ML081790400
| ML081790400 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/30/2008 |
| From: | Pickett D NRC/NRR/ADRO/DORL/LPLI-1 |
| To: | Spina J Calvert Cliffs |
| Pickett D, NRR/DORL, 415-1364 | |
| References | |
| GL-04-002, GSI-191, TAC MD4672, TAC MD4673 | |
| Download: ML081790400 (6) | |
Text
June 30, 2008 Mr. James A. Spina, Vice President Calvert Cliffs Nuclear Power Plant, Inc.
Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, MD 20657-4702
SUBJECT:
EXTENSION FOR COMPLETION OF ACTIVITIES RELATED TO GENERIC LETTER 2004-02, POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED WATER REACTORS - CALVERT CLIFFS NUCLEAR POWER PLANT, UNIT NOS. 1 AND 2 (TAC NOS. MC4672 AND MC4673)
Dear Mr. Spina:
Generic Letter (GL) 2004-02 (Agencywide Documents Access and Management Systems (ADAMS) Accession No. ML042360586) identified potential susceptibility of pressurized-water reactor recirculation sump screens to debris blockage during design-basis accidents requiring recirculation operation of emergency core cooling systems (ECCS) or containment spray systems (CSS) and on the potential for additional adverse effects due to debris blockage of flowpaths necessary for ECCS and CSS recirculation and containment drainage. The GL requested that all corrective activities be completed no later than December 31, 2007.
By letter dated December 27, 2007 (ADAMS Accession No. ML073550041), the Nuclear Regulatory Commission (NRC) staff approved your request to extend the due date for completion of corrective actions until June 30, 2008.
Subsequently, by letter dated June 18, 2008 (ADAMS Accession No. ML081710100), you requested an extension for certain activities associated with your response to GL 2004-02. The NRC staff has evaluated the information you have provided and concludes that for Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 and 2, it is acceptable to extend the due date for completion of corrective actions as described in, and to the dates stated in, the enclosed staffs evaluation.
Please contact me at 301-415-1364 if you have any questions on this matter.
Sincerely,
/RA/
Douglas V. Pickett, Senior Project Manager Plant Licensing Branch I-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-317 and 50-318
Enclosure:
As stated cc w/encl: See next page
ML073550041), the Nuclear Regulatory Commission (NRC) staff approved your request to extend the due date for completion of corrective actions until June 30, 2008.
Subsequently, by letter dated June 18, 2008 (ADAMS Accession No. ML081710100), you requested an extension for certain activities associated with your response to GL 2004-02. The NRC staff has evaluated the information you have provided and concludes that for Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 and 2, it is acceptable to extend the due date for completion of corrective actions as described in, and to the dates stated in, the enclosed staffs evaluation.
Please contact me at 301-415-1364 if you have any questions on this matter.
Sincerely,
/RA/
Douglas V. Pickett, Senior Project Manager Plant Licensing Branch I-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-317 and 50-318
Enclosure:
As stated cc w/encl: See next page Distribution:
PUBLIC LPL1-1 r/f RidsNrrDorlLpi-1 RidsNrrLASLittle RidsNrrPMDPickett RidsOgcMailCenter RidsAcrsAcnwMailCenter RidsNrrDssSsib LWhitney JGolla GDentel, R1 ADAMS Accession No. ML08179400 OFFICE LPL1-1/PM LPL1-1/LA SSIB/BC LPL1-1/BC NAME DPickett SLittle MScott as signed on MKowal DATE 06 / 30 / 08 06 / 30 / 08 06 / 27 / 08 06 / 30 / 08
Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 and 2 cc:
Mr. Michael J. Wallace, Chairman and CEO Constellation Energy Nuclear Group, LLC 750 East Pratt Street, 18th Floor Baltimore, MD 21202 Mr. Henry B. Barron, Chief Nuclear Officer Constellation Energy Nuclear Group, LLC 111 Market Place, Suite 200 Baltimore, MD 21202 President Calvert County Board of Commissioners 175 Main Street Prince Frederick, MD 20678 Mr. Carey Fleming, Esquire Sr. Counsel - Nuclear Generation Constellation Energy Nuclear Group, LLC 750 East Pratt Street, 17th floor Baltimore, MD 21202 Mr. Jay S. Gaines Director, Licensing Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, MD 20657-4702 Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 287 St. Leonard, MD 20685 Ms. Susan T. Gray Program Manager Power Plant Assessment Program Maryland Department of Natural Resources Tawes State Office Building B-3 580 Taylor Avenue Annapolis, MD 21401-23 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Ms. Kristen A. Burger, Esquire Maryland People's Counsel 6 St. Paul Centre Suite 2102 Baltimore, MD 21202-1631 Ms. Patricia T. Birnie, Esquire Co-Director Maryland Safe Energy Coalition P.O. Box 33111 Baltimore, MD 21218 Mr. Roy Hickok NRC Technical Training Center 5700 Brainerd Road Chattanooga, TN 37411-4017 Mr. Gary L. Detter Manager - Nuclear Safety and Security Constellation Energy Nuclear Group, LLC 100 Constellation Way, Suite 200C Baltimore, MD 21202
Enclosure EVALUATION OF EXTENSION REQUEST TO COMPLETE CORRECTIVE ACTIONS GENERIC SAFETY ISSUE-191, "ASSESSMENT OF DEBRIS ACCUMULATION ON PWR SUMP PUMP PERFORMANCE" (GSI-191)/
GENERIC LETTER 2004-02, "POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED WATER REACTORS" CALVERT CLIFFS NUCLEAR POWER PLANT, UNIT NOS. 1 AND 2 DOCKET NOS. 50-317 AND 50-318 By letter dated June 18, 2008 (ADAMS Accession No. ML081710100), Calvert Cliffs Nuclear Power Plant, Inc., the licensee, requested an extension for completion of corrective actions associated with your response to Generic Letter (GL) 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors. Previously, by letter dated December 27, 2007 (ADAMS Accession No. ML073550041), the Nuclear Regulatory Commission (NRC) staff approved your request to extend the due date for completion of corrective actions until June 30, 2008, for the Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 and 2.
The stated intent of this latest extension request is to allow additional time to resolve June 2008 strainer chemical effects head loss testing results which showed that one containment spray (CS) pump in each unit does not meet the required net positive suction head (NPSH). Specifically, the available NPSH for CS pump 12 (the #2 pump in Unit 1) does not meet the required NPSH by approximately 0.2 inches, and the available NPSH for CS pump 21 (the #1 pump in Unit 2) does not meet the required NPSH by approximately 4 inches.
In response to the NPSH deficits, the licensee plans to change the buffering agent in the two containments from trisodium phosphate to sodium tetraborate to reduce chemical effects products contributing to strainer head loss. The licensee anticipates the buffer change may reduce strainer head losses by 18 inches, completely eliminating the NPSH required deficits. The licensee stated that it would submit a license amendment request for the buffer change by July 31, 2008, and plans to implement the buffer change-outs for Unit 2 during that units spring 2009 refueling outage (scheduled to start February 24, 2009), and within 90 days of the NRCs approval of the license amendment, but no later than June 1, 2009, for Unit 1.
The licensee further stated that the containment buffer change would require additional strainer testing and evaluations to verify that the change is acceptable, and that testing facility and personnel scheduling constraints did not permit identification of a specific
testing date at the time of the extension request, but that the licensee would ensure that the strainer testing is conducted on a schedule to support the stated buffer change-out dates, and at the earliest opportunity available. The licensee stated that it was conducting contingency planning for potential additional modifications to be tested during the containment buffer change verification strainer head loss testing. The licensee stated that its planning would support near-term installation of the potential modifications, if needed, and that the modifications could be installed in Unit 2 during the spring 2009 refueling outage and at some as yet to be determined time for Unit 1 (see the NRC discussion of installation of contingency modifications below).
The licensee requested an extension from June 30, 2008, to September 30, 2008, to finalize the required evaluations, complete owner acceptance reviews and verifications, and submit a GL 2004-02 supplemental response.
The licensee also stated that the preliminary results of the June 2008 vendor strainer head loss testing confirmed that the previously completed removal of aluminum materials in the Unit 1 containment was necessary to produce acceptable chemical precipitant results. Therefore, the licensee stated that it also needed to remove aluminum materials from the Unit 2 containment to ensure that the design basis NPSH requirements can be met. The licensee stated that due to the high dose rates in the Unit 2 containment when the unit is operating, and the substantial manual labor required to remove aluminum materials (such as scaffolding) in a high heat environment, this activity must be performed during a plant outage. Therefore, the licensee has requested an extension for the Unit 2 aluminum material removal to the next Unit 2 refueling outage, which is scheduled to start February 24, 2009.
The NRC staff has based its reviews for granting extensions to the due date for completion of GL 2004-02 corrective actions on the criteria stated in SECY-06-0078.
Specifically, an extension may be granted if:
the licensee has a plant-specific technical/experimental plan with milestones and schedule to address outstanding technical issues with enough margin to account for uncertainties, and the licensee identifies mitigative measures to be put in place prior to December 31, 2007, and adequately describes how these mitigative measures will minimize the risk of degraded emergency core cooling system (ECCS) and containment spray system (CSS) functions during the extension period.
The SECY paper also stated that for proposed extensions beyond several months, a licensees request will more likely be accepted if the proposed mitigative measures include temporary physical improvements to the ECCS sump or materials inside containment to better ensure a high level of ECCS sump performance.
The licensees technical basis for the current extension request references the justification provided in their letter of December 10, 2007 (ADAMS Accession No. ML073450498), for their previous extension request along with the following considerations to indicate the minimization of the risk of degraded ECCS and CSS functions during the extension period:
- 1.
Calvert Cliffs NPSH evaluations do not allow crediting of containment air pressure greater than the minimum air pressure that might exist at the start of an accident.
The design basis evaluation determined negative NPSH margin for the two CS pumps at the start of sump recirculation when the sump temperature is still above 200 oF, and sump water saturation pressure is greater than that minimum containment air pressure. The licensee stated that if containment pressure were allowed to be equal to atmospheric pressure, then acceptable NPSH margin would exist for all ECCS pumps. The licensee further stated that existing analyses show that at least 0.4 psig backpressure would exist over 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br /> into a large-break loss-of-coolant accident (LOCA).
- 2.
Since the earliest a recirculation actuation signal could be received would be 30 minutes and per Figure 5-2 of NUREG/CR-6808, Knowledge Base for the Effect of Debris on Pressurized Water Reactor Emergency Core Cooling Sump Performance, all shreds of insulation would be expected to settle to the floor prior to that time, transportability of insulation shreds and other debris would be greatly diminished.
- 3.
Settling time considerations and testing results indicate that debris accumulation on the strainer would be gradual, and procedural guidance exists which identifies operator actions to be taken to mitigate debris accumulation. The licensee gave the example of pump cavitation detected by operators who respond in accordance with training received in response to NRC Bulletin 2003-01 to consider reducing the total sump flow, first by throttling high-pressure safety injection (HPSI) flow, and then if necessary turning off the CS pumps and relying on containment air coolers for atmospheric control. The licensee stated that only one HPSI pump at throttled flow is needed to provide adequate cooling for the core.
- 4.
Due to the installation of the new sump strainer and other associated changes and evaluations, there has been a significant reduction in the vulnerability to debris blockage and component wear in the recirculation system when mitigating a LOCA. For small-and intermediate-break LOCAs, the licensee stated that it expected that there will be a significant reduction in debris generation of at least one order of magnitude less than that of a large-break LOCA. With that type of reduction in the fibrous and particulate sources, the licensee stated that a functional strainer would be assured for small-and intermediate-break LOCAs given the very small negative NPSH margin of the CS pumps for the large-break LOCA case.
With regard to the criterion relating to temporary physical improvements to the ECCS sump or materials inside containment to better ensure a high level of ECCS sump performance, the NRC believes that the approximate 6,000 ft2 of replacement strainers, replacement of the HPSI pump cyclone separators to mitigate the effect of debris laden fluids passing through them, the banding or removal of calcium silicate insulation from LOCA susceptible areas inside containment, and the metal jacketing or banding of the remaining calcium silicate insulation located outside of the LOCA zones of influence to protect it from CS damage meet that criterion.
The NRC staff believes that the licensee has a reasonable plan that should result in the completion of final GL 2004-02 corrective actions that provide acceptable strainer function with adequate margin for uncertainties. The additional time requested in the June 18, 2008, letter is considered to be of low safety concern given the mitigation measures and plant improvements already in place. Based on the licensee having satisfactorily addressed the NRC GL 2004-02 due date extension criteria as discussed above, the NRC staff finds it is acceptable to extend the completion dates for GL 2004-02 corrective actions associated with strainer performance testing for Calvert Cliffs Unit Nos. 1 and 2 as follows:
(1)
Buffer change-out for Unit 2 during that units spring 2009 refueling outage (scheduled to start February 24, 2009), and buffer change-out for Unit 1 within 90 days of the NRCs approval of the license amendment to be requested by July 31, 2008, but no later than June 1, 2009, (2)
Installation, if needed, of tested contingency modifications in Unit 2 during the spring 2009 refueling outage, and, if needed, in Unit 1 as discussed below, (3)
Finalization of required evaluations, completion of owner acceptance reviews and verifications, and submittal of a GL 2004-02 supplemental response by September 30, 2008, and (4)
Unit 2 aluminum material removal during the spring 2009 Unit 2 refueling outage, which is scheduled to start February 24, 2009.
The NRC staff expects the licensee to place a high priority on completing remaining actions and updating the plants licensing bases as soon as possible, and specifically on developing contingency modifications for the upcoming strainer head loss testing which will avoid the need for future testing iterations and which will, therefore, provide assurance that GL 2004-02 corrective actions will be completed as soon as feasible.
The NRC staff accepts the licensees contingency plan to test additional modifications at the same time as the testing reflecting the buffer changes. The staff expects the near-term strainer testing to include sufficiently diverse and robust contingency modifications to demonstrate acceptable strainer function for both units. The staff accepts the licensees intent to make any additional modifications needed for Unit 2 during that units spring 2009 refueling outage. If the upcoming strainer testing indicates the need for additional modifications in Unit 1, the staff expects that the licensee will identify to the staff, before the beginning of the Unit 2 spring 2009 refueling outage, the complete set of modifications for Unit 1 and the proposed near-term dates for installation of modifications in Unit 1.