ML20128B239
| ML20128B239 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 01/29/1993 |
| From: | Parker T NORTHERN STATES POWER CO. |
| To: | |
| Shared Package | |
| ML20128B236 | List: |
| References | |
| NUDOCS 9302020442 | |
| Download: ML20128B239 (9) | |
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i UNITED STATES NUCLEAR REGULATORY COMMISSION NORTilERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PIANT DOCKET NO 50 282 50-306 REQUEST FOR AMENDMENT TO OPERATING LICENSES DPR 42 & DPR 60 LICENSE AMENDMENT REQUEST DATED JANUARY 29, 1993 Northern States Power Company, a Minnesota corporation, requests authorization for changes to Appendix A of the Prairie Island Operating License as shown on the attachments labeled Exhibits A, B, and C. Exhibit A describes the proposed changes, reasons for the changes, and a significant hazards eval-untion. Exhibits B and C are copies of the Prairie Island Technical Specifications incorporating the proposed changes. ,
This letter contains no teatricted or other defense information.
NORTilERN S Ti '0WER COMPANY By '/]_ 4A
/ Thomas M Parker Director Nuclear Licensing on thi8 y of. ._
d before me a notary public in and for said County, personally [,4ppeared homas M Parker, Director Nuclear Licensing, and being first duly sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof, and that to the best of his knowledge, information, and be-lief the statements made in it are true and that it is not interpor ' for I delay.
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l MARCA K LaCORE NOTARY PUB!!C-M!NNESOTA HINNENN COUNTY My Commrwan hues Sept 24,1H3 wwwwwwwwwwwwMAwwwws l
9302020442 930129 PDR ADOCK 05000282 P PDR
o' Exhibit A: ,
1 Prairie Island Nuclear Generating Plant j License Amendment Request Dated January 29, 1993 ;
Evaluation of Proposed Changes to the l Technical Specifications Appendix A of Operating License DPR 42 and DPR 60 i
Pursuant to 10 CrR Part 50, Sections $0.59 and 50.90, the holders of Operating Licenses DPR 42 and DPR 60 hereby propose the following changes to Appendix A,- t Technical Specifications:
Backcround Section 3,15 of the Prairie Island. Technical Specifications contains.
requirements for the operability of core exit.thermocouples for use in post accident monitoring. Those requirements were incorporated by License Amendments 78 and 71 dated August 28, 1986 and are consistent with Revision 4a of the Weatinghouse Standard Technical Specifications.
Current Section 3.15 A.1 and Table TS.3.15 1 require four core exit thermocouples to be operable per core quadrant. With only two or three core exit thermocouples operable in a core quadrant, the current
- ion' statement 3.15.A.2 allows continued operation for seven days. At the s of seven days, if four per core quadrant are not operable, the plant must be taken to hot shutdown.
The Prairic Island core exit thermocouple system consists of 36 thermocouples which monitor 121 fuel assemblies (see attached Figure). Revision 4a of the Westinghouse Standard Technical Specifications is based on Westinghouse four-loop reactors which have 51 core exit thermocouples which monitor 193 fue1L assemblies. 'As can be seen below, the cross-sectional area of the Prairie Island core is approximately half of the area of a four-loop core. Even-though the area of the Prairie Island reactor core is approximately, half the size of the four loop plants and thus the number of thermocouples per unit of-core area is higher, the smaller number of thermocouples places Prairie Island; >
at a disadvantage with respect to the four per quadrant requirement.
Number of Number of Fuel Fuel Assembly Core Area (f th Loops Assemblies Pitch (inci er),
t 2 121 7.803 51 4 193 8.466 ~ 96 Until recently the core exit thermocouples have not had significant reliability problems and the existing action statements have:not presented-a ,
problem. However, thermocouple failures occurred in 1992 on both unite.
While enough thermocouples remain operable to meet the Technical Specification requirement of four thermocouples per core quadrant,.there is the potential for additional-failures which could reduce the number of thermocouples belowl the required total' number of channels limit in some quadrants. This recent downward trend in thermocouple reliability has raised concerns with respect.to the post accident monitoring system-action statements in Section 3.15 A of the Prairie Island Technical Specifications.- It is. probable that additional-N-
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Exhibit A Pope 2 of 8 thermocouple failures will occur before repairs can be made during the next refueling outages and that it may not be possible to maintain four thermocouples per core quadrant. Since repairs could not be completed at power or within seven days, a plant shutdown would be required.
This proposed license amendment request has been initiated in response to a heightened concern with respect to the recent thermocouple failures, and their potential impact on continued plant operation.
Eroposed Channes and Reasons for Channe The proposed changes to the Prairie Island Technical Specifications are described below, and the specific wording changes to Technical Specifications are shown in Exhibits B and C.
A. Proposed channes to Technical Specification 3.15.A Current Specification 3.15.A is being revised as shown in Exhibit B. The proposed changes to Specification 3.15.A will incorporate specific action statements for inoperability of core exit thermocouples. The proposed core exit thermocouple action statements are based on the guidance in the Westinghouse Revised Standard Technical Specification. The limiting condition for operation requirement of four core exit thermocouples per core quadrant is not affected by the proposed changes.
Section 3.15.A.2 Existing action statement 3.15.A.2 is being revised to incorporate an exception to the requirements of 3.15.A.2 for the core exit thermocouples.
This is required to facilitate the incorporation of the specific core exit thermocouple action statements discussed below.
Section 3.15.A.3 The proposed new action statement 3.15.A 3 specifies the action to be taken if the number of core exit thermocouples is less than the required total number of channels specified in Table TS.3.15-1 (four per quadrant).
Continued operation would be allowed provided:
- a. Greater than or equal to four core exit thermocouples are operable in the center core region (The thermocouples in the center region are identified in the attached figure),
- b. Greater than or equal to four core exit thermocouples are operable in the outside core region,
- c. The minimum channals operable requirement (two thermocouples per quadrant) is not, and
- d. The inoperable channels are returned to operable status within 30 days or a special report to the Commission is prepared and submitted pursuant to Technical Specification 6.7.B.2 within the next 14 days outlining the action taken, the cause of the inoperability, and the plans and schedule for restoring the system to OPERABLE status.
Exhibit A Page 3 of 8 This proposed action statement is based on the guidance in Section 3.3.3 of the Revised Westinghouse Standard Technical Specifications for post accident monitoring instrumentation. The Revised Standard Technical Specifications require the operability of two core exit thermocouple channels per core quadrant. A core exit thermocouple channel is defined as two core exit thermocouples. The bases for Section 3.3.3 of the Revised Standard Technical Specifications further specifies that the two thermocouples in each channel must meet the additional requirement that one is located near the center of the core and the other near the core perimeter. The action statements associated with the post accident monitoring equipment in Section 3.3.3 would allow continued plant operation with only one channel (two thermocouples) operable per quadrant provided a report is submitted to the Commission within 14 days after the 30 day allowed out-of service time is exceeded.
The significant difference between proposed action statement 3.15.A.3 and the guidance in Revised Standard Technical Specification Section 3.3.3 is the use of thermocouple channels with specific thermocouple pairings. The bases to Section 3.3.3 of the Revised Standard Technical Specifications state that the thermocouple pairings utilized in specifying thermocouple channels should have been identified during unit specific evaluations in response to Item II.F.2 of NUREG 0737. These pairings were not identified during the unit specific evaluation for Prairie Island, and due to the smaller number of thermocouples and their distribution above the core, such pairings would be difficult to establish and maintain at Prairie Island.
Because such thermocouple pairings are not feasible for Prairie' Island, an alternative requiremeat is being proposed. The proposed Section 3.15.A.3 action requires at 1 cast four thermocouples to be operable in both the center and outside regions of the core in order to allow continued plant operation. The intent of this restriction is to provids radial temperature gradient monitoring similar to that providad by the use of the Revised Standard Technical Specification thermocouplo pairings. While the proposed action statement does not specify the location of the thornocouples within the quadrant, because the Prairit. Island core is approximately half the size of a four loop core, the requirement for four thermocouples in both the center and outside core regions will provide adequate indication of the post accident radial tempe rature distribution.
Section 3.15 6 h The proposed new action statement 3.15.A 4 specifies the action to be taken if the number of core exit thermocouples is less than the required total number of channels specified in Table TS.3.15-1 (four per quadrant) and there are less than four thermocouples operable in the center or outside core region. The proposed action statement is consistenc with the action required under the current action statement 3.15.A.2 and does not constitute any change in requirements. It is included to provide a clear statement of the action to be taken if the number of core exit thermocouples is less than the required total number of channels and there are less than four thermocouples operable in the center or outside core region.
Exhibit A '
Page 4 of 8 Section 3.15.A.5 Existing Specification 3.15.A.3 has been renumbered to 3.15.A.5 to accommodate the proposed core exit thermocouple action statements. This change does not constitute any change in requirements.
B. Proposed changes to the Baaen for Technical Soccification Section 3.15 The Bases to Technical Specification Section 3.15 are being revised, as shown in Exhibit B, to specify which core exit thermocouples are included .I in the renter core region.
Safety Evaluation '
The proposed Technical. Specification changes would allow continued plant operation with icas than the total required number of core exit thermocouplea operable provided a minimum number of thermocouples per core quadrant remain; operable, certain thermocouple radial distribution requirements are met-and a report is submitted to the Commission outlining the action taken, the cause of the inoperability, and the plans and schedule for restoring the system to OPERABLE status. The proposed actions are consistent with the intent of the Revised Westinghouse Standard Technical Specifications.
Continued plant oparation with the core exit thermocouple system in the degraded conditiun allowed by-proposed action statement 3.15.A.3 would not affect the operators ability to monitor for inadequate core cooling following ,
an accident. At'least two core exit thermocouples would be operable per core quadrant and a minimum of four thermocouples would be available in both the center and outside core regions. The smaller size of the Prairie Island core, and therefore higher density of thermocouples per unit of core area, provides.
additional assurance that core. exit temperatures can be adequately monitored with a reduced number of core exit thermocouples.
Alternate neans of monitoring for inadequate core cooling would also be available. These include che reactor vessel water level indication system, ,
the subcooling mar 6i n monitors and wide range reactor coolant system temperature.
The combination of the remaining operable core exit thermocouples:and the alternate monitoring capability will ensure that the operators will be able to-identify inadequate core cooling in a timely manner'and take approp*iate L corrective action.
Proposed action statement 3.15.A.3 does not allow unrestricted future plant '
operation with the. core exit thermocouple system _ degraded. . Continued plant-operation beyond 30 days with less than four core exit thermocouples per-quadrant would require the submittal of-a report to the NRC outlining the action taken, the cause of the.inoperability, and the plans and: schedule for restoring the system to CPERABLE status. This action is' appropriate'in lieu of a shutdown requirement since' alternative actions are identified before loss-of. functional capability, and given the likelihood of unit conditions that L would require information provided by this instrumentation.
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4 Exhibit A Page $ of 6 This report would ensure that the NRC was fully informed of the problems with the core exit thermocouple system and the planned corrective actions. This would afford the NRC the opportunity to assess the adequacy of the actions taken, the proposed corrective actions and the schedule for restoration of the system and make an independent assessment of the safety of continued plant operation. ;
In conclusion, ths health and safety of the public will not be adversely affected by the proposed Technical Specification changes.
Determination of Sicnificant flazards Considerations ?
The proposed changes to the Operating License have been evaluated to determine whether they constitute a significant hazards consideration as required by 10 CFR Part 50, Section 50.91 using the standards provided in Section 50.92.
This analysis is provided below:
- 1. The proposed amendment will not involve a significant increase in the orobability or consecuences of an accident nreviousiv evaluated.
The purpose of the post accident monitoring equipment is to display unit variables that provide information required by the control room operators during accident situations and as such help limit the consequences of an accident. The proposed changes, which will allow continued plant ,
operation with less than four core exit thermocouples par coro quadrant, have no impact on the probability of an accident because they are only used in response to accident situations.
Continued plant operation with the core exit thermocouple system in the degraded condition as allowed by the proposed core exit thermocouple action statements would not affect the operators ability to monitor for inadequate core cooling following.an accident. At least two core exit thermocouples would be op*rable per core quadrant and-a' minimum of four-thermocouples would be available in both the center and outside core ,
regions. The smaller size of the Prairie Island core, and therefore-higher density of thermocouples per unit of core area, provides additional assuruace that core exit temperatures can be adequately monitored with a reduced number of core exit thermocouples.
Alternate means of monitoring for inadequate core cooling would also be available These include the reactor vessel water level indication system, the subcooling margin monitors and vide range reactor coolant system temperature.
The combination of the remaining operable core exit thermocouples and the alternate monitoring capability will ensure that the operators ability to -
identify inadequate core cooling in a timely manner and tske appropriate corrective action will not be impaired and therefore the proposed changes will have no significant impact on the consequences of an accident.
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The core exit thermocouples perform no active role in the mitigation of an
-accident. Their inoperability will not affect the operability of any.
engineered safety features equipment or that equipments ability to mitigate the' consequences of an accident.
Exhibit A Page 6 of 8 1
Therefore, for the reasons discussed above, the proposed changes will not l significantly affect _the probability or consequences of an accident 1 previously evaluated.
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- 2. The proposed amendment will not create the possibility of a new or j different kind of accident from any accident oreviousiv analyzed. j There are no new failure modes or mechanisms associated with the proposed changes. The proposed changes do not involve _any modification of plant equipment or any changes in operational limits.- The proposed changes only modify the requirements for instrumentation used to monitor plant parameters during an accident. The core exit thermocouples are passive monitoring devices, their. failure or inoperability cannot result.in a plant accident of any kind.-
l Therefore, for the-reasons discussed above, the proposed changes do not- !
create the possibility of a new or different kind of accident from any l previously evaluated, and the accident analyses presented in the Updated i Safety Analysis Report will remain bounding. i
- 3. The proposed amendment will not involve a significant reduction in the marrin of safety. j Continued plant operation with the core exit thermocouple system in the degraded condition as allowed by the proposed core exic thermocouple action statements would not affect the operators ability to monitor for inadequate core cooling following an accident. -At-least two_ core exit.
thermocouples would be operable per core quadrant and a minimum'of four '
thermocouples would be available in both the center and outside core regions. .The smaller size of the Prairie Island core, and therefore higher density of thermocouples per unit of core ' area, provides additional assurance that core exit temperatures can be adequately monitored with a reduced number- of core exit thermocouples.
Alternate means of monitoring for inadequate ' core cooling would also be available. These include the reactor vessel water level indication system, the subcooling margin monitors and wide range reactor coolant system temperature.
The combination of the remaining operable core exit- thermocouples and the alternate monitoring capability will ensure that the operators ability to identify inadequate core cooling in a timely manner and take appropriate ,
cortactive action will not be impaired.
Therefore, for the reasons discussed above, the proposed changes will not' result in any reduction in-the plantfs' margin'of safety.
Based on the evaluation described above, and pursuant to 10 CFR Part 50, Section 50.91 Northern States Power Company has determined that operation of' the Prairie Island Nuclear Generating Plant in accordance with the proposed license amendment request does not involve any significant hazards considerations as defined by NRC regulations in 10 CFR Part 50, Section 50.92. <
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Exhibit A Pope 7 of 6 e
Environnental Assessment Northern States Power has evaluated the proposed changes and determined that:
- 1. The changes do not involve a significant hazards consideration,
- 2. The changes do not involve a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, or
- 3. The changes do not involve a significant increase in individual or cumulative occupational radiation exposure.
Accordingly, the proposed changes meet the eligibility criterion for categorical exclusion set forth in 10 CPR Part 51 Section 51. 22(c)(9).
Therefore, pursuant to 10 CFR Part 51 Section 51.22(b), an environmental assessment of the proposed changes is not required.
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(xhibit A Page 8 of 8 _
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