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SEISMIC ISOLATION OF NUCLEAR STRUCTURES

Dr. Annie Kammerer, PE Pacific Earthquake Engineering Research Center, UC Berkeley

Annie Kammerer ConsulGng

Korean Atomic Energy Research InsGtute Daejon Korea

April 2015

Overview

¨  Seismic isolaGon (SI) basics and terminology ¨  Use of SI in non-‐nuclear applicaGons ¨  Use of SI in nuclear applicaGons ¨  Design of SI systems in a risk-‐informed framework ¨  ConstrucGon and operaGonal requirements and special

consideraGons

Seismic IsolaGon Basics

Seismic IsolaGon is a method of decoupling a structure from the supporGng surface through the use of specially designed equipment. Applying the isolaGon layer below the foundaGon is called “base isolaGon.” (the focus of this presentaGon) Equipment and floors can also be isolated.

The inerGa of the structure keeps it in place as the earth moves beneath it. The relaGve displacement between the structure and ground is taken up by isolators. An base isolaGon system is composed of a “forest” of isolators siYng on pedestals (which allow access to the isolators).


Isolators/ IsolaGon Interface

FoundaGon -‐lower mat -‐pedestals -‐moat walls


Superstructure (enGre structure above the

isolators, acts as a “rigid body”)

Basemat (highly rigid mat

above the isolators)

Seismic IsolaGon Terminology

Moat (space to allow for relaGve movement)

Moat wall (could be used as hard Stop)

Clearance to Hard Stop (Distance large enough to limit pounding. Sets some isolator

properGes)

Seismic IsolaGon Terminology

¨  Low damping rubber bearing ¨  Lead (core) rubber bearing ¨  FricGon pendulum

Common Types of Isolator Units

LNG TANKS, REVITHOUSSA, GREECE Fric6on Pendulum Bearings

Use of SI in LNG FaciliGes

Courtesy of Prof. Andrew Whi^aker

LNG TANKS, INCHON, SOUTH KOREA Low Damping Rubber Bearings

Use of SI in LNG FaciliGes


SAKHALIN II PLATFORMS Fric6on Pendulum Bearings

Use of SI in Natural Gas Pla_orms


Sensi6ve and important Structures and infrastructure in the US

(tens of thousands of buildings worldwide-‐mostly in Japan)

Hearst Mining Building, UC Berkeley

Golden Gate Bridge

San Francisco City Hall

Use of SI in Other Structures

Use of Base isola6on under Nuclear Power

Reactors

Cruas-‐Meysse NPP, France

Koeberg NPP, South Africa

Base IsolaGon of Nuclear FaciliGes

Cruas-‐Meysse NPP Courtesy of Electricite de France



Cruas-‐Meysse NPP

Courtesy of Electricite de France

Other nuclear

applica6ons

Jules Horowitz Research Reactor, France

Tokamak Fusion Re

actor, Fran

ce

Emergency Response Centers at Kashiwazai-‐Kariwa, Fukushima Daiichi, and Fukushima Daini

Base IsolaGon in Nuclear FaciliGes

From INPO 11-‐005 Addendum August 2012 Lessons Learned from the Nuclear Accident at the Fukushima Daiichi Nuclear Power Sta6on “The seismically isolated emergency response centers at the Fukushima Daiichi and Daini nuclear power staGons filled a vital need in protecGng emergency response personnel and ensuring access to the site could be maintained during the accident.”

Experience in the 2011 Earthquake

¨  In 2008 NRC began research in SI ¨  NRC research addressed key items

¤  VerGcal and beyond-‐design-‐basis loading ¤  Development of isolator component for NRC’s SSI Modeling Tool (the ESSI Simulator)

¤  TesGng of full size isolator systems at large loads on eDefence to confirm analysis tools and models

¤  Development of performance-‐based criteria for regulaGon of NPPs using seismic isolaGon systems

¤  Development of determinisGc “rules of thumb” to provide conservaGve factors for performance criteria

¨  Development of NUREG & modeling tools to address NRC staff needs (also feeding into new IAEA guidance)

NRC AcGviGes

NRC-‐sponsored tesGng of SI units

DCPP Time History Lead Rubber Bearing


Fixed Base Structure

Structure Isolated with FricGon Pendulum and Lead Rubber Bearings


Drag NRC NUREG

¨  Isolator/IsolaGon system design (approach and tools)

¨  Assurance of isolaGon system performance

¨  Umbilicals and cross-‐over structures

¨  ConstrucGon QA/QC

¨  OperaGons and Maintenance

¨  NUREG developed to provide background informaGon and proposed recommendaGons for RG

Kammerer1, Whi^aker2, and ConstanGnou2

1US NRC 2University of Buffalo

Drag NRC NUREG

¨  Guidance focuses on technologies with track record in US and accepted by US pracGGoners: lead rubber, low-‐damping rubber and fricGon pendulum bearings.

¨  Guidance is provided for horizontal systems; verGcal isolaGon systems could be allowable.

¨  Guidance is focused on tradiGonal designs, though it can also be used for SMRs if any appropriate design-‐specific enhancements are included

¨  IsolaGon of equipment or floor isolaGon is allowable, but is not addressed in the NUREG.

Guidance Philosophies

¨  The isolators cannot be allowed to fail and should be removed from any realisGc sequence.

¨  Singletons that are safety related must have more stringent design criteria than more convenGonal construcGon.

¨  The potenGal for failure and cliff edge effects is removed through use of a hard stop.

¨  The concepts of FOSID and HCLPF should be incorporated to the extent possible, recognizing that seismic isolators are inherently non-‐linear.

¨  The extended DBE concept discussed in the Near Term Task Force Report should be incorporated.

Guidance Philosophies

¨  Assurance of performance must incorporate a combinaGon of prototype and producGon tesGng to physically demonstrate quanGfiable confidence levels and performance reliability in both the isolators and the umbilicals.

¨  Guidance must consider how seismic isolaGon systems could fit within a cerGfied design framework. (Design of the Basemat up is cerGfied and isolators tuned to the site)

¨  Although the guidance focuses on isolated light water reactor superstructures, the approach should be technology neutral enough to be extended to other designs, such as for small modular reactors.

¨  RealisGc approaches for achieving clear and technically based performance targets should be described.

A hard stop assures survivability

Hard Stop Requirement

TesGng Requirements

Isolator behavior, capacity, and reliability can be determined through a program of prototype tesGng. The isolator unit must have a high confidence of a low probability of failure (HCLPF) at the CHS deformaGon.

Capacity Seismic MoGon Parameter

Cond

iGon

al Probability of Failure

Example of prototype

tesGng at UCSD

TesGng Requirements

TesGng Requirements

All isolators ALSO quality tested to their deformaGon under design basis ground moGon (this will be less than the CHS) to assure that the performance is as expected. This gives very high confidence that the isolaGon system can survive earthquake loading, even if beyond design basis.

Maximum deformaGon under design basis ground moGon

The moat is sized such that there is less than 1% likelihood of any impact of superstructure with the wall under the DBE ground moGon when modeling is performed to account for difference in actual earthquake records (Gme histories) and uncertainGes in parameters.

Prob

ability from

mod

eling

<1% likelihood of impact

Design of Moat

Isolators and/or Isolation system Super-structure

Connections/ umbilicals Moat/Hard Stop

Hazard and Associated

Risk Parameter

Isolation unit and system design and

performance criteria

Approach to demonstrating unit

performance Performance expectations

GMRS+2 The envelope of the RG1.208 GMRS and the minimum foundation input motion3 for each spectral frequency

No long-term change in mechanical properties. 100% confidence of the isolation system surviving without damage when subjected to the mean displacement of the isolator system under the GMRS+ loading.

Production testing must be performed on each isolator for the mean system displacement under the GMRS+ loading level and corresponding axial force.

Superstructure design and performance must conform to NUREG-0800 under GMRS+ loading.

Umbilical line design and performance must conform to NUREG-0800 under GMRS+ loading.

The moat is sized such that there is less than 1% probability of the superstructure contacting the moat or hard stop under GMRS+ loading.

EDB4 GMRS The envelope of the ground moGon amplitude with a mean annual frequency of exceedance of 1x10-‐5 and 167% of the GMRS+ spectral amplitude

90% confidence of each isolator and the isolaGon system surviving without loss of gravity-‐load capacity at the mean displacement under EDB loading.

Prototype tesGng must be performed on a sufficient number of isolators at the CHS5 displacement and the corresponding axial force to demonstrate acceptable performance with 90% confidence. Limited isolator unit damage is acceptable but load-‐carrying capacity must be maintained.

There should be less than a 10% probability of the superstructure contacting the moat or hard stop under EDB loading.

Greater than 90% confidence that each type of safety-related umbilical line, together with its connections, remains functional for the CHS displacement. Performance can be demonstrated by testing, analysis or a combination of both.6

CHS displacement must be equal to or greater than the 90th percentile isolation system displacement under EDB loading. Moat or hard stop designed to survive impact forces associated with 95th percentile EDB isolation system displacement.7 Limited damage to the moat or hard stop is acceptable but the moat or hard stop must perform its intended function.

1)  Analysis and design of safety-‐related components and systems should conform to NUREG-‐0800, as in a convenGonal nuclear structure. 2)  10CFR50 Appendix S requires the use of an appropriate free-‐field spectrum with a peak ground acceleraGon of no less than 0.10g at the foundaGon level.

RG1.60 spectral shape anchored at 0.10g is ogen used for this purpose. 3)  The analysis can be performed using a single composite spectrum or separately for the GMRS and the minimum spectrum. 4)  The analysis can be performed using a single composite spectrum or separately for the 10-‐5 MAFE response spectrum and 167% GMRS. 5)  CHS=Clearance to the Hard Stop 6)  SC 2 SSCs whose failure could impact the funcGonality of umbilical lines should also remain funcGonal for the CHS displacement. 7)  Impact velocity calculated at the displacement equal to the CHS assuming cyclic response of the isolaGon system for moGons associated with the 95th

percenGle (or greater) EDB displacement.

Two Hazard Levels Used for Design and Assessment

Ground Mo6on Response Spectrum + same as for new non-‐SI structures

10-‐4 ground moGon with minimum FIRS (NRC Regulatory Guide 1.208)

Extended Design Basis GMRS

10-‐5 ground moGon or 1.67xDBGM




Risk Parameter

Isolation unit and system design and

performance criteria



GMRS+2 The envelope of the RG1.208 GMRS and the minimum foundation input motion3 for each spectral frequency



Superstructure design and performance must conform to NUREG-0800 under GMRS+ loading.






There should be less than a 10% probability of the superstructure contacting the moat or hard stop under EDB loading.



1)  Analysis and design of safety-‐related components and systems should conform to NUREG-‐0800, as in a convenGonal nuclear structure. 2)  10CFR50 Appendix S requires the use of an appropriate free-‐field spectrum with a peak ground acceleraGon of no less than 0.10g at the foundaGon level.

RG1.60 spectral shape anchored at 0.10g is ogen used for this purpose. 3)  The analysis can be performed using a single composite spectrum or separately for the GMRS and the minimum spectrum. 4)  The analysis can be performed using a single composite spectrum or separately for the 10-‐5 MAFE response spectrum and 167% GMRS. 5)  CHS=Clearance to the Hard Stop 6)  SC 2 SSCs whose failure could impact the funcGonality of umbilical lines should also remain funcGonal for the CHS displacement. 7)  Impact velocity calculated at the displacement equal to the CHS assuming cyclic response of the isolaGon system for moGons associated with the 95th

percenGle (or greater) EDB displacement.

Performance Criteria for the Isolator and Isola6on System

• Design and Performance Criteria • Approach to demonstra6ng Performance

Performance Criteria for the Superstructure, Connec6ons/umbilicals and Moat/hard stop




Risk Parameter

Isolation unit and system design and performance

criteria



GMRS+2 Envelope of the RG1.208 GMRS and the minimum foundation input motion3 for each spectral frequency



Super-structure design and performance must conform to NUREG-0800 under GMRS+ loading.



2) 10CFR50 Appendix S requires the use of an appropriate free-‐field spectrum with a peak ground acceleraGon of no less than 0.10g at the foundaGon level. RG1.60 spectral shape anchored at 0.10g is ogen used for this purpose.

3) The analysis can be performed using a single composite spectrum or separately for the GMRS and the minimum spectrum.

100% confidence in the isolators achieved through produc6on tes6ng of each

isolator

Super structure and internals

designed to ISRS from the design basis ground

mo6on

moat sized for <1% prob. of impact

GMRS

+




Risk Parameter

Isolation unit and system design

and performance criteria






There should be less than a 10% probability of the super-structure contacting the moat or hard stop under EDB loading.



4) The analysis can be performed using a single composite spectrum or separately for the 10-‐5 MAFE response spectrum and 167% GMRS.

6) SC 2 SSCs whose failure could impact the funcGonality of umbilical lines should also remain funcGonal for the CHS displacement.

7) Impact velocity calculated at the displacement equal to the CHS assuming cyclic response of the isolaGon system for moGons associated with the 95th percenGle (or greater) EDB displacement.

90% confidence in each isolator

achieved through prototype tes6ng

to the CHS displacements

>90% confidence in umbilical

func6onality

<10% chance of structure impac6ng moat

moat designed for EDB impact

loads

Exten

ded DB

GMRS

Design Requirements

¨  Design must: ¤  incorporate a hard stop ¤  meet the performance criteria ¤  allow for isolator inspecGon and

replacement ¤  address isolaGon system and umbilical

requirements

¨  Analyses must account for: ¤  long-‐term change in properGes ¤  variability of properGes ¤  rocking, rotaGon, and other 3D responses

Design Requirements

¨  The superstructure basemat must be able to span a lost isolator unit, even one on the perimeter.

¨  The superstructure basemat and foundaGon rag must be sufficiently rigid to assure that the verGcal loads on the isolators are relaGvely uniform.

¨  The potenGal for long-‐term se^lement must be accounted for.

AddiGonal Design ConsideraGons

¨  AddiGonal seismic monitoring equipment must be incorporated along the edge of the basemat.

¨  The SI system must be protected against, or designed for fire, high winds, flood, etc.

¨  ConsideraGon should be given to extreme loadings such as aircrag impact and explosions.

¨  Fire protecGon systems for the SI systems are safety related equipment.

¨  Design should address LOSP and other emergency condiGons. Passive systems should be used.

Design Analysis

¨  Three opGons: 1) coupled Gme domain, 2) coupled frequency domain, and 3) mulG-‐step

¨  Coupled 3D Gme domain modeling and the mulG-‐step approach have no usage restricGons

¨  Coupled frequency domain can only be used with low damping rubber bearings and in certain limited circumstances.

¨  Input moGons must have appropriate long-‐period content and duraGon.

¨  The isolator unit numerical model must be validated against actual data.

OperaGonal Requirements

¨ An in-‐unit inspecGon program is required ¨  InspecGon plan must address aging/degradaGon ¨  The isolators must recover quickly enough to withstand large agershocks within tens of minutes.

¨  Isolators should have an inherent property that passively re-‐centers the system.

¨  The protecGon of the seismic isolaGon system should be included in emergency and severe accident miGgaGon planning where appropriate

Design Process Requirements

¨ Professional peer review must be incorporated into the design and development process. (detailed list of topics is provided in NUREG)

¨ QA/QC procedures should be developed based on ANSI/ASME NQA-‐1-‐2008. 10 CFR 50, Appendix B requirements are applied to the isolator units.

¨ QA/QC approach for tesGng in ASCE 7-‐10 can be used as a base, but be enhanced to meet the criteria in the NUREG.

THANK YOU FOR YOUR KIND ATTENTION

QuesGons?

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