ML22097A130
| ML22097A130 | |
| Person / Time | |
|---|---|
| Issue date: | 03/22/2022 |
| From: | David Rudland NRC/NRR/DNRL |
| To: | |
| J. Lynch, NMSS/MSST | |
| Shared Package | |
| ML22097A145 | List: |
| References | |
| Download: ML22097A130 (15) | |
Text
RPV Emb ri t t l e me nt - Monitoring and Prediction
Remarks by
D a vi d L. R udla nd, P h. D.
Senior Technical Advisor f or M at er ials Division of New and Renew ed Licenses O f f ice of Nuclear React or Regulat ions
2022 National State Liaison Officer Conference March 22, 2022 Reactor Vessel Embrittlement
uni rra di a t e d
irra dia te d
Reactor S hel l Near t he C ore
S urv ei l l ance Capsul e
2 RPV Integrity Regulations
Appendi x A to Par t 5 0 Criterion 31 - Frac tur e Pr eventi on of R eac tor Cool ant B oundar y
10 CFR 50.60 - Acceptance 10 CFR 50.61 - F rac t ure c rit eria for frac t ure prevent ion Regulatory Guide 1.99 t oug hness requirement s measures for normal operat ion R ev 2 - Radiation for prot ec t ion ag ainst
- M ust meet Appendix G and emb ri t t l emen t o f pressurized t hermal shoc k H reactor vessel materials even t s 10 CFR 50 App G 10 CFR 50 App H
- P r es c r ip t ive
- P T limit s : HU / CD ( normal)E185-8210 CFR 50.61a - Alt er n a t e
- L ea k t es t
- P eriodic monit oring P TS r ule
- F la ng e limit sbased on 4 0-yea r life
- D if fer en t P r es c r ip t ive
- U pper s helf limit s10 C FR 50. 66 - R e qui re me nt s Embrit t lement equat ion
- must ac c ount for t he f o r t he rma l a nne a l i ng o f t he effec t s of neut ron radiat ion rea c to r pressure vessel
Embrit t lement Trend Curve, May 1988, Fit based on 177 datapoints 3
- Regulations are unchanged; surveillance program addressed in guidance
- Agin g Man agemen t Program X I. M31, Reactor Vessel Material Su rveillan ce
- Cont inues relianc e on Appendix H prog ram using AS TM E1 8 5-8 2
- G A L L Rep o r t ( N U RE G-1 80 1, Rev. 1 ) f o r lic en s e r en ewa l ( 4 0 t o 6 0 yea r s )
- s hall hav e at leas t one caps ule w ith a pr oj ected neutr on fluence equal to or exceeding the 6 0 -
y ear peak r eactor v es s el w all neutr on fluence pr ior to the end of the per iod of extended o p er atio n
- D es cr ibes us e of r econs tituted s pecimens and us e of oper ating r es tr ictions (neutr on flux, s p ec tr u m, ir r a d ia tio n temp er a tu r e, etc. )
- G AL L -S L R Rep o r t ( N U RE G-2 19 1) f o r s u b s eq u en t lic en s e r en ewa l ( 6 0 t o 8 0 yea r s )
- w ithdr aw al and tes ting of at leas t one caps ule... w ith a neutr on fluence of the caps ule betw een one and tw o times the peak neutr on fluence of inter es t at the end of the s ubs equent per iod of extended oper ation - o r d ata f r o m a p r io r tes ted c ap s u le
- S p ec if ies - it is n o t ac c ep tab le to r ed ir ec t o r p o s tp o n e th e w ith d r aw al an d tes tin g o f th at c ap s u le to achiev e a higher neutr on fluence that meets the neutr on fluence cr iter ion for the s ubs equent per iod of extended oper ation
4 M oni tori ng and P re di cti on of Embri ttl ement
- Embrit t lement Trend Curve (ETC) provides est imat es of c hange in frac t ure t oughness (T or RTN DT) as a func t ion of fluenc e
- S urveillanc e c apsule t est ing provides monit oring t o ensure ETC predic t s plant spec ific behavior properly
- To g et h er t h ey a r e u s ed t o d et er min e p r es s u r e-t emperat ure (PT) limit s for normal operat ion 40yr 60yr 80yrH e at up & C ool dow n ART 40yr 60yr 80yr ETC
D at a
RTN D T ( u)
O pe r at i ng Ti m e ( y e ar s ) / F luenc e Coolant Te mpe rat ur e ART = Ad j u s t ed Refer en c e Temp er a t u r e 5 Underprediction of Embrittlement
- E mb ri ttl emen t Tren d Cu rv e i n RG 1. 99 Rev. 2 an d 10 CF R 50. 61 does not provide appropriate embrittlement estimates at high RP V fluenc e lev els
- Embr i ttl ement Tr end Cur ve, May 1988, Fit based on 177 datapoints
- Fl uenc e f ac tor i n the tr end c ur ve i s not ac c urate at hi g h f l uenc e, bec aus e i t pr ovi des non-phys i c al f l atteni ng tr end above 4 - 6 x 10 19 n/ c m2
- S urveillanc e dat a are fit t o t he fluenc e fac t or and c an not provide g ood predic t ions of embrit t lement at hig h fluenc e levels F luenc e func t ion beg ins t o flat t en
6 Issu e - E TC
Dev iates S ta tistic a lly +180° F from mean sig n if ic a n t
- 180° F
DT41J = T41J is a measurement of embrit t lement represent ing t he shift in t ransit ion t emperat ure from brit t le t o duc t ile frac t ure at an impac t t oughness of 4 1 J
7 Surveillance Capsule Delays
- Appendix H to 10 CFR Pchanges in f racture toughness caused by neutron embrittlementart 50 requires periodic monitoring of
- ASTM s tandar d ( E1 8 5-8 2 ) des i g n f l uenc e - pl ants c hang e ( i ntended 4 0- yea r ) d es i g n f l u en c e al l ows f i nal c aps ul e f l uenc e to be 2 X R PV to current license length (e.g., 60 or 80 years)
- ASTM s tandar d ( for 4 0 year s ) per mi ts hol di ng l as t c aps ul e wi thout tes ti ng
- C o mmis s io n f in d in g ( P97- 0 4 ) th at s taf f r e v ie w o f r e q u e s ts to c h an g e c ap s u le w ith d raw al e r r y d e c is io n N R C A d min is trativ e L e tte r s c h e d u le s is limite d to v e r if ic atio n o f c o n fo r manc e w ith th e AS T M standard (i.e., not based on technical or safety considerations)
- Caps ul e wi thdraw and tes ti ng r epeatedl y del ayed i n s ome c as es to ac hi eve hi g her f l uenc e
8 I ssu e - Appe ndix H Perform a nce M onit oring M a n y lic en s ees h a ve d ela yed c apsules (t ime and/ or fluenc e),
s o me r ec en t ex a mp les :
P la n t Capsule # o f tim e s
- d elay ed
Tu r k e y P o i n t 5 4 Robinson 5 2 S u rry U 1 5 2 S u rry U 2 5 2 North Anna U1 4 2 North Anna U2 4 2 S t. L u c i e U 2 4 1 P o in t B e a c h 5 1 Capsule wit hdrawal sc hedule c hanges inc lude N ot a ll pla nt s ha ve dela yed delays in bot h t ime and/or fluenc e wit hdrawal of c apsules
9 Who is Impacted?
- E mbrittlement underprediction Pe r c e nt age of F l e e t S ur pas s i ng F l ue nc e L e v els Pe r c e nt age of PW R s S ur pas s i ng F l ue nc e L e v el s Yea r / F lu en c e 6 x 10 19 n/c m2 8 x 10 19 n/c m2 6 x 10 19 n/c m2 8 x 10 19 n/c m2 6 0 years 6% 0% 9% 0%
8 0 years 22% 10% 34% 15%
100 years 30% 20% 48% 31%
- L ack of Surveillance D ata
- Any pl a nt renew i ng l i c ens e t ha t c hoos es t o del ay l a s t c a ps ul e
10 Risk of Failure
ES D represent s t he underpredic t ion of RTN DT
L arge Uncertainties:
- U nknown frequenc y of t ransient
- Ac t ual plant fluenc e variat ions
- Are t hese analyses bounding?
Unknown plant -specific considerations
- How muc h prot ec t ion do administ rat ive and ot her operat ional limit s provide ag ains t violat ing t he P T limit ?
RG 1.99 Revision 2 Update FAVOR Scoping Study, Ma y 6, 2021, T LR R E S/ DE / C IB-2020- 09, R ev. 1, ML21126A326
11 Safe ty Margi n s I l l u strati o n
S t ruc t ural limit R e duc e d Ma rgi n Ade qua t e PT-c urve using Ma rgi n RG 1.99
Ac c urat e O pe ra t i ng PT-c u r ve Ma rgi n
U nc ert aint y
Temp, F Uncertainties increasing due to lack of surveillance, but margin is less due to embrittlement underprediction 12 S taff G o al s
- Currentlyassurance of adequate protection against brittle, regulations are sufficient for reasonable fractu r e o f ve sse l
- S taff wants to ensure in long-term operation continued reasonable assurance
- P rov ide remedies for the identified issues with RP V surveillance requirements and embrittlement predictions, o n a ri s k -informed, performance basis
- D o n o t i mp act th o se p l an ts th at ar e n o t ad ve rse l y affe cte d b y th e i ssu e s
- P l an t-specific surveillance data that coverfluence lev el s end of license
- P rojec ted fluenc e at end of license < ~3 x 10 19 n /c m 2
13 N e x t S te p s
- Staff developed a rulemaking plan to as k the Commis s ion for permis s ion to initiate a rulemaking effort
- Once approved, s taff w ill develop the technical bas is for how to chang e to rule to correct these long -term is s ues
14 Questions?
15