ML20107N022

Nonproprietary CPC Methodology Changes for Arkansas Nuclear One Unit 2 Cycle 5

ML20107N022
Person / Time
Site:	Arkansas Nuclear
Issue date:	10/31/1984
From:	ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
Shared Package
ML19269A782	List: 2CAN118402, Forwards Proprietary & Nonproprietary CEN-288(A), CPC Methodology Changes for Arkansas One Unit 2 Cycle 5. Proprietary Rept Withheld (Ref 10CFR2.790) ML20107N022
References
CEN-288(A)-NP, NUDOCS 8411140376
Download: ML20107N022 (8)

Text

_ _

Docket No. 50-368 .

CEN-288( A)-NP -

CPC Methodology Changes for Arkansas Nuclear One Unit 2 Cycle 5 October, 1984 Combustion Engineering, Inc.

Nuclear Power Systems Power Systems Group Windsor, Connecticut 8411140376 841109 PDR ADOCK 05000 P

LEGAL NOTICE THIS REPORT WAS PREPARED AS AN ACCOUNT OF WORK SPONSORED RY COMBUSTION ENGINEERING, INC. NEITHER COMBUSTION ENGINEERING NOR ANY PERSON ACTING ON ITS BEHALF:

A. MAKES ANY WARRANTY OR REPRESENTATION, EXPRESS OR IMPUED INCLUDING THE WARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTA81UTY, WITH RESPECT TO THE ACCURACY, COMPLETENESS, OR USEFULNESS OF THE INFORMATION CONTAINED IN THl3 REPORT, OR THAT THE USE OF ANY INFORMATION, APPARATUS, METHOO, OR PROCESS DISCLOSED IN THIS REPORT MAY NOT INFRINGE PRIVATELY OWNED RIGHTS;OR

8. ASSUMES ANY UA81UTIES WITH RESPECT TO THE USE OF, OR FOR DAMAGES RESULTING FROM THE USE OF, ANY INFORMATION, APPARATUS, METHOD OR PROCESS DISCLOSED IN TH13 REPORT.

7-

1.

SUMMARY

Combustion Engineering on behalf of Arkansas Power & Light Company (AP&L) will implement a number of CPC algorithm and constant changes for Arkansas Nuclear One Unit 2 (ANO-2) Cycle 5. A brief review of each CPC change is provided here. All of the changes are evolutionary in nature and represent small differences in the algorithms themselves. These changes are presently being implemented for San Onofre Unit 2 Cycle 2 (Reference 3.1) . A schedule for implementation of the changes at ANO-2 is provided in Table 1.

Detailed algorithm descriptions in the form of functional specifications and discussions of methodology changes are provided in Reference 3.2.

TABLE 1 ANO-2 CYCLE 5 MILESTONES DATE MILESTONE ACTIVITY 10/31/84 Submit CPC Software Change Document to NRC 2/1/85 Submit Reload License Amendment Request to NRC (including the Reload Analysis Report) 3/1/85 End of Cycle 4 3/15/85 Submit CPC Phase I/ Phase II Test Reports to URC 5/1/85 Startup of Cycle 5 1

1 ---- _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ .

2.

SUMMARY

OF CPC ALGORITHM AND CONSTANT CHANGES 2.1 Corrected LPD Penaltv Factor The Cycle 5 algorithms include correct implementation of the Local Power Density (LPD) Penalty Factor which AP&L committed to implement for Cycle 5 in their letter of October 18, 1983 (2CAN108307). The correction consists of modification of the CPC software to be consistent with the functional specification. This correction was first implemented in the Palo Verde Nuclear Generating Station Unit 1 (PVNGS-1) Cycle 1 software (Reference 3.3) and has been reviewed and approved by the NRC.

2.2 Hot Pin to Hot Channel Conversion Presently, POWER provides a hot pin power distribution in the form of an axial power distribution and appropriate radial peaking factors. This information is used in STATIC as if it were a hot channel power distribu-tion. CETOP-D (the design code) makes the conversion from hot pin to hot channel power directly and thus comparisons between CETOP-D and STATIC (the CPC calculation) in the CPC uncertainty analysis implicitly account for the difference.

For Cycle 5, constants will be inserted into the heat flux equations in STATIC to convert from hot pin to hot channel heat flux distribution explicitly in CPC. This change will provide a more physical approcch to the DNBR calculation. It involves minor algorithm adjustments in the CPC software and updates to the functional specification. The explicit conversion from hot pin to hot channel power was first implemented in the PVNGS-1 Cycle 1 software (Reference 3.3) and has been reviewed and approved by the NRC.

2.3 Non-Uniform Heating (F,) Correction Factor Modification Prasently, the calculation of the non-uniform heating correction factor (Fk) in the CE-1 correlation in UPDATE does not differentiate between small changes about steady state and larger changes during transients.

This results in a larger DNBR penalty than necessary during steady state operation.

2

For Cycle 5, the Ek_ algorithm will be modified to provide variable Fk factor adjustments , As a result, more accurate calculations of F will be made for small changes in operating conditions (i.e., near steady state) while calculating more conservative values of F f r large changes in operating conditions k

(i.e., transients). This change was first implemented in the PVNGS-1 Cycle 1 software (Reference 3.3) and has been reviewed and approved by the NRC.

2.4 PFMLTD and PFMLTL Range Limits The positive range limit on the CEAC penalty factor multipliers,

., will be shifted from to . This change is in anticipation of the need for a different range of values in the future and has no impact on the calculational logic. This change was first implemented in the PVNGS-1 Cycle 1 software (Reference 3.3) and has been reviewed and approved by the NRC.

2.5 Reactor Coolant Pump Pressure Rise Calculation l

The calculation of pressure rise across the reactor coolant pump in the FLOW algorithm will be modified to account for forward flow through the pump when the pump rotor is locked at or near zero RPM. This change was first implemented in the PVNGS-1 Cycle 1 software (Reference 3.3) and has been reviewed and approved by the hRC.

2.6 Reactor Power Cutback Algorithms will be added to the CPC and CEAC (Control Element Assembly Calculator) for detecting the actuation of a Reactor Power Cutback (RPC) event, for using off-line calculated RFC penalty factors, and for allow-ing the CPC calculation to more closely model core conditions without generating an inadvertent trip in the event of a RPC. Since ANO-2 does not have a RPC system, the effect of these algorithms will be nullified through the appropriate data base constants. Addressable constarts were also added to the CPC and CEAC to define the duration that the RPC flags can remain set. For ANO-2 these addressable constants will be set to zero.

, 3 1

The RPC algorithm' change was implemented in the PVNGS-1 Cycle 1 software (Reference 3.3) and has been reviewed and approved by the NRC.

2.7 Modification of Heat Flux Distribution Extrapolation in STATIC For certain CEA configurations, radial peaking factor assignments, and/or radial peaking factor multipliers, it is possible _

This _

, which results in a CPC channel trip.

Experience has shown that this condition occurs only at low power with a partially rodded core. This change ~

]inthetopofthecore.

[ ^

]Acheckis

)

~

performed for If any are detected, "

This change will result in a reduction

].

in the probability of unnecessary reactor trips. This change is being implemented in the San Onofre Nuclear Generating Station Unit 2 (SONGS-2)

Cycle 2 software (Reference 3.2) and is currently being reviewed by the NRC.

2.8 UPDATE Algorithm Improvement The UPDATE algorithm of CPC provides rapid and conservative recalculation of DNBR based upon the detailed DNBR calculation contained in the STATIC algorithm, updated state parameter measurement's, and derivatives of the DNBR. As part of the overall CPC uncertainty analysis, comparisons of UPDATE and STATIC-predicted DNBRs based on --

are used to quantify this conservatism. Presently, the UPDATE algorithm of CPC applies a penalty to the updated DNBR at all times.

4

r

- AnalgorithmchangewillbeimplementedinCycle5whichwill{

). In essence, this change minimizes excess conservatisms at normal operating conditions, but retains these conser-vatisms during transient operation.

TheCPCUPDATEalgorithmisbasedon{

]

I Thenewmethoduses{)).

]

For planned changes in plant operating conditions the change in state parameters will be relatively slow, thus causing -

~

For this type of operation )totheUPDATE

~

algorithm which will ensure the conservatism of the calculated DNBR.

This penalty factor along with the rest of the CPC calculations and 5

{ - - _ _ _ _ _ _ _ _ _ _ _ __

penalty factors en'sures that the DNBRs calculated during transients and accidents will generate a trip signal when needed.

The UPDATE penalty factor modification therefore ensures that the safety margin of the CPCs is maintained for all modes of operation. It will increasethesteadystateoperatingmargin}

which will reduce the possibility of spurious trips and increase plant operational flexibility. This change is being implemented in the SONGS-2 Cycle 2 sof tware (Reference 3.2) and is currently being reviewed by the NRC.

2.9 Power Uncertainty As a Function of Core Power Level Addressable penalty bias constants are used to adjust the thermal power and neutron-flux power level in the CPCs. Present methodology implements values of these penalty biases to bound the power level range set by CPC design requirements.

~

For Cycle 5, This change is being implemented in the SONGS-2 Cycle 2 software (Reference 3.2) and is currently being reviewed by the NRC.

2.10 Temperature Shadowing Factor Modification The temperature shadowing factor (TSF) is used to correct the CPC neutron flux power for decalibration effects resulting from changes in coolant density. A multiplier is applied to the neutron flux power calculation to correct ex-core detector response for inlet moderator temperature _

~

changes. In the current algorithm, the TSF is a ,

~

of moderator temperature change which is measured at start-up. The uncertainty in the measurement of the TSF is accommodated in the overall uncertainty term ,

6

~

the TSF on moderator temperature using a

{ex-core detector)temperaturewillbeimplementedforCycle5.

The calibration procedures will be modified accordingly.

[

]ThischangewillallowtheTSFuncertaintytobe included directly in the factor itself. This ensures a conservative correction to TSF at temperatures different from the calibration temper-ature without requiring unnecessary uncertainty allowance near the calibration temperature (which should be near nominal conditions). This change is being implemented in the SONGS-2 Cycle 2 software (Reference 3.2) and is currently being reviewed by the NRC.

3. REFERENCES i

k 3.1 CEN-284(S)-P, " Safety Analysis and CPC Methodology Changes for San Onofre Nuclear Generating Station Unit 9 No. 2 and 3," Dockets 50-361 and 50-362, June 1984.

I 3.2 CEN-281(S)-P, "CPC/CEAC Software Modifications for San Onofre Nuclear Generating Station Units 2 and 3," June 1984.

3.3 Enclosure 1-P to LD-82-039, "CPC/CEAC Software Modification for System 80," March 1982.

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