ML20207G770
| ML20207G770 | |
| Person / Time | |
|---|---|
| Issue date: | 06/10/1999 |
| From: | Carpenter C NRC (Affiliation Not Assigned) |
| To: | Mallay J SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER |
| References | |
| PROJECT-702 NUDOCS 9906140067 | |
| Download: ML20207G770 (3) | |
Text
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UNITED STATES g
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20066 4 001
- l June 10, 1999 Mr. James Mallay, Director Regulatory Affairs Siemens Power Corporation 2101 Hom Rapids Road Richland, WA 99352
SUBJECT:
MODIFICATIONS TO PROCEDURES FOR USE OF XCOBRA-T
REFERENCE:
1.
"XCOBRA-T: A Computer Code for BWR Transient Thermal-Hydraulic Core Analysis,"
XN-NF-84-105 (P)(A), February 1987.
2.
James F. Mallay (SPC) to USNRC, " Clarification of SRP Chapter 15 Analyses Performed with XCOBRA-T," NRC:98:037, June 3,1998.
3.
Don Curet (SPC) to USNRC, " Equilibrium Quality Limits for Hench-Levy Limit Line Correlation," NRC:98:044, June 25,1998.
Dear Mr. Mallay:
Reference 1 describes the licensing topical report (LTR) governing the use of the XCOBRA-T code. Page 6 of this report contains a commitment to perform critical heat flux ratio (CHFR) evaluations at every node in the hot channel. However, critical heat flux (CHF) test data for the lowest bundle flow achievable in the reactor indicates that boiling transitions does not occur in the bottom three feet of the channel under any conditions. When conditions exist such that no boiling transition occurs, the CHF correlation for the fuel cannot be reliably used to predict CHF for these conditions. Because of this, Siemens Power Corporation (which purchased the approved methods from Exxon Nuclear Corporation), has interpreted the previous commitment in a manner which allowed the exclusion of the lower three feet of the bundle from CHFR consideration. During a self discovery exercise initiated following an NRC core performance inspection, SPC's XCOBRA-T procedures were called into question by SPC staff because they did not strictly comply with the LTR.
By letter dated June 3,1998, SPC requested that the staff consider and concur with a l
modification in the procedures used to fulfill the requirement in the XCOBRA-T LTR discussed in the previous paragraph. The proposed procedure change involves using an appropriately G
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scaled and conservative Hench-Levy limit line to supplement the fuel critical heat flux 0
correlation. The application of Hench-Levy in XCOBRA-T is conservative because it is scaled f for the geometry, a Tong factor is applied to account for non-uniform axial power profiles, and a conservative factor is applied to account for local peaking. In this method, SPC will use the appropriate fuel critical heat flux correlation when the conditions in the node are within the correlation database. For cases when the correlation does not apply, the analyst will use the conservative Hench-Levy limit line to ensure that boiling transition is not occurring in the node.
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o Mr. J. Mallay The staff has considered the SPC proposal. The staff concurs with the SPC position that boiling transition is highly unlikely in the lower part of the channel. Furthermore, we consider that the Hench-Levy limit line approach proposed by SPC will conservatively assess the critical heat flux margin. It is the staff's position that fuel CHF testing should always include inlet flow and enthalpy conditions which will bound the conditions expected before and during a transient simulation. The staff, therefore, considers the proposed application of Hench-Levy acceptable only for those conditions (mass flux and equilibrium quality) below which boiling transition was not observed in the experimental facility using the most limiting bottom peaked axial power distribution.
I Furthermore, SPC's commitment to control this application of Hench-Levy by incorporating the guidelines presented in this letter and references 2 and 3 above into EMF-868(P), " Plant Transient at Rated and Off-Rated Conditions," is acceptable to the staff.
q Sincerely, Original signed by:
Cynthia A. Carpenter, Chief Generic Issues, Environmental, Financial and Rulemaking Branch Division of Regulatory improvement Programs Office of Nuclear Reactor Regulation Project No. 702 QlSTRIBUTION:
Public PGEB R/F FAkstulewicz CCarpenter EWang Aulese JWermiel RCaruso DMatthews i
DOCUMENT NAME: CHFCLRF2 To receive a copy of this document, indicate in the box:
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- See previous concurrence f,
I OFFICE PGEB C:SRXB*
SC:PGM C:PGEB NAME EWang JWermiel FAksfGeGIcz CCarpenter/V DATE 06/09 /99 06/ 09 /99 08T4/99 06/6 /99 OFFICIAL RECORD COPY f
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Mr. J. Mallay The staff has considered the SPC proposal. The staff concurs with the SPC position that boiling transition is highly unlikely in the lower part of the channel. Furthermore, we consider that the Hench-Levy limit line approach proposed by SPC will conservatively assess the critical heat flux margin. It is the staff's position that fuel CHF testing should always include inlet flow and enthalpy conditions which will bound the conditions expected before and during a transient simulation. The staff, therefore, considers the proposed application of Hench-Levy acceptable only for those conditions (mass flux and equilibrium quality) below which boiling transition was not observed in the experimental facility using the most limiting bottom peaked axial power distribution. Furthermore, SPC's commitment to control this application of Hench-Levy by incorporating the guidelines presented in this letter and references 2 and 3 above into EMF-868(P), " Plant Transient at Rated and Off-Rated Conditions," is acceptable to the staff.
Sincerely, Gn Tb' W Cy6 thia A. Carpenter, Chief Generic issues, Environmental, Financial and Rulemaking Branch Division of Regulatory improvement Programs Office of Nuclear Reactor Regulation Project No. 702 l
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