ML14183B230
| ML14183B230 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 07/07/2014 |
| From: | Robinson L R License Renewal Projects Branch 1 |
| To: | |
| Robinson L R, 415-4115 | |
| References | |
| TAC MF1879, TAC MF1880, TAC MF1881, TAC MF1882 | |
| Download: ML14183B230 (7) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 July 7, 2014
LICENSEE: Exelon Generation Company, LLC
FACILITY: Byron Station, Units 1 and 2 Braidwood Station, Units 1 and 2
SUBJECT:
SUMMARY OF TELEPHONE CONFERENCE CALL HELD ON JUNE 24, 2014, BETWEEN THE U.S. NUCLEAR REGULATORY COMMISSION AND EXELON GENERATION COMPANY, LLC CONCERNING DRAFT REQUEST FOR ADDITIONAL INFORMATION, SET 36, PERTAINING TO THE BYRON STATION AND BRAIDWOOD STATION, LICENSE RENEWAL APPLICATION (TAC NOS. MF1879, MF1880, MF1881, MF1882)
The U.S. Nuclear Regulatory Commission (NRC or the staff) and representatives of Exelon Generation Company, LLC (Exelon or the applicant), held a telephone conference call on June 24, 2014, to discuss and clarify the staff's draft request for additional information (DRAI),
Set 36, concerning the Byron Station, Units 1 and 2, and the Braidwood Station, Units 1 and 2, license renewal application. The telephone conference call was useful in clarifying the intent of the staff's DRAIs.
provides a listing of the participants, and Enclosure 2 contains a listing of the DRAIs discussed with the applicant, including a brief description on the status of the items.
The applicant had an opportunity to comment on this summary.
/RA/ Lindsay Robinson, Project Manager Projects Branch 1 Division of License Renewal Office of Nuclear Reactor Regulation
Docket Nos. 50-454, 50-455, 50-456, and 50-457
Enclosures:
- 1. List of Participants
- 2. List of Draft Request for Additional Information
cc w/encls: Listserv
ML14183B230 *concurred via email OFFICE LA:DLR PM:RPB1:DLR BC:RPB1:DLR PM:RPB1:DLR NAME YEdmonds LRobinson YDiazSanabria LRobinson DATE 07/2/14 07/7/14 07/7/14 07/7/14
SUBJECT:
SUMMARY OF TELEPHONE CONFERENCE CALL HELD ON JUNE 24, 2014, BETWEEN THE U.S. NUCLEAR REGULATORY COMMISSION AND EXELON GENERATION COMPANY, LLC CONCERNING DRAFT REQUEST FOR ADDITIONAL INFORMATION, SET 36, PERTAINING TO THE BYRON STATION AND BRAIDWOOD STATION, LICENSE RENEWAL APPLICATION (TAC NOS. MF1879, MF1880, MF1881, MF1882)
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RidsNrrPMByron Resource RidsNrrPMBraidwood Resource ----------------------------------
LRobinson DMcIntyre, OPA
EDuncan, RIII
JBenjamin, RIII
AGarmoe, RIII JMcGhee, RIII JRobbins, RIII
VMitlyng, RIII
PChandrathil, RIII ENCLOSURE 1 TELEPHONE CONFERENCE CALL BYRON STATION, UNITS 1 AND 2, AND BRAIDWOOD STATION, UNITS 1 AND 2 LICENSE RENEWAL APPLICATION LIST OF PARTICIPANTS June 24, 2014 PARTICIPANTS AFFILIATIONS Lindsay Robinson U.S. Nuclear Regulatory Commission (NRC) Allen Hiser NRC Seung Min NRC Aloysius Obodoako NRC John Hufnagel Exelon Generating Company, LLC (Exelon)
Al Fulvio Exelon Don Warfel Exelon Pete Tamburro Exelon Gary Becknell Exelon Don Brindle Exelon Ralph Wolen Exelon
ENCLOSURE 2 DRAFT REQUEST FOR ADDITIONAL INFORMATION BYRON STATION, UNITS 1 AND 2, AND BRAIDWOOD STATION, UNITS 1 AND 2, LICENSE RENEWAL APPLICATION June 24, 2014
The U.S. Nuclear Regulatory Commission (NRC or the staff) and representatives of Exelon Generation Company, LLC (Exelon or the applicant), held a telephone conference call on June 24, 2014, to discuss and clarify the following draft request for additional information (DRAI), Set 36, concerning the Byron Station, Units 1 and 2, and the Braidwood Station, Units 1 and 2, license renewal application (LRA).
DRAI 3.1.2.3.4-1a Applicability
- Byron Station (Byron) and Braidwood Station (Braidwood), Unit 1
=
Background===
- By letter date May 12, 2014, the applicant responded to request for additional information (RAI) 3.1.2.3.4-1 which addressed loss of fracture toughness in Byron and Braidwood, Unit 1 steam generator internal structural supports. In its response, the applicant revised license renewal application Table 3.1.2-4 by deleting the aging management review (AMR) line item which manages loss of fracture toughness for Byron and Braidwood, Unit 1 steam generator tube support lattice bar attachment components made of cast austenitic stainless steel (CASS). The deleted AMR line item indicated that these CASS components are exposed to treated water greater than 482 degrees Fahrenheit and may experience loss of fracture toughness due to thermal aging embrittlement. Byron and Braidwood manage both by the Steam Generators program.
The applicant further stated that loss of fracture toughness due to thermal aging embrittlement is not applicable to these steam generator CASS internal components (i.e., internal supports and structures and tube support plates and U-bend supports). The applicant reviewed the Grimes' letter to Walters on License Renewal Issue No. 98-0030, "Thermal Aging Embrittlement of Cast Stainless Steel Components," dated May 19, 2000, (ADAMS Accession Number ML003717179) and provided the following justification for excluding the steam generator tube support lattice bar attachment components, fabricated from SA-351 CF3M CASS, from being susceptible to thermal aging embrittlement.
The concern associated with thermal aging embrittlement is the reduction in fracture toughness of a component at low temperatures (i.e., room temperature) and the potential for non-ductile failure at low temperatures. The material properties at high temperature are not affected. Therefore, fracture of a CASS component is not expected at low temperatures. Since the loading on the CASS components at low temperature is negligible, the possibility that loss of fracture toughness would render the component incapable of performing its function without showing any visual evidence of cracking, deformation, or damage is also negligible.
The staff reviewed the Grimes' letter, dated May 19, 2000, and notes that it states that aging of CASS at reactor operating temperatures of 280-350 degrees Celsius (536-662 degrees Fahrenheit) can lead to changes in the mechanical properties of these materials, depending on the characteristics of the material and the environment to which the component is exposed.
The effects of thermal aging on materials include increases in the tensile strength, hardness, and Charpy impact energy transition temperature, as well as decreases in ductility, fracture toughness, and impact strength.
Further, NUREG/CR-6923, "Expert Panel Report on Proactive Materials Degradation Assessment" February 2007, states that:
Thermal aging of CASS at boiling water reactor and pressurized water reactor operating temperatures is characterized by an increase in hardness and tensile strength and a decrease in ductility, impact strength and toughness. In addition, the "brittle-ductile" transition temperature increases and the upper shelf decreases (emphasis added).
The upper shelf decrease described in NUREG/CR-6923 relates directly to behavior of CASS at operating temperatures, contrary to the assertion in the RAI response that the concerns with thermal aging embrittlement only apply at low temperatures.
As cited in the Grimes' letter, thermal aging of CASS results in reduced toughness, which means that the aged CASS component can tolerate smaller flaw sizes. Since the toughness of CASS is not directly measureable, the Grimes' letter and the Generic Aging Lessons Learned (GALL) Report cite that thermal aging of CASS can be appropriately managed by inspections to demonstrate that flaws of a potentially critical size are not present in the CASS component.
In addition, GALL Report AMP XI.M12 states that for high-molybdenum content steels (SA-351 Grades CF3M, CF3MA, and CF8M or other steels with 2.0 to 3.0 wt. percent Mo), static-cast steels with >14 percent ferrite and centrifugal-cast steels with >20 percent ferrite are potentially susceptible to thermal embrittlement. Static-cast high-molybdenum steels with 14 percent ferrite and centrifugal-cast high-molybdenum steels with 20 percent ferrite are not susceptible.
Issue: Thermal aging embrittlement of CASS may result in reduction in fracture toughness of a component at operating conditions (i.e., 536-662 degrees Fahrenheit), contrary to the assertion in the RAI response that it only applies at low temperatures. The reduction in fracture toughness of CASS requires adequate aging management.
Request: 1. Please provide the composition, ferrite content, and the fabrication method to determine if the SA-351 CF3M CASS components are susceptible to thermal aging embrittlement in accordance with the guidance of aging management program (AMP) XI.M12. If so, a) Justify the assertion in the response to RAI 3.1.2.3.4-1 that the concern associated with thermal aging embrittlement is a reduction in fracture toughness and a potential for non-ductile failure at low temperatures (i.e., room temperature).
b) Discuss how the proposed examinations will be adequate to provide assurance that the CASS components will not have flaws that could either (a) challenge the ability of the component to perform its intended safety function during normal operation, transient, and accident conditions; or (b) result in the generation of loose parts that could adversely affect the performance of other parts of the steam generator or downstream components.
Discussion
- The applicant requested clarification on the staff's concern. No edits were made to this request. This question will be sent as a formal request titled: "RAI 3.1.2.3.4-1a."