ML123540455
| ML123540455 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 12/19/2012 |
| From: | Richard Guzman Plant Licensing Branch 1 |
| To: | Vanags U State of VT, Dept of Public Service |
| Guzman R, NRR/DORL 415-1030 | |
| References | |
| TAC ME7733 | |
| Download: ML123540455 (3) | |
Text
From:
Guzman, Richard To:
Vanags, Uldis
Subject:
Response to State Comments: Vermont Yankee License Amendment Request - Steam Dryer Inspection Frequency Date:
Wednesday, December 19, 2012 11:30:36 AM Good afternoon Mr. Vanags,
Thank you for forwarding the Vermont Public Service Departments comments in its letter dated December 6, 2012. The letter has been added to the NRCs Agencywide Documents Access and Management System (ADAMS) as accession no. ML11363A049.
In its letter, Vermont DPS expressed concern in the approval of the referenced license amendment request (LAR) stating that, the Department is concerned at the request for a three-cycle inspection protocol and does not feel NRC should accept it, particularly if the inspection of the steam dryer in RFO 31 were to reveal any new cracks or propagation of existing flaws beyond the acceptable growth rate. The NRC staff understands the concern stated in the Vermont DPS letter, and has considered the comments from the state in its review of the proposed LAR.
The NRC staff has evaluated the proposed change to the operating license and has determined that performing a baseline inspection during RFO 31 and re-inspections every third RFO cycle in accordance with the guidance contained in Boiling Water Reactor Vessel and Internals Project (BWRVIP)-139-A, BWR Vessel and Internals Project Steam Dryer Inspection and Flaw Evaluation Guidelines, with additional provisions in license condition (LC) 3.S., are acceptable and provide reasonable assurance for maintaining adequate level of safety and quality. The NRC staffs conclusion is based, in part, on the following:
- The successive steam dryer inspections indicated that the majority of cracks that were identified in the drain channel weld in the steam dryer were due to intergranular stress-corrosion cracking (IGSCC). These cracks were characterized as IGSCC due to their appearance (intermittent and jagged), and their location near heat-affected zones areas. The licensee determined that these cracks originated at cold worked areas due to grinding. The licensee also observed cracking in lifting lugs, dryer leveling screws, the steam dam plate, and a unit end plate. For new cracks found during steam dryer inspections, the NRC staff verified that GEH and the licensee performed evaluations to support continued operation of the steam dryer without repair. The visual inspections conducted during RFOs 28 and 29 confirmed that all previously identified indications have not grown, further supporting the GEH and licensee evaluations.
- The licensee performed preemptive modifications in which it used IGSCC resistant austenitic stainless steel base and weld metals, which reduce the possibility of IGSCC occurrence.These modifications were implemented to minimize the occurrence of fatigue as a result of EPU operation; since no IGSCC has been observed in the modified areas, it can be concluded that thus far, the aging degradation due to IGSCC has been adequately contained in these areas.
Historically, it was recognized that implementation of an EPU might result in cracking due to fatigue in steam dryer components. The fact that no fatigue crack
has been found during these inspections indicates that thus far, there is no active aging degradation due to fatigue in the VY steam dryer. Hence, the NRC staff agrees with the licensee that the preemptive modifications that were performed on the steam dryer reduced the stresses through a more uniform load distribution.
- Five successive inspections during RFOs 24, 25, 26, 27, and 28 and an additional inspection of the drain channel weld during RFO 29 showed that IGSCC crack growth was arrested. Thus far, the inspection criteria addressed in General Electric Service Information Letter (GE SIL) 644, Revision 2, and the BWRVIP-139-A has been met. Additionally, no fatigue-induced flaws were observed after the implementation of the EPU. As indicated by the licensee and reviewed by the NRC staff, no through-wall cracking nor any structural damage has been observed and the existing flaws have not shown to cause any detrimental effect on the functionality and structural integrity of the steam dryer; acoustic monitoring of the main steam system was performed during and after commencement of EPU operation, and no detrimental effect due to acoustic issues has been identified; and monitoring of the main steam system moisture carryover is performed, and to date, no abnormal moisture carryover has been noted.
- The absence of IGSCC crack growth and any new fatigue cracking after the EPU implementation in May 2006 provides technical justification for the licensee to perform their next inspection during RFO 31. Based on the monitoring of all previously identified indications since 2004 during RFOs 24 thru 29, which showed no crack growth, the NRC staff concludes that the proposed performance of steam dryer inspections at every third RFO cycle is acceptable with a condition requiring the licensee to inspect the steam dryer during RFO 31 and to provide all future inspection results, including those from RFO 31, demonstrating that the inspection results and evaluations are consistent with those from RFO 24 to RFO 29.
- Additionally, the steam dryer inspection during RFO 31 will provide information on steam dryer performance over two operating cycles in support of an extension of the steam dryer inspection interval to every third RFO. If the steam dryer inspection during RFO 31 or a later steam dryer inspection every third RFO identifies unacceptable indications, the licensee will be required (via a provision in the revised LC 3.S.) to inspect the steam dryer every RFO to determine the cause and rate of growth of the unacceptable indications until the licensee can develop justification to extend the inspection interval beyond each RFO. Based on that evaluation, the licensee may submit a future license amendment to extend the steam dryer inspection interval beyond every RFO.
Based on the items discussed above, the NRC staff has concluded there is reasonable assurance that the activities authorized by the proposed amendment can be conducted without endangering the health and safety of the public, and that such activities will be conducted in compliance with the Commissions regulations.
The staffs technical evaluation will be documented in a forthcoming safety evaluation (SE) for this amendment request. The above message will be referenced in Section 4.0 of the SE. I will provide you an advanced copy of the amendment and SE once it is issued to the licensee. Please extend my thanks to Commissioner Miller for her comments, and forward her the above message, as appropriate.
Sincerely,
Rich Guzman Sr. Project Manager NRR/DORL US NRC 301-415-1030 Richard.Guzman@nrc.gov
From: Vanags, Uldis [1]
Sent: Monday, December 17, 2012 10:42 AM To: Guzman, Richard
Subject:
RE: Where to mail comments - Vermont Yankee License Amendment Request - Steam Dryer Inspection Frequency
Hi Richard: Commissioner Miller sent a comment letter to NRC last week and copied you. I am not sure why you havent received it yet so I attached it to this email. Please let me know if you have any questions.
- Thanks, Uldis