ML20127E670

Safety Evaluation Supporting Amend 66 to License NPF-6

ML20127E670
Person / Time
Site:	Arkansas Nuclear
Issue date:	05/07/1985
From:	Office of Nuclear Reactor Regulation
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ML20127E661	List: ML20127E659 ML20127E670
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NUDOCS 8505200156
Download: ML20127E670 (12)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 56 TO FACILITY OPERATING LICENSE NO. NPF-6 ARKANSAS POWER & LIGHT COMPANY ARKANSAS NUCLEAR ONE, UNIT 2 DOCKET NO. 50-368

1.0 INTRODUCTION

By letters dated November 9,1984 (Ref.1) and January 28, 1985 (Ref. 2),

respectively, Arkansas Power and Light Company (the licensee) proposed changes to the ANO-2 Core Protection Calculator (CPC) methodology and Technical Specifications.

In addition to the proposed Technical Specification changes, the licensee also submitted CEN-289(A)-P (Ref. 3) for a revised fuel rod bow penalty calculation.

In connection with the CPC methodology changes, the licensee by letter dated March 29,1985 (Ref. 4) also submitted CPC/CEAC Data Base Listing, Phase I and Phase II Software Verification Test reports.

Our evaluation of these submittals follows.

2.1 CPC Methodoloqy Changes The changes to the ANO-2 CPC methodology as described in CEN-288(A), "CPC Methodolo

.te,n (10) gy Changes for Arkansas One Unit 2 Cycle 5" (Ref. 5) consist of items. They are evaluated below:

(1) Implementation of LPD PF with Failed CEACs:

.An error was discovered previously in the ANO-2 CPC software where a penalty factor (PF) associated with failure of both Control Element Assembly Calculators (CEACs) was not applied to the Local Power Density (LPD) calculation required by the CPC functional specification. Although the licensee had found no safety implication of this software error, they had comitted by a letter dated Octotter 18,1983 (Ref. 6) to correct the CPC software error prior to initial reactor criticality for Cycle 5.

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proposed modification is to fulfill this commitment to bring the CPC software consistent with the functional specification and is acceptable.

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(2) Conversion of Hot Pin to Hot Channel Peaking Factors:

A discrepancy exists in the ANO-2 CPC software where the hot pin radial

- peaking factors were used as the hot channel peaking factors. This is inconsistent with;the off-line CETOP-D thermal-hydrualic calculation.

The proposed modification is to apply the correct factors of hot channel to hot pin peaking factor ratios to the hot channel power distribution calculation. This modification makes the hot channel linear heat rate distribution consistent with the hot pin' input values.

The modification has been reviewed and approved by NRC for CESSAR-80 t

plants (Ref. 7) such as Palo Verde Unit I and is therefore acceptable.

(3) Transient Adjustment of Non-Uniform Heating Correction Factors:

This modification is related to transient adjustment in the UPDATE program of the non-uniform axial power shape F-factor for DNBR calculation. A new adjustment formula is used for updating the STATIC calculated F-factor based on the updated quality resulting from change in reactor conditions.

The new formula incorporates a coefficient whose value depends on the direction of the change in quality margin, i.e., a constant coefficient is used for the updated quality below the static critical quality where-as another constant coefficient is used for the updated quality greater than the other critical quality. This change has been reviewed and approved previously for CESSAR-80. The licensee has also indicated that the same method is used in the determination of the constant coefficients in the adjustment equation. Therefore,.the modification for ANO-2 is acceptable.

(4) PFMLTD and PFMLTL Range Limits

<The Type II addressable constants PF and PF are the CEAC penalty factors for DNBR an590 calcubIkons. multipliers to When positive L

numbers are input for those multipliers, they are applied to the fractional parts (the part greater than 1.0) of the penalty factors. These multipliers permit adjustment of the slopes of the curves used to derive the penalty factors in the CEACS. The positive allowable range limits of PF and are proposed to be shifted to smaller values. The changeFIR PF th5Nklowable ranges provides flexibility to set the values of PF and PF This change has been approved previously for CESSAR-80 akTks th$$o.re acceptable.

(5) RC Pump Pressure Rise Calculation:

This modification is related to the rapid pump flow coastdown events, such as a locked rotor event, where the pump affinity law does not apply for pumps at near zero speed. The pump pressure rise calculation is modified to include an algorithm in the FLOW program to account for a very rapid occurrence of negative head across a RC pump. This additional algorithm, which applies to the region of the forward flow through the pump at or near zero RPM, makes use of the data provided by the RC pump vendor. A new constant is added to the curve fit coefficients for the pump characteristics for the forward flow-low pump speed region.

This modification represents an improvement to the pump pressure rise calculation and-is consistent with CESSAR-80 and San Onofre 2/3 CPC.

Therefore this modification is acceptable.

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. '(6) Reactor Power Cutback System:

An algorithm for Reactor Power Cutback (RPC) system is added to the ANO-2 CPC software. Tha RPC system is designed to eliminate power imbalance without a reactor trip 'ar large turbine load rejection and loss of one main feedwater pump events. During the RPC mode, pre-detemined smaller penalty factors.for CEA deviation are used by the CPC. After the RPC mode, the CPC' returns to the nomal mode where larger CEA deviation PFs are used by CPC. Since ANO-2 does not have a RPC system, the effect of

. numbers are input for those multipliers, they are applied to the fractional-parts (the part greater than 1.0) of the penalty factors. These multipliers pemit adjustment of the slopes of the curves used to derive the penalty factors in the CEACS. The positive allowable range limits of PF The change 5LE nd a

PF are proposed to be shifted to smaller values.

th5$1owable ranges provides flexibility to set the values of PF and PF This change has been approved previously for CESSAR-80 abTks thNo.re acceptble.

this algorithm will be nullified through appropriate data base constants. The licensee also proposes to add an addressable constant RPCLIM defining the maximum RPC mode duration. As shown in the ANO-2 CPC/CEAC Data Base Listing, RPCLIM (which is designated as TCBSP in the functional design specification) is set to 0 and therefore the reactor power cutback system is nullified. Since the CE CPC Owners Group is planning to standardize the CPC software for all CPC plants, addition of the RPC algorithm, which has been approved for other CPC plants, to the ANO-2 CPC is acceptable. However, use of any value of RPCLIM other than zero will require NRC approval with the RPCLIM detemined through appropriate safety analysis to ensure no violation of the specified acceptable fuel design limit of DNBR.

(7).. Modification of Heat Flux Distribution Extrapolation:

The hot pin axial power distribution is extrapolated in the STATIC l

algorithm by an extrapolation from a 20-node. representation to a 21-node representation. For certain CEA configurations, this extrapolation could result in negative values of heat flux in the top node. The heat flux extrapolation algorithm is modified by adding a flux value check to prevent a non-physical zero or negative nodal heat-flux. This modification has been approved for San Onofre Units 2 and 3 (Ref. 8) and is therefore acceptable for ANO-2.

(8) Improvement to UPDATE Algorithm:

The CPC detailed DNBR calculation is performed in the STATIC algorithm i

routine. Since the STATIC calculation is performed only once every two seconds, the DNBR is updated every 0.1 second within the two seconds in-l terval in the UPDATE routine using the STATIC-calculated DNBR and the change in the state parameters, such as hot channel mass flow, heat flux and quality at the minimum DNBR node. Presently, the CPC UPDATE algorithm applies a penalty to the updated DNBR at all times. This algorithm is modified so that the penalty factor is applied only when the updated-DNBR i

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that the methodology used for generating penalty factors is the same as that used in San Onofre. Therefore, this modification is acceptable.

(9) Power Measurement Uncertainty:

Power measurement uncertainties are conservatively added to the thermal and neutron powers in the CPC core power calculation. These uncertainties

' include the CPC neutron flux synthesis error, the secondary calorimetric power measurement error, the secondary calorimetric power to the CPC power calibration allowance, and the thermal-power transient offset.

These mrtainties-are treated as bias terms and are added together to be app..ed to CPC through the addressable constants, BERR0 and BERR2, which are the overall uncertainty biases for themal and neutron power, respectively. Since the secondary calorimetric power measurement has a higher measurement uncertainty at lower power conditions.due to higher instrumentation error and noise level, the revised CPC software will incorporate an algorithm to calculate the power-dependent measurement uncertainty for the secondary calorimetric power. This approach has been approved for San Onofre Units 2 and 3.

The licensee also indicated that the same method used in San Onofre is used in ANO-2 to determine the power dependent uncertainty values. Therefore, this modification is acceptable. Since the secondary calorimetric power measurement error is dependent on the power level at which the calorimetric measurement. is performed, an addressable constant PCALIB is added to the CPC for the detemination of uncertainty. PCALIB is defined as the calorimetric power at the time the latest calibration was perfomed.

(10) Temperature Shadowing Factor Algorithm Modification:

The temperature shadowing factor (TSF) is a moderator temperature-dependent multiplier applied to the neutron power calculation in the CPC to correct the excore detector response to the decalibration effects i

due to changes in inlet coolant density. The current CPC calculates T

TSF as a simple function of the change in moderator temperature slope which is determined in start up testing. The modification will be

n made in the calculation of TSF so that TSF is a function of inlet moderator temperature consistent with 'the off-line TSF data. The slope of the correction for temperature is chosen to bound all ex-pected TSF data. Therefore, the TSF uncertainty is included directly in the TSF itself. There is no need to further incorporate the TSF uncertainty in the overall uncertainty factors used in the CPC DNBR and LHR calculations.

In addition, since the TSF algorithm is changed, an addressable constant, TCREF, defined as the reference cold leg temperature, is added to and the TSF correction multiplier, CORR 1, is removed from the CPC addressable constants. This modification has been approved for San Onofre Units 2 and 3 CPCs and the licensee has indicated that'the same method is used in ANO-2 for the determination of the TSF function. Therefore this modification is acceptable.

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': :2.2 CPC/CEAC Data Base Constants By letter dated March 29,-1985(Ref.4),thelicenseesubmittedCEN-296(A),

"ANO-2 CPC and CEAC Data Base Listing" (Ref. 9) and Enclosure 1-P to A-CE-R-92,

" Typical Data Base Constants for Arkansas Nuclear One Unit 2".

The latter document provides those data base constants relevant to the proposed CPC soft-ware changes and the values are extracted from CEN-296(A). The licensee also indicated that the methodology used for generating these constants is the same as used for San Onofre Units 2 and 3 which has been approved previously. We have reviewed the values of these constants and find them acceptable.

2.31 Verification of CPC/CEAC Software Modification Implementation:

The. implementation of the CPC/CEAC software modifications translates the system functional requirements into modules of machine executable coding and integrates these modules into a'real time software system. The overall CPC/CEAC software implementation is verified through the Phase I an' Phase II software verification tests. _By letter dated March 29, 1985, the-licensee submitted ANO-2 CPC/CEAC Phase I and Phase II test reports, CEN-298(A) (Ref. 10)'and CEN-162(A) (Ref. 11).

The Phase I. test was performed at the CEAC Single Channel Unit on relatively small, single-entry / single-exit segments of modules. The objective was to verify the implementation of CPC/CEAC ~ software. Sufficient test cases were

, chosen to exercise each functional branch in the application program and executive software system. Expected results for the application program test cases'were generated by either the CPC FORTRAN Simulation Code or by h&nd calculations by the test engineer based on the system functional requirements.

When test case input had been selected and expected results had been generated, a test tape was prepared -to be read by the automated Phase I test program.

Whenever the actual value differed from the expected value by more than 0.1

- percent, an analysis -of the error was perfonned to assure that the deviation was not caused by a coding error. There were several branches not exercised because of the fact that the assigned constant values made it impossible to branch on certain conditions.

In these cases the module was verified by inspection to assure correct implementation. The executive software was tested through the debug program, CLUB, which was used to-insert test execution and to examine results. The report indicated that the overall Phase I test was performed in accordance with the approved Phase I test procedures and that the

- test results show no coding error in the application program and executive software. Therefore, the implementation of CPC/CEAC software into machine executable modules has been verified correctly.

The objectives of the Phase II tests are to verify that the CPC/CEAC software modifications have been properly integrated with the CPC/CEAC software and system hardware, and that the static and dynamic operation of the integrated system is consistent with the predictions of design analyses. These objectives were achieved by comparing the response to that projected by the CPC/CEAC FORTRAN Simulation Code. The test was perfonned in the Single Channel CPC and the test. cases were selected in accordance with the approved procedure described in CEN-39(A)-P, Revision 02 (Ref 12).

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. The Phase II testing consisted of Input Sweep Tests (ISTs), Dynamic Software Verification Tests (DSVTs) and Live Input Single Parameter Tests (LISPS).

ISTs were utilized to determine the processing uncertainties inherent in the CPC/

CEAC designs. Thousands of cases were run in the ISTs-and the resulting uncertainties were factored into the acceptance criteria for the DSVT and LISP.

The DSVT is a real time exercise of the CPC software to verify the dynamic response of the integrated CPC software with design analyses by detemining whether the initial DNBR and LPD calculations and the trip time of each transient are within the acceptance criteria predicted by the FORTRAN Simulation Code...In contrast to the DSVT where the transient CPC input values are read from a storage device, the LISP test is a real-time exercise with transient input values generated from an external source and read through the CEAC/CPC input hardware. The LISP test is to verify that the dynamic response of the trip time of the integrated CPC/CEAC software / hardware system is consistent with the design analysis prediction during operational modes approximating plant conditions. These tests have shown that in all cases the CPC/CEAC calculated results are within the acceptance criteria. Therefore, we conclude that the CPC/CEAC software has been implemented correctly.

3.0 Rod Bow Penalty:

The ifcensee proposed in its letter of January 28, 1985 (Ref. 2) to revise the DNBR limit used by the CPC.

In support of the this DNBR limit revision, the licensee submitted a topical report CEN-289(A) entitled " Revised Rod Bow Penalties for Arkansas Nuclear One Unit 2" (Ref. 3).

Fuel rod bowing results in closure of the channel gap between fuel rods and therefore affects thermal-h The effects of fuel rod bowing on the critical heat. flux (ydraulic behavior.CHF)'and DNBR are accounted for th penalty on DNBR. The method of calculation of rod bow penalty is described in CENPD-225 and its supplements (Ref. 13). This method applies a statistical convolution of the CHF data (both bowed and unbowed) and channel gap closure data to derive a rod bow penalty on DNBR. The method has been approved by NRC except for a scaling factor for channel gap closure calculation. The~ scaling factor is used for extrapolation of channel gap closure data from one fuel agsemblytoanotherfuelassemblyofdifferentgeometry. A scaling factor of L /I was derived in CENPD-225, where L is the span length between two adjacent grids and I is the moment of inertia of fuel rod cladding. This scaling l

factor was based on the fact that the deflection at the mjd-span of a simple column subject to a compressive load is proportional to L /I.

However, since the mechanism governing rod bowing is complicated and not well established, the derivation of the scaling factor assuming a simple column s questionable at best. The staff therefore rejected the scaling factor of L{/I proposed in CENPD-t 225 and imposed a scaling factor of L/I, which results in more severe rod bowing i

when extrapolating from the 14x14 to 16x16 fuel assemblies.

l ANO-2 irradiation fuel data to support the scaling factor of L[/I.C N-289(A) provides The data obtained as part of a CE/EPRI Fuel Performance Characterization program consist of five sets of channel width measurements from three fuel bundles at different i

fuel exposures. Figure 1 of CEN-289(A) provides a comparison between the measured channel closure data from the 16x16 fuel bundles and the calculg/I, res ted results from the channel closure equation using scaling factors of L/I and L l

for extrapolating from the 14x14 to 16x16 bundles. The values of L's and I's l

for both the 14x14 and 16x16 fuel-assemblies and the scaling factors L/I and 1

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L/I(whtceL/I=(L/I)16x16/(L/I)14x14andL/I=(L/I)16x16f(L/I)14x14)are provided in Table 3 of CEN-289(A). Since L/I is larger than L /I use of the i

scaling iactor L/I in the chgnnel closure equation will calculate more severe channel closure than using L /I. Figure 1 of CEN-j89(A) shows that the calcu-lated channel closure results using both L/I and L /I are much higher than the 2

- measured channel closure. Therefore, the licensee concluded that use of L /I

- as a scaling factor is justified. However, the channel closure equation includes a batch-to-batch variation correction factor of greater than 1.0 which distorts the calculated channel gap closure to a more severe value. For the purpose of-

. evaluating the ability of a scaling factor to fit the data, we removed the batch-to-batch correction factor from the equation. The staff calculations with re-moval of the batch-to-batch correctiog/I provides a better prediction than show that use of the scaling factor L

- and still results in a more conservative (more severe) prediction of chan closure than the measured data. We therefore conclude.that the scaling factor of L.

2 is acceptable for ANO-2 fuel. This scaling factor of L /I rather than L/I will be used in ANO-2 for the calculation of fuel rod bowing augmentation

factor and poison rod bowing augmentation factor.

The rod bow penalty or DN8R is re-calculated using the approved method described ig Supplement 3 to CENPD-225 with the exception of the scaling factor being L /I instead of L/I. The input to the calculation is also changed as follows:

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The hot rod average hegt flux is changed from 0.387x10 6

.to 0.374x10 Btu /hr-ft 2.

The reactor pressure is reduced from 2475 to 2422 psia e

The licensee indicates that these new values are expected to bound future cycles. Therefore use of these values in the rod bow penalty calculators is.

- acceptable. Figure 4 provides a rod bow DNBR penalty as a function of fuel burnup. Specifically, at fuel exposure of 30,000 MWD /MTU, the rod bow penalty ig"0.5 percent DNBR. This figure is the result of calculations using the L /I correction and the new values of hot rod average heat flux and reactor i-pressure. Since we now find these to be acceptable, this rod bow penalty is j

. acceptable.

.4.0 Technical Specification Changes:

l-The staff has reviewed the proposed modifications to the ANO-2 Technical i

Specifications as presented in the letter dated January 28, 1985. Our l

evaluations follows.

l 4.1 DNBR:

4 The DNBR limit in Technical Specifications 2.1.1.1, Safety Limits Reactor Core DNBR, Table 2.2 Limiting Safety System Settings Reactor Trip Setpoints, Bases ?.1.1, Reactor Core, and Bases 2.2.1, Reactor Trip Setpoints, is to be changed from 1.24 to 1.25.

The Surveillance Requirement 4.2.4.4 on l

rod bow penalty is to-be deleted. As result of application of statistical combination of uncertainties described in CEN-139(A) (Ref.14), the DNBR limit i

of 1.26 was approved by the staff. The DNBR Ifmit of 1.26 includes a fuel l

rod bow penalty of 2.0% on DNBR. Starting in Cycle 3, the HID-1 spacer grids I~

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. are used in ANO-2 fuel assemblies to replace the standar~d grids which were used in the previous fuel assemblies and the test assemblies in the develop-ment of the CE-1 critical heat flux correlation. The staff had imposed a penalty of 0.01 on DNBR to account for CHF effect due to the slight difference between the HID-1 and standard grids. This penalty of 0.01 should be added to the DNBR limit. The DNBR limit trip setpoint of 1.24 was acceptable because the difference between the approved DNBR limit and 1.24 is compensated by an increase in the value of the CPC addressable constant BERR1, which is a penalty factor applied to the core power in the CPC DNBR calculation. As described in Section 3 of this Safety Evaluation, the rod bow penalty is 0.5 percent at fuel exposure of 30,000 MWD /MTU. Using 0.5 percent rather than 2 percent rod bow penalty, the DNBR limit is 1.24. With the addition of 0.01 DNBR to account for HID-1 spacer grids, the final DNBR limit is 1.25.

Therefore, the proposed Technical Specification change of DNBR limit to 1.25 is acceptable. Since the rod bow penalty and grid effect penalty are already in-corporated in the DNBR limit, there is no need to increase the value of BERRI.

Surveillance Requirements 4.2.4.4 requires that the rod bow penalty on DNBR as a function of fuel exposure should be verified to be included in the COLSS and CPC DNBR calculations at least once per 31 days. As discussed in Section 3, the rod bow penalty has been determined to be 0.5 percent at a fuel exposure of 30,000 MWD /MTU. Because of the physical burndown effect, a fuel assembly with burnup exceeding 30,000 MWD /MTU will not be subject to a limiting DN8R condition, therefore 30,000 MWD /MTU is a cutoff point for rod bow penalty calculation.

Since the ' rod bow penalty of 0.5 percent at 30,000 MWD /MTU has been incorporated in the minimum DNBR limit, the Surveillance Require-ment 4.2.4.4 can be deleted.

4.2 CPC Addressable Constants:

Changes are made to the CPC addressable constants defined in Table 2.2-2,

" Core Protection Calculator Addressable Constants", of the ANO-2 Technical Specifications. These changes are evaluated as follows.

(a) Azimuthal Tilt Allowance (TR):

l' The addressable constant TR is an azimuthal power tilt allowance used in CPC as a power multiplier to increase the hot pin radial peaking. TR is frequently l

changed during restarts following reactor trips with transient core xenon conditions. Technical Specification 3.2.3, Limiting Condition for Operation, requires that the azimuthal power tilt (Tq) be less than or equal to the l

azimuthal power tilt allowance (TR) used in CPC. Surveillance Requirement 4.2.3 specifies that above 20% rated thermal power, the Tq shall be determined to be within the limit (i.e., < TR) by (a) continuously monitoring the tilt with COLSS when the COLSS is oEerable, (b) verifying at least once per 31 days that the COLSS azimuthal tilt alarm is actuated when Tq >TR;'(c) using the incore detectors at least once per 31 days to independently confirm the validity

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of the COLSS calculated Tg; and (d) calculating the tilt at least once per 12 i

hours when the COLSS is inoperable. This LCO limit is to ensure that the design l

safety margins are maintained.

If the LC0 is not met, specific actions are required per Technical Specification 3.2.3.

Therefore, LC0 3.2.3 does prohibit operation with a non-conservative value of TR used in CPC. Previously, COLSS used an " arithmetic average" technique to calculate a core average azimuthal tilt value. Using this method, single noise input is enhanced by accumulating the magnitude component without considering the directional effect. The calcu-lation in COLSS has been modified to use a " planar vector average" technique i

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. _ hich. performs a vector sum of the individual tilt ~ estimates at each axial w

plane for the calculation of the average tilt value of each plane. This planar average technique reduces the noise effects by allowing possible cancellation of some of_ the random components of noise. Therefore, an-appropriately low tilt value is calculated when there is no tilt in the core.

This calculation has also been demonstrated to agree well with the arithmetic average method when there is a true tilt in the core. The planar vector

-average technique for the estimation of azimuthal power tilt is also used in

'the approved CECOR code. Therefore, this modification to COLSS is acceptable.

The purpose of the Technical Specification change to lower the minimum allow-able value of TR is to reflect the reduced COLSS tilt estimate in the situation where there is' no appreciable azimuthal power tilt in the core. However, since.the minimum value of azimuthal tilt is 1.0, use of 1.0 for the TR in the CPC would result in frequent occurrences of the azimuthal tilt exceeding the TR, and therefore violating Technical Specification 3/4.2.3. This would-increase the burden of the plant operators for compliance with the Action requirements specified in the Technical Specification. Therefore, the proposed Technical Specification change to reduce the minimum allowable value of TR from 1.02 to 1.0 is not acceptable. We reconnend that the licensee propose a minimum allow-able TR greater than 1.0 which provide a trade-off in power penalty versus

excessive operator actions.

(b) Power Calibration Constants TPC and KCAL:

-TPC and KCAL are power calibration constants used in the CPC calculations of the thermal (a T) and neutron powers, respectively, to reflect calibration against the-secondary calorimetric power. These calibration constants require frequent change to the CPC during power operation. Technical Specification 3.3.1, Limiting Condition for Operation, specifies that as a minimum, the

-reactor protective instrumentation channels (e.g., CPC, DN8R and LPD functions) and bypasses shall be operable. Since thennal and neutron powers are important patameters in the DNBR and LPD trip functions, Surveillance Requirement 4.3-1

. specifies periodic calibration of the CPC calculated thermal and neutron flux powers.

Specifically, Note #2 of Technical Specification Table 4.3-1 requires that above 15% of rated thermal power, (at least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />)- the linear

. power level signals and the CPC addressable constant multipliers (TPC and KCAL) should be' adjusted to make the CPC delta T power and CPC nuclear power calculations agree with.the calorimetric calculations. if the absolute difference is greater than 2%.

Since the thermal and neutron powers have a direct impact on the CPC DNBR and LPD calculations and respective trip functions, this surveillance requirement

. provides adequate assurance that the CPC calculated reactor powers are either accurate or conservative. The addressable constants TPC and KCAL provide adequate means to ensure that reactor power meets the surveillance requirement.

The licensee is concerned that there may be instances where the calibrations of thennal and neutron powers require the calibration constants to be entered into the CPC outside their allowable ranges specified in Table 2.2-2.

Since the thermal and neutron powers are the primary safety-related parameters in the DNBR and LPD calculations, it is important for these parameters to be within the required calibration limits. Therefore, the proposed changes to lower the allowable values of TPC and KCAL from 0.9 and 0.85 to 0.8 and 0.65, respectively, are acceptable.

. (c) Change from CORR 1 to TCREF:

The Type II addressable constant, point ID No. 98, CORRI is replaced by TCREF, defined as the reference cold leg temperature. This change is necessary due to' the change in the CPC TSF calculational algorithm. The change is accept-able-as described in Section 2.1, Item 10, " Temperature Shadowing Factor Algorithm Modification", of this SER.

(d) Addition of addressable constant RPCLIM:

A Type II addressable constant RPCLIM (Note: RPCLM in the proposed Table 2.2-2, Reference 2, is a typographic error) defined as the reactor power cutback time limit is added as point ID #IO3. This. change is necessary due to the addition of the reactor power cutback algorithm to the ANO-2 CPC, and is acceptable as described in Section 2.1, Item 6, " Reactor Power Cutback System", of this SER.

(e) Addition of Addressable Constant PCALIB:

The addition of PCALIB as a Type I addressable constant is related to a CPC algorithm modification where a power-dependent measurement uncertainty for the secondary calorimetric power is used in the core power calculation.

PCALIB is defined as the calorimetric power at the time of the latest cali-bration. The addition of PCALIB as an addressable constant is acceptable as discussed in Section 2.1 Item 9, " Power Measurement Uncertainty", of this SER.

5.0 Evaluation Findings

The staff has reviewed the changes to the ANO-2 CPC methodolgy, the CPC/CEAC data base document, the Phases I and II CPC verification tests, the revision to the ANO-2 rod bow penalty, and the proposed changes to ANO-2 Technical Specifications.

Based on the evaluation given in the preceding sections, the staff has found all of these items acceptable with the exception of the proposed change to lower the allowable value of the Type I addressable constant TR, azimuthal r

tilt allowance, to 1.0.

The staff recommends that the licensee propose a new L

minimum allowable value of TR greater than 1.0 which provides a trade-off between power penalty and excessive operator actions.

!I 6.0 Environmental Consideration:

This amendment involves a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.

The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents l

that may be released offsite, and that there is no significant increase L

in individual or cumulative occupational radiation exposure. The l

Comission has.previously published a proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 651.22(c)(9).

Pursuant to 10 CFR 951.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

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Conclusion:

We have concluded, based on the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations, and the issuance of the amendment will not be inimical to the common defense and security or to

-the health and safety of the public.

Date: May 7,1985 Principal Contributor:

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REFERENCES:

1.

Letter from J. T. Enos (AP&L) to J. R. Miller (NRC), " Arkansas Nuclear One - Unit 2. Docket No. 50-368, License No. NPF-6, CPC Methodology Changes for Cycle 5", November 9,1984 2.

Letter from T. G. Campbell (AP&L) to J. R. Miller (NRC), " Arkansas Nuclear One - Unit 2, Docket No. 50-368, License No. NPF-6, Proposed Technical Specifications Change Request ANO-2 CPC Update", January 28, 1985.

3.

CEN-289(A)-P, " Revised Rod Bow Penalties for Arkansas Nuclear One Unit 2", Docket No. 50-368. December 1984.

4.

Letter from T. G. Campbell (AP&L) to J. R. Miller (NRC), " Arkansas Nuclear One - Unit 2, Docket No. 50-368, License No. NPF-6, CPC Methodology Changes for Cycle 5, Additional Information Submittal".

March 29, 1985.

5.

CEN-288(A)-P, "CPC Methodology Changes for Arkansas Nuclear One Unit 2 Cycle 5", Docket No. 50-368, October 1984 6.

Letter from J. R. Marshall (AP&L) to J. R. Miller (NRC), " Arkansas Nuclear One-Unit 2, Docket No. 50-368, License No. NPF-6, Correction of CPC Soft-were Discrepancy", October 18, 1983.

7 -P to LD-82-039 " CPC/CEAC Software Modifications for System 80", Dockets STN-50-470F, March 1982.

8.

CEN-281(S)-P, "CPC/CEAC Software Modifications for San Onofre Nuclear Generating Station Units No. 2 and 3", July 1984 9.

.CEN-290(A)-P, Revision 00-P,"ANO-2CPCandCEACDataBasesListing".

Docket 50-368, March 1985.

10, CEN-298(A)-P, Rev. 00, " Arkansas Nuclear One Unit 2, Core Protection Calculator System Phase ! Design Qualification Test Report" Docket No.

50-368, March 1985.

7

11. CEN-162(A)-P, Revison 01-P, "CPC/CEAC System Phase II Software Verifications l

Test Report". Docket No. 50-368, March 1985.

i

12. CEN-39(A)-P, Revision 02,"CPCProtectionAlgorithmSoftwareChange Procedure", Docket 50-368 December 21, 1978.

I

13. CENPD-225-P, " Fuel & Poison Rod Bowing" Combustion Engineering, Inc.

l October 1976, Supplement 3-P, June 1979.

i

14. CEN-139(A)-P, " Statistical Combination of Uncertainties: Combination of System Parameter Uncertainties in Thermal Margin Analyses for Arkansas Nuclear One Unit 2", November 1980.