ML22143A838
| ML22143A838 | |
| Person / Time | |
|---|---|
| Issue date: | 05/25/2022 |
| From: | David Dijamco NRC/NRR/DNRL/NVIB |
| To: | |
| Kalikian R, 301-415-5590 | |
| Shared Package | |
| ML22143A408 | List: |
| References | |
| Download: ML22143A838 (8) | |
Text
Reactor Vessel Steel Supports for Subsequent License Renewal David Dijamco U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of New and Renewed Licenses Vessels and Internals Branch 2022 Materials Technical Exchange Public Meeting
- May 25, 2022
Content
- Where the evaluation fits in licensing
- Plants that have been evaluated
- Basic designs
- NUREG-1509, Radiation Effects on Reactor Pressure Vessel Supports
- Some thoughts on the evaluation (based on completed reviews) 5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 2
Where it fits in current approach to licensing
- SRP-SLR (NUREG-2192) 3.5.2.2.2.6 Reduction of Strength and Mechanical Properties of Concrete Due to Irradiation
- Proposing a separate subsection for RV support steel is underway
Purpose:
determine if a plant-specific aging management program(s) (or enhancement(s) to existing AMP(s)) is/are needed
- Foremost aging effect: embrittlement of structural steel due to irradiation
- Only for subsequent (80-year) license renewal (SLR)
- 60-year initial license renewal not a concern
- Based on resolution of generic safety issue 15 and conclusions in NUREG-0933, Revision 3 (search NUREG-0933 in public website)
- Based on results of consequence analyses that showed RV vessel loads are still supported with postulated broken supports
- Thus, not evaluated for 60-year initial renewal 5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 3
Plants that have been evaluated
- Safety evaluation issued: Turkey Point, Peach Bottom, Surry, North Anna, Point Beach
- Ongoing reviews: Oconee and St Lucie 5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 4
Four basic designs (Figures are from NUREG/CR-5320, available from OSTI.gov)
Neutron shield tank Support skirt 5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 5
Four basic designs (continued)
(Figures are from WCAP-14422, Rev. 2-A and NUREG/CR-5320)
Short column Long column 5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 6
Technical evaluation guidance document is NUREG-1509
- Initial screening: Section 4.2
- Evaluation criteria: Section 4.3
- Fracture mechanics approach (Figure 4-3)
- Applied stresses compared to critical stress
- Reference flaw sizes compared to critical flaw size
- Transition temperature approach (Figure 4-4)
- Nil-ductility transition temperature (NDTT) of the steel component (adjusted for embrittlement +
margin) is lower than lowest service temperature for that component
- Embrittlement curve: Figure 3-1
- Shift in NDTT vs radiation exposure (expressed in displacements per atom [dpa])
- Based on structural steel data 5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 7
Some thoughts on the evaluation
- Consider:
- Neutron energies down to 0.1 MeV
- Upper-bound curve of Figure 3-1 of NUREG-1509
- Other relevant aging effects due to irradiation (e.g., loss of bolt preload) and how they will be managed
- Aging effects due to irradiation for nonconcrete/nonmetallic materials (e.g., loss of lubricant in sliding surfaces) associated with RV support structure
- Conservatisms in analysis should be clearly described in the application.
- Food for thought:
- Is there a radiation exposure level below which an evaluation is not needed (similar to 1E17 n/cm2 threshold for vessels)?
- Guidance for the RV support steel evaluation still underway.
5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 8