seismic isolation presentaition smirt 23 v2 · overview!...

LICENSING OF SEISMICALLY ISOLATED NPPS IN THE USA

Regulatory challenges and guidance

Annie Kammerer & Andrew WhiHaker SMiRT Special Session on Seismic IsolaKon

SMiRT 23 August 2015

Acknowledgments

¨ Informed by our work for: ¤  Idaho NaKonal Laboratory ¤ NRC seismic isolaKon research acKviKes

¨ Thanks to the NRC LBNL research team and research review group: ¤ Robert Budnitz, Robert Kennedy, Nilesh Chokshi, Donald Moore, James Johnson, Antonio Godoy, Jon Stewart, and Boris Jeremic

Overview

¨  Risk-‐informed performance-‐based framework ¨ DeterminaKon of performance and acceptance criteria ¨  AddiKonal design, construcKon, and operaKonal consideraKons

¨  Seismic ProbabilisKc Risk Assessment consideraKons and opportuniKes

¨  CerKfied design (10 CFR Part 52) consideraKons for seismically-‐isolated (SI) Advanced Reactors

NRC Base Isolation Research By

Nilesh Chokshi and Jose A. Pires Office of New Reactors

Office of Nuclear Regulatory Research, Division of Engineering US Nuclear Regulatory Commission

Base Isolation Panel

Commonalities and differences: implementing seismic isolation in a global NPP economy

SMiRT 23

August 11, 2015 Manchester, United Kingdom

Acknowledgements & Disclaimer

Acknowledgements: ¨  Annie Kammerer (formerly NRC) ¨  Bret Tegeler (formerly NRC) ¨  Scott Stovall (NRC) ¨  Mohamed Shams (NRC)

Disclaimer This briefing was prepared under the auspices of an agency of the U.S. Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party’s use, or the results of such use, of any informaKon, apparatus, product, or process disclosed in this paper, or represents that its use by such third party would not infringe privately owned rights. The views expressed in this report are not necessarily those of the U.S. Nuclear Regulatory Commission

Purpose & Agenda

u Purpose u Present summary of on-‐going NRC research u Address views and expectaKons for reviews

u Agenda u  NRC research on base isolaKon u  Reviews: views/expectaKons u  Summary

NRC Seismic Isolation Research

u Effort IniKated in 2008

u Technical experts at NRC, LBNL, SUNY-‐Buffalo, UC-‐Davis u  IsolaKon user elements (UELs) developed for OpenSees and

Abaqus u  TesKng of selected isolators u  Technical bases for understanding the performance of base

isolaKon systems when subjected to earthquake ground moKons

u  Technical bases for formulaKon of a set of regulatory criteria and guidance

u  NRC’s ESSI simulator work ongoing


u Research addresses key items u  VerKcal and beyond-‐design-‐basis loading

§  Showed that 3D modeling is necessary

u  Development of isolator component UELs (Will be publically available) u  Support formulaKon of performance-‐based criteria for regulaKon of

NPPs using seismic isolaKon systems (NUREG ch. 8 & 9) u  Modeling of low damping rubber bearings (UELs) u  Modeling of sliding bearings accounKng for variaKon in Kme of axial

pressure, sliding velocity and temperature (UELs) u  Response history analysis of nuclear power plants u  SelecKon and scaling of ground moKons u  Impact on surrounding wall (moat)


u AddiKonal research (University of Nevada, Reno) u  TesKng of isolator systems to confirm analysis tools, models, and

assumpKons (tesKng performed on e-‐Defense – contractor report under review)

u  SensiKvity study on isolator mechanical properKes completed – Showed that modeling the isolator properKes during loading require Kme domain modeling

u  NUREG/CR-‐7196 (publicaKon expected by September 2015)

u  InteracKon with IAEA-‐ISSC-‐EBP Working Area 2 u  Insights gained also inform IAEA-‐ISSC-‐EBP collaboraKve research on SI u  Cognizance of internaKonal acKviKes and guidance

§  E.g., translaKon of JEAG guidance (through a collaboraKve program with NRA-‐J, former JNES)


u Technical basis for formulaKon of a set of regulatory criteria and guidance u  Draj NUREG report u  Collect and summarize exisKng technical informaKon u  Develop bases for recommendaKons addressing design, construcKon, and

operaKonal needs u  Review regulatory guidance in codes and standards and in other countries

u Status u  Draj is currently in internal NRC review u  Publica(on an(cipated in 2015 u  Guidance development, e.g., SRP update, depending on level of industry

interest

Reviews: Views & Expectations

u Staff encourages innovaKve designs, such as base isolated structures

u New designs for innovaKve structures must saKsfy regulaKons

u Staff expects design to be based on sound engineering principles and validated methods


REGULATIONS u  ExisKng Nuclear Power Plant fleet designed in compliance with the

regulaKons: u  GDC 1: Quality standards and records – Structures, systems, and components important

to safety shall be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety funcKons to be performed.

u  GDC2: Design bases for Protec(on against natural phenomena – Structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornados, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety funcKons.

u  New designs for innovaKve structures must saKsfy the above regulaKons u  Lack of applicable codes and standards will result in more effort to

demonstrate compliance with the regulaKons REVIEW GUIDANCE u  Standard Review Plan framework is applicable to innovaKve structures

Risk-‐Informed Framework

¨  The introducKon of new elements can be challenging in any framework. A risk-‐informed framework requires that the enKre hazard curve is considered, which includes beyond design basis loading levels.

¨  A risk-‐informed framework provides a clearer basis to develop performance and acceptance criteria that meet safety objecKves. The impact in terms of risk reducKon can be calculated.

¨  If risk-‐ and performance-‐objecKves can be demonstrably met with high reliability, a technology can be shown to be appropriate for NPPs. This important because defining acceptable “margin” for equipment whose intended funcKon is miKgaKon of seismic moKon at all loading levels is challenging.

Terminology

Performance and Acceptance Criteria

Isolator units

Prototype TesKng

IsolaKon System

Umbilicals & Cross Overs

Moat Design & Clearance

Design Basis Criteria

Beyond Design Basis Criteria

Super structure is designed using appropriate seismic moKons as if it were convenKonally founded

Load Defi

niKo

ns


Design Basis Criteria

Beyond Design Basis Criteria

�Defined by Regulatory Guide 1.208

Load Defi

niKo

ns

�ASCE 4 uses criteria from ASCE 43-‐05 (DOE) �NRC definiKon must be meaningful within current framework (to be defined in NUREG)

Total hazard curve is used for SPRA


Isolator units

Equipment

Some redundancy

IsolaKon System

Structural element

No redundancy

•  Isolators eventually fail if taken to very high shear displacements

•  The deformaKon of installed isolator units are fairly uniform due to aHachment to upper and lower foundaKons

•  Upper and lower foundaKon should be designed accommodate failure of a few isolators

Clearance to Hard Stop

•  The hard stop physically limits deformaKon of the isolators to within a range with very high reliability.

•  It also provides a limit to the deformaKon of umbilicals and cross-‐over structures

•  However, the moat wall should be far enough out from the superstructure to limit the potenKal for pounding


Input ground moKons based on 1)  Design Basis Spectra 2)  Beyond Design Basis Spectra

Displacement

Prob

ability

density

1% probability of touching

wall

10% probability of touching

wall

DBGM

BDBGM

Desig

n Ba

sis

Displacemen

t

3D Time-‐domain Non-‐Linear SSI Model


•  Some addiKonal mechanism to reduce or eliminate pounding may be considered. Balance of compressibility versus addiKonal deformaKon

•  Alternately a protocol to incorporate pounding may be needed, though any impact should be minimal based on performance requirements

Clever soluKon here could be beneficial.

Acceptance Criteria

Isolator units

High confidence in performance at design (100% producKon tesKng)

High confidence in properKes to CHS (prototype

tesKng)

IsolaKon System

Appropriate structural

performance accounKng for moat size, foundaKon sKffness, and

Klt.

Umbilicals & Cross Overs

Must conform to NUREG 0800

given the design loads

Some high confidence level (e.g., 90%) of safety funcKon

at CHS displacement

Moat & CHS

Acceptance based on

appropriate probability of contact and associated loading

DB

BDB


u PotenKal Analysis Challenges u  Nonlinear behavior of isolaKon system u  Understanding applicability and limitaKons of

methods u  ValidaKon of methods through tesKng/

benchmarking u  EvaluaKon and interpretaKon of analysis results for

their adequacy u  Ground moKon selecKon and scaling u  Earthquake soil-‐structure interacKon

AddiKonal Design ConsideraKons

¨ Design of cross-‐over structures and umbilicals for (possibly much) larger displacements

¨ Moat and moat cover new elements ¨  AddiKonal seismometers are required

¤  Free field, lower foundaKon, locaKons around the perimeter of the upper base mat, top of structure, at key locaKons within the structure

¨  AddiKonal Klt-‐meters are required ¤  FoundaKon, upper basemat, moat walls

¨  Fire suppression system protecKng isolator units must be safety-‐related

AddiKonal Design ConsideraKon

¨  Peer review of the SI system design and protocols should be conducted and address a number of areas:

¤  Review of numerical models of isolators; ¤  Review of the SSI analysis and the resulKng in-‐structure response spectra; ¤  Review of displacement and force calculaKons for the isolator units and all

associated structures, systems, and components; ¤  Review of the analysis and design of the umbilicals; ¤  Review of the analysis and design of the hard stop; ¤  Review of the seismic monitoring program; ¤  Review of the prototype test program; ¤  Review of the producKon (quality control) test program; ¤  Review of the isolator inspecKon and post-‐installaKon tesKng program; and ¤  Review of post-‐earthquake inspecKon protocols; and ¤  Review of design or protecKon measures against other external events.

ConstrucKon & OperaKons

¨  ConstrucKon ¤  Consistency with the design assumpKons should be verified during construcKon phase, as appropriate. Areas of special inspecKon include: n  Isolator bolt Kghtness n  Levelness of pedestals and isolator units n  Levelness of upper and lower basemats n  SeHlement of isolaKon system/distance between basemats at construcKon

¨  OperaKons ¤  Isolator unit specimens kept at locaKon and under the same condiKons as the in-‐service units should be periodically removed and tested.

¤  Periodic visual inspecKons on the isolators and the surrounding area should be conducted

Seismic PRA

¨ OpportuniKes ¤  A simple cost/benefit analysis of SI systems during design does not show the real impact of SI, parKcularly if only considering margin.

¤  The methods for incorporaKng human factors into SPRA for an isolated system deserves addiKonal work and careful consideraKons. The current methods don’t capture the full benefit.

¤  By using SPRA as part of the design process, addiKonal opKmizaKon can be achieved, while improving safety. (See the Paper by Budnitz and WhiHaker, “OpportuniKes for Improving the RegulaKons Governing the Seismic Safety of Large Nuclear InstallaKons”)

Seismic PRA

¨  Challenges ¤ V/H raKos make use of screening tables problemaKc ¤ CorrelaKons may need addiKonal review and consideraKon. NRC is currently working on correlaKons of like components, which may provide insight

¤ The potenKal for pounding may need to be considered in some regulatory frameworks, depending on the performance and acceptance criteria chosen.

Design

Hazard Input

SPRA

Interaction

Plant Design

SPRA Inputs

Risk information (Risk parameters and insights)

Hazard and design information

PRA results

Finalize Design

Safety/performance objecKves met and design opKmized

Risk reduction improvements or design optimizations developed

cooperatively by design and PSA experts. Results fed back into design.

Identify areas for improvement

Risk and Performance Requirements

Commercial Considerations

Yes

No Incr

easi

ng d

etai

l

Opportunity for design optimization using SPRA

Licensing under 10 CFR Part 52

¨ Part 52 is used for cerKfied designs ¨ Although seismic isolaKon can be used to “tune” and reduce horizontal ground moKons such that the “site specific” moKons (GMRS+SI) fall under the CerKfied Seismic Design Response Spectrum (CSDRS), the verKcal moKons are not reduced. ¤ Damping elements, verKcal isolaKon systems, and other approaches can be applied to address verKcal moKons

¤ Vendors may need mulKple design (could have mulKple verKcal spectra with one horizontal spectra)


¨ Currently regulatory guidance documents have gaps or inconsistencies with seismically isolated technology. For example, in DC/COL-‐ISG-‐017: ¤ Some inconsistencies in the definiKons (next slide) when used for SI

¤ Assumes use of frequency-‐domain codes (SASSI) ¤ Central and Eastern US-‐based definiKons

¨  These are a funcKon of the challenges/objecKves at the Kme of wriKng. Not intended to be limiKng, but should be idenKfied and addressed.

¨  The NRC allows applicants to use other approaches with jusKficaKon


•  GMRS is the site-‐specific ground moKon defined at the ground surface or a hypotheKcal free field (See RG1.208)

•  FIRS with SI is compaKble with GMRS and accounts for SI system •  CSDRS is SI located at the FIRS level and include minimum shaking levels as per code


u PotenKal Design Challenges u  Lack of detailed design informaKon at the Design CerKficaKon

stage u  Lack of applicable codes (under development in ASCE 4 & 43) u  Lack of detailed site informaKon u  Performance criteria u  ConsideraKon of uncertainKes, defense-‐in-‐depth, and seismic

margin early in the design process u  ConsideraKon of environmental effects, such as material

aging, creep, operaKng temperature, and exposure to moisture early in the design process


u  IdenKficaKon of significant design informaKon (Design CerKficaKon) u  CriKcal SecKon DescripKon u  Tier 2* InformaKon u  ITAAC

Summary u New and innovaKve design is encouraged u New designs for innovaKve structures making use of base isolaKon must saKsfy regulaKons

u Base isolated designs should be based on sound engineering principles and validated methods

u ConsideraKon of uncertainKes, defense-‐in-‐depth, and seismic margin should be considered early in the design cerKficaKon process

u Environmental effects, such as material aging, creep, operaKng temperature, and exposure to moisture, should also be considered early in the design.

Summary

¨  A number of challenges and opportuniKes exist for incorporaKng SI into NPPs, parKcularly in the area of advancing SPRA for SI faciliKes. IncorporaKng SPRA into the design process would be beneficial.

¨  A clear set of performance criteria can be developed that can be demonstrated to meet safety and risk objecKves. AddiKonal design, construcKon, and operaKonal consideraKons must also be incorporated.

¨  Some inadvertent gaps or inconsistencies exist in NRC guidance documents. AddiKonal work to idenKfy these gaps and inconsistencies is ongoing (at INL).

Thank You

QuesKons?

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