ML20236D262

Topical Rept Evaluation of CEN-348(B)-P, Extended Statistical Combination of Uncertainties. Rept Acceptable

ML20236D262
Person / Time
Site:	Calvert Cliffs
Issue date:	10/21/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20236D256	List: ML20236D253 ML20236D262
References
NUDOCS 8710280095
Download: ML20236D262 (2)

Text

. _ _ - _ _ _ .

k I

04s 9 MU

• q, [ fg- NUCLEA'R REGULATORY COMMISSION

((

' WASHINGTON, D. C,. 20555 c.

\ .*e.w

]

l

, SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION  !

BALTIMORE GAS: AND ELECTRIC COMPANY

> CAi. VERT CLIFFS NUCLEAR POWER PLANT, UNIT NOS. 1 AND 2' ,

1 DOCKET NOS. 50-317 AND 50-318 REVIEW 0F TOPICAL' REPORT CEN-348(B)-P 1 i

" EXTENDED STATISTICAL COMBINATION OF UNCERTAINTIES" l i

-]

1. INTRODUCTION-

'By.. letter dated March 17, 1987, Baltimore Gas and Electric Company-(BG&E)  !

requested NRC review and' approval of CEN-348(B)-P, " Extended Statistical .

. Combination of-Uncertainties". The extended statistical combination of

-uncertainties >(ESCU)methodisanenhancementoftheexistingstatistical

> combination of uncertainties:(SCU) methodology previously reviewed and approved:

by'the NRC (Ref. 1). The report' describes an improved method for statistically.

combining the uncertainties involved in the departure from nucleate boiling (DNB) related analog protection and monitoring system setpoints.

j l

The licensee has defined the input data required for a detailed thermal- "

, hydraulic analysis by type: (1)' system parameters which describe the physical system'and are not monitored during~ reactor operation ~ and (2) state parameters-which describe the operational state of the reactor and are monitored during 1 operation. There is a degree of. uncertainty in the value used for each of the j input parameters used in the design safety analyses. In the past, these 1 uncertainties had been handled by assuming that each variable affect

• j DNB was l at the most adverse limit of its uncertainty range. The assumption that all factors are simultaneously at their most adverse values leads-to conservative restrictions in reactor operation. Therefore, the SCU methodology was developed to' statistically combine uncertainties in the calculation of new limits for 3 Calvert Cliffs. These limits ensure with at least a 95 percent probability and a 95' percent confidence level (95/95) that neither DNB nor' fuel centerline melt will occur. Part 1 of the methodology (Ref. 2) described the application of (LPD) and thermal margin /

the low SCU pressure to the development (TM/LP) of the local limiting safety system power density (LSSS).

settings 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. Part3(Ref.4)usedSCUmethodstodefinelimiting conditions for operation (LC0).

8710290095 871021 PDR ADOCK 05000317 P pon

,f -  ;

'(P {

4- ,

2.0- EVALUATION-As mentioned above,:the existing SCU method (Refs.~2, 3, and 4) treats uncer-

tainties in two groups. -The uncertainties in one' group (system parameter uncertainties and critical heat function (CHF) correlation uncertainties) The are statistically combined-to generate.a DNBR probability density function.

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 prob .

ability density functions for LSSS and LC0 processes. The 95/95 limits of .

these functions are then applied as overpower penalties in the. generation of

~

l LSSS and LC0 setpoints. 4 Although the uncertainties within each group are combined statistically and a

-95/95 probability / confidence level. generated for esch group, the resultant uncertainties of the two. groups are effectively combined in a deterministic 2 manner due to the separate application of.the two uncertainty limits. The '

proposed ESCU methodology would incorporate the DNBR probability density.  ;

. function, which is generated by statistically combining the system parameters l 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 uncertainties and the' uncertainty treatment procedure L

described for the proposed ESCU methodology and has determined that the resultant pena' ties applied to the setpoint calculations adequately incorporate all un- l

. certainties at the 95/95 probability / confidence level. The 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 95/95 probability / confidence i

• level assurance against DNB occurring during steady state operation or anticipated i

-operational occurrences, a

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

1. Letter from D. H. Jaffe (NRC) to A. E. Lundvall (BG&E), "Regarding Unit 1 Cycle 6 License Approval (Amendment D 1 to DPR-53 and SER)," Appendix A to Attachment, June 24, 1982.

2. " Statistical Combination of Uncertainties Part 1," CEN-124(B)-P, December 1979.

3. " Statistical Combination of Uncertainties Part 2," CEN-124(B)-P, January 1980.

4 " Statistical Combination of Uncertainties Part 3," CEN-124(B)-P, March

< 1980.

1 L