ML060950351

GALL AMP: XI.M12, Thermal Aging Embrittlement of Cast Austenitic Stainless Steel (CASS) (Audit Worksheet GALL Report AMP)

ML060950351
Person / Time
Site:	Vermont Yankee
Issue date:	02/28/1998
From:	Morgan M NRC/NRR/ADRO/DLR/RLRC
To:	Office of Nuclear Reactor Regulation
morgan M NRR/NRC/DLR/RLRC, 415-2232
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References
TAC MC9668
Download: ML060950351 (6)

Text

AUDIT WORKSHEET GALL REPORT AMP PLANT: ______________________________

LRA AMP: __________________________ REVIEWER: ______________________

GALL AMP: XI.M12, Thermal Aging Embrittlement of Cast Austenitic DATE: __________________________

Stainless Steel (CASS)_

Program Auditable GALL Criteria Documentation of Audit Finding Element Program A. The reactor coolant system components are inspected in Consistent with GALL AMP: Yes No Description accordance with the American Society of Mechanical Engineers Document(s) used to confirm Criteria:

(ASME) Boiler and Pressure Vessel Code,Section XI. This inspection is augmented to detect the effects of loss of fracture toughness due to thermal aging embrittlement of cast austenitic stainless steel (CASS) components. This aging management Comment:

program (AMP) includes (a) determination of the susceptibility of CASS components to thermal aging embrittlement based on casting method, molybdenum content, and percent ferrite, and B. (b) for potentially susceptible components, as defined Consistent with GALL AMP: Yes No below, aging management is accomplished through either Document(s) used to confirm Criteria:

enhanced volumetric examination or plant- or component-specific flaw tolerance evaluation. Additional inspection or evaluations to demonstrate that the material has adequate fracture toughness are not required for components that are not Comment:

susceptible to thermal aging embrittlement.

C. For pump casings and valve bodies, based on the Consistent with GALL AMP: Yes No assessment documented in the letter dated May 19, 2000, from Document(s) used to confirm Criteria:

Christopher Grimes, Nuclear Regulatory Commission (NRC), to Douglas Walters, Nuclear Energy Institute (NEI), screening for susceptibility to thermal aging is not required. The existing ASME Section XI inspection requirements, including the Comment:

alternative requirements of ASME Code Case N-481 for pump casings, are adequate for all pump casings and valve bodies.

XI.M12 Thermal Aging Embrittlement of Cast Austenitic Stainless Steel (CASS) 1

Program Auditable GALL Criteria Documentation of Audit Finding Element

1. Scope of A. The program includes screening criteria to determine which Consistent with GALL AMP: Yes No Program CASS components are potentially susceptible to thermal aging Document(s) used to confirm Criteria:

embrittlement and require augmented inspection. The screening criteria are applicable to all primary pressure boundary and reactor vessel internal components constructed from SA-351 Grades CF3, CF3A, CF8, CF8A, CF3M, CF3MA, CF8M, with Comment service conditions above 250°C (482°F). The screening criteria for susceptibility to thermal aging embrittlement are not applicable to niobium-containing steels; such steels require evaluation on a case-by-case basis. For potentially susceptible components, aging management is accomplished either through volumetric examination or plant- or component-specific flaw tolerance evaluation.

B Based on the criteria set forth in the May 19, 2000 NRC letter, Consistent with GALL AMP: Yes No the susceptibility to thermal aging embrittlement of CASS Document(s) used to confirm Criteria:

components is determined in terms of casting method, molybdenum content, and ferrite content. For low-molybdenum content (0.5 wt.% max.) steels, only static-cast steels with >20%

ferrite are potentially susceptible to thermal embrittlement. Comment:

Static-cast low-molybdenum steels with 20% ferrite and all centrifugal-cast low-molybdenum steels are not susceptible. For high-molybdenum content (2.0 to 3.0 wt.%) steels, static-cast steels with >14% ferrite and centrifugal-cast steels with >20%

ferrite are potentially susceptible to thermal embrittlement.

Static-cast high-molybdenum steels with 14% ferrite and centrifugal-cast high-molybdenum steels with 20% ferrite are not susceptible. In the susceptibility screening method, ferrite content is calculated by using the Hulls equivalent factors (described in NUREG/CR-4513, Rev. 1) or a method producing an equivalent level of accuracy (+/-6% deviation between measured and calculated values). A fracture toughness value of 255 kJ/m2 (1,450 in.-lb/in.2) at a crack depth of 2.5 mm (0.1 in.)

is used to differentiate between CASS materials that are nonsusceptible and those that are potentially susceptible to XI.M12 Thermal Aging Embrittlement of Cast Austenitic Stainless Steel (CASS) 2

Program Auditable GALL Criteria Documentation of Audit Finding Element thermal aging embrittlement. Extensive research data indicate that for nonsusceptible CASS materials, the saturated lower-bound fracture toughness is greater than 255 kJ/m2 (NUREG/CR-4513, Rev. 1).

C For pump casings and valve bodies, screening for Consistent with GALL AMP: Yes No susceptibility to thermal aging embrittlement is not required. The Document(s) used to confirm Criteria:

staffs conservative bounding integrity analysis shows that thermally aged CASS valve bodies and pump casings are resistant to failure. For all pump casings and valve bodies greater than nominal pipe size (NPS) 4 in., the existing ASME Comment:

Section XI inspection requirements, including the alternative requirements of ASME Code Case N-481 for pump casings, are adequate. ASME Section XI, Subsection IWB, requires only surface examination of valve bodies less than NPS 4 in. For valve bodies less than NPS 4 in., the adequacy of inservice inspection (ISI) according to ASME Section XI has been demonstrated by an NRC-performed bounding integrity analysis (Reference letter from Christopher Grimes dated May 19, 2000).

2. Preventive A. The program consists of evaluation and inspection and Consistent with GALL AMP: Yes No Actions provides no guidance on methods to mitigate thermal aging Document(s) used to confirm Criteria:

embrittlement.

Comment:

3. Parameters A. The AMP monitors the effects of loss of fracture toughness Consistent with GALL AMP: Yes No Monitored/ on the intended function of the component by identifying the Document(s) used to confirm Criteria:

Inspected CASS materials that are susceptible to thermal aging embrittlement. For potentially susceptible materials, the program consists of either enhanced volumetric examination to detect and size cracks or plant- or component-specific flaw tolerance Comment:

evaluation (loss of fracture toughness is of consequence only if cracks exist).

XI.M12 Thermal Aging Embrittlement of Cast Austenitic Stainless Steel (CASS) 3

Program Auditable GALL Criteria Documentation of Audit Finding Element

4. Detection of A. For pump casings and valve bodies and not susceptible Consistent with GALL AMP: Yes No Aging Effects piping, no additional inspection or evaluations are required to Document(s) used to confirm Criteria:

demonstrate that the material has adequate fracture toughness.

For potentially susceptible piping, because the base metal does not receive periodic inspection per ASME Section XI, the CASS AMP provides for volumetric examination of the base Comment:

metal, with the scope of the inspection covering the portions determined to be limiting from the standpoint of applied stress, operating time, and environmental considerations. Examination methods that meet the criteria of the ASME Section XI, Appendix VIII, are acceptable.

B Alternatively, a plant- or component-specific flaw tolerance Consistent with GALL AMP: Yes No evaluation, using specific geometry and stress information, can Document(s) used to confirm Criteria:

be used to demonstrate that the thermally-embrittled material has adequate toughness.

Comment:

5. Monitoring A. Inspection schedules in accordance with IWB-2400 or IWC- Consistent with GALL AMP: Yes No and Trending 2400 and reliable examination methods provide timely detection Document(s) used to confirm Criteria:

of cracks.

Comment:

6. Acceptance A. Flaws detected in CASS components are evaluated in Consistent with GALL AMP: Yes No Criteria accordance with the applicable procedures of IWB-3500 or Document(s) used to confirm Criteria:

IWC-3500.

Comment:

B Flaw tolerance evaluation for components with ferrite content Consistent with GALL AMP: Yes No up to 25% is performed according to the principles associated Document(s) used to confirm Criteria:

with IWB-3640 procedures for submerged arc welds (SAW),

disregarding the Code restriction of 20% ferrite in IWB-XI.M12 Thermal Aging Embrittlement of Cast Austenitic Stainless Steel (CASS) 4

Program Auditable GALL Criteria Documentation of Audit Finding Element 3641(b)(1). Extensive research data indicate that the lower-bound fracture toughness of thermally aged CASS materials Comment:

with up to 25% ferrite is similar to that for submerged arc welds (SAWs) with up to 20% ferrite (Lee et al., 1997). Flaw evaluation for piping with >25% ferrite is performed on a case-by-case basis by using fracture toughness data provided by the applicant.

7. Corrective A. Repair is performed in conformance with IWA-4000 and IWB- Consistent with GALL AMP: Yes No Actions 4000 or IWC-4000, and replacement in accordance with IWA- Document(s) used to confirm Criteria:

7000 and IWB-7000 or IWC-7000. As discussed in the appendix to this report, the staff finds the requirements of 10 CFR Part 50, Appendix B, acceptable to address the corrective actions.

Comment:

8. A. Site quality assurance (QA) procedures, review and approval Consistent with GALL AMP: Yes No Confirmation processes, and administrative controls are implemented in Document(s) used to confirm Criteria:

Process accordance with the requirements of 10 CFR Part 50, Appendix B. As discussed in the appendix to this report, the staff finds the requirements of 10 CFR Part 50, Appendix B, acceptable to address the confirmation process and administrative controls. Comment:

9. A. See Item 8, above. Consistent with GALL AMP: Yes No Administrative Document(s) used to confirm Criteria:

Controls Comment:

10. Operating A. The AMP was developed by using research data obtained on Consistent with GALL AMP: Yes No Experience both laboratory-aged and service-aged materials. Based on this Document(s) used to confirm Criteria:

information, the effects of thermal aging embrittlement on the intended function of CASS components are effectively managed.

Comment:

XI.M12 Thermal Aging Embrittlement of Cast Austenitic Stainless Steel (CASS) 5

EXCEPTIONS Item Program Elements LRA Exception Description Basis for Accepting Exception Documents Reviewed Number (Identifier, Para.# and/or Page #)

1.

2.

ENHANCEMENTS Item Program Elements LRA Enhancement Description Basis for Accepting Enhancement Documents Reviewed Number (Identifier, Para.# and/or Page #)

1.

2.

DOCUMENT REVIEWED DURING AUDIT Document Number Identifier (number) Title Revision and/or Date 1.

2.

3.

4.

XI.M12 Thermal Aging Embrittlement of Cast Austenitic Stainless Steel (CASS) 6