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 2022 Materials Technical Exchange Public Meeting
- May 25, 2022 U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of New and Renewed Licenses Vessels and Internals Branch
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 5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 5
Support skirt Neutron shield tank (Figures are from NUREG/CR-5320, available from OSTI.gov)
Four basic designs (continued) 5/25/2022 RV Supports - Subsequent License Renewal l May 2022 Materials Technical Exchange Public Meeting 6
(Figures are from WCAP-14422, Rev. 2-A and NUREG/CR-5320)
Short column Long column
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