ML20210V539

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Summary of 970731 Meeting W/W in Rockville,Md to Discuss Axial Offset Anomalies.List of Attendees & Questions Provided by NRC Prior to Meeting Encl
ML20210V539
Person / Time
Issue date: 09/16/1997
From: Craig C
NRC (Affiliation Not Assigned)
To: Matthews D
NRC (Affiliation Not Assigned)
References
NUDOCS 9709240040
Download: ML20210V539 (146)
v • d • e


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NUCLEAR REGULATORY COMMISSION 3

g WAsHINeToN, D.C. SeteHeM 1

September 16.-1997 j

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' MEMORANDUM TO: David Ei. Matthews, Chief -

R Generic lasues and Environmental

' Projects Branch _

Division of Reactor Program Management -

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Office of Nuclear Reactor Regulation FROM:-

Claudia M. Craig, Senior Project Mana

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Generic issues. and Environmental.

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Projects Branch 1

Division of Reactor _ Program Management r y

Office of Nuclear Reactor Regulation-p

SUBJECT:

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SUMMARY

OF MEETING WITH WESTINGHOUSE TO DISCUSS AXIAL

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OFFSETANOMALIES

<The subject meeting was held at the Nucicar Regulatory Commission (NRC) offices in n

Rockville, Maryland on July 31_,1997, between representatives of Westinghouse and the NRC staffc NRR staff requested Westinghouse to' discuss axial offset anomalies (AOA). Attachment.

1 la a list of questions the NRC staff providend Westinghouse prior to the meeting." Attachment 2 ~

' is a list of meeting participants. By separate letter dated August 28,1997; Westinghouse-

' Li-provided both proprietary and non-proprietary' versions of the material presented at the t meeting.; Attachment 3 is a copy of the non-proprisiary version of the presentation material /

The meeting consisted of an introduction which included a description of the AOA

characteristics; the history of the affected plants and a brief discussion of the root cause, a Qtd presentation by Texas Utilities on the Comanche Peak experience with AOA, and a y

presentation by Union Electric Company on the Callaway experience with AOA.' This was.

followed by a proprietary presentation by Westinghouse on the roat cause and finally a presentation on the safety analysis.

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The key characteristics of the AOA are core axial offset becomes r ore negative than predicted,

' typically at bumupe of 5,000 to 10,000 MWD /MTU, incore maps show higher AO deviations for higher power feed assemblies, and flux depressions in the upper half of the core are maximum gg

' below the grids.; AOA has oeen observed in a number of plants for the last several years with a

maximum axial offset observed of -13%.

p Some feed assemblies have sub-cooled nucleate boiling to an extent that enhances crud -

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buildup in the_ upper. spans. This sub-cooled boiling causes boron to concentrate in the porous

crud layer, concentrating a localized neutron poison; The flux'is depressed in the upper regions 7

m c of the core, causing the power to shift to the lower region of the core and resulting in a _ negative -

+

l axial offset. l The boron can be released from the crud layer when the subcooled boiling is QD3Tb

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9709240040 970916 A.(23 rt/- h v d PDR TOPRP.EMVWEST C

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1 2-September 16, 1997..

D Matthews

- The susceptibilty factors for AOA are significant sub-cooled boiling, crud buildup on the fuel and long cycles. From a safety perspective the key impacts are shutdown margin and power

. distribution surveillance factors, Attachments: As stated -

_ cc w/atts:. See next page e

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September 16. 1997

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- D.- Matthews Tho' susceptibility factors for AOA are significant sutH;ooled boiling [ Crud buildup on the fuel and long cycles. From a safety perspective the key impacts are shutdown _ margin and power -

distribution surveillance factors.-

Attachments: As stated l cc w/stts:' See next page -

DISTRIBUTION'

-See attached page DOCUMENT NAME: -7_31_97.h4 OFFICE PGEBna a SRXB;BC(A)

PGEB:(A)SC,,

NAME CCraib AL TCollins W MCase $ h DATE O / R /97 4 / 1/f /97 Cl ' /c? - /97 V

t OFFICIAL RECORD COPY f

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DISTRIBUTION w/ attachments: Summary of July 31i 1997, meeting with

- Westinghouse dated Sentomber 16, 1997 CentrolFile PUBLIC PGEB R/F-MCase CCraig W

W Eddal SCollins/FMiraglia RZimmerman DMatthews BSheron GHolahan TCollins MChattertT HScott, RES Hornstein, AEOD WBurton BWestreich DPowers, RIV.

EKendrick JUh!o LKopp LPhillips s

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QUESTIONS ON WESTINGHOUSE AXIAL POWER DISTRIBUTION ANOMALY

~

' 1)

In addition to Callaw'ay, what other Westinghouse plants have or are experiencing a similar axial power distribution anomaly?

2)

What are the characteristics of these plants in terms of:

l a) cycle length b) boron concentration c) peaking factors i

d) fueltypes l

3)

What type of chemistry cordrol is used to reduce the amount of crud deposition?

4)

What has b6an the effect on shutdown margin in the affected plants?

5)

What are the effects of crud burst in conjunction with reactivity insertion due to transients such as rod ejection?

6)

What are the constituents of the crud deposits?

7)

Do crud deposits have any effect on control rod drop times?

8)

Have any plant trips resulted from crud bursts?

9)

What types of generic communication has Westinghouse issued to licensees concoming this anomaly?

10)

What are the observed effects on TS monthly reactivity balances?

11)

How do boron letdown curves compare with predictions?

1

- 12)

What is root cause of the power distribution anomaly?

t ATTACHMENT 1 4

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WESTINGHOUSE / NRC MEETING AXlAL OFFSET ANOMALIES JULY 31,1997 MEETING PARTICIPANTS NAME ORGANIZATION Egan Wang NRC/NRR/PGEB Jeffrey R. Socker Westinghouse CNFD James W. Knaup Union Electric Co.

Tod A. Moser Union Electric Co.

James R. Dwight Westinghouse Sumit Ray Westinghouse Alan Passwater Union Electric Co.

James Moose Union Electric Co.

Randy Irwic.

Union Electric Co.

Mickey Kiligore TU Electric Roger D. Walker TU Electric Lynn Conner Doc-Search Associater, Job Delunch NAEsco, Seabrook Station Bobby C. Armstrong Southern Nuclear Glenn Nelses WCNOC Pete Kennamore WCNOC Scott Ferguson WCNOC Dan Risher Westinghouse Wdliam Burton NRC/NRR/DRPM/PECB Barry Westreich NRR/DRPW/PDIV-Il Mark Cote Yankee Atomic Joe Kormuth Westinghosue Dale Powers NRC/ Region IV Edward Kendrick -

NRC/NRR/SRXB Jennifer Uhle NRC/NRR/RPSB Larry Kopp NRC/NRR/SRXB Billy Fellers TU Electric David P. Goodman '

TU Electric David Perkini-TU Electric Jchn Bosma TU Electric Steve Maler TU Electric George Sabol Westinghouse CNFD Muffet Chatterton NRC/NRR/SRXB Jim Lyons NRC/NRR/SRXB Larry Phillips NRC/NRR/SRXB ATTACHMENT 2

WESTINGHOUSE NON-PROPRIETART CLASS 3 NRC AOA Meeting Agenda Introduction - Westinghouse Axial Offset Anomaly Charactenstics

)

History of Affected Plants Brief Root Cause Discussion

- TU Presentation LE Pre,sentation I

W Root Cause Presentation t

W Safety Analysis Presentation Discussion 4

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AOA - Key Characteristics l

Core Axial Offset becomes more negative than predicted, typically at burnups of 5,000-10,000 MWD /MTU l

Incore maps show higher AO deviations for j

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higher power feed assemblies Flux depressions in upper half of core are l

maximum below grids i

i Measured and Predicted Axial Offset Callaway Cycle 6 15.0 1

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s Axial Offset Anomaly History of Affected Westinghouse Plants Plant Cycle With AOA Cycle Without Maximum AO AOA Deviation Callaway 1,2,3,7 4

5 5

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9 8

7 9 (op) 13 Millstone 3 1,2,3,5,6 (op) 4 5

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s Axial Offset Anomaly History of Affected Plants Plant Cycle Fuel Type Peaking Factor With AOA (FDH Limit) /

kw/ft Callaway 4

17X17,.360, IFM 1.65 / 5.69 5

17X17,.360, IFM 1.65/ 5.69 6

17X17,.360, IFM 1.65 / 5.69 8

1 TX17,.360, IFM 1.65 / 5.69 9 (op) 17X17,.360, IFM 1.65 / 5.69 Millstone 3 4

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17X17,.360, IFM 1.65 / 5.69 7 (op) 17X17,.360, IFM 1.65 / 5.69 Vogtie 2 3

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Non Westinghouse

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Axial Offset Anomaly History of Affected Plants Plant Cycle Design Maximum HFP With AOA Cycle Length Boron (EFPD)

Concentration (ppm)

Callaway 4

440 1300 5

440 1300 6

450 1400 8

480 1400 9 (op) 470 1400 Mllistone 3 4

510 1700 Vogtle 1 4

430 1650 6

480 1500 7 (op) 490 1500 Vogtle 2 3

470 1600 4

460 1400 5

460 1400 Wolf Creek 9 (op) 520 1550 Catawba 1 8

390 1200 Comanche Peak 2 3

500 1400 Seabrook 5

530 1400 l

l e

AOA Root Cause t

Crud builds up on upper spans ofhigh l

power fuel assemblies i

Boron absorbs into the crud, concentrating a i

i localized neutron poison l

Flux depressed in upper regions of the core, causing AO to move down (negative)

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i AOA Root Cause (Continued) j i

%me feed assemblies have sub-cooled l

nucleate boiling to an extent that enhances crud buildup in the upper spans l

Sub-cooled boiling causes boron to i

l concentrate in porous crud layer Boron can be released from the crud layer l

when subcooled boiling is reduced u

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Susceptibility Factors l

l Significant sub-cooled boiling

- High coolant temperatures j

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- Higher peaking factors j

- High power density L

Crud buildup on fuel L

- Some crud on fuel is not unusual

- Individual plant differences can affect crud j

buildup i

Long cycles i

- High soluble boron

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Safety Significance Impact of AOA on Fuel And Accident Analysis Thoroughly Considered j

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Key Impacts Are Shutdown Margin And j

Power Distribution Surveillance Factors i

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- These Are Updated For Plants With AOA t

l All Fuel /S on-LOCA/LOCA Design And Safety Criteria Continue to Be Met l

No Adverse Impact on Safe Plant Operation i

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r AOA Industry Communications Westinghouse Fuel Users' Group i

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preser_tations i

Westinghouse Reactor Engineers' Seminars l

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j Westinghouse Technology User's Group 1

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Presentation Outline l

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Data from plant instrumentation i

Similarities of affected plants l

Fuel visual examinations for crud deposition Mechanism of AOA Crud chemical analyses Coolant chemistry influence and recommendations 4

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l Axial Offset Anomaly Characteristics l

Flux depressed in top-half of core

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Depression similar at structural and P

L mixing grids Maximum depression just upstream of l

grid AAO driven by feed fuel - largest offset l

in high-power assemblies l

AO deviation starts at 4-10 GWD/MTU

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Hot Channel Sub-Cooled Boiling Duty i

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i Plant / Cycle i

(Solid bars lu!!d in@Caesons of AO ariomaly)

Assasnps.w.s 8 W Chaaae'. '* a ed ca N (Shaded bar - possible AO anomaly) wcouP3s 2 7 25 91 2 A. as tw gewee shape eased d tres!i ture has ased tN f

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L Visual Observations on Fuei i

I Plants / Cycles l

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Callaway EOC 5,6,7 l

Millstone 3 EOC 4 I

i Observed more crud than expected i

(nFirst and largest visual exam campaign j

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Visual Observations on Crud

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i Crud only in top half of fuel. No crud below span l

l

4. Consistent with negative AO.

Most crud in hottest span 6 Feed fuel has more crud than 2CY or 3CY fuel l

l More crud on high power assemblies, faces j

Little or no crud above grid, but increases up f

l span, consistent with flux depression

Axial Offsst Proportional to Crud Index on Fecd Fuel CaNaway Cycle 5 Region G Crud Evaksation I

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8 Axial Offset Proportional to Crud on 2 CY Fuel Callaway Cycle 4 Region E and Cycle 5 Region F Crud Evaluation nu, f

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More Crud on High Power Faces CaNaway Region G Crud index versus Average Power at Assembly Face O

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Callaway CY5 AO change associated with crud release l

1 Trip occurred near EOC 5 AO shift from -4 to +6%

Significant crud release followed trip and restart 4

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Pre-Trip M-P Asial bffeet 1%I

AO Anomaly is Crud Induced i

Crud only in top half of fuel consistent with o

negative offset l

Crud highest just below grids agrees with flux l

depression More crud on assemblies with high AAO Crud release near EOC-5 Callaway associated with rapid AO Shift - 4% to + 6%

Assemblies with largest AAO prior to trip were most affected by the trip

Effects of Crud on AOA Evaluated I

Physical presence of Ni Fe _xO is x

3 4

insufficient to depress flux Increase in extent of sub-cooled boiling i

- Rougher surface

- More nucleation sites I

- Slight increase in surface temperature Boron concentration within crud j

- Liquid within crud enriched by boiling j

- Boron compounc precipitation within crud

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Plant Data Evaluation l

i Plant data analyzed

- Pressure increases

- Power reductions

- Temperature reductions Data indicate boiling insufficient to explain AO deviation I

- Pressure coefficient of reactivity similar to core model i

without voiding

- Anomalous reactivity decreases with power, but still present j

at 70% power Low voiding indicates instantaneous release of reactivity not i

possible Boron concentration in crud is most likely cause of AO deviation f

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NitC floot Cause Analyss AOA ppt i

r Model for Boron Concentration in Crud i

Sub-cooled boiling in porous deposit results in. concentration of soluble boron in liquid i

within the deposit Boron-enriched liquid leads to formation of j

l boron-rich " solids" 1

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Crud Is Medium for Boron Concentration Porous Crud

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Vapor " Chimneys" 5

Vapor Bubbles Coolant in Boron Concentration = C.

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Vapor Out Boron Concentration - 0 i

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l Critical Aspects of Model 4

L Formation of B " solids"in crud requires i

B-concentration in liauid within crud to solubility limit Most of B retained in " solid" form j

[B] in crud sensitive to boiling, thickness 1

- [B] varies as Crud properties important

- Thickness - coolant chem, impurities

- Composition - reaction, adsorption of B Boron concentration, release is reversible i

.l Boron Release and Uptake with Power at Callaway 4

Power reduction to 30% April 7,8,1993 l

l

- Li release of 644g l

- Boron Equivalent (e.g., as LiBO ) = 1012g 2

Power increase to 100%

- Li uptake = 450g

- Boron equivalent = 707g Boron to cause observed Axial offset difference

- Assumes no Bm depletion

+(a.c)

- B release on power reduction =

=1

- B pickup on power increase =

Good agreement with boron model 1

i i

Crud Scraping and Analysis AOA Cycles Callaway EOC 6

't Millstone S EOC 4 Non-AOA Cycle i

Callaway EOC 7 l

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NitC Iloot Cause Analysis AOA ppt i

l Callaway EOC 6 Assemblies Scraped for Crud i

t Axial i

Assy.

Core Assy.

Crud Offset No.

Region Location Power index M-P m 1

I H88 88 C8 1.34

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H12 8A L13 1.30

-8.4 H03 8A N13 0.95

-6.9 G32 7B J9 1.16

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G87 7B M9 0.98 8.4*

I E81 SC H8 0.99 l

I Assemblies not instrumented in cycle 6. AO values based on those of instrumented assemblies symmetrical positions.

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l CALLAWNY EOCs 5&6 CRUD EVALUATION I

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AXIAL OFFSET DIFFERENCE (NEGATIVE) j i

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Callaway EOC 6 Crud Average Surface Concentration and Thickness of Sample Deposits

1. Once-Bumt Fuel High Power (H-88, H-12)

Ave. Power (H-03)

Surf. Conc Ths Surf. Conc Thickness Span mg/dm*

microns mg/tkw microns

2. Twice-Bumt Fuel High Power (G-32)

Ave. Power (G-87)

~~

Surf. Conc Thickness Surf. Conc Thickness Span mg/dm microns mg/dm microns l

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6 Callaway EOC 6 Crud Average Surface Concentration and Thickness i

of Sample Deposits (contd>

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3. Thrice-Bumt Fuel l

Average Power (E-81)

Surface Conc Thickness 1

Span mg/dm microns

' Analysis suspect due to small amount of crud.

i con.c=m io es 89. MS 209 (64564 i

Callaway EOC 6 Crud Composition (Preliminary)

Concentrations in Weight Percent (Span 6) l l

I i

t i

b I

k i

I l

i i

t NHC 11001 Cause Arudysis AOA ppt 4

i t.

Millstone 3 EOC 4 Crud Data Axial Offset Assembly Number Relative Power Crud index (M-P) %

-7.2 1.29 l-

  • u>

-8.3 F-88 j_

1.29 F Average Surface Concentration and Thickness of Crud Thickness Surface Conc.

(microns)

.,y, (mg/dm )

Span 9

Corsammio #96 IIS WI504 "Only one sample from span 48

MILLSTONE 3 EOC 4 CRUD ANALYSIS l

AVERAGE COMPOSITION ON F-ASSER88 LIES (WT. %)

+(s.c) i t

i i

l

  • Only one sample from span 48.

Millstone 3 Feed Fuel Crud EOC 2 vs. EOC 4 Average Surface Concentration mg/dm*

span EOC2 EOC4 Ratio C4/C2

_.__t i

Cottedson to #96 ll6 (6/15/'37) 1

)

(

~

Callaway EOC 7

?

l Assemblies Scraped for Crud

SUMMARY

OF CALLAWAY CYCLE 6 AND 7 OPERATM)NAL DATA i

i C$8 3

Cycle 7 i

i Power at AO Value Amoesutdy Poorer at AO Valise Amoesntdy i

12004

(%)

Cnsd 11998

(%)

Cnssi Irulem l

F/A RAWD/RETU leM9ex WREWRfiU

'~ ~

H - 12 0.488

-1.3 1.300

-4.4 H. se 1.044

-2.1 1.340

-11.8 l

J -3s 1.321

-1.8 t

J - 40 1.305

-1.9 J - 93 1.31

-1.8 1

I

Callaway CY 6, CY 7 Crud Comparisons Average Surface Concentration and Thickness - Span 6 Feed Fuel Twice Bumed Fuel CY6' CY7 CY 6 CY7' l

H-12, H-88 J-38, J-40, J-39 G-32, G-87 H-12, H-88 mg/dm p

mg/dm p

mg/dm p

mg/sw

.p

  • (ax) m h

e Corredson to 895-213 (6/15/97)

O

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L Callaway Crud Chemical Composition Avenage C-;_.g ::r -; of Crud frone Span S l

froen High Power Feed Fuel frosse Cycles e and 7 7

+(as)

L L

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l I

k i

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1 a

L I

Summary of Crud Scrape Data i

l 1

Crud thickness in proportion to extent of AOA L

Crud concentrations as expected, except l

+(s.c) j

-~

(

Ni/Fe ratios >

Crud removal observed when driving forces for crud deposition decreased l

l l

l I

NRC Hool Cause Arolysis AOA ppt

i i

Mechanism of AOA Some level of sub cooled boiling on feed fuel Sub-cooled boiling exacerbates crud deposition Boron concentrates within porous crud deposit Under some conditions, solubility limit of B-rich solid, e.g., LiBO, exceeded 2

L, Power suppression due to B-rich solid within crud.in l

top spans of high-power fue!

NitC 11001 Cause Analysis AOA ppt lL -

f-l Approaches for AOA Mitigation

)

i Minimize extent of sub-cooled boiling through core i

(

design optimization Minimize crud deposition through coolant chemistry control

+

- Li/B pH control strategy

- Elevated pH at BOC

- Coolant corrosion product management 4

I i

Nur pana Caeete Analyses AOA pot

Axial Offset Anomaly Safety Evaluation

(

i Nuclear Regulatory Commission 7/31/97 i

t J. R. Secker

)

Westinghouse Commercial Nuclear Fuel Division I

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i Plant Experience l

h I

~

Reactivity Changes Associated With Axial o

l Offset Anomaly Occur Slowly Boron Compounds No Longer Present in f

l l

Crud On Return to Critical Following Plant Trip (~12-24 hours)

Boron Compound Returns to Crud During l

i Power Ascent i

I 3

i

'~

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l

~

l l

Plant Experience i

Effect of Small AO Deviations Are Much i

l Smaller Than Uncertainties / Conservatism Applied to Safety Analysis Inputs AOA Does b ot Increase Control Rod Drop l

Time t

AOA Has Not Caused Any Plant Trips j

4 I

i 1.

l Conservative Assumptions for Safety Evaluation i

i

[

Small Rapid Reactivity Release From Liquid j

Boric Acid Concentrated in Cmd 9

j ofTotal Reactivity Associated With AOA l

i Release Rate i.

~

~

Observed Plant Behavior Indicates This j

Assumption is Very Conservative l

Dissolution of Boron Compound Occurs Slowly l

Enough (Hours) to Not Affect Safety Analysis Assumptions 1

~

l i

i l

Conservative Assumption for l

Shutdown Margin i

Assumes Instantaneous Reactivity Addition l

Following Plant Trip Very Conservative Assumption Relative to i

Plant Behavior - Dissolution of Boron Compound Does Not Occur Instantaneously t

~-

f Fuel / Core Analysis l

Fuel Related Inputs to Safety Analysis j

I Most Parameters Are Not Affected and i

Remain Bounded By FSAR Safety Analysis 4

l Reactivity Coefficients, Kinetics Parameters, Power Distributions l

l Parameters Affected:

Shutdown Margin t

l Relaxed Axial Offset Control (RAOC) Peaking l

Factor Surveillance Factors, W(zj 4

2

~

Fuel / Core Analysis l

I i

s DNBR j

- Crud Has Negligible Affect on DNBR

- Core Limits Remain Applicable for DNB Protection Fuel Rod Design

- Most Design Criteria Unaffected l

- Corrosion Model Database Includes Plants With Crud /AOA - Callaway and Millstone 3

- Results in Fuel Temperature Increase at Intermediate Burnups. BOC Temperatures are Still the t

i Highest x

~

l

i 3

Non-LOCA Accident Analysis t

q i

All Non-LOCA Events Reviewed 4

l Most Accidents Not Affected

- Input Parameters Remain Bounded

)

i

-- HZP Events Not Effected Since Boron Compound Not Present at 4

l HZP l

- Beginning of Cycle Events Not Affected Since Cmd is Not Present l

- Limiting DNB Events Result in Increased Subcooled Boiling - No l

Additional Reactivity Insertion i

Accidents Sensitive to Transient Reactivity Release Maintain Margins To Safety Analysis Limits 9

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Non-LOCA Accidents l

Crud Release Rod Withdrawal At Power Core Analysis Shows Substantial Margin To l

Maximum Reactivity Insertion Rate Without I

Crud l

l Limiting Case is Not Maximum Reactivity

)

Insertion Rates - Intermediate Rates Show Minimum DNBR Increased Reactivity Insertion Rate Results in Earlier Plant Trip n

t Non-LOCA Accidents j

l Crud. Release Rod Ejection At Power l

i

- Very Fast Transient l

- Plant Trip Occurs in 0.1 Sec I

- Control Rod Insertion in Core in 0.5 Sec l

- Nuclear Power Rise Limited By Doppler Feedback - Thermal l

l Power Increase is Small l

l

- Small Change in Clad Temperature l

- Although There is Little Time for Crud Release to Occur, Event

?

Was Evaluated Assuming Crud Release From Ejected Rod

)

Assembly and Surrounding Assemblies

- Bounding Reactivity Insertion And Peaking Factor Limits Still l

Met 4

12 i

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Loss of Coolant Accidents 1

i Power Shapes Remain Bounded l

Reactivity From Crud Release Offset By Voiding (Large Break) and Trip (Small Break)

Beginning of Cycle Fuel Temperatures Are Still Highest l

l Since Presence of Crud At Later Burnups Results in Only f

a Small Fuel Temperature Increase t

i on Small Break LOCA Minimal PCT Impact No Affect on Large Break LODA PCT Since BOC is f

Limiting (No Crud) j I

i

~-

o

i Safety Evaluation Summary Impact of AOA on Fuel And Accident l

Analysis Thoroughly Considered i

Key Impacts Are Shutdown Margin And j

Power Distribution Surveillance Factors l

These Are Updated For Plants With AOA i

l All Fuel /N~on-LOCA/LOCA Design And l

Safety Criteria Continue to Be Met No Adverse Impact on Safe Plant Operation I

^

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oct'

= Mr. Moholas J. Liperulo

"!n.ifEe Electric Corporation Mail Stop ECE 415 P.O. Box 355 Pittsburgh, PA 15230-0355 Mr. Henry A. Sepp Westinghouse Electric Corporation

' Mail Stop ECE 4-07A P.O. Box 355 Pittsburgh, PA 15230-0355 -

' Mr. Andrew Drake, Project Manager Westinghouse Owners Group-

- Mail Stop ECE 5 ' P.O. Box 355 Pittsburgh, PA 15230-0355 i

.j -

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  • f umiso STATES p

)Z2 NUCLEAR REGULATORY COMMISSION 4

'#e..

+

September 16, 1997 MEMORANDUM TO: David B. Matthews, Chief Generic issues and Environmental Projects Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation FROM:

Claudia M. Craig, Senior Project Mana

, ~ d '(L C

Generic lasues and Environmental

{

Projects Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation

SUBJECT:

SUMMARY

OF MEETING WITH WESTINGHOUSE TO DISCUSS AXIAL OFFSET ANOMAllES The subject meeting was held at the Nuclear Regulatory Commission (NRC) offices in Rockville, Maryland on July 31,1997, between representativos of Westinghouse and the NRC staff. NRR staff requested Westinghouse to discuss axial offset anomalies (AOA). Attachment 1 is a list of questions the NRC staff piovided Westinghouse prior to the meeting. Attachment 2 is a list of meeting participants. By separate letter dated August 28,1997, Westinghouse provided both proprietary and non-proprietary versions of the material presented at the meeting. Attachment 3 is a copy of the non-proprietary version of the presentation material.

The meeting consisted of an introduction which included a description of the AOA characteristics, the history of the affected plants and a brief discussion of the root cause, a presentation by Texas Utilities on the Comanche Peak experience with AOA, and a presentation by Union Electric Company on the Callaway experience with AOA. This was followed by a proprietary presentation by Westinghouse on the root cause and finally a presentation on the safety analysis.

The key characteristics of the AOA are core axial offset becomes more negative than predicted, typically at burnups of 5,000 to 10,000 MWD /MTU, incore maps show higher AO deviations for

' higher power feed assemblies, and flux depressions in the upper half of the core are maximum below the grids. AOA has been observed in a number of plants for the last several years with a maximum axial offst' observed of 13%.

Some feed assemblies have sub-cooled nucleate boiling to an extent that enhances crud buildup in the upper spans. This sub-cooled boiling causes boron to concentrate in the porous crud layer, concentrating a localized neutron poison. The flux is depressed in the upper regions of the ccre, causing the power to shift to the lower region of the core and resulting in a negative axial offset. The boron can be released from the crud layer when the subcooled boiling is reduced.

. _ = -

=,

e 2-September 16, 1997 D. Matthews The susceptibility factors for AOA ars significant sub-cooled boiling, crud buildup on the fuel and long cycles. From a safety perspective the key impacts are shutdown margin and power distribution surveillance factors.

I Attachments: As stated cc w/stts: See next page i

e

}

I h

I i

t

'A L

m

_. _, _ _. ~

s D. Matthews 2

l The susceptibility factors for AOA are significant sub-cooled boiling, crud buildup on the fuel and long cycir s. From a safety perspective the key impacts are shutdown margin and power s

distribution surveillance factors.

Attachments: As stated cc w/atts: See next page DISTRIBUTION:

See attached page DOCUMENT NAME: 7_31.97. MIN

\\

OFFICE PGEBAi m SRXB:BC(A)

PGEB:(A)SC,

NAME CCraiksbL TCollins

'l4,'

MCase A

.I,

DATE C / R /97 4/1/f /97

' ' l 'l

/97 6

i OFFICIAL RECORD COPY i

l

. =.

S.

i DISTRIBUTION w/ attachments: Summary of July 31,1997, meeting with Westinghouse dated sentember 16, 1997 Central File PUGUC PGEB R/F MCase CCraig W

M E-Mail.

SCollins/FMiraglia RZimmerman DMatthews BSheron GHolahan TCollins MChatterion HScott RES HOmstein, AEOD WBurton BWestreich DPowers, RIV EKendrick JUhle LKopp LPhillips y

v v

+v w

=v w

e -

t s.,

i QUESTIONS ON WESTINGHOUSE j

AXIAL POWER DISTRIBUTION ANOMALY l

1) in addition to Callaway, what other Westinghouse plants have or are experiencing a i

similar axial power distribution anomaly?

[

2)

What are the characteristics of these plants in terms of:

a) cyclelength b) boron concentration

.- c)- peaking factors d) fueltypes

' 3)

What type of chemistry controlis used to reduce the amount of crud deposition?

t 4)

What has been the effect on shutdown margin in the affected plants?

5)

What are the effects of crud burst in conjunction with reactivity insertion due to transients such as rod ejection?

4 l

6)

What are the constituents of the crud deposits?

7)

Do crud deposits have any effect on control rod drop times?

8)

Have any plant trips resulted from crud bursts?

g)

What types of generic communication has Westinghouse issued to licensees concerning this anomaly?

10)

What are the observed effects on TS monthly reactivity balances?

11)

How do bcron letdown curves compare with predictions?

12)-

What is root cause of the power distribution anomaly?

l ATTACHMENT 1 f

6 2

-:.~.--.-,..,,,._..

.-.,..--...-._..-.a_..3

WESTINGHOUSE / NRC MEETING i

AXIAL OFFSET ANOMAllES JULY 31,1997 MEETING PARTICIPANTS hl6ME ORGANIZATION Egan Wang NRC/NRR/PGEB Jeffrey R. Socker Westinghouse CNFD James W. Knaup Union Electric Co.

Tod A. Moser Union Electric Co.

James R. Dwight Westinghouse Sumit Ray Westinghouse Alan Passwater Union Electric Co.

James Moose Union Electric Co.

Randy Irwin Union Electric Co.

Mickey Killgore TU Electric Roger D. Walker TU Electric Lynn Conner Doc-Search Associates Job Delunch NAESCo, Seabrook Station Bobby C. Armstrong Southern Nuclear Glenn Nelses WCNOC Pete Kennamore WCNOC Scott Ferguson WCNOC Dan Risher Westinghouse William Burton NRC/NRR/DRPM'PECB Barry Westreich NRR/DRPW/PDIV Il Mark Cote Yankee Atomic Joe Kormuth Westinghosue Dale Powers NRC/ Region IV Edward Kendrick NRC/NRR/SRXB Jennifer Uhle NRC/NRR/RPSB Larry Kopp NRC/NRR/SRXB Billy Fellers TU Electric David P. Goodman TU Electric David Perkini TU Electric John Bosma TU Electric Steve Maler TU Electric George Sabol

- Westinghouse CNFD Muffet Chatterton NRC/NRR/SRXB Jim Lyons NRC/NRR/SRXB Larry Phillips NRC/NRR/SRXB ATTACHMENT 2

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'JES?INGIIOUSE NON-PROPRIETARY CLASS 3 NRC AOA Meeting 4

Agenda 1

- Introduction - Westinghouse t

l Axial Offset Anomaly Characteristics History of Affected Plants i

Brief Root Cause Discussion

- TU Presentation i

- UE Presentation

- W Root Cause Presentation i

- W Safety Analysis Presentation

- Discussion

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l Core Axial Offset becomes more negative l

than predicted, typically at burnups of

~

l 5,000-10,000 MWD /NITU Incore maps show higher AO deviations for l

higher power feed assemblies 4

Flux depressions in upper half of core are l

l maximum below grids i

i i

t

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'l

1 Measured and Predicted Axial Offset Callaway Cycle 6 15.0 4_ _.

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INCORE PolHT (Point 1 is Top) i l

Axial Offset Anomaly History of Affected Westinghouse Plants Plant Cycle With AOA Cycle Without Maximum AO AOA Deviation Callaway 1,2,3,7 4

-5 5

-7 6

9 8

-7 9 (op) 13 Millstone 3 1,2,3,5,6 (op) 4 5

Vogtle 1 1,2,3,5 4

-3.5 6

-6 7 (op)

-3 Vogtle 2 1,2,6 (op) 3

-3 4

-3 5

-3 Wolf Creek 18 9 (op)

-6 Catawba 1 1-7, 9 8

-4.5 Comanche Peak 2 3

1,2 3.5 Seabrook 1-4 5

-3

Axial Offset Anomaly History of Affected Plants Plant Cy'cle Fuel Type Peaking Factor With AOA (FDH Limit) /

kwltt Callaway 4

17X17,.360, IFM 1.6". / 5.69 5

17X17,.360, IFM 1.65 / 5.69 6

17X17,.360, IFM 1.65 / 5.69 8

17X17,.360, IFM 1.65 / 5.69 9 (op) 17X17,.360, IFM 1.65, v.69 Millstone 3 4

17X17,.374, IFM 1.'O / 5.44 Vogtle 1 4

17X17,.360, IFM 1.65 / 5.44 6

17X17,.360, IFM 1.65 / 5.69 7 (op) 17X17,.360, IFM 1.65 / 5.69 Vogtle 2 3

17X17,.360, IFM 1.65 / 5.69 4

17X17,.360, IFM 1.65 / 5.69 5

17X17,.360, IFM 1.65 / 5.69 Wolf Creek 9 (op) 17X17,.374, IFM 1.65 / 5.69 Catawba 1 8

Non Westinghouse 7/5.44 Comanche Peak 2 3

Non Westinghouse 1.55 / 5.44 Seabrook 5

17X17,.374 1.65 / 5.44

Axial Offset Anomaly History of Affected Plants Plant Cycle Design Maximum HFP With AOA Cycle Length Boron (EFPD)

Concentration (ppm)

Callaway 4

440 1300 5

440 1300 6

450 1400 8

480 14C0 9 (op) 470 1400 Millstone 3 4

510 1700 Vogtle 1 4

430 1650 6

480 1500 7 (op) 490 1500 Vogtle 2 3

470 1600 4

460 1400 5

460 1400 Wolf Creek 9 (op) 520 1550 Catawba 1 8

390 1200 Comanche Peak 2 3

500 1400 Seabrook 5

530 1400 l

i AOA Root Cause Crud builds up on upper spans of high power fuel assemblies j

~

i Boron absorbs into the crud, concentrating a 4

localized neutron poison Flux depressed in upper regions of the core, causing AO to move down (negative)

I I

AOA Root Cause (Continued)

Some feed assemblies have sub-cooled nucleate boiling to an extent that enhances crud buildup in the upper spans Sub-cooled boiling causes boron to concentrate in porous crud layer Boron can be released from the crud layer when subcooled boiling is reduced

i l

Susceptibility Factors Significant sub-cooled boiling

- High coolant temperatures

- Higher peaking factors l

}

- High power density Crud buildup on fuel

]

l

- Some crud on fuel is not unusual

- Individual plant differences can affect crud buildup Long cycles I

L

- High soluble boron i

9 l

Safety Significance Impact of AOA on Fuel And Accident Analysis Thoroughly Considered Key Impacts Are Shutdown Margin And Power Distribution Surveillance Factors j

- These Are Updated For Plants With AOA All Fuel /Non-LOCA/LOCA Design And Safety Criteria Continue to Be Met No Adverse Impact on Safe Plant Operation q

~

}

t i

s AOA Industry Communications 4

i i

Westinghouse Fuel Users' Group presentations

~

Westinghouse Reactor Engineers' Seminars l

Westinghouse Technology User's Group presentations EPRI Programs ISPO SOER 96-2 l

/

\\

Presentation to NRC f

Root Cause Analysis of Axial Offset Anomaly July 3~1,1997 Dr. George P. Sabol, Manager Westinghouse Electric Corporation CNFD Development Programs nac noot Cause Analyses ADA ppt

Presentation Outline Data from plant instrumentation j

Similarities of affected plants

-l Fuel visual examinations for crud deposition I

Mechanism of AOA Crud chemical analyses Coolant chemistry influence and recommendations i

[

fJitC llool Cause Analysis AOA ppt

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7 l

l Axial Ciffset Anomaly Characteristics t

Flux depressed in top-half of core t

Depression similar at structural and-mixing grids l

Maximum depression just upstream of i

i grid AAO driven by feed fuel - largest offset l

l in high-power assemblies AO deviation starts at 4-10 GWD/MTU

~

(

...., - e..... r.... a,,,s...c A DA twil

- - - - - - - - - - =

i Similarities of AO-Affected Plants Predicted sub-cooled boiling j

High coolant temperature High surface heat flux

~

Boiling is necessary, but not sufficient

)

V. C. Summer is prime exception

)

l

~

Hot Channel Sub-Cooled Boiling Duty i

t i

i I

i Plant / Cycle Assawngderwis (Soled bats had indCBitons of AO anomaly) i s e channet. ec==co rone enees (Stahd bar - possible AO anomaly) utcour as 7 7 25 si 2 4..e ma,*c go e. shape ined I

.i nesh m.el has ased Mweets l

l

\\

Visual Observations on Fuel Plants / Cycles (1)

~

Callaway EOC 5,6,7 i

Millstone 3 EOC 4 Observed more crud than expected

)

(i)

First and largest visual exam campaign

I Visual Observations on Crud Crud only in top half of fuel. No crud below span

4. Consistent with negative AO.

)

Most crud in hottest span 6 Feed fuel has more crud than 2CY or 3CY fuel i

More crud on high power assemblies, faces l

Little or no crud above grid, but increases up j

span, consistent with flux depression

i l

1 Axial Offset Proportional to Crud index on Feed Fuel Callaway Cycle 5 Region G Crud Evaluation L

l l

l 1

l I

l l

l l

I l-t i

a l

t k

a n

o

(

i 7

~ Axial Offset Proportional to Cnxf on 2 CY Fuel Callaway Cycle 4 Region E and Cycle 5 Region F Crud Evaluation

- 44ui i

k l

~. -

O

~' -

I l

I l-More Crud on High Power Faces Callaway Region G Crud index versus Average Power at Assembly Face i

I t

i i

l i

i O

s h

v

l i

Callaway CY5 AO change associated with crud release t

l Trip occurred near EOC 5 AO shift from -4 to +6%

i I

Significant crud release followed trip and restart I

I i

l I

I I

NilC Ilool Cause Analyses AOA ppe I

i

,.I, i

i l

i i

1 N

I I

i o

I ch 6W 0

OJ U a M O

t

~o g

N o

C U

_.3 cc o

o

@}

T"

.6 Eo 1

=

l c5 o oo 1

c n

l U'

a m

i A4 o

3 0tt o

.e.

i o

M1 a

a k

m2 o

n c

N x

m N

T C

o 2

1 l

i e

z a

a

=

g a

e s

e n

(%) dpi Supnolled e6uet40 noeno leiry

AO Anomaly is Crud Induced I

Crud only in top half of fuel consistent with i

negative offset Crud highest just below grids agrees with flux

)

l depression More crud on assemblies with high AAO Crud release near EOC-5 Callaway associated with rapid AO Shift - 4% to + 6%

Assemblies with largest AAO prior to trip were most affected by the trip

Effects of Crud on AOA Evaluated Physical presence of Ni Fe _xO is x

3 4

insufficient to depress flux Increase in extent of sub-cooled boiling

- Rougher surface 1

- More nucleation sites

- Slight increase in surface temperature j

Boron concentration within crud

~

- Liquid within crud enriched by boiling 1

- Boron compound precipitation within crud

.l lij

~

^ ~ ~ ~

i Plant Data Evaluation 1

i Plant data analyzed

- Pressure increases

~

- Power reductions

- Temperature reductions Data indicate boiling insufficient to explain AO deviation

- Pressure coefficient of reactivity similar to core model without voiding l

- Anomalous reactivity decreases with power, but still present at 70% power Low voiding indicates instantaneous release of reactivity not j

possible 3

Boron concentration in crud is most likely cause of AO deviation l

i tillC 11oot Cause Anahss AOA ppi

t I

k l

Model for Boron Concentration in Crud q

Sub-cooled boiling in porous deposit results in. concentration of soluble boron in liquid-within the deposit i

i Boron-enriched liquid leads to formation of boron-rich " solids" t

l

--~.!

^

}

1

)

~

Crud is Medium for Boron Concentration

  • t a.c)

Porous Crud i

f l

Vapor " Chimneys" 5

Vapor Bubbles j

l t

Coolan!in Boron l

l Clad i

Concentration = C.

1 i

Wall O* vapor out Boron Concentration - 0 j

r l

C(x) = Boron Concentration i

(

in Liquid Within Crud i

OO i

s t

  • (a.c) c C,

j

~

w C

i l

I I

C.

X 5

i

\\

~

)

I t

l Critical Aspects of Model Formation of B " solids"in crud requires B-concentration in liauid within crud to solubility limit Most of B retained in " solid" form

[B] in crud sensitive to boiling, thickness l

- [B] varies as j

.~,

Crud properties important j

- Thickness - coolant chem, impurities

- Composition - reaction, adsorption of B

{

Boron concentration, release is reversible j

i

~-

f 1

i L

i j

i l

Boron Release and Uptake with Power at Callaway J

Power reduction to 30% April 7,8,1993 4

- Li release of 644g

- Boron Equivalent (e.g., as LiBO ) = 1012g 2

I Power increase to 100%

l l

- Li uptake = 450g j

i L

- Boron equivalent = 707g l

Boron to cause observed Axial offset difference l

- Assumes no BS depletion nu.

I l

- B release on power reduction =

l

- B pickup on power increase =

"~>

i Good agreement with boron model l

l l

l i

L l

i i

l; l

Crud Scraping and Analysis l

l AOA Cycles Callaway EOC6 l

l Millstone 3 EOC 4 l

l I

Non-AOA Cycle Callaway EOC7 l

l

\\

Nf 4C floot Cause Anasyses AOA ppe

~

i I

i i

t Callaway EOC 6 Assemblies Scraped for Crud i

I Q

I Assy.

Core Assy.

Crud Offset No.

Region Locauon Power index M-P %

i i

H88 8B C8 1.34

-11.6 H12 8A L13 1.30

-8.4 H03 8A N13 0.95

-6.9 i

l l

l G32 78 J9 1.16 i

-9.6*

G87 7B M9 0.98 8.4*

E81 SC H8 0.99

_,i i

l i

i

)

Assemblies not instrumented in cycle 6. AO values based on those of i

instrumented assemblies symmetrical positions.

I

\\

CALLAWAY EOCs S&6 CRUD EVALUATION o

X rJ Ob o

3E O

w O

4E tas>

__sa 2m W

M

~

4 l

AXIAL OFFSET DIFFERENCE (NEGATIVE)

~.

6 i

Callaway EOC 6 Crud r

Average Surface Concentration and Thickness of Sample Deposits l

1. Once-Bumt Fuel l

1 l

High Power (H-88, H-12)

Ave. Power (H-03)

Surf. Conc Thihs Surf. Conc Thickness l

Span mg/dm' microns mg/dm' microns l

i i

I

2. Twice-Bumt Fuel

~

High Power (G-32)

Ave. Power (G-87)

~

~

l Surf. Cone Thickness Surf. Conc Thickness j

Spian mg/dm microns mg/dm microns M

t i

i Callaway EOC 6 Crud i

Average Surface Concentration and Thickness i

of Sample Deposits (coned) l

3. Thrice-Bumt Fuel f

\\

1 Average Power (E-81)

Surface Conc Thickness l

span mg/dm' microns

.., [

r l

r l

  • Analysis suspect due to small amount of crud.

l i

i l

I Correcmon to 295 89. #95 209. (6/I597) l l

l

?

a

k 6

3 Ie k

s n

o, 5

8 O

h k

3I n

5

l l

Millstone 3 EOC 4 Crud Data Axial Offset Assembly Number Relative Power Crud index (M-P) %

t-

-7.2 l

nui F-88 1.29

-8.3 F 1.29 1

l l

L Average Surface Concentration and Thickness of Crud l

1 l

i l

Surface Conc.

Thickness Span (mg/dm )

(microns)

.., lr 2

i t

?

l l

l l

)

l "Only one sample from span 48 co mio s iis g,nsmo

~.

l

A 4

  • 0 7

E la u

-5 8

1 i

bU 1

a 1

)

l Millstone 3 Feed Fuel Crud EOC 2 vs. EOC 4 Average Surface Concentration mg/(kr/

EOC2 EOC4 Ratio C4/C2

~

Span m

Conecton so #96116 (6/t'w"31)

O g

~

Callaway EOC 7 Assemblies Scraped for Crud

SUMMARY

OF CALLAWAY CYCLE S AND 7 OPERATIONAL DATA CN8 Cycto7 12coe

(%)

cnns 11ses

(%)

cmd omsex F/A anroesTU heden WRADMETU

]

l 1.300

-4.4 H - 12 9.4se

-1.3 H - as 1.444

-2.1 1.340

-11.4 J -3e 1.321

-1.8

~

~

J_m 1.305

-1.8 J - 93 1.31

-18 r

Callaway CY 6, CY 7 Crud Compqrisons Average Surface Concentration and Thickness - Span 6 Twice Bumed Fuel Fced Fuel CY6 CY 7 CY 6 CY7 H-12, H-88 J-38, J-40, J-39 G-32, G-87 H-12, H-88 mg/6T p

mg/dia p

z mg/svi p

mg/dm p

e

  • (a t I

~

m I

Correchon to #95 213 (6f35f97)

P O

4 4-m

Callaway Crud Chemical Composition A -.g.c-=; = = enc m 8,o.,s,e.

troen High Power Feed Fuel Grosse Cycles S and 7 w

I r

M

i R

i Summary of Crud Scrape Data i

Crud thickness in proportion to extent of AOA Crud conceritrations as expected, except j

. <.o Ni/Fe ratios >

l Crud removal observed when driving forces for crud i

deposition decreased l

l l

l i

i NRC HmW Cause Mses AOA ppt

Mechanism of AOA Some level of sub cooled boiling on feed fuel Sub-cooled boiling exacerbates crud deposition -

Boron concentrates within porous crud deposit Under some conditions, solubility limit of B-rich solid, e.g., LiBO, exceeded 2

Power suppression due to B-rich solid within crud in top spans of high-power fuel NitC !!ool Cause Anasyses AOA g42

Approaches for AOA Mitigation Minimize extent of sub-cooled boiling through core design optin.ization

~

Minimize crud deposition through coolant chemistry control

- Li/B pH control strategy

- Elevated pH at BOC

- Coolant corrosion product management usar sanns ca..w An.4vses ADA pot

i Axial Offset Anomaly Safety Evaluation Nuclear Regulatory Commission 7/31/97 J. R. Secker Westinghouse Commercial Nuclear Fuel Division

Safety Evaluation Fuel Non-LOCA LOCA 2

Plant Experience Reactivity Changes Associated With Axial Offset Anomaly Occur Slowly

~

~

Boron Compounds No Longer Present in Crud On Return to Critical Following Plant 1

Trip (~12-24 hours)

Boron Compound Returns to Crud During Power Ascent 4

Plant Experience Effect of Small AO Deviations Are Much

~

Smaller Than Uncertainties / Conservatism Applied to Safety Analysis Inputs AOA Does Not Increase Control Rod Drop Time AOA Has Not Caused Any Plant Trips

~-

a

Conservative Assumptions for Safety Evaluation Small Rapid Reactivity Release From Liquid Boric Acid Concentrated in Crud ofTotal Reactivity Associated With AOA 1

Release Rate

~

Observed Piant Behavior Indicates This Assumption is Very Conservative Dissolution of Boron Compound C ct ' Slowly Enough (Hours) to Not Affect Safety Analysis Assumptions 5

_ =.

Conservative Assumption for L

Shutdown Margin j

Assumes Instantaneous Reactivity Addition Following Plant Trip Very Conservative Assumption Relative to Plant Behavior - Dissolution of Boron j

Compound Does Not Occur Instantaneously i

s i

j

Fuel / Core Analysis Fuel Related Inputs to Safety Analysis Most Parameters Are Not Affected and Remain Bounded By FSAR Safety Analysis Reactivity Coefficients, Kinetics Parameters, Power Distributions

. Parameters Affected:

Shutdown Margin Relaxed Axial Offset Control (RAOC) Peaking Factor Surveillance Factors, W(z)

~

7

^

l l

i L

l l

Fuel / Core Analysis t

i I

DNBR l

- Crud Has Negligible Affect on DNBR l

- Core Limits Remain Applicable for DNB Protection

)

Fuel Rod Design

- Most Design Criteria Unaffected l

- Corrosion Model Database Includes Plants With I

Crud /AOA - Callaway and Millstone 3

+(a.c)

- Results in Fuel Temperature Increase at t

Intermediaie~ Burnups. BOC Temperatures are Still the Highest 3

x l

~.

I i

Non-LOCA Accident Analysis All Non-LOCA Events Reviewed Most Accidents Not Affected l

- Input Parameters Remain Bounded j

- HZP Events Not Effected Since Boron Compound Not Present at l

HZP

- Beginning of Cycle Events Not Affected Since Crud is Not Present

- Limiting DNB Events Result in Increased Subcooled Boiling - No f

Additional Reactivity Insertion j

Accidents Sensitive to Transient Reactivity Release Maintain Margins To Safety Analysis Limits 9

I l

l-

m m.

gb l

I Xon-LOCA Accidents l

Crud Release l

l i

i Rod Withdrawal At Power Rod Ejection At Power j

l l

l i

l i.

1 io t

f i

~

Non-LOCA Accidents l

Crud Release Rod Withdrawal At Power Core Analysis Shows Substantial Margin To Maximum Reactivity Insertion Rate Without Crud Limiting Case is Not Maximum Reactivity Insertion Rates - Intermediate Rates Show Minimum DNBR Increased Reactivity Insertion Rate Results in Earlier Plant Trip ii

i i

Non-LOCA Accidents Crud Release l

Rod Ejection At Power i

i l

- Very Fast Transient

- Plant Trip Occurs in 0.1 Sec

- Control Rod Insertion in Core in 0.5 See

- Nuclear Power Rise Limited By Doppler Feedback - Thennal Power Increase is Small

- Small Change in Clad Temperature

- Although There is Little Time for Crud Release to Occur, Event Was Evaluated Assuming Crud Release From Ejected Rod Assembly and Surrounding Assemblies

- Bounding Reactivity Insertion And Peaking Factor Limits Still l

Met 1

i g7

Loss of Coolant Accidents 1

Power Shapes Remain Bounded Reactivity From Crud Release OiTset By Voiding (Large Break) and Trip (Small Break)

Beginning of Cycle Fuel Temperatures Are Still Highest Since Presence of Crud At Later Burnups Results in Only a Small Fuel Temperature Increase j

4(a.c) on Small Break LOCA Minimal PCT Impact No Affect on Large Break LOCA PCT Since BOC is Limiting (No Crud) 13 i

e Safety Evaluation Summary Impact of AOA on Fuel And Accident Analysis Thoroughly Considered

~

i Key Impacts Are Shutdown Margin And

~

Power Distribution Surveillance Factors These Are Updated For Plants With AOA l

All Fuel /Non-LOCA/LOCA Design And Safety Criteria Continue to Be Met No Adverse Impact on Safe Plant Operation 14

t,

. cc:

Mr. Nicholas J. Liparulo Westinghouse Electric Corporation Mail Stop ECE 4 '

P.O. Box 355 i

Pittsburgh, PA 15230-0355 Mr. Henry A. Sepp Westinghouse Electric Corporation Mail Stop ECE 4-07A

- P.O. Box 355 Pittsburgh, PA 15230-0355 Mr. Andrew Drake, Project Manager Westinghouse Owners Group Mail Stop ECE S P.O. Box 355 Pittsburgh, PA 15230-0355 4

4 4

4 2

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