ML20236W023
| ML20236W023 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 07/29/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20236W018 | List: |
| References | |
| NUDOCS 9808050031 | |
| Download: ML20236W023 (5) | |
Text
- _ _ _ _ _ _ _ _ - _ _.
pwa k
UNITED STATES p
g j
NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30006 4 001
"%...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.177 TO FACILITY OPERATING LICENSE NO. DPR-46 NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION l
DOCKET NO. 50-298
1.0 INTRODUCTION
By letter dated February 10,1997, as supplemented by letters dated December 26,1997, i
July 16, and July 28,1998, the Nebraska Public Power District (NPPD) (the licensee) submitted a
{
request for changes to the Technical Specifications (TS) for the Cooper Nuclear Station (CNS).
i The requested changes would revise the TS to reflect the adoption of the BWR Owners' Group (BWROG) Long-Term Solution Stability System Option 1-D in addressing reactor operation in or near a region of potential thermal hydraulic instability. The licensee's submittal consisted of a plant specific licensing topical report (LTR), supporting application of the previously approved Long-Term Stability Solution Option 1-D to Cooper and a description of the associated TS l
changes. The LTR and the BWROG Long-Term Stability Solutions methodology are identified as References 1 and 2, respectively. The proposed changes are part of the licensee's long-term actions in response to NRC Generic Letter (GL) 94-02, "Long-Term Solutions and Upgrade of Interim Operating Recommendations for Thermal Hydraulic Instabilities in Boiling Water Reactors," dated July 11,1994.
The December 26,1997, July 16, and July 28,1998, letters provided clarifying information and an administrative change that did not change the basis for the NRC staff's initial proposed no significant hazards consideration determination (62 FR 14462).
2.0 EVALUATION t
The BWROG Long-Term Stability Solutions Generic Option 1-D consists of two parts. First, an exclusion region in the power to flow map is established within which power oscillations are credible. Should the unit enter this region, operators are instructed to immediately exit the region L
and to scram the plant should power oscillations be detected. Second, a statistical method is l
employed to show that the existing flow-biased Average Power Range Monitor (APRM) scram is sufficient to shutdown the plant in the event of oscillations before the Safety Limit Minimum l
Critical Power Ratio (SLMCPR) is violated. This method is described in NEDO-32465-A l
(Reference 3). In Reference 2, it was concluded that before Option 1-D can be applied to a plant, the unit must meet several criteria. First, the core must be small and, therefore, tightly coupled. Second, the core must have relatively tight inlet orificing. Cooper is a medium power BWR/4 with 548 fuel bundles. The supporting analysis (Reference 1) confirms that the core-wide decay ratio far exceeds the channel decay ratio over a wide range of operating conditions. This 9900050031 990729 PDR ADOCK 05000298 P
. means that Cooper is most likely to experience core-wide (fundamental mode), as opposed to out-of-phase (higher mode), oscillations. The second criterion %s been demonstrated to favor the core-wide mode over the out-of-phase mode. Cooper has a peripheral orifice size 9%
smaller than a typical BWR/4. Cooper, therefore, meets the two criteria necessary to use Option 1-D.
In addition to meeting the acceptance criteria stated above for an Option 1-D plant, licensees have a choice of either using power distribution controls while operating or using an on-line stability monitor. NPPD has opted to use an on-line stability monitor to provide operators with a means to detect degradation of the stability margin. The staff finds this approach acceptable for Cooper.
The detect and suppress methodology, as described in NEDO-32465-A (Reference 3), was used to calculate the maximum MCPR during a postulated power oscillation event. This method allows demonstration, with a high statistical certainty, that the SLMCPR will not be violated before the flow-biased APRM system trips the plant. The procedure outlined in NEDO-32465-A is acceptable for Cooper and was properly applied. The final MCPR (FMCPR) was calculated to be 1.13. Since this is still above the SLMCPR of 1.07, the calculation demonstrates that, with a 95 percent probability and a 95 percent confidence (the 95/95 value), power oscillations will be successfully terminated.
In order for the analysis presented in Reference 1 to be applicable to all fuel cycles, specific reload confirmation values have been developed. The LTR establishes design changes which do not require the FMCPR calculation to be redone. For these cases, the calculations in Reference 1 are assumed to apply to the operating cycle under consideration. This approach has also been proposed and approved for the Monticello and Duane Amold units and General Electric has performed confirmatory calculations to demonstrate that the approach is valid. This approach is also acceptable for Cooper.
Review of individual TS changes necessary to implement Option 1-D follows:
Chanae to Paae 17 This change adds a discussion to the Bases about the APRM flow-biased scram providing protection to the safety limit during postulated stability events. This change is consistent with Option 1-D and is acceptable.
Chances to Paoe 98 These changes remove requirements to check APRM and LPRM noise levels which were required when using the Interim Stability Corrective Actions (ICAs) requested by NRC GL 88-07.
Removing these sections is consistent with the implementation of Option 1-D and is acceptable.
These changes also add revised TS 3.3.F.3, to require that, with no recirculation loops in operation, the reactor shall be placed in the hot shutdown condition within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
l
. The current TS do not explicitly address this condition. The addition of this requirement will help to ensure that the plant will not be operated close to a region where thermal-hydraulic instabilities can occur. The staff has determined, based on operating experience, that the proposed completion time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is reasonable to reach a mode of operation (Hot Shutdown) for which the Limiting Conditions for Operation do not apply. Twelve hours is sufficient time to conduct the mode change in an orderiy manner without challenging plant systems. Therefore, the staff finds this change acceptable.
Chanaes to Paoes 98s. 98b. and 98c These pages are removed. Removal of these pages eliminates the operating restrictions on the reactor that were imposed consistent with GL 88-07 and the ICAs. They are not needed when l
using Option 1-D and, therefore, removing them is acceptable.
Chanae to Paae 103 This change inserts a discussion into the Bases section covering the reactor recirculation pumps.
The change states that operation in natural circulation (i.e., no recirculation loops operating) can lead to thermal hydraulic instabilities and that 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is a reasonable time to reach Hot Shutdown following a flow event. Based on operating experience, the staff has determined that 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is sufficient time to conduct the mode change in an orderly manner without challenging I
plant systems. This change reflects the change to TS 3.3.F.3 and is acceptable.
I Chance to Pace 212a This change to TS 3.11.D instructs operators to immediately initiate actions to exit the exclusion region if it is entered. This change will help to avoid challenges to the safety limit MCPR, consistent with the application of the BWROG long-term stability solution Option 1 D methodology, and is therefore acceptable to the staff.
Chances to Paoes 214a and 214b The discussion in the Bases is revised to reflect the new approach for avoiding and protecting the fuel from thermal-hydraulic instabilities, consistent with the long-term stability solution Option 1-D methodology. References to the methodology are also included in the Bases. The staff finds these changes acceptable.
Chances to caos 234 These changes revise TS 6.5.1.G, " Core Operating Limits Report," by relocating the power / flow map, which defines the Stability Exclusion Region, to the COLR by including it in the list of cycle-
)
specific parameters; adding references to the NRC-approved reports, *BWR Owners' Group 1
Long-Term Stability Solutions Licensing Methodology," NEDO 31960 and NEDO-31960, Supplement 1; and removing the core flow MCPR adjustment factor, K,. The relocation of the power / flow map, defining the stability exclusion region, to the COLR will allow the licensee to l
revise this cycle-specific parameter as appropriate, provided that such changes are determined using the NRC-approved methodologies also referenced in TS 6.5.1.G. The staff has I
. determined that these methodologies are acceptable for application to the Cooper Nuclear Etation, and that the use of these methodologies will ensure that the values of cycle-specific parameters are determined such that all applicable limits of the plant safety analyses are met. A license amendment would be required prior to using a methodology for calculating the stability exclusion region other than the methodologies specified in TS 6.5.1.G.
In addition, the core flow MCPR adjustment factor, K,, is deleted from TS 6.5.1.G, as it is no longer applicable, as discussed in the staff's safety evaluation related to Amendment No.151, dated November 29,1991. This factor was inadvertently retained due to an administrative oversight. The staff finds tha proposed changes to page 234 acceptable.
The staff has reviewed the changes proposed by the Nebraska Pdlic Power District to implement the BWROG Long-Term Stability Solution Option 1-D ai the Cooper Nuclear Station.
The changes corrist of modifying the TS to make them consistent with Option 1.J relocating the power-to-flow map and the associated stability exclusion region to the Core Operating Limits Report; and referencing the NRC-approved methodologies for calculation of the power /fbw map in TS 6.5.1.G. The staff concludes that the changes are acceptable for the plant-specific application of Option 1-D at Cooper, as discussed above.
3.0 STATE CONS _ULTATION in accordance witi the Commission's regulations, the Nebraska State official was notified of the proposed issuance of the amendment. The State official had no comment.
4.0 ENVIRONMENTAL CONSIDERATION
The ramendment 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 cnd changes surveillance requirements. Th6 i4RC staff h s 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 occupational radiation exposure. The Commission has previouslyissued a proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding (62 FR 14462). The amendment also changes recordkeeping or reporting requiremen;s. Accordingly, the amendment meets the eligibility criteria for categorical exc'usion set forth in 10 CFR 51.22(c)(9) and (c)(10). 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.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangerod by operation in the proposed manner, (2) such activities will be conducted in e,ompliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to tha common defenn and security or to the health c.nd safety of the public.
i
(
\\
),
i
6.0 REFERENCES
I
- 1. " Application of the ' Regional Exclusion with Flow-Biased APRM Neutron Flux Scram' Stability Solution (Option 1-D) to the Cooper Nuclear Station," GENE-A13-00395-01, j
November 1996.
j
- 2. "BWR Owners' Group Long Term Stability Sofutions Licensing Methodology,"
NEDO-31960-A, June 1991, and NEDO-31960-A, Supplement 1, March 1992.
- 3. "BWR Owners' Group Reactor Stability Detect and Suppress Solutions Licenring Basis Methodology and Reload Applications," NEDO-32465-A, May 1995.
Principal Contributor; A. Ulses, NRR j
Date: July 29, 1998 l
l l
f
. _ _ _ _ _ _ _ _ _ _ _ - _ - _ _ _ _ _ - _ - _ _ _ _ _ _