ML20116D996
| ML20116D996 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 09/25/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20116D885 | List:
|
| References | |
| FOIA-96-237 NUDOCS 9608050038 | |
| Download: ML20116D996 (4) | |
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. SAFETY' EVALUATION OF TOPICAL REPORT CEN-348(B)-P
" EXTENDED STATISTICAL COMBINATION OF UNCERTAINTIES" BALTIMORE GAS AND ELECTRIC COMPANY CALVERT CLIFFS NUCLEAR POWER PLANT UNITS 1 AND 2 i
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INTRODUCTION
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By letter dated March 17, 1987, Baltimore Gas and Electric Company (BGE) j requested NRC review and approval of CEN-348(B)-P, " Extended Statistical Combination of Uncertainties". The extended statistical combination of l
uncertainties (ESCU) method is an enhancement of the existing statistical l.
combination of uncertainties (SCU) previously reviewed and approved by the NRC I
(Ref. 1). The report describes an improved method for statistically combining
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f the uncertainties involved in the departure from nucleate boiling (DNB) j l
related analog protection and monitoring system setpoints.
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The licensee has defined the input data required for a detaNled p
thermal-hydraulic analysis by type:
(1) system parameters which describe the
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physical system and are not monitored during reactor operatiori and-(2) state l
parameters which describe the operational state of the reactor and are
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monitored during operation. There is a degree of uncertainty in the value
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l-used for each of the input parameters used in the design safety analyses.
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the past, these uncertainties had been handled by assuming that each variable l
affecting DNB was at the most adverse limit of its uncertainty range. The l7 assumption that all factors are simultaneously at their most adverse values i
leads to conservative restrictions in reactor operation. Therefore, the SCU methodology was developed to statistically combine uncertainties in the calculation of new limits for Calvert Cliffs. These limits ensure with at least a 95 percent probability and a 95 percent confidence level (95/951 that j
neither DNB nor fuel centerline melt will occur. Part 1 of the methodology j
(Ref. 2) described the application of the SCU to the development of the local
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power density (LPD) and thermal margin / low pressure (TM/LP) limiting safety 1^
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9608050038 960731 PDR FOIA DINICOL96-237 PDR
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i system settings (LSSS). These are used in the analog reactor protection system to protect against fuel centerline melt and DNB respectively. Part 2 (Ref. 3) used SCU methods to develop a new DNB ratio (DNBR) limit. Part 3 (Ref. 4) used SCU methods to define limiting conditions for operation (LCO).
l 2.0 EVALUATION 4
l As mentioned above, the existing SCU method (Refs. 2, 3, and 4) treats uncertainties in two groups. The uncertainties in one group (system parameter uncertainties and CHF correlation uncertainties) are statistically combined to generate a DNBR probability density function. The 95/95 probability / confidence level limit of this function is then used as the setpoint analysis minimum DNBR.
the uncertainties in the other group (state parameter uncertainties, axial shape index (ASI) uncertainties, and processing uncertainties) are statistically combined to generate overpower error probability density functions for LSSS and LCO processes. The 95/95 limits of these functions are then applied as overpower penalties in the generation of LSSS and LCO setpoints.
t Although the uncertainties within each group are combined statistically and a 95/95 probability / confidence level generated for each group, the resultant uncertainties of the two groups are effectively combined in a deterministic manner due to the separate application of the two uncertainty limits. The proposed ESCU methodology would incorporate the DNBR probability density function, which 1s generated by statistically combining the system parameters and CHF correlation uncertainties, into the protection and monitoring system stochastic simulation models together with the ASI, state parameter, and processing uncertainties.
The staff has reviewed the unceltainties and the uncertainty treatment procedure described for the proposed ESCU methodology and has determined that the resultant penalties applied to the setpoint calculations adequately incorporate all uncertainties at the 95/95 probability / confidence level. The
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I analytical methods reviewed and approved show that for CE 14x14 fuel, a DNBR limit of 1.15 with the uncertainty penalties derived in the report provides a f
95/95 probability / confidence level assurance against DNB occurring during j
steady state operation or anticipated operational occurrences.
3.0 CONCLUSION
The staff has reviewed the ESCU methodology presented in CEN-348(B)-P and finds it to be an acceptable method for statistically combining uncertainties for the TM/LP LSSS and DNB LCOs for Calvert Cliffs Units 1 and 2 utilizing CE 14x14 fuel.
4.0 REFERENCES
Letter from D. H. Jaffe (NRC) to A. E. Lundvall (BGE), "Regarding Unit 1 1.
Cycle 6 License Approval (Amendment #71 to DPR-53 and SER) " Appendix A to Attachment June 24, 1982.
" Statistical Combination of Uncertainties Part 1," CEN-124(B)-P December 2.
1979.
" Statistical Combination of Uncertainties Part 2." CEN-124(B1-P, January 3.
1980.
" Statistical Combination of Uncertainties Part 3," CEN-124(B)-P March 4.
1980.
i, ENCLOSURE 2 CALVERT CLIFFS UNITS 1 AND 2 SYSTEMATIC ASSESSMENT OF LICENSEE PERF0PMANCE Functional Areas 1.
Management Involvement in Assuring Quality.
Technical review of the submittal indicates that the management reviews are timely and technically appropriate.
Rating: Category 1 2.
Approach to Resolution of Technical Issues from a Safety Standpoint.
The licensee showed a general understanding of the technical issue and used acceptable approaches.
Rating: Category 1 3.
Responsiveness to NRC Initiatives N/A 4.
Enforcement History N/A 5.
Operational and Construction Events N/A 6.
Staffing (including Management) l N/A i
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Training and Qualification Effectiveness
Reference:
NRC Manual Appendix 0516 - Systematic Assessment of Licensee Performance I
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