ML14171A627

10 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 and Significant Change/Error Report

ML14171A627
Person / Time
Site:	Hatch
Issue date:	06/20/2014
From:	Pierce C R Southern Co, Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-14-0900
Download: ML14171A627 (8)

Text

Charles R. Pierce Southern Nuclear Regulatory Affairs Director Operating Company, Inc. 40 Inverness Center Parkway Post Office Box 1295 Birmingham.

Alabama 35201 Tel 205.992.7872 Fax 205.992.7601 June 20, 2014 Docket Nos.: 50-321 50-366 U. S. Nuclear Regulatory Commission A TIN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant Units 1 and 2 10 CFR 50.46 ECCS Evaluation Model SOUTHERN A COMPANY NL-14-0900 Annual Report for 2013 and Significant Change/Error Report Ladies and Gentlemen:

In accordance with the requirements of 10 CFR 50.46(a)(3)(ii), Southern Nuclear Operating Company (SNC) is submitting the enclosed Edwin I. Hatch Nuclear Plant (HNP) Units 1 & 2 emergency core cooling system (ECCS) evaluation model significant change/error report. On May 21, 2014 SNC received four separate notifications from its fuel vendor, General Electric Hitachi I Global Nuclear Fuel (GEH/GNF), of change/error reports which each included the estimated effect on the HNP limiting ECCS analysis fuel peak cladding temperature (PCT). GEH/GNF performed evaluations of the HNP SAFERIGESTR loss of coolant accident (LOCA) analysis of record (AOR), and concluded estimated PCT impacts of 0°F, +10°F, +20°F, and -20°F for 10 CFR 50.46 reporting purposes.

The combined notifications, along with the previously reported +1 0°F change/error from the HNP ECCS Model Annual Report for 2012 (ML 13357 A71 0) constitute a significant change/error requiring a 30 day report. This report is provided in the Enclosure.

The requirements of 1 0 CFR 50.46(a)(3)(ii) also include an annual report by licensees of changes to, or errors in, acceptable ECCS models that affect the temperature calculation and the estimated effect of changes or errors on the limiting ECCS analysis.

During the 2013 calendar year, there were no additional changes/errors to the ECCS model that impacted the AOR PCT.

U. S. Nuclear Regulatory Commission NL-14-0900 Page2 This letter contains no NRC commitments.

If you have any questions, please contact Ken McElroy at (205) 992-7369.

Respectfully submitted, C. R. Pierce Regulatory Affairs Director CRP/RMJ/Iac

Enclosure:

Hatch Nuclear Plant 10 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 & Significant Change/Error Report cc: Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President

& CEO Mr. D. G. Bost, Executive Vice President

& Chief Nuclear Officer Mr. D. R. Vineyard, Vice President-Hatch Mr. B. L. lvey, Vice President

-Regulatory Affairs Mr. D. R. Madison, Vice President-Fleet Operations Mr. B. J. Adams, Vice President

-Engineering Mr. G. L. Johnson, Regulatory Affairs Manager -Hatch RTYPE: CHA02.004 U.S. Nuclear Regulatory Commission Mr. V. M. McCree, Regional Administrator Mr. R. E. Martin, NRR Senior Project Manager -Hatch Mr. E. D. Morris, Senior Resident Inspector-Hatch Edwin I. Hatch Nuclear Plant 10 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 and Significant Change/Error Report Enclosure Hatch Nuclear Plant 10 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 & Significant Change/Error Report Enclosure to NL-14-0900 Hatch Nuclear Plant 1 0 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 & Significant Change/Error Report Edwin 1. Hatch Nuclear Plant Unit 1 SAFERIGESTR*LOCA Analysis Model Table 1-1a-Current Changes/Errors Description A new version of SAFER04A has been released (-E4). This version resolves several accumulated observations docketed on software control tracking tools, which are reported as Evaluation Model changes for an ECCS-LOCA calculation utilizing the updated SAFER code compared to earlier versions:

The following updates are reported:

1. Fix for a non-physical, low prediction of channel wall temperature for quenched nodes due to alternate heat transfer mechanisms while the quench front traverses the node; 2. Fix of a logic flaw which slowed progression of the re-wetting front as a result of quench front reaching two-phase level; 3. Fix of the boundary treatment between downcomer steam and liquid nodes; 4. Fix of input manipulation in core wide metal water reaction calculation, which inadvertently replaced the smeared local peaking factor constant with the input unsmeared local peaking factor in the subsequent group calculation, causing the fraction of rods assigned to each group to be slightly different;

5. Fix of a rare occurrence wherein the code aborts when attempting to divide by zero in the pressure rate of change calculation, checking mass of the node when the core is partially empty; and 6. Removal of a discontinuity when using the dynamic gap conductance model, if the fuel rod gap is initially closed and the calculation predicts gap opening. Sensitivity calculations have demonstrated that these several items individually and collectively have insignificant effect on calculated peak cladding temperature.

A new version of SAFER04A has been released (-E4). This version resolves several accumulated observations docketed on software control tracking tools, the current item being reported as an Evaluation Model error for an ECCS-LOCA calculation utilizing earlier versions and corrected in the updated SAFER code revision.

A logic error has been isolated occurring with an indication that the expected system mass diverges from the calculated actual system mass. This occurs when upper plenum liquid mass and core spray flow rate is low; system mass is gradually lost due to core spray being discarded, resulting in marginally less ECCS flow credited as reaching the core. A new version of SAFER04A has been released (-E4). This version resolves several accumulated observations docketed on software control tracking tools, the current item being reported as an Evaluation Model error for an ECCS-LOCA calculation utilizing earlier versions and corrected in the updated SAFER code revision.

Due to calculation of a non-physically low for droplet flow above a two-phase level in the core, an earlier version of the model imposed a minimum core It has been observed that for cores with greater voiding (more steam flow), this minimum could be non-conservative, actually driving the steam flow slightly, and offering inappropriate steam cooling benefit above the core two phase level. A new version of SAFER04A has been released (-E4). This version resolves E-1 Estimated Effect PCT 0 F) 0 +10 +20 -20 Enclosure to NL-14-0900 Hatch Nuclear Plant 10 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 & Significant Change/Error Report several accumulated observations docketed on software control tracking tools, the current item being reported as an Evaluation Model error for an ECCS-LOCA calculation utilizing earlier versions and corrected in the updated SAFER code revision.

A counter current flow limitation (CCFL) is applied on the interface between the hot bundle and the lower plenum. The pressure head applied at that location is based on the liquid water level in the bundle. It was found, upon exercising the routine to define CCFL, the output would replace the pressure head with a value revised by that calculation, resulting in a representation of pressure head slightly different from that of the calculated water level in the bundle. The iteration scheme for CCFL has been fixed in the SAFER04A E4 model so that, consistently, the level head is applied whenever CCFL is calculated in that location.

Table 1-1b-Summary of Changes/Errors (2013} Description None affecting PCT Table 1-1c-Cumulative Impact of Changes/Errors Description

• Changes/Errors Previously Reported (Reference

1)

• Summary of Changes/Errors (2013)

• Current Changes/Errors (Reference 2, 3, 4, 5) Cumulative Total E-2 Estimated Effect PCT) N/A GE14 (Of) 10 0 50 60 Enclosure to NL-14-0900 Hatch Nuclear Plant 10 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 & Significant Change/Error Report Edwin I. Hatch Nuclear Plant Unit 2 SAFERIGESTR*LOCA Analysis Model Table 1-2a-Current Changes/Errors Description A new version of SAFER04A has been released (-E4). This version resolves several accumulated observations docketed on software control tracking tools, which are reported as Evaluation Model changes for an ECCS-LOCA calculation utilizing the updated SAFER code compared to earlier versions:

The following updates are reported:

1. Fix for a non-physical, low prediction of channel wall temperature for quenched nodes due to alternate heat transfer mechanisms while the quench front traverses the node; 2. Fix of a logic flaw which slowed progression of the re-wetting front as a result of quench front reaching two-phase level; 3. Fix of the boundary treatment between downcomer steam and liquid nodes; 4. Fix of input manipulation in core wide metal water reaction calculation, which inadvertently replaced the smeared local peaking factor constant with the input unsmeared local peaking factor in the subsequent group calculation, causing the fraction of rods assigned to each group to be slightly different;

5. Fix of a rare occurrence wherein the code aborts when attempting to divide by zero in the pressure rate of change calculation, checking mass of the node when the core is partially empty; and 6. Removal of a discontinuity when using the dynamic gap conductance model, if the fuel rod gap is initially closed and the calculation predicts gap opening. Sensitivity calculations have demonstrated that these several items individually and collectively have insignificant effect on calculated peak cladding temperature.

A new version of SAFER04A has been released (-E4). This version resolves several accumulated observations docketed on software control tracking tools, the current item being reported as an Evaluation Model error for an ECCS-LOCA calculation utilizing earlier versions and corrected in the updated SAFER code revision.

A logic error has been isolated occurring with an indication that the expected system mass diverges from the calculated actual system mass. This occurs when upper plenum liquid mass and core spray flow rate is low; system mass is gradually lost due to core spray being discarded, resulting in marginally less ECCS flow credited as reaching the core. A new version of SAFER04A has been released (-E4). This version resolves several accumulated observations docketed on software control tracking tools, the current item being reported as an Evaluation Model error for an ECCS-LOCA calculation utilizing earlier versions and corrected in the updated SAFER code revision.

Due to calculation of a non-physically low l1p for droplet flow above a two-phase level in the core, an earlier version of the model imposed a minimum core l1p. It has been observed that for cores with greater voiding (more steam flow), this minimum l1p could be non-conservative, actually driving the steam flow slightly, and offering inappropriate steam cooling benefit above the core two phase level. A new version of SAFER04A has been released (-E4). This version resolves E-3 Estimated Effect (ll PCT 0 F) 0 +10 +20 -20 Enclosure to NL-14-0900 Hatch Nuclear Plant 1 0 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 & Significant Change/Error Report several accumulated observations docketed on software control tracking tools, the current item being reported as an Evaluation Model error for an ECCS-LOCA calculation utilizing earlier versions and corrected in the updated SAFER code revision.

A counter current flow limitation (CCFL) is applied on the interface between the hot bundle and the lower plenum. The pressure head applied at that location is based on the liquid water level in the bundle. It was found, upon exercising the routine to define CCFL, the output would replace the pressure head with a value revised by that calculation, resulting in a representation of pressure head slightly different from that of the calculated water level in the bundle. The iteration scheme for CCFL has been fixed in the SAFER04A E4 model so that, consistently, the level.head is applied whenever CCFL is calculated in that location.

Table 1-2b-Summary of Changes/Errors (2013) Description None affecting PCT Table 1-2c -Cumulative Impact of Changes/Errors Description

• Changes/Errors Previously Reported (Reference

1)

• Summary of Changes/Errors (2013)

• Current Changes/Errors (Reference 2, 3, 4, 5) Cumulative Total E-4 Estimated Effect PCT) N/A GE14 (OF) 10 0 50 60 Enclosure to NL-14-0900 Hatch Nuclear Plant 1 0 CFR 50.46 ECCS Evaluation Model Annual Report for 2013 & Significant Change/Error Report

References:

1. Letter from C. A. Pierce to USNRC (NL-13-2576), "Edwin I. Hatch Unclear Plant Units 1 and 2, Vogtle Electric Generating Plant Units 1 and 2, 10 CFR 50.46 ECCS Evaluation Model Annual Report for 2012," dated December 23, 2013 2. GEH/GNF Notification Letter 2014-01, May 21, 2014 3. GEH/GNF Notification Letter 2014-02, May 21, 2014 4. GEH/GNF Notification Letter 2014-03, May 21, 2014 5. GEH/GNF Notification Letter 2014-04, May 21, 2014 E-5