the Technical Specifications.
NSP believes that the health and safety of the public is protected by interpreting the auxiliary feedwater system to be operable during plant startup and shutdown with the auxiliary feedwater pump selector switches in SHUTDOWN AUTO or MANUAL and the pump discharge valves throttled in accordance with current Prairie Island Technical Specifications as proposed in this letter. Through these interpretations the plant will continue to operate in a safe manner, in compliance with the Technical Specifications.
Your timely response to this request for interpretation would be appreciated, since Prairie Island Unit 1 is scheduled to shutdown for refueling on October 18,1997 and the auxillary feedwater system will be required to operate in SHUTDOWN AUTO with the pump discharge valves throttled during the plant shutdown, in this letter we have maria no new Nuclear Regulatory Commission cornmitments. If you have any questions related to this letter, please contact myself or Dale Vincent at 612-388-1121.
MdY dits f
Joel P. Sorensen Plant Manager, Prairie Island Nuclear Generating Plant c:
Regional Administrator-Ill, NRC NRR Project Manager, NRC Senior Resident inspector, NRC State of Minnesota Attn: Kris Sanda J E Silberg
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