ML20204F861

Forwards Response to NRC 830315 Questions on Sensitivity Studies Performed on Retran Analysis.Approval Requested Prior to Scheduled Startup Following Next Refueling Outage

ML20204F861
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	04/26/1983
From:	Bordine T CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Crutchfield D Office of Nuclear Reactor Regulation
References
NUDOCS 8305020294
Download: ML20204F861 (6)

Text

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@ Consumers Company General offices: 1945 West Parnall Road, Jackson, MI 49201 e (517) 788 0550 April 26, 1983 Dennis M Crutchfield, Chief Operating Reactors Branch No 5 Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - RESPONSE TO NRC STAFF QUESTIONS ON MCPR TECHNICAL SPECIFICATION CHANGE REQUEST Consumers Power Company submitted a technical specification change request on December 20, 1982 to replace the current operating limits based on the Minimum Critical Heat Flux Ratio (MCHFR) with the Minimum Critical Power Ratio (MCPR).

Technical specification limits based on MCPR are consistent with the transient analyses submitted July 15, 1981 in the Systematic Evaluation Program (SEP)

" Plant Transient Analysis of Big Rock Point Nuclear Reactor" and the NRC requirement of August 3, 1977.

Consumers Power Company committed in a conference call on March 15, 1983, to provide the staff with the results of studies used in determining the sensitivity of the MCPR calculations with respect to the input parameters.

The attached pages comprise our response to staff questions on sensitivity studies performed on the RETRAN analysis. As stated in our December 20, 1982 submittal, this request is necessary for Big Rock Point to increase thermal power level. Your approval is requested prior to our scheduled start-up following the next refueling outage. A ten week refueling outage is currently scheduled to commence on May 13, 1983.

Thomas C Bordine Staff Licensing Engineer CC Administrator, Region III, USNRC NRC Resident Inspector-Big Rock Point Attachment 0\

oc0483-0182a142 8305020294 830426 PDR ADOCK 05000155 P PDR

SENSITIVITY STUDY OF RETRAN ANALYSIS Consumers Power Company Big Rock Point Plant April 26, 1983 4 pages ic0483-0182bl42

SENSITIVITY STUDY OF RETRAN ANALYSIS After submittal of the " Plant Transient Analysis of Big Rock Point Nuclear Reactor" Report on July 15, 1981, a sensitivity study was performed in the latter part of 1981. The sensitivity study involved varying particular parameters and determining the effect on plant parameters, especially the effect on the minimum critical power ratio (MCPR). The analysis was done in the same manner as the Systematic Evaluation Program (SEP) analysis using the most limiting transient, Turbine Trip without bypass (TTw/oBP) as the base case from which to vary the parameters and compare the resulting MCPR.

The discussion of the different sensitivity studies follow. In the majority of studies the parameters were varied by + 25%. The parameters were varied over a relatively large range so the effect on MCPR would be readily apparent.

1. Turbine Valve Closure Time - The turbine Valve closure time was varied by

+ 25% from the TTw/oBP base case value of 0.5 seconds. The effect of varying the valve closure time is very small. The MCPR increases for both increasing and decreasing the valve closure time. The results are shown in the table below.

Base Case +25% -25%

Valve Closure Time (sec) 0.5 .625 .375 Initial CPR 1.681 1.681 1.681 MCPR 1.406 1.409 1.410 MCPR Change from N/A +.003 +.004 Base Case

2. Core Bypass Flow - The core bypass was varied by +25% from the TTw/oBP flow rate. Flow through the core was varied so the flow rate through the reactor vessel as a whole was the same as in the base case. As can be seen from the table below, increasing the bypass flow decreased the MCPR i but the ACPR for the transient remained the same. This was not true for j the bypass flow decrease.

Base Case +25% Bypass -25% Bypass Initial CPR 1.681 1.661 1.697 I

MCPR 1.406 1.386 1.411 MCPR Change from N/A -0.020 +0.005 Base Case-l ACPR During Transient 0.275 0.275 0.286 nu0483-0182c142

S:nsitivity Study 2 Big Rock Point Plant l April 26,- 1983

3. Screm Rod Worth - The scram curve used for rod worth combined the slowest reactivity insertion rates from Cycle 17, Beginning of Cycle (B0C) and End of Cycle (EOC) scram curves. This was further reduced by 25% as an additional conservatism. For the sensitivity study, the scram curve used in the base case was increased and decreased by 25%. As can be seen from the table below, changing the scram rod worth has virtually no effect on MCPR.

Base Case +25% -25%

Initial CPR 1.681 1.681 1.681 MCPR 1.406 1.407 1.406 MCPR Change from N/A +.001 0 Base Case

4. Scram Time - The scram curve in the Big Rock Point RETRAN Model includes a 0.375 second delay time to account for the time interval between the energizing of the scram solenoid valve and the beginning of rod movement.

In the sensitivity study, the 0.375 second delay was increased by 33% to 0.5 seconds. The resulting decrease in the MCPR was 0.004. The results are shown in the table below.

Base Casa 0.375 Delay Base Case +33%(.5 Delay)

Initial CPR 1.681 1.681 MCPR 1.406 1.402 MCPR Change from N/A -0.004 Base Case

5. S/A The values used for delayed neutron fraction (S) and prompt neutron lifetime (A) in the RETRAN model were for BOC-17 and EOC-17. A sensitivity study was performed on the values used in the TTw/oBP base case (BOC-17) by varying S/A by +25%. This resulted in a neglible change in the MCPR. In contrast to the sensitivity study, the actual predicted change in S/A from the start of Cycle 17 to the end is only 14.3%. The results of the sensitivity study follow.

i nu0483-0182c142

Sensitivity Study 3 Big Rock Point Plant April 26, 1983 Base Case +25% S/A -25% /A

$/A Value (sec-1) 192.8 241.0 144.6 Initial CPR 1.681 1.681 1.681 MCPR 1.406 1.408 1.403 MCPR Change from N/A .002 .003 Base Case

6. Doppler Coefficient - As stated in the July 15, 1981 submittal, it was determined that the most negative values of the doppler coefficient were in G1 fuel at EOC and the least negative values occur in the G2U fuel at B0C. G2U B0C doppler coefficients were used in TTw/oBP transient analysis. In the sensitivity study the doppler coefficient was increased by 25% and reduced by 12.5% and 25% from the values used in the TTw/oBP analysis (base case). _The results are shown below.

Base Case +25% -12.5% -25%

Initial CPR 1.681 1.681 1.681 1.681 MCPR 1.406 1.414 1.402 1.398 MCPR Change from N/A +.008 .004 .008 Base Case

7. Void Coefficient - The void coefficients used in RETRAN analysis are shown in Table 2.6 and explained on Page 4 of the July 15, 1981 submittal. The TTw/oBP tran.iient was one where positive reactivity was added by the collapse of the voids and hence the B0C void coefficients were used.

These coefficients were further increased by 25% for analysis conserva-tism. Two sensitivity runs were made, one increasing the coefficients in the base RETRAN case by an additional 25% and another decreasing the base case by 25%. The sensitivity cases conclude that increasing the nominal BOC-15 void coefficients by 25% is conservative. The results are shown below.

l Base Case +25% -25%

Initial CPR 1.681 1.681 1.681 l MCPR 1.406 1.395 1.442 MCPR Change from N/A .011 +.036 Base Case t

nu0483-0182c142

S:nsitivity Study 4 Big Rock Point Plant April 26, 1983 Conclusion The results of the sensitivity studies demonstrated that even for large changes in the various inputs to the RETRAN model, the MCPR value changed very little.

Percent Change MCPR-MCPR(Base)

Parameter in Parameter MCPR Base Turbine Valve Closure +25% +.2%

-25% +.3%

Core Bypass Flow +25% -1.4%

-25% +.3%

Scram Rod Worth +25% +.1%

-25% 0 Scram Time +33% .3%

$/A +25% +.1%

-25% .2%

Doppler +25% +.6%

-12.5% .3%

-25% .6%

Void Coefficient +25% .8%

-25% +2.6%

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