ULNRC-06045, Response to Request for Additional Information Closure of Option 2 to Address In-Vessel Mitigative Measures for Potential In-Vessel Blockage

Response to Request for Additional Information Closure of Option 2 to Address In-Vessel Mitigative Measures for Potential In-Vessel Blockage

ML13305A125
Person / Time
Site:	Callaway
Issue date:	10/31/2013
From:	Maglio S Ameren Missouri, Union Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC MC4671, ULNRC-06045
Download: ML13305A125 (6)

Text

~'t-.

WAmeren Callaway Plant MISSOURI October 31,2013 ULNRC-06045 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 10 CFR 50.54(+/-)

Ladies and Gentlemen:

DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.

FACILITY OPERATING LICENSE NPF-30 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI)

RE: CLOSURE OF OPTION 2 TO ADDRESS IN-VESSEL MITIGATIVE MEASURES FOR POTENTIAL IN-VESSEL BLOCKAGE (TAC NO. MC4671)

References:

1. Ameren Missouri Letter to NRC, ULNRC-05989, "Path Forward for Resolution ofGSI-191," dated May 16,2013 (ML13136A290)

2. NRC Letter, "Callaway Plant Unit 1 -Request for Additional Information Re: Closure of Option 2 to Address In-Vessel Mitigative Measures for Potential In-Vessel Blockage (TAC No. MC4671),"

dated September 23, 2013 (ML13263A168)

On September 23, 2013, the Nuclear Regulatory Commission (NRC) issued a Request for Information to Union Electric Company (dba Ameren Missouri) regarding Ameren Missouri's intended path forward to follow the Option 2 risk-informed approach for the resolution of Generic Safety Issue (GSI)-191, "Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance" for Callaway Plant, Unit 1 (Callaway). The NRC Staff determined additional information was needed to complete their review of GSI -191 resolution plans for Option 2 plants, including Callaway, which had not addressed mitigative measures to deal with potential in-vessel blockage.

The attachment to this letter provides the requested information, and supplements information that was provided by Ameren Missouri in its letter dated May 16, 2013 (Reference 1).

This letter does not contain new commitments. If there are any questions, please contact me at 573-676-8719 or J.P. Kovar at 314-225-1478.

PO Box 620 Fulton, MD 65251 AmerenMissouri.com

ULNRC-06045 October 31,2013 Page 2 I declare under penalty of perjury that the foregoing is true and correct.

Sincerely,

~nA-2 Scott A. Maglio Regulatory Affa rs Manager Executed on: I (J I 3 i / Zo 13 JPK/nls

Attachment:

Defense-In-Depth Measures for In-Vessel (Core) Blockage

ULNRC-06045 October 31, 2013 Page 3 cc: Mr. Steven A. Reynolds Acting Regional Administrator U.S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Fred Lyon Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 0-8B 1 Washington, DC 20555-2738

ULNRC-06045 October 31,2013 Page 4 Index and send hardcopy to QA File A160.0761 Hardcopy:

Certrec Corporation 4150 International Plaza Suite 820 Fort Worth, TX 76109 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)

Electronic distribution for the following can be made via Responses and Reports ULNRC Distribution:

A. C. Heflin F. M. Diya C. 0. Reasoner III B. L. Cox L. H. Graessle S. A. Maglio T. B. Elwood Corporate Communications NSRB Secretary STARS Regulatory Affairs Mr. John O'Neill (Pillsbury Winthrop Shaw Pittman LLP)

Attachment to ULNRC-06045 Page 1 of2 Defense-In-Depth Measures for In-Vessel (Core) Blockage NRC Question:

Please provide the mitigative measures, in place or planned, to deal with potential in-vessel blockage at Callaway Plant. If all mitigative measures have not been implemented, please provide the schedule for implementing them.

Ameren Missouri Response:

Multiple methods exist for detection of a core blockage condition as manifested by an inadequate reactor coolant system (RCS) inventory or inadequate core heat removal. The primary methods include use of the core exit thermocouples (CET) and reactor vessel level indication system (RVLIS). This monitoring would be initiated early in the event in accordance with the Emergency Operating (EOP) procedures through the Critical Safety Function Status Trees. The monitoring is directed to be performed continuously after completion of diagnosis of the event. In addition, emergency response personnel in the Technical Support Center (TSC) or Emergency Operations Facility (EOF) would maintain oversight ofplant status through review of Safety Parameter Display System that includes both CET and RVLIS data. Additional methods for detection of a core blockage condition include monitoring of containment radiation levels by the TSC or EOF staff, or receipt of an alarm in the control room resulting from a radiation monitor alarm setpoint being exceeded.

To mitigate the effects of potential debris-induced core blockage, EOP ECA-1.1, "Loss of Emergency Coolant Recirculation," directs the operators to take actions to restore, preserve or maintain core cooling, including:

• Reduce RCS injection flow rate to meet minimal heat removal requirements

• Refill the Refueling Water Storage Tank (RWST).

• Provide core cooling by steaming through the steam generators.

• Establish alternate injection paths to recover the core.

• Restart Reactor Coolant Pumps (RCPs).

The operators would also inform the TSC of the condition. The TSC would evaluate the condition and recommend the actions, as necessary, to the operators to restore core heat removal. In addition to those listed above, the actions recommended by the TSC may include:

• Perform EOP ES-1.4, Transfer to Hot Leg Recirculation.

Attachment to ULNRC-06045 Page 2 of2 Additional strategies that may be used to mitigate the effects of core blockage by injecting reactor makeup water or fire protection water into containment are described in the following Severe Accident Management Guidelines (SAMGs):

• SAG-4, Inject into Containment

• SAG-8, Flood Containment.

In addition to the defense-in-depth measures listed above, Ameren Missouri has evaluated the recommendations made by Westinghouse in Direct Work DW-12-013, which provided additional background information for EOP procedures regarding the potential for debris to block core flow after transfer to cold leg recirculation. This information has been added to the background documents for EOP procedures ES-1.3, "Transfer to Cold Leg Recirculation;" FR-C.l, "Response to Inadequate Core Cooling;" FR-C.2, "Response to Degraded Core Cooling;" and CSF-1, "Critical Safety Function Status Tree."