ML17306B263

Forwards Response to NRC 921211 Request for Addl Info Re Core Damage Assessment Procedures Utilized at Facilities, Consisting of Results of Investigation Into Possible Omissions in Procedures

ML17306B263
Person / Time
Site:	Palo Verde
Issue date:	01/11/1993
From:	Conway W, James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
212-01122-WFC-A, 212-1122-WFC-A, NUDOCS 9302020004
Download: ML17306B263 (6)

Text

acczx,zmTze DocuvtzNT DIsmrOuTrod sYsTzm REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS) 1 ACCESSION NBR:9302020004 DOC.DATE: 93/Ol/ll NOTARIZED:

NO DOCKET FACIL:STN-50-528 Palo Verde Nuclear Station, Unit 1, Arizona Publi 05000528 STN-50-529 Palo Verde Nuclear Station, Unit 2, Arizona Publi

. 05000529 STN-50-530 Palo Verde Nuclear Station, Unit 3, Arizona Publi 05000530 AUTH.NAME AUTHOR AFFILIATION CONWAY,W.F.

Arizona Public Service Co. (formerly Arizona Nuclear Power R

LEVINE,J.M.

Arizona Public Service Co. (formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION I

MARTIN,J.B.

Region 5 (Post 820201)

SUBJECT:

Forwards response to NRC 921211 request for addi info re core damage assessment procedures utilized at facilities, consisting of results of investigation into possible omissions in procedures.

DISTRIBUTION CODE:

IE01D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: General (50 Dkt)-Insp Rept/Notice of Violation Response NOTES:STANDARDIZED PLANT Standardized plant.

Standardized plant.

D 05000528 05000529 D

05000530 D

RECIPIENT ID CODE/NAME PD5 PD INTERNAL: ACRS AEOD/DEIB AEOD/TTC NRR MORISSEAUiD NRR/DLPQ/LPEB10 NRR/DREP/PEPB9H NRR/PMAS/ILPB 2

NUDOCS-ABSTRACT OGC/HDS1 RGN5 FILE 01 COPIES RECIPIENT LTTR ENCL ID CODE/NAME 1

1 TRAMMELL,C 2

2 AEOD 1

1 AEOD/DSP/TPAB 1

1 DEDRO 1

NRR/DLPQ/LHFBPT 1

1 NRR/DOEA/OEAB 1

1 NRR/PMAS/ILPB 1

1 1

NRR/PMAS/ILRB12 1

1 OE 'R 1

1 '~EG F LE 02 1

1 COPIES LTTR ENCL 1

1 1

1 1

1 1

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1 1

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1 1

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1 EXTERNAL: EG&G/BRYCE,J.H.

NSIC 1

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1 NRC PDR 1

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D NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM PI-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

D S

TOTAL NUMBER OF COPIES REQUIRED:

LTTR 25 ENCL 25

Arizona Public Service Company P,O, BOX 53999

~

PHOENIX. ARIZONA85072-3999 I'

~

WILLIAIAF. CONWAY EXECUTIVEVICEPRESIDENT NUCLEAR 212-01122-WFC/ACR January 11, 1993 Mr. John B. Martin Regional Administrator, Region V

=

U. S. Nuclear Regulatory Commission 1450 Maria Lane, Suite,210 Walnut Creek, California 94596-5368

Reference:

Letter dated December 11, 1992, from K. E. Perkins, Jr., NRC Region V, to W. F. Conway, APS

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Units 1, 2, and 3 Docket Nos. STN 50-528/529/530

Response

to NRC Request for Information File: 93-056-026 93-070-026 The referenced letter requested that Arizona Public Service Company (APS) respond to information pertaining to core damage assessment procedures at PVNGS. The enclosure to this letter provides the results of APS'nvestigation.

If you'have any questions regarding. this letter, please contact Mr. A. Carter Rogers at (602) 340-4041.

WFC/ACR/c.d.

Sincerely,

/v(~

Enclosure - Response to NRC Request for Information cc:

J. A. Sloan 9302020004 930111 PDR ADOCK 05000528 P

PDR

ENCLOSURE RESPONSE TO NRC REQUEST FOR INFORMATION DATED DECEMBER 11, 1992

RESPONSE.TO NRC REQUEST FOR INFORMATION DATED DECEMBER 11, 1992 NRC REQUEST I

The core damage assessment procedures at PVNGS contain omissions which can result in non-conservative results when core damage assessments (CDA) are performed.

These omissions may include:

1.

Failure to account for 1-131 production from Te-131.

2.

Failure to account for Xe-133 production from four (unspecified) precursors.

These omissions may cause errors in CDAs of up to 20%.

APS RESPONSE A review conducted in response to this NRC request determined that the PVNGS radiological core damage assessment procedure does not account for post shutdown I-131 production from Te-131, and Xe-133 production from four precursors.

However, the assertion that this calculational approximation results in non-conservative core damage assessments was not substantiated.

Not accounting for the post shutdown production of l-131 and Xe-133 from precursors could result in a post-accident assessment that core damage is slightly greater that it actually is, but could not result in underestimating core damage.

PVNGS procedure, 74CH-9ZZ47, "Core Damage Assessment,"

was developed using Combustion Engineering Owners'roup

'(GEOG) Task 467, "Development of the Comprehensive Procedure Guideline for Core Damage Assessment," issued in July, 1983.

The methodology compares post shutdown reactor coolant fission product concentrations against theoretically determined (using the ORIGEN code) available fission product inventory of the core at the time of shutdown.

For these two determinations (time-of-shutdown fission product inventory and post=

shutdown reactor coolant-fission theoretical product concentration),

production from parent decay was examined.

In accordance with the guidance provided by GEOG Task 467, production of fission nuclides from precursors (parents) is accounted for in determining the core's fission product inventory at the time of shutdown.

However, parent decay is not accounted for in determining post-shutdown reactor coolant concentrations.

Task 467 suggests, and 74CH-9ZZ47 directs, simple decay correction factors for fission nuclides from the time of post accident sampling to the time of reactor shutdown, not taking into consideration parent decay production.

Page 1

- The result of neglecting parent decay is a decay-corrected activity (concentration) greater than what is actually present.

For the case of l-131, the error would be approximately 3%.

For the Xe-133 case, the error would be approximately 20%. Furthermore, this approach is generic for all fission nuclides produced from precursor'(parent) decay after shutdown.

The assertion that this can result in non-conservative core damage assessments is not substantiated.

Since the measured Xe-133 concentration (or l-131) would be greater than-what.would be predicted without considering the precursors, the assessment results in a greater core-damage estimate than what is actually present.

C I

The ramifications of over-estimating core damage could potentially result in minor changes in the public evacuation thresholds, i.e.,

public evacuation could.=be recommended, unnecessarily or slightly sooner than actual conditions warrant.

The change in threshold, if one did occur, would. vary with the nuclide being utilized in the radiological analysis assessment of core damage.

For example, for the two isotopes of concern (I-131 and Xe-133), reliance on l-131 would not cause any significant change in-the recommendation, while'eliance on Xe-133 could possibly result in either unnecessarily categorizing the core damage as an NRC Fuel Damage Category 3

(Intermediate Cladding Failure-10%

to 50%

gas gap release) or making the recommendation to evacuate slightly earlier than otherwise.

This could result in an unnecessary or earlier 2 to 5 mile radius evacuation (upon Category 3 entry). The next evacuation threshold for Palo Verde (5 to 10 mile radius) does not occur until Category 5 (Initial Fuel Pellet Overheating).

Due to the confirmation nuclides necessary for such..

a categorization, the over-estimation of Xe-133 would not have any impact on this or any subsequent evacuation scope.

The radiological core damage assessment is one of four assessment methods utilized by PVNGS.

Use of the other assessment methods, in conjunction with the CDA procedure; provides reasonable assurance that any recommendations for protective action will be appropriate.

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