ML15328A513
| ML15328A513 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 11/24/2015 |
| From: | David Gudger Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CAC MF5588 | |
| Download: ML15328A513 (6) | |
Text
Exelon Generation ~,
November 24, 2015 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Calvert Cliffs Nuclear Power Plant, Unit 1 Facility Operating License No. DPR-53 NRG Docket No. 50-317 200 Exelon Way Kennett Square. PA 19348 www.exeloncorp.com 10 CFR 50.55a
Subject:
Relief Request for Dissimilar Metal Butt Weld Examinations
References:
- 1) Letter from D. Gudger (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "Relief Request for Dissimilar Metal Butt Weld Examinations," dated March 5, 2015
- 2) Letter from A. Chereskin (U.S. Nuclear Regulatory Commission) to B. Hanson (Exelon Generation Company, LLC), "Calvert Cliffs Nuclear Power Plant, Unit No. 1 - Request for Additional Information Regarding:
Relief Request for Dissimilar Metal Butt Weld Examinations (CAC No.
MF5588)," dated November 3, 2015 In the Reference 1 letter, in accordance with 1 O CFR 50.55a, "Codes and standards,"
Paragraph 1 O CFR 50.55a(z)(2), Exelon Generation Company, LLC (Exelon), proposed an alternative to the requirements of 1 O CFR 50.55a(g)(6)(ii)(F) regarding examination coverage of dissimilar metal butt welds on the basis that complying with the specified requirement would result in hardship or unusual difficulty.
In the Reference 2 letter, the U.S. Nuclear Regulatory Commission requested additional information. Attached is our response.
There are no regulatory commitments in this letter.
If you have any questions concerning this letter, please contact Tom Loomis at (610) 765-5510.
Respectfully, Davi T. Gudger Manager - Licensing & Regulatory Affairs Exelon Generation Company, LLC
Response to RAI -
Relief Request for Dissimilar Metal Butt Weld Examinations November 24, 2015 Page2
Attachment:
Response to Request for Additional Information for Relief Request RR-ISl-04-10 cc:
Regional Administrator, Region I, USNRC USNRC Senior Resident Inspector, CCNPP Project Manager [CCNPP] USNRC
Attachment Response to Request for Additional Information for Relief Request RR-ISl-04-10
Question:
Response to Request for Additional Information for Relief Request RR-ISl-04-1 O Page 1 of 3
- 1. Recent operational experience (OE) with in-service inspection (ISi) of dissimilar metal butt welds (DMBW) in nuclear power plants include several instances of human errors in the application of qualified nondestructive examination (NOE) procedures. These errors have resulted in degraded examination performance such as incomplete examination coverage, identification of service-induced defects where none exist, or failure to identify service-induced defects. The industry formed the NOE Improvement Focus Group (NIFG) to address this OE and develop improved guidelines for the examination of DMBW. Verify that the NIFG guidance will be implemented during the DMBW examinations at CCNPP1 in 2016 or justify how your examinations will avoid the issues present in the OE.
Response
Exelon Generation Company, LLC (Exelon) is aware of operating experience with the inservice inspection of Dissimilar Metal Butt Welds and works closely with industry issue programs to revise and develop guidelines to improve the examinations and address issues such as those pointed out in this RAI. As directed by the NOE Action Plan Committee and the PWR Materials Management Program (PMMP) and Boiling Water Reactor Vessel and Internals Project (BWRVIP) Executive Oversight Committees, the NOE Improvement Focus Group (NIFG) was formed to address NOE improvement and extent of condition actions in response to DMBW OE.
Exelon actively participates in these organizations. Specifically, Exelon NOE procedures have adopted the NFIG and applicable Industry Issue Program NEl-03-08 Mandatory, Needed and Good Practice guidance elements. These procedures will be in effect during the Calvert Cliffs Nuclear Power Plant (CCNPP), Unit 1 DMBW examinations.
Question:
- 2. As a defense in depth measure for indications which may exist in the areas that cannot be examined and may grow through-wall, leakage monitoring is useful in the early detection of through-wall cracks. Describe the leakage monitoring used for the reactor coolant pressure boundary, including leak rates or trends that would cause actions to be taken to determine the location of leaks.
Response
The normal method for characterizing the Reactor Coolant System (RCS) identified and unidentified leakage at CCNPP, Units 1 and 2 is by means of a reactor coolant inventory analysis (commonly called a water balance inventory) performed under Operations Surveillance Test Procedures STP 0-27-1 and STP 0-27-2. The inventory balance is performed as required by CCNPP Technical Specifications. The procedure is performed at a surveillance interval of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The procedure methods use the recommendations and guidance in WCAP-16423-NP
("Pressurized Water Reactor Owners Group Standard Process and Methods for Calculating RCS Leak Rate for Pressurized Water Reactors") and WCAP-16465-NP ("Pressurized Water Reactor Owners Group Standard RCS Leakage Action Levels and Response Guidelines for Pressurized Water Reactors").
Leak detection at CCNPP is also provided by three systems: 1) containment sump level alarm system; 2) containment atmosphere particulate monitoring system, and; 3) containment atmosphere gaseous radioactivity monitoring system. These systems have high level and alert
Response to Request for Additional Information for Relief Request RR-ISl-04-1 O Page 2 of 3 status alarms in the control room. These systems also have Technical Specification required monitoring every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The sensitivity of the containment radioactivity monitors varies depending on the amount of radioactivity in the primary coolant. The time to detect a 0.1 gpm leak with the containment atmosphere radioactivity monitors varies from 61 minutes for 1 %
failed fuel to 1743 minutes for 0.001% failed fuel. The containment sump alarm response is also variable dependent on the location of the leak, how much vapor condenses, and where it condenses.
CCNPP Technical Specifications also requires that the containment atmospheric radiation monitor and containment sump alarm be operable or other compensatory actions be taken, such as performing the water balance leak rate calculation more frequently. Therefore, a significant step change in RCS unidentified leakage (i.e., 0.25 gpm) will be readily apparent from the results of the water inventory balance calculation and would also likely be detectable through at least one of the three leak detection systems.
In addition, procedure ER-AP-331-1003, "RCS Leakage Monitoring and Action Plan,"
establishes the controls and expectations for monitoring RCS leakage under the Exelon Nuclear Boric Acid Corrosion Control (BACC) program and the PWR Owner's Group (PWROG)
Operations Subcommittee "Needed" Recommendations under letters OG-07-387 and OG 400, and associated guidance for these recommendations contained in WCAPs 16423 and 16465. This procedure defines the methodology used to establish acceptable baseline values, establish unidentified leakage action levels, establishes the criteria used to ensure adequate monitoring of RCS leakage occurs, and establishes the minimum actions that could be taken at each action level to ensure the safe operation of the plant. This procedure also addresses abnormal trends in RCS primary system leakage indicators, such as tritium, containment atmospheric radiation monitor particulate, containment fan cooler performance, etc. which may provide indication of leaks much smaller than Technical Specification and PWROG RCS leakage levels.
Therefore, the RCS Leakage Monitoring and Action Plan procedure ensures that RCS leakage is within Technical Specification limits and provides early detection of negative trends based on statistical analysis.
The procedural Action Levels contained within ER-AP-331-1003 are as follows:
Action Level 1 :
One seven day rolling average of unidentified RCS inventory balance is greater than 0.1 gpm.
Nine consecutive unidentified RCS inventory balance values greater than the baseline mean [µ] value.
Action Level 2:
Two consecutive unidentified RCS inventory balance values greater than 0.15 gpm.
Two of three consecutive unidentified RCS inventory balance values greater than the baseline mean plus two times the standard deviation (µ+2cr).
Action Level 3:
Response to Request for Additional Information for Relief Request RR-ISl-04-10 Page 3 of 3 One unidentified RCS inventory balance value greater than 0.3 gpm.
One unidentified RCS inventory balance value greater than the baseline mean value plus three times the standard deviation (µ+3o).
Defined actions for each Action Level are contained in ER-AP-331-1003.
Question:
- 3. The NRG staff requests confirmation that the licensee will continue to evaluate new technologies and approaches that offer nondestructive examination exam coverage improvements as they become available. The goal of each examination should be to obtain 100% examination coverage of the required exam volume.
Response
Exelon will continue to evaluate new technologies and approaches that offer nondestructive examination improvements, including exam volume coverage improvement, as they become available. As new ultrasonic techniques and tooling are qualified, Exelon reviews the new tooling and techniques for improved performance as well as increased inspection coverage.