ML20024E296

Forwards Orthotropic Plant Assumptions, Effect of Thermal Stress Analysis Procedure, Forces on Shear Key, Displacements at South Wall & West Wall Shear Keys, & Effect of Liner Forces in Safety Margins

ML20024E296
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	08/03/1983
From:	Bordine T CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Crutchfield D Office of Nuclear Reactor Regulation
Shared Package
ML20024E297	List: ML20024E296 ML20024E301 ML20024E304 ML20024E309 ML20024E312 ML20024E314
References
NUDOCS 8308100206
Download: ML20024E296 (13)

Text

I Consumers Power Company General offices: 1945 West Parnali Road, Jackson, MI 49201 * (517) 788-0550 August 3, 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 CONCERNS - AMENDMENT 2 TO SPENT FUEL RACK ADDITION

" CONSOLIDATED APPLICATION" Our analysis of the structural integri,ty of the spent fuel pool at elevated temperatures was enclosed in Consumers Power Company submittal dated January 10, 1983. NRC Staff review and response to our submittal yielded a Safety Evaluation Report dated May 16, 1983, requesting additional information before the Staff would approve plant start-up following our current refueling outage. Additional information was supplied by letter dated June 8 and June 10, 1983. Consumers Power Company committed, at a meeting held on July 6, 1983 with NRC Staff representatives, to provide additional analyses addressing two concerns. These two concerns were related to the handling of material properties input associated with orthotropic plate conditions; and, the use of " temperature steps" instead of " time steps" in the ANSYS computer code.

Consumers Power Company representatives again met with NRC Staff representa-tives on July 28, 1983 to present the results of these additional analyses.

These results are provided as attachments to this letter and are identified as follows:

1.

Orthotropic Plate Assumptions 2.

Effect of Thermal Stress Analysis Procedure 3.

Forces on the Shear Key 4.

Displacements at South Wall and West Wall Shear Keys 5.

The Effect of Liner Forces in the Safety Margins.

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oc0783-0239a142 8308100206 830803 PDR ADOCK 05000155 P

PDR

D M Crutchfield, Chief 2

Big Rock Point Plant NRC Staff Concerns-Amendment 2 August 3, 1983 It was concluded during the July 28, 1983 meeting that the attachments satisfy the stated concerns and the results are within the proper bounds. We request your formal approval and prompt issuance of the Safety Evaluation Report so that the Big Rock Point Plant can be started up on schedule.

%dasaw Thomas C Bordine Staff Licensing Engineer CC Administr$ tor, Region III, USNRC NRC Resident Inspector-Big Rock Point Attachment l

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oc0783-0239a142 l

LICENSING CORRESPO!1DENCE - RECORD

SUMMARY

DATE: DRAFT - for review & comment DOCKET 50-155 LICENSE DPR-6 BIG ROCK POINT PLANT RESPONSE TO STAFF QUESTIONS ON MCPR TECHNICAL SPECIFICATION CHANGE R

SUMMARY

Provides Consumers Power Company responses to staff questions on RETRAN and COBRA analyses by describing parameters and assumptions used to calculate MCPR.

j COMMITMENTS MADE:

None.

C0hMITHENTS CLOSED:

6/8/83 telephone commitment.

Previous MRC/CP Co Correspondence:

Special Distribution:

CPC letters dated 8/31/77, 10/30/78 KDBrienzo 7/15,81, 11/04/82, 4/26/83 WJBeckius JAUmbarger JRKneeland AIR No UFI No I

740-22*13*10 I

740-70*01*07*01 Individuals Providing Information:

Individuals Assigned Responsibility for Implementing Commitments:

GFPratt None.

JAMeincke Concurrences:

(

Cost / Budget Impact:

Actual / Potential Year (s)

DJVandeWalle Materials / Parts l

GFPratt Labor JAMeincke Capital-WGFogg Contractors Originator:

i LLCastiglione ic0783-0237bl42 f.

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DRAFT - Rev 1 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 STAFF QUESTIONS ON MCPR TECHNICAL SPECIFICATION CHANGE REQUEST A conference call was held between Consumers Power Company and the NRC on July 3, 1983. The purpose of the call was to discuss the Minimum Critical Power Ratio (MCPR) technical specification change request submitted on April 26, 1983. As a result of that conversation, lists of RETRAN analysis parameters and COBRA analysis assumptions were developed for further clarification.

The attached response reflects our interpretation of the questions presented by the Staff during the above referenced telecon. As stated in our December 20, 1982 submittal, this request is necessary for Big ock Point to increase thermal power level. Your prompt approval is requested.

t Thomas C Bordine (Signed)

Thomas C Bordine Staff Licensing Engineer CC Administrator, Region III, USNRC NRC Resident Inspector-Big Rock Point Attachment 1

oc0783-0237a142 Y

e Consumers Power Company Big Rock Point Plant Docket 50-155 RETRAN ANALYSIS SENSITIVITY (Draft) 4 pages ic0783-0237bl42 V'

r RETRAN SENSITIVITY ANALYSIS Question Show that the RETRAN analysis is conservative by evaluating the sensitivity of the model (in terms of AMCPR/ initial MCPR) to the following parameters:

Void Coefficient Doppler Coefficient Scram Reactivity Prompt Neutron Heating Void Fraction Model (Homogeneous Assumption)

Fuel Heat Transfer Model System Inertia (L/A)

Core Pressure Drop (or Core Bypass Flow)

Separator Inertia (L/A)

Separator AP Steamline Pressure Loss (Loss Coefficient)

Evaluate to include Sensitivity Study or if sensitivity is known, provide a written basis why the analysis assumed a conservative value of the parameter.

Response

The results of sensitivity studies that had been performed in the latter part of 1981 were submitted in correspondence to the NRC dated April 26, 1983.

These studies reported on the sensitivity of Turbine Valve Closure Time, Core Bypass Flow, Scram Rod Work, Scram Time, p/A, Doppler Coefficient, and Void Coefficient. The results of further sensitivity studies follow.

One difference in the following analysis from the previous sensitivity study was the new analysis uses the RETRAN/ COBRA model developed for the Technical Specification Change Request of December 20, 1982.

Therefore, this study has.

an initial Critical Power Ratio (CPR) of 1.591 as opposed to 1.681 of the 1981 study.

1) Steam Line Pressure Loss - The steam line loss coefficients in junctions 140, 150, 160, 170 and 180 (see attachment 1) were increased 50% and decreased 50% from the base case. The results below show that MCPR is insensitive to changes in steam line pressure losses.

Base Case 0.5 x Base Case 1.5 x Base Case Coefficients Coefficients Initial CPR 1.591 1.591 1.591 MCPR 1.320 1.321 1.320 MCPR change from N/A

+0.001 0.0 base case MCPR-MCPR N/A

+0.08%

0.0%

Base) 100%

(Base) l nu0783-0237c142

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RETRAN Analysis Big Rock Point Plant Date Steam Separator Inertia - The steam separator inertia (b/A base case of 2) 0.63 was increased by 100% to 1.26.

A neglible decrease in MCPR'was observed as a result of doubling the separator inertia. The results are shown below.

Base Case 2.0 x Base Case Inertia Initial CPR 1.591 1.591 MCPR 1.320 1.318 MCPR change from N/A

-0.002 base case MCPR-MCPR(Base) x 100%

(Base)

3) Fuel Heat Transfer Model - The gap. conductivity was varied to show sensitivity of MCPR to changes in the heat transfer parameters for the fuel.

In the RETRAN model, the base case gap conductivities are listed in Table I (" Gap Conductivities"). These conductivities were selected so the fuel temperatures and stored energies at different power level; matched those calculated in XN-76-21, " Design Report for Big Rock Point Reactor Reload G-3 Fuel, Addendum 4."

The fuel temperature in XN-76-21 was calculated by the GAPEX computer code. The results of the sensitivity runs are shown below. As can be seen, for even large changes in Gap conductivity, MCPR changes very little.

Base Case

+25%

+300%

Initial CPR 1.591 1.591 1.591 MCPR 1.320 1.308 1.298 MCPR change from N/A

-0.012

-0.022 from base case' MCPR-MCPR(Base)

/A

-0.9%

-1.7%

(Base)

TABLE I Gap Conductivities Temp (*F Base Case

+25%

+300%

(Btu /ft-hr-F) 0.0

.044

.055

.132 333.0

.052

.065

,.156

.12

.150

.36

,900.0 1200.0

.1745

.218125

.5235 2500.0

.1745

.218125

.5235

4) Prompt Neutron Heating - In the RETRAN/ COBRA analysis for the MCPR Technical Specification Change Request, 97% of the heat was assumed to be nu0783-0237c142 c,

RETRAN Analysis 3

Big Rock Point Plant Date generated in the fuel and 3% in the moderator, which is consistent with NX-76-21. The normal valves for heat generated in the full range from 90 to 95%. The 97% figure used in the RETRAN/ COBRA is conservative because j

reducing the heat gen'erated in the fuel correspondingly reduces the heat flux and increases the MCPR.

5) System Inertia and Separator AP - Sensitivity studies were not done on these parameters because they would have no effect on the MCPR for the turbin trip without bypass transient. The MCPR in the transient occurs very early (<3 seconds) before any variations in flow can manifest themselves. The results of varying the steam line pressure loss and core i

bypass sesnitivity studies verified this. The A CPR did not change even though the parameter was varied.

6) Void Fraction Model (Homogeneous Assumption) - In a homogeneous model the i

vapor velocity equals the liquid velocity as opposed to a slip model where the vapor velocity is greater than the liquid velocity.

In the homogeneous model, the equality of the vapor and liquid flows over predicts the void fraction as compared to a slip model.

In the turbine trip without bypass transient where the void collapse produced the rapid reactivity addition, it is conservative to use a homogeneous model because it produces the largest reactivity addition.

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BRP SYSTEM NODAL!ZATION DIACRAM I

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Consumers Power Company Big Rock Point Plant Docket 50-155 a

DESCRIPTION OF COBRA ANALYSIS MAJOR ASSUMPTIONS (Draft)-

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I" DESCRIPTION OF COBRA ANALYSIS MAJOR ASSUMPTIONS Question: Describe the method used to calculate MCPR (ie, COBRA analysis).

Discuss major analysis assumptions including:

Friction Factor Form Loss Coefficients Two-Phase Friction Multiplier Gap Conductance Nodalization Time Step Size Link between RETRAN and COBRA Void Fraction Model Subcooled Void Model Heat Transfer Model in different flow regions L/A input Describe the specific input to friction factor and form loss coefficients to justify their conservativeness. Describe why each assumption is conservative.

Response: A one quarter core geometry was used to perform the thermal margin analysis. The single-phase friction factors and form loss coefficients shown in Table I, " Big Rock Point Friction and Form Loss Coefficients," are based upon experimental data obtained by Exxon (Reference 1) during the hydraulic and fretting corrosion tests performed using the Reload G fuel design. The current fuel

' design has the same hydraulic characteristics as the Reload G fuel.

Any minor differences would be insignificant compared to the high form loss coefficients of the flow distribution orifice in each fuel assembly channel.

The Modified Armond void correlation was used for this analysis based upon our analysis of the data contained id Reference 2.

l Several correlations were compared with the General Electric data and the modified Armond model void correlation was~ judged to provide the best results for the data obtained near the operating pressure of the Big Rock Point Plant core. A subcooled void fraction model was not utilized for this analysis. The Armond model was selected for the two phase friction multiplier. A sensitivity study was performed using the homogeneous two phase friction multiplier correlation. The ACPR calculated using the Armond correlation is the same as the ACPR for the homogeneous correlations.

The RETRAN computer code analysis provided the boundary condition of normalized heat flux, core flow rate, core inlet enthalpy and core exit pressure for the COBRA thermal margin analysis. The data

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is read directly from the RETRAN restart file. The location of each of the four above variables plus the location of the transient time parameter are input parameters for the COBRA computer code.

A time step size of 0.2 seconds was selected for most of the COBRA analyses. The line printer plot produced at the end of the COBRA i

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COBRA Analysis Mzjor Anaumptican (Centd) 2 Big Rsck Point Plant Date out is reviewed to ensure that the minimum CPR was found.

If the CPR curve was flat near the minimum, the time step was reduced to ensure that the MCPR was calculated.

The axial node size selected for this series of thermal margin cal-culations is four inches. Since the XNB CPR correlation is based upon channel average properties, a small axial node size is not required. The node size was reduced to approximately three inches for the TTW/0BP Transient and the calculated thermal margins did not change.

The COBRA code analysis did not contain a thermal model of the fuel rods, therefore, the pellet to clad gap conductance was not a required input variable. The normalized heat flux was obtained from the RETRAN analysis as described above.

REFERENCES

1) " Evaluation of hydraulic and Fretting Corrosion Behavior of Big Rock Point Reload G Fuel", XN-73-20, (June 1973).

(Exxon proprietary report.)

2) " Steady State and Transient Void Fraction in Two-Phase Flow Systems.

Final Report for the Program of Two-Phase Flow Investigation.", GEAP-5417, (January 1967).

nu0783-0237d142

TABLE II Big Rock Point Friction and Form Loss Coefficients Inlet K*

Standard channel 13.50 Peripherical channel 69.40 Lower End Fitting

.800 Spacer Grid 1.020 Upper End Fitting 1.060

• Based on nominal flow area of a fuel assembly in the' flow channel.

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