ML20214T859
| ML20214T859 | |
| Person / Time | |
|---|---|
| Issue date: | 11/28/1986 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20214T821 | List: |
| References | |
| NUDOCS 8612090036 | |
| Download: ML20214T859 (15) | |
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SAFETY EVALUATION REPORT 0F WESTINGHOUSE TOPICAL REPORT WCAP-10054, ADDENDUM 1 .
1.0 INTRODUCTION
NUREG-0737 Item II.K.3.30 required industry to demonstrate its small break j loss of coolant accident (SBLOCA) methods continue to comply with the requirements of Appendix K to 10 CFR 50. In response to this requirement, Westinghouse submitted a description of its NOTRUMP code (Reference 1) and itsSBLOCAevaluationmodel(Reference 2)asappliedtoaWestinghouse nuclearsteamsupplysystem(NSSS). These topical reports were reviewed by the staff and found acceptable as documented in Reference 3.
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Westinghouse submitted WCAP-10054, Addendum 1 (Reference 4) which describes the application of the Westinghouse SBLOCA evaluation model to the CombustionEngineering(CE)NSSSandisintendedtosatisfyNUREG-0737 Item II.K.3.30 for these plants. Supplemental information supporting the topical report was provided in Reference 5.
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- This report evaluates WCAP-10054, Addendum 1. It specifically addresses
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compliance of the Westinghouse SBLOCA evaluation model for the CE NSSS i- to the requirements of Appendix K to 10 CFR 50 and compliance with the requirements of NUREG-0737 Item II.K.3.30.
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2.0 EVALUATION OF COMPLIANCE TO APPENDIX K TO 10 CRF 50 WCAP-10054, Addendum 1 describes the methodology used to apply the Westinghouse NOTRUMP code to the CE NSSS. The report specifically 4
8612090036 861128 PDR TOPRP ENVWEST C PDR
discusses the differences in the CE NSSS, as compared to the Westinghouse NSSS, and examines the application of the Westinghouse SBLOCA evaluation model to the CE NSSS. This evaluation included an examination of the specificmodelingfeatures(i.e.,equationsandassumptions)utilizedin the NOTRUMP code, and their applicability to the CE NSSS. Other modeling features of the NOTRUMP code such as the solution techniques and general code formulations, which were not impacted by the NSSS design differences were not modified. The staff has concluded that this approach is acceptable and limited its review of the previously approved SBLOCA evaluation model using the NOTRUMP code to assuring that the impact of the NSSS design differences were properly accomodated. Detailed discussions of this assessment is provided in this section.
In addition to examining the impact of design differences, a sample small break LOCA spectrum was provided in WCAP-10054, Addendum 1. This analysis was reviewed by the staff and the results are reported in Section 2.8.
2.1 Loop Layout ,,.
The CE NSSS has a two hot leg, four cold leg layout which is different from the Westinghouse "n" hot leg "n" cold leg design. To simulate this design difference, the noding utilized for the NOTRUMP code has been modified from that described in Reference 2. The staff has reviewed the differences in the noding utilized for representing the CE NSSS as compared to that approved for the Westinghouse NSSS. The staff has concluded that the noding utilized appropriately reflects the loop layout and is, therefore, acceptable.
The CE design specifies a 42" I.D. hot leg in comparison to the Westinghouse design which has a hot leg of 29.5" I.D. The dif-ferences in the hot leg diameter are accounted for by the input data used for the NOTRUMP code. Additionally, it was noted that the transition boundary in horizontal two-phase flow is only weakly dependent on pipe diameter for large diameter pipes. The staff reviewed the models utilized in the NOTRUMP code and has concluded that the effect of the larger diameter pipes is appropriately considered in the equations utilized. Thus, accounting for the effects of the larger hot leg pipe diameter via the code input is acceptable.
l The primary flow from the hot leg enters the steam generator through an inclined steam generator inlet nozzle. The inclination of this nozzle is different for the two NSSS designs. Westinghouse examined the effect of the nozzle inclination on the flooding correlation utilized in the NOTRUMP code to represent this portion of the NSSS. Q It was shown, via a sensitivity study, that the difference in the flooding correlations for the two NSSS designs result in essentially the same total mass behavior during the SBLOCA. Thus, the staff finds that the flooding correlation proposed in WCAP-10054, Addendum 1 for the CE NSSS is acceptable.
The loop seal venting behavior plays an important role for small cold leg LOCAs in which the break size is large enough to deplete
4 the system mass inventory so that the break becomes uncovered yielding predominantly steam break flow. There are significant geometric differences in the loop seals between the two NSSS designs. For the CE NSSS, the horizontal section of the loop seal is at approximately the same elevation as the top of the core, whereas in the Westinghouse NSSS design, the horizontal loop seal pipe elevation lies at nearly the mid-core elevation. As a result, there is much less of an inner vessel, (i.e., upper plenum, core and lower plenum) level depression required to initiate loop seal venting in the CE NSSS design.
Geometric differences in the loop seals are explicitly treated in the NOTRUMP input. Modifications to the loop seal noding were made for the application of NOTRUMP to the CE NSSS design due to loop layout differences. The staff has reviewed these noding differences and, based upon the break spectrum analyses presented in Section 4 of WCAP-10054, Addendum 1, noted that the noding utilized for the CE NSSS design produces consistent behavior in the loop seal venting behavior. Thus, the staff finds the loop seal noding acceptable.
WCAP-10054, Addendum 1 did not address differences in the steam generator design and their impact on the SBLOCA evaluation model.
Westinghouse provided supplemental information, in response to a staff request, in Reference 5 to address this impact. The staff I noted that the NOTRUMP code description includes mechanical separator l
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- f". 5-models and questioned their applicability to the CE NSSS. Westinghouse stated that these models are not used in the SBLOCA evaluation model.
Thus, the staff finds that differences in the separator design does not affect the evaluation model.
i With respect to the steam generator heat transfer models, Westinghouse noted that the heat transfer coefficients in the NOTRUMP code are regime dependent and that the correlations used consider the effects of geometry differences via the code input. Based upon staff review of the NOTRUMP heat transfer models, as given in Reference 3. and the fact that the models appropriately account for the effect of geometriv differences, the staff finds that no modifications to the NOTRUMP code are needed to simulate the CE plant steam generators.
2.2 Control Element Assembly (CEA) desion The CE upper internals design provides for several flowpaths for communication between the upper plenujn and the upper head. The CEAs can include a shroud through which flow from the upper head can reach the upper plenum in addition through flow through the CEAs themselves. Westinghouse performed sensitivity studies to investigate the modeling of the flow between the upper head and upper plenum.
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The results showed that the noding scheme proposed in WCAP-10054 .
Addendum 1 provided nearly identical inner vessel mixture levels in comparison to detailed representation of the various flow paths available. Based upon these sensitivity studies, the staff concludes that the modeling utilized to represent the CE upper intervals design is acceptable.
2.3 Upper Head Bypass Flow The CE upper head design provides for negligible bypass flow from the top of the downcomer through the upper head in comparison to that available for a Westinghouse plant with a cold upper head. To reflect this difference, the SBLOCA evaluation model was modified and included a revised assumption for the initial upper head fluid temperature.
The staff has examined the approach proposed in WCAP-10054, Addendum 1 and concluded it will result in a conservative prediction of SBLOCA behavior. Thus, the staff finds the treatment of upper head bypass flow for the CE NSSS acceptable.
2.4 Fuel Assembly Design ,
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Both the NOTRUMP and LOCTA-IV (Reference 6) codes calculate the core l heat transfer during periods of steam cooling based upon the correlations j developed in Reference 7. Westinghouse verified that these steam cooling relations are equally applicable to the range of hydraulic l
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l diameters typical of Westinghouse designed assemblies being reloaded l
into CE plants. Since the steam cooling correlations explicitly '
include the hydraulic diameter effect and the hydraulic diameters for i the Westinghouse-designed assemblies being reloaded into CE plants are comparable to the range of hydraulic diameters for Westinghouse fuel in Westinghouse plants, the staff concludes that the steam cooling relations in References 1 and 6 are applicable for the CE NSSS.
2.5 Fuel Rod Design The fuel clad swelling and rupture model in LOCTA-IV is described in Reference 6. Modifications to the LOCTA-IV code to represent the rod burst behavior for the fuel loaded into the CE NSSS is described in Reference 8 and is applied in an identical manner in the SBLOCA evaluation model for the CE NSSS. Since this model has previously been approved by the staff, the staff finds this approach acceptable.
2.6 Pumped Safety and Accumulator Injection The angle between the cold leg and safety injection line of the CE NSSS is different than that of the Westinghouse NSSS. In WCAP-10054, Addendum 1, the impact of this design difference was evaluated. It was determined that the behavior of the safety injection fluid entering the NSSS would be similar for both designs. In addition, the approach utilized in the NOTRUMP code to represent the non-equilibrium behavior
. of the injected fluid is based upon conservative input assumptions.
The staff has examined the information provided and has concluded that the evaluation model will conservatively model the non-equilibrium behavior of the injected fluid and is, therefore, acceptable.
The accumulator polytropic expansion coefficient utilized in NOTRUMP '
is based upon the accumulator blowdown test performed at the Callaway 1
site in 1982. For CE plants with 600 psig accumulators, the coefficient which was derived from this test is directly applicable. For those CE plants with 200 psig accumulators, Westinghouse reexamined.these tests using the final portion, wherein the pressure varied from 223.6 to 194.0 psig, to determine the polytropic expansion coefficient. The staff has reviewed the results of these tests and has confirmed that the coefficients specified in WCAP-10054, Addendum 1 an acceptable.
2.7 Reactor Coolant Pumps i
The reactor coolant pumps are modelled using the equivalent density model described in Reference 1. CE p6mp specific parameters and homologous curves are to be used as input to the NOTRUMP code when applied to the CE NSSS. Based upon a review of the discussion i
presented in Section 3.7 of WCAP-10054, Addendum 1, the staff finds a
the proposed model acceptable.
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l 2.8 Break Spectrum Analyses Within Sections 4 and 5 of WCAP-10054, Addendum 1, a sample break spectrum analysis was performed. This break spectrum was performed for the Millstone 2 plant. Analyses were performed for 3 , 4 , and 6-inch cold leg pump discharge breaks. These cases resulted in peak cladding temperatures of 1301*F,1975*F and 1165 F, respectively.
In addition, 4-inch line breaks were also analyzed in the pump suction and hot leg piping resulting in peak cladding temperatures of 1412*F and 1673*F, respectively. Thus, based upon these analyses, it was concluded that a 4-inch line break in the cold leg pump discharge piping was the worst case break.
The staff reviewed these calculations for conformance with Section C.1 of Appendix K. With respect to the specific plant analyzed (Millstone 2),
the staff was concerned that a break size which did not rely upon the accumulator injection to recover the core inventory could result in a higher peak cladding temperature. ,1,n Reference 5, Westinghouse sub-l mitted additional information which demonstrated that a break of approximately a 3.5 inch line would not result in accumulator injection.
l Westinghouse conservatively estimated the peak cladding temperature l
l for this break and demonstrated that it was bounded by the 4-inch line break. Based upon these results, the staff concludes that the spectrum l analyses performed for Millstone 2 satisfies,the requirements of 1
Section C.1 of Appendix K.
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The staff also expressed concern that this break spectrum analysis' may not be applicable for all CE plants. In Reference 5, Westinghouse stated that any future analyses for a CE plant will include analysis of a representative spectrum of small breaks to identify the limiting break. The staff finds this commitment acceptable.
2.9 Sumary of Compliance with Appendix K to 10 CFR 50 Within Reference 3, the staff concluded that the NOTRUMP code and its application to the Westinghouse NSSS fully complied with the requirements of Appendix K to 10 CFR 50. Within WCAP-10054, Addendum 1, Westinghouse described the modifications to the NOTRUMP code and its application for the CE NSSS. As discussed in detail above, the staff finds all the proposed modifications acceptable. Thus, the staff finds that the application of the NOTRUMP code to the CE NSSS, as described in WCAP-10054, Addendum 1, complies with the requirements of Appendix K to 10 CFR 50, with the exception of the break spectrum requirements of Section C.1 of Appendix K. The staff has concluded that the si .
analyses is WCAP-10054, Addendum 1 demonstrates compliance to this section for the Millstone 2 plant, however, the results may not be generically applicable for all CE plants. The staff finds the Westinghouse comitment to perform representative break spectrum analyses for future calculations for other CE NSSS designs acceptable for demonstrating compliance with this section.
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_ 11 3.0 EVALUATION OF COMPLIANCE TO NUREG-0737 ITEM II.K.3.30 NUREG-0737, Item II.K.3.30 required industry to demonstrate its SBLOCA methods continued to comply with the requirements of Appendix K to 10 CFR 50. As stated in II.K.3.30, specific staff concerns regarding small-break LOCA models were provided in the analysis sections of the Bulletin and Orders Task Force reports for each LWR vendor. NUREG-0611 and NUREG-0635 addressed the staff concerns regarding the Westinghouse and CE NSSS methods, respectively.
Within Reference 3, the staff evaluated the conformance of References 1 and 2 to the concerns documented in NUREG-0611. The staff reviewed NUREG-0635 and determined that it contained many of the concerns expresssd in NUREG-0611. Thus, many of the previous staff evaluations in Reference 3 are equally applicable to application of the NOTRUMP code to the CE NSSS.
Three concerns were identified from NUREG-0635 which needed to be i examined specifically for the CE NSSS design or were not identified in NUREG-0611. Westinghouse addressed these concerns in Reference 5.
These concerns are evaluated below.
3.1 Noncondensible Affects on Condensation Heat Transfer l
NUREG-0635 requested an assessment of the effects of noncon-densible gases on condensation heat transfer in the CE plants.
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Within Reference 2 Westinghouse demonstrated that the effect of noncondensible gases on the small-oreak LOCA transient for a Westir.ghouse NSSS would be minimal. Westinghouse stated, in Reference 5, that the effects of noncondensible gases for a CE plant would be the same. The staff concluded in Reference 3, that due to the limited amount of noncondensible gases available i during a design bases SBLOCA event, minimal impact is expected.
This was also confirmed by test results obtained from Semiscale experiments. Based upon the foregoing, the staff agrees that j noncondensible gases is also expected to have a minimal impact on the CE NSSS. Thus, this concern is resolved.
3.2 Primary Metal Heat NUREG-0635 requested confirmation that adequate accounting of stored energy (heat) within the primary system metal structures are included in the CE plant model. Westinghouse described, in Reference 5, the components in the plant for which metal heat is modeled. Verification of the primary metal heat modeling was provided by the LOFT and SEMISCALE simulations documented in l Reference 2. Based upon the verification results, the staff concludes that adequate accounting of stored metal heat is included in the NOTRUMP model for the CE NSSS and this item is resolved. '
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l 3.3 Modeline of Break Flow NUREG-0635 requested validation of applying a 1.0 discharge co-efficient on both the subccoled and saturated break flow models.
Westinghouse concluded that its subcooled break flow model slightly overpredicts subcooled break flow, while the Moody break flow model provides an accurate calculation of the break flow for steam discharge. Two-phase discharge through the break is expected to occur over a short time period.
The staff reviewed the break flow results presented in Section 4 of WCAP-10054, Addendum 1 and agrees that the two-phase break flow occurs over a small time period. Additionally, the staff believes that the Westinghouse subcooled break flow model will produce reasonable, but somewhat conservative, break flow rates;
~i the Moody break flow model is also reasonable for steam discharges.
Thus, the staff has concluded that the use of a 1.0 discharge coefficient for both the subcool'Ed and saturated break flow models is acceptable.
3.4 Summary of Compliance to NUREG-0737 Item II.K.3.30 Based upon the foregoing, the staff has concluded that WCAP-10054, Addendum 1 addresses the concerns of NUREG-0635 and NUREG-0611.
f As noted in Section 2.9, the staff also finds that the Westinghouse SBLOCA evaluation model satisfies the requirements of Appendix K to 10 CFR 50. Therefore, the staff finds that WCAP-10054, Addendum I satisfies NUREG-0737, Item II.K.3.30.
4.0 REFERENCES
- 1. Meyer, P. E. and Kornfilt, J., "NOTRUMP-A Nodal Transient Small Break and General Network Code," WCAP-10079, November 1982.
- 2. Lee, N., Tauche, W. D. and Schwarz, W. R., " Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code," WCAP-100S4, December 1982.
- 3. Letter, C. O. Thomas (NRC) to E. P. Rahe (Westinghouse),
Subject:
Acceptance for Referencing of Licensing Topical Report WCAP-10054 l
(Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code),May 21, 1985.
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- 4. Bajorek, S. M., " Addendum To The Westinghouse Small Break ECCS Evaluation l
Model (WCAP-10054) Using the NOTRUMP Code for the Combustion Engineering NSSS," WCAP-10054, Addendum 1, July 1984.
! 5. Letter, Rahe, E. P., Jr. (Westinghouse) to L' ons, y J. (NRC), " Response to the NRC Request for Additional Information on Topical Report WCAP-10054,
, Addendum 1," October 23, 1976.
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- 6. Bordelon, F. M. et al., "LOCTA-IV Program: Loss of Coolant Transient Analysis," WCAP-8305, June 1974.
- 7. Yeh, H. C. et al., " Heat Transfer Above the Two-Phase Mixture Level Under Core Uncovery Conditions in a 336-Rod Bundle," EPRI-NP-2161, December 1981.
- 8. Ferguson, K. L. and Kemper, R. M., "ECCS Evaluation Model for Westinghouse Fuel Reloads of Combustion Engineering NSSS," WCAP-9528, June 1979.
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