ML15161A123

Annual 10CFR 50.46 Report for Calendar Year 2014 Emergency Core Cooling System Evaluation Changes

ML15161A123
Person / Time
Site:	Arkansas Nuclear
Issue date:	06/09/2015
From:	Stephanie Pyle Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
OCAN061501
Download: ML15161A123 (6)

Text

0CAN061501

June 9, 2015

U.S. Nuclear Regulatory Commission

ATTN: Document Control Desk

11555 Rockville Pike

Rockville, MD 20852

SUBJECT:

Annual 10 CFR 50.46 Report for Calendar Year 2014 Emergency Core Cooling System Evaluation Changes

Arkansas Nuclear One - Units 1 and 2

Docket Nos. 50-313 and 50-368

License Nos. DPR-51 and NPF-6

REFERENCE:

1. Entergy letter to NRC, "Special Report, Licensee Event Report 50-313/2014-002-00, Special Report - Significant Change in Peak

Cladding Temperature," dated December 22, 2014 (1CAN121405)

(ML14357A098)

2. NRC email to Entergy dated February 27, 2015, "Request for Additional Information - ANO- 1 Report Regarding Changes in Peak Cladding

Temperature ECCS Analysis (per 10 CFR 50.46 and 10 CFR 50.73) -

TAC No. MF5545" (1CNA021504) (ML15061A155)

3. Entergy letter to NRC, "Responses to Request for Additional Information Report Regarding Significant Change in Peak Cladding Temperature for

ECCS LOCA Analysis Pursuant to 10 CFR 50.46 and 10 CFR 50.73,"

dated March 30, 2015 (1CAN031505) (ML15090A307)

Dear Sir or Madam:

10 CFR 50.46(a)(3)(ii) requires licensees to report annually each change to or error discovered

in an acceptable evaluation model or in the application of such model for the emergency core

cooling system that affects the peak cladding temperature (PCT). Entergy Operations, Inc. has

reviewed the small and large break loss-of-coolant accident (LOCA) PCT evaluations for both

Arkansas Nuclear One, Units 1 and 2 (ANO-1 and ANO-2).

Entergy Operations, Inc.

1448 S.R. 333 Russellville, AR 72802

Tel 479-858-4704 Stephenie L. Pyle Manager, Regulatory Assurance A rkansas Nuclear One

0CAN061501 Page 2 of 2

A deficiency was identified in the ANO-1 large break LOCA evaluation model. When this

deficiency was accounted for, a significant change in the PCT resulted. This change was

reported via Reference 1. In the course of its review, the NRC staff has determined that

additional information is required to complete its evaluation (Reference 2). Entergy's response

to the NRC's request for additional information (RAI) was provided in Reference 3.

No issues were identified for ANO-2 in 2014 that impacted the results reported for the calendar

year 2013.

A summary / overview of the information required to be submitted each year is attached to this submittal.

This submittal fulfills the reporting requirements referenced above.

This letter contains no new regulatory commitments.

If you have any questions or require additional information, please contact me.

Sincerely, ORIGINAL SIGNED BY STEPHENIE L. PYLE

SLP/rwc

Attachment:

Summary / Overview of Information for Arkansas Nuclear One, Units 1 and 2 10 CFR 50.46 Annual Report for 2014

cc: Mr. Marc L. Dapas Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511

NRC Senior Resident Inspector Arkansas Nuclear One P. O. Box 310

London, AR 72847

U. S. Nuclear Regulatory Commission

Attn: Ms. Andrea E. George

MS O-8B1 One White Flint North

11555 Rockville Pike

Rockville, MD 20852 Attachment to 0CAN061501 Summary / Overview of Information for Arkansas Nuclear One, Units 1 and 2 10 CFR 50.46 Annual Report for 2014 Attachment to 0CAN061501

Page 1 of 3

Summary / Overview of Information for Arkansas Nuclear One, Units 1 and 2 10 CFR 50.46 Annual Report for 2014 Analysis of Record (AOR)

Peak Clad Temperature (PCT), (°F)

Evaluation Model (EM) Used AOR Date Adjustment as of End-of-Year (EOY) 2013, (°F) Net PCT at the EOY 2013, (°F) New Adjustments for Calendar Year 2014, (°F)

Net PCT at the EOY 2014, (°F)

ANO-1 Small-Break

Loss-of-Coolant

Accident (SBLOCA) 1459 RELAP5 / MOD2-B&W February 2011 None 1459 (estimated)

None 1459 (estimated)

Large-Break Loss-of-Coolant

Accident (LBLOCA) 2008.1 RELAP5 / MOD2-B&W July 2005 None 2008.1 (estimated)

None (Note) 2008.1 (estimated)

ANO-2 SBLOCA 2111 S2M October 2007 None 2111 (analyzed)

None 2111 (analyzed)

LBLOCA 2144 1999 EM January 2008 None 2144 (analyzed)

None 2144 (analyzed)

Attachment to 0CAN061501

Page 2 of 3

Note On November 25, 2014, AREVA NP Inc. (AREVA) notified Entergy Operations, Inc. (Entergy) of

a deficiency in the Arkansas Nuclear One, Un it 1 (ANO-1) Emergency Core Cooling System (ECCS) evaluation model (EM). When the deficiency is accounted for, the Large Break

Loss-of-Coolant Accident (LBLOCA) Peak Clad Temperature (PCT) was estimated to exceed

2200 °F and the absolute value of the deficiency is greater than the requirement of

10 CFR 50.46(a)(3)(ii). Exceeding 2200 °F resulted in ANO-1 making an 8-hour NRC

notification on November 25, 2014.

The current LOCA EM for Babcock & Wilcox (B&W) plants uses the fuel performance code

TACO3. The identified deficiency is in the thermal conductivity model in this computer code.

The deficiency is that the code does not adequately represent the reduction in fuel thermal

conductivity with burnup. This issue was discussed in NRC Information Notice (IN) 2009-23

"Nuclear Fuel Thermal Conductivity Degradation".

TACO3 does not model the thermal conductivity degradation (TCD) with burnup explicitly, but has adjustments to the methodology and increases in the LOCA fuel temperature inputs that

can compensate for TCD not being modeled. These adjustments were intended to compensate

for the non-conservative thermal conductivity model in TACO3.

The continued use of this code was previously evaluated by AREVA in 2009 following the NRC

issuance of IN 2009-23. In 2009, it was concluded that sufficient conservatisms in both code

predictions and LOCA methodology compensated for a lack of TCD models. However this

evaluation has been challenged and reversed based on recent LOCA initialization studies.

Based on the new LBLOCA initializations, it is concluded that the LOCA EM that uses TACO3 must be modified by application of additional fuel temperature uncertainty to account for the

effects of TCD based on COPERNIC2, a code that models TCD adequately, as a function of

burnup.

An evaluation was performed by applying the EM change to a Lower-Loop (LL) LBLOCA plant model with an axial power shaped peaked at the 2.506-foot (ft) core elevation with a middle-of-

life (MOL) burnup condition. The results of the evaluation show that the original limiting MOL

case cladding temperatures at the 2.506 ft core elevation were increased by 481 °F for the

ruptured node and 288 °F for the unruptured node. The results of this evaluation can be

generically applied to all B&W plants. These ruptured and unruptured node cladding

temperature deltas were applied to the ANO-1 full spectrum of MOL cases and led to an

increase in limiting PCT of 388 °F. An evaluation of the cladding temperatures at end-of-life (EOL) has confirmed that the MOL results remain limiting. Also it is noted that the cladding

temperatures at beginning-of-life (BOL) remain unaffected by TCD. When applying the

estimated PCT increases with the revised EM approach, the limiting PCT was estimated to be

2396 °F, which is in excess of 2200 °F. This LBLOCA EM model change results in a significant

increase to the calculated PCT.

In order to reduce the PCT to less than 2200 °F, AREVA recommended linear heat rate (LHR)

limit reductions on October 21, 2014, and suggested that it was prudent to administratively

implement any changes as a compensatory measure. The compensatory measures recommended a 2 kilowatt/foot reduction in the MOL LHRs. Imposition of the compensatory Attachment to 0CAN061501

Page 3 of 3

measures assures that the PCT will be equal to the PCT prior to the EM correction and thus will be less than 2200 °F. Pending the completed analysis, ANO-1 will maintain the compensatory

measures.

The local oxidation and whole core hydrogen also remain well within the 10 CFR 50.46

acceptance criteria for the LBLOCA scenarios. With the MOL LHR limit reduction, the core

geometry remains amenable to cooling and acceptable long-term cooling is unaffected by these

changes.