Text

Safety Evaluation Supporting Changes to Data Base Constants for Facility Core Protection Calculator Software
	ML17299A328
Person / Time
Site:	Palo Verde
Issue date:	05/15/1985
From:	; NRC
To:	;
Shared Package
ML17299A327	List: ML17299A326; ML17299A328;
References
	NUDOCS 8506060298
	Download: ML17299A328 (24)
	v • d • e

~

'I

~

l ENCLPSURE 1

SER ON PVNGS-1 CPC/CEAC SOFTWARE

'1. 0 INTRODUCTION By letter dated December 3, 1984 (Ref. 1), Arizona Public Service Company (the licensee) submitted the following documents for staff review:

(a)

CEN-25(v)-P, Revision Ol, "PVNGS-1 Cycle 1

CPC and CEAC Data Base Listing", September 1984

'(b)

CEN-217(v)-P, Revision 02, "CPC/CEAC System Phase I Software

..Yerification.Test Report", September,

1984, and (c)

CEN-219(v)-P, Revision 02, "CPC/CEAC System Phase II Software Verification Test Report", September 1984.

These documents were submitted in connection with Revision Ol of the Palo Verde Unit 1

CPC Software where changes had been made to some data base constants.

Even though no modification has been made to the CPC software algorithm, the changes to the values of the CPC data base constants have to be reviewed to ensure that the Specified Acceptable Fuel Design Limits (SAFDL) on Departure from Nucleate Boiling (DNB) and central fuel melt will not be violated during normal operations and anticipated operational occurrences.

850bob0298 85051 5 ADOCK 050005a8 PDR

I P

~

2.0 STAFF EVALUATION

2. 1 Chan es to Values of Data Base Constants Reference 1 provides a brief description of the changes made to the data base constants and the reasons for these changes.

They are as follows:

(1)

Chan e to the Flow Constants As a result of design modifications to the reactor coolant

pumps, the pump characteristic curve (head-capacity curve) has changed.

This change has resulted in a slight change in pump related flow constants.

In response to 'a staff question (Ref. 2), the licensee provided a

comparison between the original and the revised pump characteristic curves and the curve-fit results.

'The licensee also provided a

comparison between the original and the revised flow constants for the curve fits of the pump characteristic curves.

A comparison of the calculated reactor coolant flow rate for a four-pump coastdown case was also made between the original and the revised pump characteristics.

The results show only small difference in the coolant flow rates.

We therefore conclude that the change to the flow constants is acceptable.

The values of these constants in the data base listing are consistent.

with the revised values.

(2)

Chan e to DNBR Set oint In the original CPC software, a conservative ONBR setpoint of 1.25 was used while awaiting NRC review of a DNBR limit using the statistical combination of uncertainties (SCU) (Ref. 3).

Subsequently, the staff review of the SCU topical was completed and a

DNBR limit of 1.231 was approved.

Therefore, the DNBR setpoint in the Revision 01 of the PVNGS-1 CPC software is changed from 1.25 to 1.231 as shown in the data base listing.

This change is acceptable.

(3)

Chan e to Hi h Pressurizer Pressure Set oint The high pressurizer pressure trip setpoint in the Revision 01 of the CPC software is changed to be consistent with the value specified in Table 2.2-1 of Technical Specification, "Reactor Protective Instru-mentation Trip Setpoint Limits".

This change, as shown in the data base listing, is acceptable.

(4)

Chan e to CEAC-Ino erable Penalt Factors The penalty factors (PF) applied to the DNBR and local power density (LPD) calculations with both CEACs out-of-service are reduced in Revision Ol of the CPC software.

The licensee, in response to a staff I

question (Ref. 2), attributed the penalty factor reduction to two aspects.

First, when both CEACs are out-of-service, new restrictions are imposed in the Technical Specification 3.3.1 where the lead control rod bank insertion is limited to 15 percent and the reactor power is reduced by 15 percent within one hour of CEA misalignment.

The credit for this power reduction is considered in the determination of the required penalty factors to be applied when CEAs are inoperable.

The penalty factors consist of a static component and a time-dependent component accounting for the effect of xenon redistribution.

The xenon redistribution component of the PF can therefore be reduced by an amount corresponding to the power reduction.

Secondly, the maximum increase of planar radial peaking factor (Fxy) from a CEA withdrawal event was originally calculated with 2-D ROCS.

The more detailed 3-D ROCS is used in the Fxy calculation which results in lower maximum Fxy and lower penalty factors.

These two considerations have resulted in lower overall PFs applied to DNBR and LPD calculations.

The licensee provided a quantitative analysis to derive the final PFs required for Revision 01 of CPC software system.

These values are consistent with the penalty factors provided in the data base listing and are acceptable.

~

.I (5)

Chan e to Inward CEA Deviation Penalt Factors

. The single CEA inward deviation penalty factors are reduced to 1.0 in Revision 01 of the PVNGS-1 CPC software.

With the reduction in PFs, additional restrictions have been added to the Palo Verde Technical Specifications.

These restrictions include CEA insertion limits imposed in TS 3.1.3.2 and TS';1.3.6, and a power reduction within ten minutes after a CEA deviation per Figure 3. 1.2.B.

The PF reduction is

~ also made possible by crediting the required overpower margin '(ROPM) reserved in the Core Operating Limit Supervisory System (COLSS).

With the reduction of PFs, the SAFDLs on DNB and fuel melt are assured by the ROPM preserved by COLSS in the determination of power operating limit and by the restrictions on CEA insertion and the requirement on power reduction.

This approach has been reviewed and approved for

'operation of San Onofre Units 2 and 3.

In response to a staff question, the licensee also provided a quantitative analysis specific to Palo Verde Unit I to justify the reduction of inward CEA deviation PFs to 1.0.

We conclude that this change is acceptable.

However, we also plan an additional evaluation of the integrated revised system due to the increased intricacy of the

CPC, COLSS and Technical Specifications.

A comprehensive evaluation will be performed on a

generic submittal" of the CPC software modifications to be submitted in August 1985 as a part of a CPC/COLSS Improvement Program initiated by the CE CPC Oversi'ght Committee. 'n the meantime, we request that, within three months after the end of Cycle 1 operation, the licensee submit a

g1 summary of the CPC operational experience at Palo Verde Unit I providing, in. particular, a record of operator interactions with the CPC and COLSS systems and a history of CPC initiated reactor trips.

~

,I (6)

Chan e in EXECUTIVE. Pro ram..;-.

Two changes are made to the EXECUTIVE program.

The CEAC display coding is modified in that the color code assigned to the deviated CEA will blink white (rather than black) on a black background on CRT.

This results in a better visibility; also, the internal testing process and auto-restart process after a loss of power are improved to stabilize the operators module digital display.

Since these changes do not impact the CPC reactor tt ip function and since the changes represent improvement to the EXECUTIVE system, these changes are acceptable.

2.2 CPC Software Verification The licensee performed the CPC/CEAC.Phase I and Phase II software veri-fication tests to insure proper implementation of the software.

The test results are presented in CEN-217(v)-P, Revision 02 and CEN-219(v)-P, Revision 02.

These tests were performed in accordance with the approved verification procedures described in CEN-39(A)-P, Revision 02.

The results show that all test results are within their respective acceptance criteria and, and therefore, no software implementation error exists.

3.0

SUMMARY

ANO CONCLUSION The staff has reviewed the data base listing and the Phase I and Phase II Verification Tests associated with Revision 01 of the Palo Verde Unit I CPC/CEAC software system.

We have found that the changes to the CPC data base constants are acceptable and that the Phase I and Phase II test results have verified the correctness of CPC/CEAC software implementation.

Therefore, Revision 01 of the CPC/CEAC system is acceptable for PVNGS-I Cycle I operation.

However, even though the reduction of penalty factors is found acceptable for PVNGS-1 Cycle 1 operation, we plan an additional evaluation of the integrated revised system due to the increased intricacy

of CPC, COLSS and the Technical Specifications.

A comprehensive evaluation will be performed on.a generic submittal of the CPC software modifications to be submitted in August 1985 as a part of CPC/COLSS improvement program initiated by the CE CPC Oversight 'Committee.

In the meantime, we request that the licensee submit a summary of the CPC operational experience at Palo Verde Unit I within three months after the end of Cycle 1 operation.-

The summary should include a record of operator, interactions with CPC and COLSS systems and a history of CPC initiated reactor trips.

REFERENCES 1.

Letter from E.

E.

Van Brunt, Jr.

(Arizona Public Service Company) to G.

W. Knighton (NRC), "Palo Verde Nuclear Generating Station (PVNGS)

Unit 1, Docket No. STN-50-528, PVNGS Unit 1 CPC/CEAC Software, File:

84-056-026, G.1.01. 10", December 3, 1984.

""2.

CEN-297(v'), Rev.

1, "Response to NRC questions on PVNGs-1 Rev. Ol, CPC Software",

February 1985.

3.

Enclosure I'-P to LD-82-054, "Statistical Combination of Uncertainties, Combination of System Parameter Uncertainties in Thermal Margin Analyses for System 80," submitted by letter from A. E. Scherer (CE) to D. G.

Eisenhut (NRC), Docket No. STN-50-470F, May 14, 1982.

ENCLOSURE 1

SER ON PVNGS-1 CPC/CEAC SOFTllARE

1. 0 INTRODUCTION By letter dated December 3, 1984 (Ref. 1), Arizona Public Service Company (the licensee) submitted the following documents for staff review:

(a)

CEN-25(v)-P, Revision 01, "PVNGS-1 Cycle 1

CPC and CEAC Data Base Listing", September 1984

'(b)

CEN-217(v)-P, Revision 02, "CPC/CEAC System Phase I Software

..Verification. Test Report", September.

1984, and (c)

CEN-219(v)-P, Revision 02, "CPC/CEAC System Phase II Software Verification Test Report", September 1984.

These documents were submitted in connection with Revision Ol of the Palo Verde Unit 1

CPC Software where changes had been made to some data base constants.

Even though no modification has been made to the CPC software algorithm, the changes to the values of the CPC data base constants have to be reviewed to ensure that the Specified Acceptable Fuel Design Limits (SAFDL) on Departure from Nucleate Boiling (DNB) and central fuel melt will not be violated during normal operations and anticipated operational occurrences.

2.0 STAFF EVALUATION

~ p

2. 1 Chan es to Values of Data Base Constants Reference 1 provides a brief description of the changes made to the data base constants and the reasons for these changes.

They. are as follows:

(I)

Chan e to.the Flow Constants.

As a result of design modifications to the reactor coolant

pumps, the pump characteristic curve (head-capacity curve) has changed.

This change has resulted in a slight change in pump related flow constants.

In response to 'a staff question (Ref. 2), the licensee provided a

'comparison between the original and the revised pump characteristic curves and the curve-fit results.

The licensee also provided a

comparison between the original and the revised flow constants for the curve fits of the pump characteristic curves.

A comparison of the calculated reactor coolant flow rate for a four-pump coastdown case was also made between the original and the revised.

pump characteristics.

The results show only small difference in the coolant flow rates.

We therefore conclude that the change to the flow constants is acceptable.

The values of these constants in the data base listing are consistent with the revised values.

(2)

Chan e to DNBR Set oint In the original CPC software, a conservative DNBR setpoint of 1.25 was used while awaiting NRC review of a DNBR limit using the statistical'ombination of uncertainties (SCU) (Ref. 3).

Subsequently, the staff review of the SCU topical was completed and a

DNBR limit of 1.231 was approved.

Therefore, the DNBR setpoint in the Revision Ol of the PVNGS-I CPC software is changed from 1.25 to 1.231 as shown in the data base listing.

This change is acceptable.

(3)

Chan e to Hi h Pressurizer Pressure Set oint The high pressurizer pressure trip setpoint in the Revision 01 of-the CPC software is changed to be consistent with the value specified in Table 2.2-1 of Technical Specification, "Reactor Protective Instru-mentation Trip Setpoint Limits".

This change, as shown in the data base listing, is acceptable.

(4)

Chan e to CEAC-Ino erable Penalt Factors The penalty factors (PF) applied to the DNBR and local power density (LPD) calculations with both CEACs out-of-service are reduced in Revision Ol of the CPC software.

The licensee, in response to a staff 1