ML17300B236
| ML17300B236 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 12/29/1989 |
| From: | Conway W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML17300B237 | List: |
| References | |
| 161-02727-WFC-J, 161-2727-WFC-J, NUDOCS 9001080012 | |
| Download: ML17300B236 (24) | |
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REGULATORY INFORMATION, DISTRIBUTION SYSTEM (RIDS))I.
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FACIL:STN-50-529 Palo Verde Nuclear Station, 89/12/29 NOTARIZED: YES Unit 2, Arizona Publi t OCKET...
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AUTH. NAME AUTHOR AFFILIATION ,'I Arizona Public Service Co. (formerly Arizonat Nuclea
'ONWAY,W.F.
Pow'er RECIP.NAME RECIPIENT AFFILIATION t Document Control Branch (Document. Control. Desk) 'R
SUBJECT:
Application for emergency amend to License NPF-51,'.
temporarily excluding shutdown CEAs 27 & 41 from testing.
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Arizona Public Service Company P.O. BOX 53999 ~ PHOENIX, ARIZONA85072<999 WILLIAMF. CONWAY 161- 02727-MFC/JRP EXECUTIVEVICE PRESIDENT NUCLEAR December 29, 1989 Docket No. STN 50-529 Document Control Desk U. S. Nuclear Regulatory Commission Mail Station Pl-37 Washington, D. C. 20555
Dear Sirs:
Sub] ect: Palo Verde Nuclear Generating Station (PVNGS)
Unit 2 Emergency Technical Specification Amendment Request Section 4.1.3.1.2 File: 89-F-005-419.05; 89-056-026 This letter requests an emergency amendment to PVNGS Unit 2 Technical Specification Surveillance Requirement 4.1.3.1.2. The proposed change would temporarily exclude shutdown CEAs 27 and 41 from the testing required in Surveillance Requirement 4.1.3.1.2. CEAs 27 and 41 are shutdown group B CEAs. The required safety function of these CEAs is to fully insert into the reactor core in response to a reactor trip signal. These CEAs are required to remain fully withdrawn during all times that the reactor is critical per Technical Specification Limiting Condition for Operation (LCO) 3.1.3.5. The only time that these CEAs are required to move other than in response to a reactor trip is during monthly CEA exercise testing per Technical Specification Surveillance Requirement 4.1.3.1.2.
The basis of this surveillance requirement is to demonstrate that all applicable CEAs are operable and will insert into the core when required. All performances of this test to date conclusively show that CEAs 27 and 41 can perform the required safety function; that is, both CEAs are not obstructed and will insert fully into the core if required.
The proposed change would exclude shutdown CEAs 27 and 41 from the testing required by surveillance requirement 4.1.3.1.2 for the duration of Unit 2 cycle 2 operation (until restart from the second refueling outage). This would result in postponement of the surveillance test on CEAs 27 and 41 only twice. This change is requested because both CEAs 27 and 41 are exhibiting a ground fault condition which can lead to slipping or dropped CEAs when the CEA with the ground is exercised. Therefore, by not exercising CEAs 27 and 41 the probability of a drop of any CEA will be avoiding unnecessary reactor trips and/or potential operation of the reactor 'educed outside the bounds of previously analyzed conditions.
The emergency situation exists in that failure to act in a timely way would result in shutdown of the unit in order to perform the 31 day surveillance requirements..
There would be a significant schedule and economic impact if this amendment IIOL.
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Document Control Desk 161-02727-MFC/JRP U. S. Nuclear Regulatory Commission December 29, 1989 Page 2 were not processed prior to January 9, 1989. Failure to meet this date would not allow enough remaining effective full power days of operation in this cycle to meet the requirements of the reload analysis report prior to the commencement of the upcoming refueling outage in late February, 1990.
This situation was created October 14, 1989 when grounds were discovered on two CEA lower lift coils in Unit 2. At that time, a Justification for Continued Operation (JCO) was written to operate Unit 2 until the next refueling outage when the CEA grounds could be corrected. The JCO stated that APS would continue to perform CEA exercising on the grounded CEAs by shutting down the Unit to preclude the possibility of multiple CEA slips or drops occurring during power operation.
This JCO stipulation was made because no analysis of, record existed to justify operation with the potential of multiple CEA slips or'rops at power nor did an analysis of record'xist which would justify not performing CEA operability tests.
Since that time APS has been pursuing analytical justification which would support suspending CEA testing on the grounded CEAs or'n analysis which would provide adequate assurance that multiple CEA'drops or 'slips, would not violate a Specified Acceptable Fuel Design Limit (SAFDL). Neither of these approaches has provided verified acceptable results in the current time. frame. Thus, in order to provide adequate technical justification in a timely'anner which would preclude a shutdown of Unit 2, we necessarily undertook a Probabilistic Risk Assessment (PRA) approach to the matter.'his study was completed in the last week and is submitted as the basis for this request.
Since no analysis which justified not testing the grounded CEAs existed before this week and testing of Unit, 2 CEAs is required to be performed by January 9, 1989, an Emergency Technical Specification Amendment is respectfully requested. Although the condition which necessitates this request has existed for some time there has not been an analysis available to support this request until recently and this submittal has been processed in as timely a manner as prudently possible.
Enclosed with this amendment request is a copy of the following attachments:
A. Description of Amendment Request B. Purpose of the Technical Specification C. Need for the Technical Specification change D. Basis for No Significant Hazards Consideration E. Safety Analysis of the Proposed Change Request F. Environmental Impact Consideration Determination G. Revised Technical Specification Page H. Study of Risk Impact of a 90 Day Suspension of Testing for Two Unit 2 CEAs Pursuant to 10 CFR 50.91(b)(1) a copy of this request has been forwarded to the Arizona Radiation Regulatory Agency. This amendment is requested by January 9, 1989.
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hazards consideration if operation of the facility in accordance with a proposed amendment would not: (1) involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety. A discussion of these standards as they relate to the amendment request follows:
Standard 1 - Involve a significant increase in the probability or consequences of an accident previously evaluated.
CEAs 27 and 41 are Shutdown Group B CEAs. The required safety function of these CEAs i's to fully insert'into'he reactor core in response to a reactor trip signal. These CEAs are required to remain fully withdrawn during all times that the reactor is critical per Technical Specification Limiting Condition for Operation (LCO) 3.1.3.5. The only time that these,CEAs are required to move other than'in response to a 1
reactor trip is during monthly CEA exercise testing per Technical Specification Surveillance Requirement 4.1.3.1.2.
The basis of this surveillance requirement is to demonstrate that all applicable CEAs are determined to be operable so that the CEA will insert into the core when required. All performances of this test to date conclusively show that CEAs 27 and 41 can perform the required safety function, that is CEAs 27 and 41 are not obstructed and will insert fully into the core if required.
The proposed change would exclude shutdown CEAs 27 and 41 from the testing required in Surveillance Requirement 4.1.3.1.2 for the duration of cycle 2 operation (until restart from the second refueling outage).
This change is requested because both CEAs 27 and 41 are exhibiting a ground fault condition which can lead to CEA slips or drops when the CEA with the ground is exercised. By not exercising these CEAs the probability of a drop of any CEA will be reduced.
Document Control Desk 161-02727-WFC/JRP U. S. Nuclear Regulatory Commission December 29, 1989 Page 3 If there are any questions concerning this request, please contact Mr. R. A. Bernier at (602) 340-4295.
Sincerely, WFC/JRP/tlg Attachments cc: G. W. Knighton (all w/Attachments)
T. L. Chan M. J. Davis J. B. Martin T. J. Polich C. F. Tedford
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161-02727-WFC/JRP December 29, 1989 STATE OF ARIZONA )
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COUNTY OF MARICOPA )
I, W. F. Conway,'epresent that I am Executive Vice President Nuclear, that the foregoing document has been signed by me on behalf of Arizona Public Service Company with full authority to do so, that I have read such document and know its contents, and that to the best of my knowledge and belief, the statements made therein are true and correct.
W. F. nway Sworn to before me this day of Notary Public My Commission Expires:
Ny CenmMon Exphes June 5, 199)
kl ATTACHMENT A. DESCRIPTION OF THE PROPOSED AMENDMENT The proposed change would temporarily exclude shutdown CEAs 27 and 41 from the testing required in Surveillance Requirement 4.1.3.1.2. Surveillance Requirement 4.1.3.1.2 requires that each full-length CEA not fully inserted and each part-length CEA which is inserted in the core shall be determined to be OPERABLE by movement of at least 5 inches in any one direction at least once per 31 days. CEA 41 has previously slipped into the core. CEA 27 is exhibi.ting the grounding phenomenon which can lead to future CEA slippage'. This phenpmenon is expected to continue each time CEA 27 is exercised. Slipped or dropped CEAs result in unnecessary perturbations in the core power distribution and could result in a reactor trip. In addition, the potential exists that other unrelated CEAs may slip into the core as a result of the continued exercising of CEAs 27 and 41. This could potentially put the plant in a configuration outside the analysis reported in the FSAR (CESSAR Section 15.4.3-Amendment 7 describes the analysis of one dropped CEA but multiple CEA drop events are not analyzed).
All performances of this test to date conclusively show that CEAs 27 and 41 can perform the required safety function, the CEAs can be inserted into the core.
Leaving CEAs 27 and 41 at the fully withdrawn position for the rest of cycle 2 operation is not expected to significantly increase guide tube wear.
Examinations of the guide tubes following cycle 1 operation showed little wear.
B. PURPOSE OF THE TECHNICAL SPECIFICATION The specifications of this Section ensure that (1) acceptable power distribution limits are maintained, (2) the minimum SHUTDOVN MARGIN is maintained, and (3) the potential effects of CEA misalignments are limited to acceptable levels. Surveillance Requirements 4.1.3.1.2 requires that each full-length CEA not fully inserted and each part-length CEA which is
inserted in the core shall be determined to be OPERABLE by movement of at least 5 inches in any one direction at least once per 31 days. The basis of this surveillance requirement is to demonstrate that all applicable CEAs are determined to be operable such that the CEAs will insert into the core when required.
C. NEED FOR TECHNICAL SPECIFICATION CHANGE The proposed change would exclude shutdown CEAs 27 and 41 from the testing required in Surveillance Requirement 4.1.3.1.2 for the duration of cycle 2 operation (until restart from the second refueling outage). This change is requested because both CEAs 27 and 41 are exhibiting a ground fault condition which can lead to CEA slips or drops when the CEA with the ground is exercised. By not exercising these CEAs the probability of a drop of multiple CEA slips or drops will be reduced, limiting unnecessary reactor trips and the potential operation of the; reactor outside the bounds of previously analyzed conditions. If CEAs 27 and 41 are exempted from testing per Surveillance Requirement 4.1.3.1.2, the probability of either of these CEAs becoming inoperable (stuck) is slightly increased; However, this slightly increased probability is offset by the following:
If any 'single CEA would not drop into the core when required, this condition is still within the bounds of the safety analyses. All analyses in which Shutdown CEA reactivity is crucial require, that the most reactive rod be assumed to remain stuck out (reference Section 15.0.3.3.3 of CESSAR Amendment 7).
- 2. In addition the amount shutdown would not be affected by this change because it is determined considering a single malfunction resulting in the highest worth CEA failing to insert.
D. BASIS FOR NO SIGNIFICANT HAZARDS CONSIDERATION The Commission has provided standards for determining whether a significant hazards consideration exists as stated in 10 CFR 50.92. A proposed amendment to an operating license for a facility involves no significant
'I If CEAs 27 and 41 are exempted from testing per Surveillance Requirement 4.1.3.1.2, the probability of either of these CEAs becoming inoperable (stuck) is slightly increased. However this slightly increased probability is offset by the following:
If any single CEA would not drop into the core when required, this condition is still within the bounds of the safety analyses. All analyses in which Shutdown CEA reactivity is critical require that the most reactive rod be assumed to remain stuck out (reference Section 15.0.3.3.3 of CESSAR Amendment 7).
In addition the amount shutdown would not be affected by this change because it is determined considering a single malfunction resulting in the highest worth CEA failing to insert.
Standard 2 - Create the possibility of a new or different kind of accident from any accident previously evaluated.
The proposed change could affect the analyses assumptions with respect to dropped or stuck CEAs. These conditions are discussed as follows.
I CESSAR section 15.4.3-Amendment 7 describes the analysis of one dropped CEA but multiple CEA drop events are not analyzed. The proposed change is requested for the duration of Unit 2 cycle 2'peration to avoid
'nnecessary reactor trips and/or potential operation of the reactor outside the bounds of previously analyzed conditions.
Surveillance Requirement 4.1.3.1.2 requires that each full-length CEA not fully inserted and each part-length CEA which is inserted in the core shall be determined to be OPERABLE by movement of at least 5 inches in any one direction at least once per 31 days. CEA 41 has slipped into the core during the last performance of this test. CEA 27 is exhibiting the grounding phenomenon which can lead to future CEA slippage. This phenomenon is expected to continue each time CEA 27
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is exercised. Slipped or dropped CEAs result in unnecessary perturbations in the core power distribution and could result in a reactor trip. In addition, the potential exists that other unrelated CEAs may slip into the core as a result of the continued exercising of CEAs 41 and 27. This could potentially put the plant in a configuration outside the analysis reported in the FSAR (ie. CESSAR section 15.4.3-Amendment 7 describes the analysis of one dropped CEA but multiple CEA drop events are not analyzed). Therefore by reducing the possibility of multiple CEA drops, the possibility of an accident of a different type than any previously evaluated in the FSAR will not be created.
Therefore by reducing the possibility of multiple CEA drops, the possibility of an accident of a different type than any previously evaluated in the FSAR will not be created.
Stuck CEA s All analyses in which Shutdown CEA reactivity is crucial require that the most reactive rod be assumed to remain stuck out (reference Section 15.0.3.3.3 of CESSAR Amendment 7).
ll The condition of more 'than one stuck CEA is not within the bounds of the safety analyses. However, the probability of CEAs 27 and 41 becoming stuck is very small. In addition, an analysis of the shutdown capability of Unit 2 with CEAs 27 and 41 stuck shows that there is if sufficient scram reactivity to ensure subcriticality no significant change in core temperature occurs.
This shutdown margin could decrease if a significant overcooling event such as a steam line break occurs. However the probability of a reactor trip in conjunction with both CEAs 27 and 41 stuck in conjunction with a steam line break event is very small.
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The small incremental increase in the risk of stuck CEAs incurred by not testing CEAs 27 and 41 will be offset by the following administrative controls:
The CPCs will be armed to generate a reactor trip on any single 12 finger CEA deviation (stuck or dropped CEA) through the use of an overly conservative addressable constant multiplier. In addition, both CEACs must be operable during monthly CEA exercising.
Reactor Operators are trained to immediately initiate emergency boration in the event any CEA is not fully inserted following a reactor trip.
Standard 3 -'nvolve a significant reduction in a margin of safety.
All performances of this test to date conclusively show that CEAs 27 and 41 can be inserted into the core. If any single CEA would not drop into the core when required this condition is still within the bounds of the Safety Analyses'here is sufficient scram reactivity to ensure subcriticality upon a reactor trip if no significant change in core temperature occurs and both CEA 27 and 41 are stuck out.
This shutdown margin could decrease if a significant overcooling event such as a steam line break occurs. However the probability of a steam line break event in conjunction with CEAs 27 and 41 stuck is very small. A study of this probability showed that the incremental core damage risk incurred by suspending testing of two CEAs for a 90 day period is not significant. Even under a series of conservative modeling assumptions the risk of even localized fuel damage is much less than 1% of the base case PRA core damage frequency for PVNGS.
E. SAFETY ANALYSIS OF THE PROPOSED CHANGE RE UEST The suspension of testing of CEAs 27 and 41 in Unit 2 until the end of the next refueling outage does not significantly increase the risk of fuel damage and may in fact enhance the safety of operation of Unit 2. Not
performing two shutdown and startup cycles for the purpose of testing CEAs 27 and 41, as currently required, would minimize the possibility of an unnecessary reactor trip and subsequent challenges to safety systems during these transients. An analysis of the shutdown capability of Unit 2 with the worst 2 CEAs stuck, show that there is sufficient scram reactivity to ensure subcriticality if no significant changes in core temperature occur. Thus if both 27 and 41 failed to insert upon a reactor trip the Unit would still be in a condition previously analyzed in the Final Safety Analysis Report (FSAR). The only time when the failure to insert of CEAs 27 and 41 would create the possibility of not being in a previously analyzed condition would be during an RCS overcooling event such as a main steam line break or a stuck open main steam safety valve or atmospheric dump valve. To evaluate the effect on overall plant safety of suspension of testing of CEAs 27 and 41 in Unit 2 until the end of the next refueling outage a Probability of Occurrence Analysis was performed.
The results of this'study showed that even under a series of conservative modeling assumptions the incremental"core damage risk incurred by suspending testing of two CEAs for a 90 day period is much less than 1$ of the base case PRA,core damage frequency for PVNGS Unit 2. This conclusion was determined by analyzing the combined probability of a reactor trip and subsequent RCS overcooling along with the failure of both the parked CEAs to insert on demand. " This was determined to be the only situ'ation under which failure of these two CEAs to insert could potentially lead to fuel damage.
Thus, deferring testing until the end of the next refueling cycle will eliminate placing the Unit in four transient conditions (2 startups and 2 shutdowns) late in the fuel cycle and reduce the possibility of a reactor trip and subsequent safety system actuation occurring during the transients.
This reduction in risk is offset by the marginal (much less than 1%)
increase in core damage frequency due to suspending testing of CEAs 27 and 41 until the end of the next refueling outage. Therefore suspension of testing CEAs 27 and 41 until the next refueling outage would not significantly increase the probability of core damage and may in fact enhance the safe operation of Unit 2.
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F. ENVIRONMENTAL IMPACT CONSIDERATION DETERMINATION The proposed Technical Specification change request does not involve an unreviewed environmental question because operation of PVNGS Unit 2 in accordance with this change would not:
Result in a significant increase in any adverse environmental impact previously evaluated in the Final Environmental Statement (FES) as modified by the staff's testimony to the Atomic Safety and Licensing Board, Supplements to the FES, Environmental Impact Appraisals, or in I
any decisions o'... the Atomic Safety and Licensing Board; or Result in a significant change in effluents or power levels; or
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Result in matters not previously reviewed in the licensing basis for PVNGS which may have a significant environmental impact.
G. REVISE TECHNICAL SPECIFICATION PAGE
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