ML20073M289
| ML20073M289 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 10/07/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20073M287 | List: |
| References | |
| NUDOCS 9410140258 | |
| Download: ML20073M289 (6) | |
Text
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~ -j NUCLEAR REGULATORY COMMISSION 5,
f WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO, 75 TO FACILITY OPERATING LICENSE N0. NPF-47 ENTERGY OPERATIONS. INC.
RIVER BEND STATION. UNIT 1 DOCKET NO. 50-458
1.0 INTRODUCTION
By application dated September 12, 1994, as supplemented by letter dated September 30, 1994, Entergy Operations, Inc. (the licensee) requested changes to the Technical Specifications (TSs) (Appendix A to facility Operating License No. NPF-47) for the River Bend Station, Unit 1.
The proposed changes would revise TS 3/4.2.2, "APRM Setpoints," to permit operation in accordance with the Boiling Water Reactor Owners' Group (BWROG) guidelines on improved BWR thermal-hydraulic stability.
The proposed amendment would revise the formula for calculating the average power range monitor (APRM) flow biased simulated thermal power-high reactor trip and flow biased neutron flux-upscale control rod block trip setpoints T-factor specified in TS 3/4.2.2.
The proposed changes are necessary to support implementation of recommendations contained in NRC Generic Letter 94-02, "Long-Term Solutions and Upgrade of Interim Operating Recommendations for Thermal-Hydraulic Instabilities in Boiling Water Reactors."
2.0 BACKGFOUND The licensee requested changes to the River Bend Station (RBS) TS Section 3/4.2.2, APRM Setpoints.
This change requested a change to the slope of the APRM flow-biased scram and rod block lines (AFBSL).
The requested change will allow the licensee to operate the facility with a larger axial peaking factor than currently authorized.
The licensee requested this change to meet the most conservative option of the BWROG's Guidelines for Stability Interim Corrective Action.
This option recommends that a four-foot core-average boiling boundary (FFBB) be maintained in the core.
The core-average boiling boundary is the axial elevation of the transition from sub-cooled to saturated fluid conditions on a core-average basis.
Maintaining FFBB minimizes the potential of operating in or near the Instability Region, thereby minimizing the potential for core power oscillations.
To maintain FFBB, the licensee needs to operate with a total peaking factor (TPF) larger than currently authorized for this facility.
Specification 3/4.2.2 of the River Bend TSs requires adjusting the APRM setpoints whenever the "T-factor" is less than or equal to 1.0.
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definition, T-factor is the ratio of Fraction of Rated Thermal Power (FRTP) to Core Maximum Fraction of Limiting Power Density (CMFLPD).
Thus, when CMFLPD 2 FRTP (T s 1.0), the APRM setpoints must be adjusted.
High CHFLPD is the result of a large Linear Heat Generation Rate (LHGR) which corresponds to a large TPF.
When a large TPF causes the T-factor to be less than or equal to 1.0, the TSs require adjustment of the APRM setpoints.
The licensee's proposal would change the slope of AFBSL allowing a larger CHFLPD.
- However, if CMFLPD becomes much larger than desired for a given FRTP, the proposed change would maintain the current T-factor definition, thus applying the more j
restrictive AFBSL setpoint at higher TPF.
3.0 EVALVATION The BWR0G Guidelines for Stability Interim Corrective Action proposed five options.
The option pursued by the licensee, maintaining FFBB, is considered acceptable based on review conducted by consultants and the NRC staff, and appears to be the most conservative option proposed by the BWROG.
To maintain FFBB, the licensee needs to obtain a higher peaked axial power shape resulting in a higher axial peaking factor.
With limited control over radial peaking factor and no operational control over the local peaking factor, the higher axial peaking factor would result in a higher CMFLPD.
When operating at less than rated thermal power (FRTP < l.0), the T-factor could become less than one when the axial peaking factor becomes large.
To avoid having to adjust the AFBSL downward at higher TPF, one alternative is to change TS 3/4.2.2. This section requires changing the APRM setpoints when T s 1.0 (which requires adjusting the AFBSL downward).
By adjusting the AFBSL, control rod blocks occur at earlier steps, potentially preventing continuation of startup. To startup with slightly larger TPF than previously authorized, there is a need to change TS 3/4.2.2.
Plants analyzed for certain operational strategies, such as Maximum Extended Operating Domain (ME00), Maximum Extended Load Line Analysis (MELLA), Extended Load Line Limit Analysis (ELLA), or using the General Electric " ARTS" program, are independent of the AFBSL.
For plants authorized to use these operational strategies, no credit is taken for the AFBSL in any analyzed transients.
Since no credit is taken for the AFBSL, the plants will be safe even during and after the analyzed transients.
For this plant, the staff needed to ascertain that operation above the existing AFBSL is safe. Since this plant has not been analyzed for any of the operational strategies noted above (ME00, MELLA, or ELLA), no analysis exists verifying operation beyond the AFBSL to be safe.
Therefore, the staff requested that the licensee verify that no credit is taken for the AFP.i'. in any of their analyses.
In a letter dated September 30, 1994, the licensee stated that the current safety analyses take no credit for the APRM flow-biased scram.
With no credit taken for the AFBSL in the analyzed transients, and by not having to adjust
the AFBSL downward, the plant would be safe with slightly higher total peaking factor in analyzed transients.
Therefore, the request to change the slope of the "T" line can be granted.
This request is to change the slope of the line to above the existing line (Original T-1 Line) to a new line (Modified T-1 Line), but below a bounding (Peaking Upper Bound) line.
The proposed equation for the new line is:
T 3 X FRTP + 1 provided CMFLPD s 0.6 X FRTP + 0.4 4 X CMFLPD otherwise, FRTP CMFLPD With the proposed definition, CMFLPD can increase to a value without causing the T-factor to become less than 1.0, without requiring applying the APRM setpoint change. The adjusted upward line for the new setpoint change requirement is called the Modified T-1 Line, and is about half way between the Original T-1 line and Peaking Upper Bound (PUB) line.
Above the PUB line, the definition of the T-factor reverts back to the current, more restrictive definition.
Since the licensee verified that in the analyzed transients and accidents credit is not taken for the AFBSL, the necessity to rely on these lines become diminished.
By operating with a higher axial peak, the plant maintains a four-foot core-average boiling boundary, which reduces the potential of experiencing core power oscillations. The staff concludes that the proposed TS change does not adversely affect plant safety and will result in a net benefit to the safe operation of the facility and, therefore, is acceptable.
4.0 FINAL N0 SIGNIFICANT MZAR S CONSIDERATION DETERMINATION l
River Bend Station experienced a reactor scram on September 8, 1994.
In order to startup the reactor while imalementing the recommendations of GL 94-02, the licensee requires the requested TS amendment prior to restarting the facility from the current outage.
Therefore, in their letter dated September 12, 1994, the licensee requested that this amendment be issued on an exigent basis.
The request for exigent action was based on the licensee's expectation that the facility would be returned to power operation in a relatively short period of time following the reactor scram.
The licensee's outage plan included inspection of reactor vessel internal components as part of their investigation into the cause of the scram, as well as in-core sipping of all fuel assemblies to locate and replace an assembly with a leaking fuel pin. The staff estimated that these outage activities would extend beyond the public comment period provided by an exigent notice, and therefore chose to issue an individual 30-day Federal Reaister notice to provide the maximum time period possible for public comment.
4,
The Federal Reaister notice was published on September 22, 1994, and provides a public comment period which expires on October 21, 1994.
The Federal Reaister notice provides that, should circumstances change during the notice period such that failure to act in a timely way would result, for example, in derating or shutdown of the facility, the Commission may issue the license amendment before the expiration of the 30-day notice period, provided that its final determination is that the amendment involves no significant hazards consideration.
The licensee has completed their investigation into the reactor scram cause and is currently preparing to commence reactor startup on approximately October 9, 1994.
Failure to issue this TS change would prevent the licensee from starting up the plant utilizing NRC staff recommendations which will reduce the potential for experiencing core power oscillations. The current status of the facility represents a change in circumstances, in that it was not anticipated that the licensee would be prepared to restart the facility prior to completion of the 30-day notice period.
The Commission's regulations in 10 CFR 50.92 state that the Commission may make a final determination that a license amendment involves no significant hazards consideration if operation of the facility in accordance with the amendment would not (1) involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) create the possibility of occurrence of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety.
The Commission has determined that the amendment involves no significant hazards consideration per 10 CFR 50.92, based on the licensees's analysis provided in their September 12, 1994, letter and presented below:
1.
The request does not involve a significant increase in the probability or consequences of an accident previously evaluated.
This change only redefines the APRM setpoints T-factor.
The modified APRM setpoints T-factor does not change or affect operator required actions in relation to the APRM setpoints T-factor and is only applied at different power peaking for given reactor power.
Therefore, this change only affects the precursors to events that can be initiated as a result of different power peaking.
The only event affected is the formation of coupled thermal-hydraulic and neutronic oscillations (reactor stability).
Since the modified APRM setpoints T-factor allows power distributions which permit the application of stability controls to increase stability margin, the probability for initiation of reactor instability is significantly reduced.
Therefore, this change does not involve a significant increase in the probability of any event previously evaluated.
The consequence of a reactor instability event is minimized since the initial reactor conditions are associated with very stable power distributions.
These stable conditions are established using stability controls which are permitted with the modified APRM setpoints T-factor.
Since the initial reactor conditions are very stable, the severity of a postulated reactor instability event is
significantly diminished.
In addition, the modified APRM setpoints T-factor is confirmed to provide adequate LHGR [ linear heat 1
generation rate] protection at off-rated conditions for other anticipated events.
Protection of other-thermal limits for all limits for all previously analyzed events is accomplished by specific limits that are independent of the APRM setpoints T-factor.
These are the power and flow dependent MCPR [ minimum critical power ratio] Operating Limits which provide protection from fuel'dryout and the rated MAPLHGR [ maximum average planar linear heat-generation rate] limit which provides protection of the peak clad temperature for the DBA'[ design-basis accident] LOCA [ loss-of-coolant accident].
Therefore, the proposed change does not involve a significant ina ;.ae in the consequences of any event previbusly evaluated.
The proposed change in APRM setpoints T-factor permits implementation of appropriate reactor stability controls and maintains adequate off-rated LHGR margin for all operating conditions.
This change, therefore, does not involve a significant increase in the probability and consequences of any event previously evaluated.
2.
The request does not create the possibility of occurrence of a new or different kind of accident from any accident previously evaluated.
This change only redefines the APRM setpoints T-factor. The proposed changes do not involve any new modes of operation or any plant modifications.
The ability to implement reactor stability controls do not result'in any new precursors to an accident.
Therefore, the proposed changes do not create the possibility of a new or different type of accident from any accident previously analyzed.
3.
The request does not involve a significant reduction in a margin of safety.
The change in the APRM setpoints T-factor definition allows the implementation of reactor stability controls during reactor operation at off-rated conditions which significantly improve the reactor stability performance.
This is accomplished by achieving very stable power distributions outside the stability excluded region.
Since the initial reactor conditions are very stable, the severity of a postulated reactor instability event is significantly diminished.
The modified APRM setpoints T-factor accommodates higher power peaking to support the required stability controls. The modified APRM setpoints T-factor has been confirmed to provide adequate LHGR protection.
Operation with higher peaking without APRM gains or flow bias trip setpoints adjustment does not involve a reduction in a' margin of safety because the higher power peaking resulting from the APRM setpoints T-factor modification are below applicable LHGR
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limits.
For power peaking conditions that result in APRM setpoints 1
T-factor less than one, an adjustment to the APRM gains or trip setpoints is made to provide additional LHGR protection.
Additionally, an upper bound-is placed on power peaking by the modified APRM setpoints T-factor definition.
Therefore, the modified APRM setpoint T-factor does not involve a reduction in a margin of safety because the higher power peaking resulting from the APRM setpoints T-factor modification is below applicable LHGR limits.
Protection of other thermal limits for all previously analyzed events is accomplished by specific limits that are independent of the T-factor.
These are the power and flow dependent MCPR Operating Limits which provide protection from fuel dryout and the rated MAPLHGR limit which provides protection of the peak clad temperature for the DBA LOCA. The proposed change does not result in an increase -in core damage frequency. Therefore, the proposed change does not involve a significant reduction in the margin of safety evaluated.
5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Louisiana State Official.
was notified of the proposed issuance of the amendment.
The State official had no comments.
6.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. The NRC staff has made a final determination that the amendment involves no significant hazards consideration, and has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occbpational radiation exposure.
Accordingly, the amendment meets 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 amendment.
7.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance taat the 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 Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Kombiz Salehi Date: October 7, 1994
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