ML14115A440
| ML14115A440 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 04/24/2014 |
| From: | Siva Lingam Plant Licensing Branch II |
| To: | Hightower R Duke Energy Corp |
| References | |
| ME9633 | |
| Download: ML14115A440 (4) | |
Text
1 NRR-PMDAPEm Resource From:
Lingam, Siva Sent:
Thursday, April 24, 2014 3:12 PM To:
Hightower, Richard (Richard.Hightower@duke-energy.com)
Cc:
Quichocho, Jessie; Rosenberg, Stacey; Regner, Lisa; Barillas, Martha; Cheruvenki, Ganesh
Subject:
H. B. Robinson, Unit 2 PWR Vessel Internal Program Plan for Aging Management - Request for Additional Information (RAIs) (TAC No. ME9633)
Please note the following official follow-up RAI on the subject matter, and provide your response within 60 days from this e-mail:
In a letter dated January 8, 2014 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML14016A279), the U.S. Nuclear Regulatory Commission (NRC) staff issued a follow-up request for additional information (RAI), RAI-5(b)-1, as a part of its review of the aging management program (AMP) for the reactor vessel internals (RVI) at H.B. Robinson [Robinson Nuclear Plant (RNP)]. RAI-5(b)-1 is in reference to the AMP related to RNPs cast austenitic stainless steel (CASS) lower support columns in the reactor vessel. By a letter dated February 19, 2014 (ADAMS Accession No. ML14056A193), Duke Energy Progress, Inc. (the licensee) responded to RAI-5(b)-1 and provided delta ferrite values for all of its 68 lower support columns. The NRC staff reviewed the licensees response and determined the need to issue this follow-up RAI, based on the new staff consensus on the threshold limits for neutron irradiation embrittlement (IE) and thermal embrittlement (TE) of CASS materials. The bases for the NRC staffs new consensus on the threshold limits are described in Attachment 1 of this e-mail.
The licensees response to RAI-5(b)-1 indicated that 6 of the 68 columns have delta ferrite content greater than 15%, which, when combined with an expected neutron exposure greater than 0.45 dpa, would indicate the need to consider the columns susceptible to TE and IE.
RAI-5(b)-1-1:
To enable evaluation of the susceptibility of these 6 columns to embrittlement, either:
a) provide the neutron exposures for these columns and assess their susceptibility to IE and TE consistent with Attachment 1, or b) provide a functionality evaluation of the lower support structure considering the effects of IE and TE for those 6 columns for which TE could not be screened out.
ATTACHMENT 1 MRP-227-Action Item 7 in the NRC staffs safety evaluation (SE) for the MRP-227-A Threshold limits developed by the staff for thermal (TE) and neutron embrittlement (NE) in cast austenitic stainless steel (CASS).
=
Background===
On March 12, 2014, the NRC staff held a conference call with MRP-EPRI members and conveyed the staffs position (addressed below) related to the threshold limits for thermal (TE) and neutron irradiation embrittlement (IE) in cast austenitic stainless steel (CASS).
Based on the lower bound estimate of fracture toughness of austenitic stainless steel materials as a function of fluence from NUREG/CR-7027, Degradation of LWR Core Internal Materials Due to Neutron Irradiation, the NRR staff proposes that the fluence screening criteria in the Grimes letter dated May 19, 2000 (ADAMS
2 Accession No. ML003717179), for all CF-3 and CF-8 materials be increased to 0.45 dpa (displacements per atom (dpa) = 3x1020 n/cm2 (E > 1MeV)), as described in the following tables. Furthermore, the NRC staff proposes that CF-3 and CF-8 materials in an RVI component can be treated as a wrought stainless steel when the ferrite levels are low enough such that significant TE is not expected to occur; with the current state of knowledge, the staff considers the maximum ferrite level is 15%. In MRP-175 and MRP-227, wrought stainless steel requires aging management when the neutron fluence > 1.5 dpa.
Therefore, the NRC staff recommends that the current Grimes letter be revised to read as followsthe CF-3 and CF-8 materials can be treated as a wrought stainless steel for aging management when the ferrite content is less than or equal to 20% and its exposure to neutron fluence is 0.45 dpa. For CF-3 and CF-8 materials that are exposed to a fluence value > 0.45 dpa and < 1.5 dpa, aging management is required when the ferrite content exceeds 15%. Above 1.5 dpa, all stainless steel RVI components are considered susceptible to loss of fracture toughness and require aging management.
Proposed NRC position on Screening of CASS Reactor Vessel Internal Components The NRC staff requires licensees/applicants to consider embrittlement from both TE and IE. The NRC staff would consider screening for susceptibility to embrittlement based on fluence and ferrite content (measured or calculated from Hulls equation and summarized in Tables A, B, and C shown below) to be conservative.
Table A Screening for Components with < 0.45 dpa neutron exposure Molybdenum (wt. %)
Casting Method Susceptibility Delta ferrite %
High 2.0-3.0%
(CF-8M) static TE
> 14%
No 14%
centrifugal TE
> 20%
No 20%
Low 0.5% max (CF-3 and CF-8) static TE
> 20%
No 20%
centrifugal No All Table B Screening for Components with 0.45 dpa neutron exposure 1.5 dpa Molybdenum (wt. %)
Casting Method Susceptibility Delta ferrite %
High 2.0-3.0%
> 10%
No 10%
> 15%
No 15%
Low 0.5% max (CF-3 and CF-8) static TE + IE
> 15%
No 15%
centrifugal No All Table C Screening for Components with > 1.5 dpa neutron exposure Molybdenum (wt. %)
Casting Method Susceptibility Delta ferrite %
3 High 2.0-3.0%
> 10%
IE 10%
> 15%
IE 15%
Low 0.5% max (CF-3 and CF-8) static TE + IE
> 15%
IE 15%
centrifugal IE All Siva P. Lingam U.S. Nuclear Regulatory Commission Project Manager (NRR/DORL/LPL2-2)
Brunswick Steam Electric Plant Robinson Steam Electric Plant Location: O8-D5; Mail Stop: O8-G9a Telephone: 301-415-1564; Fax: 301-415-1222 E-mail address: siva.lingam@nrc.gov
Hearing Identifier:
NRR_PMDA Email Number:
1241 Mail Envelope Properties (Siva.Lingam@nrc.gov20140424151100)
Subject:
H. B. Robinson, Unit 2 PWR Vessel Internal Program Plan for Aging Management - Request for Additional Information (RAIs) (TAC No. ME9633)
Sent Date:
4/24/2014 3:11:53 PM Received Date:
4/24/2014 3:11:00 PM From:
Lingam, Siva Created By:
Siva.Lingam@nrc.gov Recipients:
"Quichocho, Jessie" <Jessie.Quichocho@nrc.gov>
Tracking Status: None "Rosenberg, Stacey" <Stacey.Rosenberg@nrc.gov>
Tracking Status: None "Regner, Lisa" <Lisa.Regner@nrc.gov>
Tracking Status: None "Barillas, Martha" <Martha.Barillas@nrc.gov>
Tracking Status: None "Cheruvenki, Ganesh" <Ganesh.Cheruvenki@nrc.gov>
Tracking Status: None "Hightower, Richard (Richard.Hightower@duke-energy.com)" <Richard.Hightower@duke-energy.com>
Tracking Status: None Post Office:
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