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{{#Wiki_filter:RPV Embrittlement - Monitoring and Prediction Remarks by David L. Rudland, Ph.D.
{{#Wiki_filter:RPV Emb ri t t l e me nt - Monitoring and Prediction
Senior Technical Advisor for Materials Division of New and Renewed Licenses Office of Nuclear Reactor Regulations 2022 National State Liaison Officer Conference March 22, 2022


Reactor Vessel Embrittlement unirradiated irradiated Reactor Shell CORE    Near the Core Surveillance Capsule 2
Remarks by


RPV Integrity Regulations Appendix A to Part 50 Criterion 31 - Fracture Prevention of Reactor Coolant Boundary 10 CFR 50.60 - Acceptance                                        10 CFR 50.61 - Fracture criteria for fracture prevention      Regulatory Guide 1.99      toughness requirements Rev 2 - Radiation measures for normal operation                                    for protection against embrittlement of
D a vi d L. R udla nd, P h. D.
* Must meet Appendix G and             reactor vessel materials pressurized thermal shock H                                                            events
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
* Prescriptive 10 CFR 50 App G                    10 CFR 50 App H Embrittlement equation
* ASME Sec XI App G
* Surveillance per ASTM
* PT limits: HU/CD (normal)            E185-82                  10 CFR 50.61a - Alternate
* Leak test
* Periodic monitoring        PTS rule
* Flange limits                        based on 40-year life
* Different Prescriptive
* Upper shelf limits                10 CFR 50.66 - Requirements    Embrittlement equation
* must account for the              for thermal annealing of the effects of neutron radiation    reactor pressure vessel Embrittlement Trend Curve, May 1988, Fit based on 177 datapoints 3


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
* AS M E S ec X I Ap p G* S u r veilla n c e p er ASTM Embrit t lement equat ion
* 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
License Renewal
License Renewal
* Regulations are unchanged; surveillance program addressed in guidance
* Regulations are unchanged; surveillance program addressed in guidance
* Aging Management Program XI.M31, Reactor Vessel Material Surveillance
* Agin g Man agemen t Program X I. M31, Reactor Vessel Material Su rveillan ce
  - Continues reliance on Appendix H program using ASTM E185-82
- Cont inues relianc e on Appendix H prog ram using AS TM E1 8 5-8 2
  - GALL Report (NUREG-1801, Rev. 1) for license renewal (40 to 60 years)
- 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 )
      - shall have at least one capsule with a projected neutron fluence equal to or exceeding the 60-year peak reactor vessel wall neutron fluence prior to the end of the period of extended operation
- 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 -
      - Describes use of reconstituted specimens and use of operating restrictions (neutron flux, spectrum, irradiation temperature, etc.)
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
  - GALL-SLR Report (NUREG-2191) for subsequent license renewal (60 to 80 years)
- 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. )
      - withdrawal and testing of at least one capsule . . . with a neutron fluence of the capsule between one and two times the peak neutron fluence of interest at the end of the subsequent period of extended operation - or data from a prior tested capsule
- 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 )
      - Specifies - it is not acceptable to redirect or postpone the withdrawal and testing of that capsule to achieve a higher neutron fluence that meets the neutron fluence criterion for the subsequent period of extended operation 4
- 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 ?


Monitoring and Prediction of Embrittlement
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
* Embrittlement Trend Curve (ETC) provides estimates of change in fracture toughness (T or RTNDT) as a function of fluence
* Surveillance capsule testing provides monitoring to ensure ETC predicts plant specific behavior properly
* Together they are used to determine pressure-temperature (PT) limits for normal operation 40yr 60yr 80yr                            Heatup & Cooldown Embrittlement (T)
ART                                      40yr 60yr 80yr Max Pressure per ETC Data 10 CFR 50 App. G RTNDT(u)
Operating Time (years)/Fluence                          Coolant Temperature ART = Adjusted Reference Temperature                  5


Underprediction of Embrittlement
11 Safe ty Margi n s I l l u strati o n
* Embrittlement Trend Curve in RG 1.99 Rev. 2 and 10 CFR 50.61 does not provide appropriate embrittlement estimates at high RPV fluence levels
  - Embrittlement Trend Curve, May 1988, Fit based on 177 datapoints
  - Fluence factor in the trend curve is not accurate at high fluence, because it provides non-physical flattening trend above 4-6 x 1019 n/cm2
                                            - Surveillance data are fit to the fluence factor and can not provide good predictions of embrittlement at high fluence levels Fluence function begins to flatten 6


Issue - ETC
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
                                                                                    +180°F Deviates Statistically from mean significant
                                                                                    -180°F DT41J = T41J is a measurement of embrittlement representing the shift in transition temperature from brittle to ductile fracture at an impact toughness of 41J 7


Surveillance Capsule Delays
Ac c urat e O pe ra t i ng PT-c u r ve Ma rgi n
* Appendix H to 10 CFR Part 50 requires periodic monitoring of changes in fracture toughness caused by neutron embrittlement
  - ASTM standard (E185-82) allows final capsule fluence to be 2X RPV design fluence - plants change (intended 40-year) design fluence to current license length (e.g., 60 or 80 years)
  - ASTM standard (for 40 years) permits holding last capsule without testing
* Commission finding (Perry decision NRC Administrative Letter 97-04) that staff review of requests to change capsule withdrawal schedules is limited to verification of conformance with the ASTM standard (i.e., not based on technical or safety considerations)
  - Capsule withdraw and testing repeatedly delayed in some cases to achieve higher fluence 8


Issue - Appendix H Performance Monitoring Many licensees have delayed capsules (time and/or fluence),
U nc ert aint y
some recent examples:
Plant    Capsule # of times
                                                              #    delayed Turkey Point    5        4 Robinson        5        2 Surry U1      5        2 Surry U2      5        2 North Anna U1    4        2 North Anna U2    4        2 St. Lucie U2    4        1 Point Beach      5        1 Capsule withdrawal schedule changes include Not all plants have delayed delays in both time and/or fluence          withdrawal of capsules 9


Who is Impacted?
Temp, F Uncertainties increasing due to lack of surveillance, but margin is less due to embrittlement underprediction 12 S taff G o al s
* Embrittlement underprediction Percentage of Fleet Surpassing Fluence Levels        Percentage of PWRs Surpassing Fluence Levels Year/Fluence    6 x 1019 n/cm2  8 x 1019 n/cm2 6 x 1019 n/cm2 8 x 1019 n/cm2 60 years            6%              0%            9%              0%
* Currentlyassurance of adequate protection against brittle, regulations are sufficient for reasonable fractu r e o f ve sse l
80 years          22%              10%            34%            15%
* S taff wants to ensure in long-term operation continued reasonable assurance
100 years          30%              20%            48%            31%
* Lack of Surveillance Data
    - Any plant renewing license that chooses to delay last capsule 10


Risk of Failure ESD represents the underprediction of RTNDT Large Uncertainties:
- 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
* Unknown frequency of transient
* 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
* Actual plant fluence variations
* Are these analyses bounding?
Unknown plant-specific considerations
* How much protection do administrative and other operational limits provide against violating the PT limit?
RG 1.99 Revision 2 Update FAVOR Scoping Study, May 6, 2021, TLR RES/DE/CIB-2020-09, Rev. 1, ML21126A326 11


Safety Margins Illustration Structural limit                  Reduced Margin Adequate PT-curve using                                      Margin RG 1.99 Pressure, psi Accurate                            Operating PT-curve                            Margin Margin Uncertainty Temp, F Uncertainties increasing due to lack of surveillance, but margin is less due to embrittlement underprediction 12
- 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


Staff Goals
13 N e x t S te p s
* Currently, regulations are sufficient for reasonable assurance of adequate protection against brittle fracture of vessel
* Staff developed a rulemaking plan to as k the Commis s ion for permis s ion to initiate a rulemaking effort
* Staff wants to ensure continued reasonable assurance in long-term operation
* 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
  - Provide remedies for the identified issues with RPV surveillance requirements and embrittlement predictions, on a risk-informed, performance basis
* Do not impact those plants that are not adversely affected by the issues
  - Plant-specific surveillance data that covers end of license fluence level
  - Projected fluence at end of license < ~3 x 1019 n/cm2 13


Next Steps
14 Questions?
* Staff developed a rulemaking plan to ask the Commission for permission to initiate a rulemaking effort
* Once approved, staff will develop the technical basis for how to change to rule to correct these long-term issues 14


Questions?
15}}
15}}

Revision as of 07:08, 18 November 2024

Reactor Vessel Embrittlement Presentation on March 22, 2022
ML22097A130
Person / Time
Issue date: 03/22/2022
From: David Rudland
NRC/NRR/DNRL
To:
J. Lynch, NMSS/MSST
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ML22097A145 List:
References
Download: ML22097A130 (15)
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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
  • AS M E S ec X I Ap p G* S u r veilla n c e p er ASTM Embrit t lement equat ion
  • 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

License Renewal

  • 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

  1. 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

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