ML20009E196
| ML20009E196 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 07/22/1981 |
| From: | Withrow G CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8107270216 | |
| Download: ML20009E196 (4) | |
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CORSumBIS Power Company 4,
c.4.r. ome : 212 W.st Michigen Avenue, Jackson, Michigan 49201 * (517) 788 4550 i[
U July 22,1981 h
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Director, Nuclear Reactor Regulation Att Mr Dennis M Crutchfield, Chief Operating Reactors Branch No 5 US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - IICENSE DPR BIG ROCK POINT PLANT - ECCS OPERATING LIMITS - SINGLE LOOP OPERATION NRC letter dated June 9, 1981 provided Amendment No hh to Facility Operating License No DPR-6 for the Big Rock Point Plant. This amendment authorized a change in reactor operating limits for two reactor coolant recirculation loop operation and noted that the NRC Staff evaluation of single recirculation loop operation was continuing.
Informal discussions between the Staff and Consumers Power Company have provided answers to questions informally received from the Staff. Per Staff request, to this letter is provided to document one of these questions and our response. This attachment proposes a new value (20".) for reduction of two-loop MAPLHGR limits for EXXON fuel during single-loop operation.
C' WhdhY Greg C dithrov Senior Licensing Engineer CC JGKeppler, USNRC NRC Resident Inspector - Sig Rock Point Plant crutchfield-br
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s 8107270216 810722 PDR ADOCK 05000155 P
Response To NRC Question Pertaining to EXXON Fuel Limits Question The proposed technical specification change on ECCS operating limits for single loop operation reduces MAPLHGR limits by 10% from the two-loop values for Exxon fuel types. Provide additional discussion to justify the conclusion that the MAPLHGR limits for Exxon fuel are relatively insensitive to flow reduction under sing;e-loop operation. In particular, address why the sensitivity of MAPMGR to flow can be derived on the bases of a fuel heatup analysis performed t:y GE for GE fuel.
Response
A comparison of allowable total bundle peak LHGR for both GE and Exxon fuel is provided on the attached table. It is necessary to compare total bundle MGRs rather than MAPMGRs due to the fact that each fuel type has a different number of fuel rods and therefore a different total active fuel length. As can be seen from the table, the Exxon fuel performs better under LOCA conditions than the GE fuel. This is due to the fact that the Exxon fuel is an 11 x 11 fuel rod design whereas the GE fuel is a 9 x 9 design. Thus the Exxon fuel operates at a lover MGR for an equivalent bundle power which results.in lower fuel temperatures and thus better LOCA performance. In addition, the Exxon fuel has k inert rods located in the interior of the bundle, which act as radiation heat sinks during the LOCA, and therefore result in slightly improved performance. However, increased number fuel roads in the bundle is by far the'most important factor contributing to the improved LOCA performance for Exxon fuel.
Two sets of MAPLHGR limits for Exxon fuel are shown on the table. The first set (labeled GE SAFE / ENC HUXY) is based on methodology very similar to that used by GE.
The GE SAFE code blowdown results are used in HUXY to define the reactor pressure transient, time of core uncovery and time of rated spray flow. - HUXY determines the time to transition boiling based on a conservative dryout time correlation. The Ellion. film boiling correlation is used between the time of dryout and core uncovery. Adiabatic heatup of the fuel is assumed until' rated spray time and then the Appendix K spray cooling heat transfer coefficients are applied. The set labeled ENC RELAPh/HUXY are based on the latest ENC approved methodology for_non-jet pump BWRs. This methodology allows credit to be taken for heat transfer coefficients calculated in RELAPh during the blovdown phase (defined as the period prior to rated core spray). This significant. improvement is reflected in the higher allovable MAPLHGRs.
When the 10% reduction in MAPLHGR limits for Exxon fuel was originally proposed (see LER R0-77-20) it was based on the following logic: First, for GE fuel a 55 reduction in MAPLHGR is required for single-loop operation; and second, Exxon fuel generally performs 5% better than GE fuel in terms of allowable bundle power; thus a 10% reduction in MAPLHGR vill assure that the Exxon fuel bundles are operated at about the same power level as the GE fuel bundles when only one-loop is in service. Because the Exxon fuel is known to perform better under LOCA conditions, operation at approximately the same power level as the GE fuel assures that the 10CFR50.46 LOCA limits vill not be exceeded for Exxon fuel should a LOCA occur while operating with a loop out cf service.
2 Since the 10% reduction in MAPLHGR was originally proposed, the Exxon fuel has been reanalyzed for LOCA using the ENC improved methodology. The improved methodology results in an i=provement in MAPLHGR limits of approximately 105 for Exxon fuel.
It may be argued that this 10% improvement is not justified for single-loop operation without doing the analysis explicitly. Thus for single-loop operation CPCo'. proposes to reduce the MAPLHGR limits for Exxon fuel by 20% (the 10% originally proposed plus the 10% due to the improved ENC methodology) from that allowed for two-loop operation.
9 Limit on Total Bundle Peak Linear lleat Generation Rate (kw/f t )*
One-Locp Two-Loop Operating Limits Operating Limit Planar Average Reload F Modified F Reload G-3 Reload G-3 Modified F l
Exposure (Nd/STM)
(CE SAFE /CilASTE)
(CE SAFE / CHASTE)
(GE SAFE / ENC llUXY) (ENC RELAP4/IlUXY)
(GE SAFE /CilASTE) l 0
760 836 200 724 722 686 10,000 74 7 75 2 867 714 798 10,422 20,000 662 661 628 l
20,320 877 807 21,194
- MAPLHGR x (Number of Fuel Rods per Bundle)
-Q