ML15161A123
| ML15161A123 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 06/09/2015 |
| From: | Pyle S 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)
- 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 Arkansas 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). Entergys response to the NRCs 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, Unit 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.