ML19134A229
| ML19134A229 | |
| Person / Time | |
|---|---|
| Issue date: | 05/21/2019 |
| From: | David Dijamco Division of Materials and License Renewal |
| To: | |
| Shared Package | |
| ML19136A264 | List:
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| References | |
| Download: ML19134A229 (22) | |
Text
Exclusion of 25 deg F Embrittlement in Topical Report PWROG-15109-NP David Dijamco Technical Reviewer Office of Nuclear Reactor Regulation Division of Materials and License Renewal 2019 Annual Materials Exchange Public Meeting May 21-22, 2019
Topics
- Exclusion of 25F embrittlement - what is it?
- NRCs position (May 2018 public meeting)
- Summary of PWROG-15109-NP and technical basis in the report for excluding 25F embrittlement
- Summary of NRCs evaluation of PWROG-15109-NP technical basis 2
What is the 25F embrittlement exclusion?
- Recommendation from TLR-RES/DE/CIB-2013-01 (ML14318A177)
- Details in the TLR; presented by EPRI in May 2018 (ML18141A392)
- Embrittlement may be excluded if RTNDT< 25F
- Considered scatter in RTNDT surveillance capsule data (prior 2002) in the neighborhood of 1 x 1017 n/cm2 (E > 1 MeV) 3
What is RTNDT?
4 30 ft-lb T30 T30 = RTNDT
NRCs position (May 2018 Public Meeting, ML18141A456)
- TLR is not an acceptable basis for neglecting embrittlement effects if RTNDT or T30 less than 25F.
- Current NRC position is described in RIS 201411: RPV toughness calculations must account for radiation effects for those materials with fluence greater than 1017 n/cm2 (E > 1 MeV), without exclusion even if RTNDT or T30 less than 25F.
- NRC staff is prepared to review any industry proposal which provides an adequate technical basis for the proposal.
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Summary of PWROG-15109-NP
- Objective is to demonstrate that pressure-temperature (P-T) limits for reactor pressure vessel (RPV) nozzles are bounded by the P-T limits in the traditional beltline location (RPV shell).
- Developed generic P-T limits for RPV nozzles and compared with all NRC-approved P-T limits in the RPV shell to show nozzles are bounded.
- Topical report can be referenced if nozzle fluence is below a threshold corresponding to RTNDT of 25F.
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Summary of PWROG-15109-NP
- ART = initial properties + embrittlement 7
= initial RTNDT + RTNDT + margin
Summary of PWROG-15109-NP
- Best-estimate Cu wt. % from 178 inlet and outlet nozzle forgings
- Upper limit Ni wt. % for SA-508 Cl 2
Summary of PWROG-15109-NP 9
25F 4.28 x 1017 n/cm2
The supplement to PWROG-15109-NP (ML19091A089) included a technical basis for excluding RTNDT of 25F.
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Summary of Technical Basis in PWROG-15109-NP for excluding 25°F 11 Data used to develop ASTM E900 trend curve Standard deviation = 18.6F
Summary of Technical Basis in PWROG-15109-NP for excluding 25°F
- 18.6F < 25F but
- Reasonable compared to standard deviation from known embrittlement trend curves for forgings:
- 17F (RG 1.99, Rev 2)
- 18.6F (10 CFR 50.61a, Cu 0.072 wt %)
- 19.6F (10 CFR 50.61a, Cu > 0.072 wt %)
- and
- For RPV matl with high Cu (highly embrittled), RTNDT at 0.99 x 1017 n/cm2
- 24.5F (Cu = 0.30 wt %)
- 25.4F (Cu = 0.28 wt %)
- 29.6F (Cu = 0.35 wt %)
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Summary of NRCs evaluation of PWROG-15109-NP technical basis
- The technical basis presents compelling reasons for excluding 25F but to ensure reasonable assurance, the staff performed an independent assessment of the safety impact of including 25F in the generic nozzle P-T limits developed in the report.
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Summary of NRCs evaluation of PWROG-15109-NP technical basis
- Independent safety assessment Focused on PWRs in which the nozzle has largest potential to become limiting
- Shell matls (inc shell welds) with low Cu content (screen in)
- Nozzle fluence at end of life < 1 x 1017 n/cm2 (screen out)
Summary of NRCs evaluation of PWROG-15109-NP technical basis
- Independent safety assessment Further screening by taking the generic nozzle ART calculated in the report for 1/4T flaw (43F) and adding the 25F (and corresponding margin) to it in the ART formula.
Two ways:
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Summary of NRCs evaluation of PWROG-15109-NP technical basis
- Independent safety assessment
2) 16
+ 25F 43F 25F 2(02 + 12.52) due to bounding stress difference between nozzle corner and shell geometry
= 118F
Summary of NRCs evaluation of PWROG-15109-NP technical basis 17 Nozzle and traditional beltline (shell) have same RTNDT shell nozzle shell + 25F
Summary of NRCs evaluation of PWROG-15109-NP technical basis
- Independent safety assessment
2) 18
+ 25F
-66.4F 25F 2(54.52 + 12.52)
= 95F
Summary of NRCs evaluation of PWROG-15109-NP technical basis
- Independent safety assessment Further screening of 18 units by looking at limiting RTNDT values RTNDT < 95F (very suspect, screen in) 95F < RTNDT < 118F (questionable, screen in)
RTNDT > 118F (ok, screen out) 4 units 19
Summary of NRCs evaluation of PWROG-15109-NP technical basis
- Independent safety assessment For 4 units, compared generic nozzle P-T limits with their approved traditional beltline (shell) P-T limits Used generic nozzle ARTs, but have to remove 25F due to stress Thus, 118F 93F and 95F 70F For two units, shell P-T limits bound 93F nozzle P-T limits For one unit, shell P-T limit coincides with 93F nozzle P-T limit For last unit, shell P-T limit coincides with 70F nozzle P-T limit Given conservatisms in generic nozzle ART, P-T limit methodology, 1/4T flaw no safety impact 20
Summary of NRCs evaluation of PWROG-15109-NP technical basis
==
Conclusions:==
- Considering the staffs independent safety assessment, the 25F embrittlement exclusion as used in PWROG-15109-NP is acceptable.
- For other applications, the NRC will need adequate technical basis for acceptability of 25F embrittlement exclusion.
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