SEISMIC RESISTANT DESIGN OF NUCLEAR POWER ......Thermal Power India-II, Dec 2007 For seismic design...

Thermal Power India-II, Dec 2007

SEISMIC RESISTANT DESIGN

OF NUCLEAR POWER PLANTS IN INDIA

By

A.G.CHHATRE CHIEF ENGINEER

(REACTOR COMPONENT - STRESS ANALYSIS & SEISMOLOGY)

NPCIL, Mumbai


Presentation will cover • Basics of Geology & Seismology • Damages to Industrial Structures & equipment during past

earthquakes • Derivation of Design Basis Ground Motion • Approaches to be followed for Seismic Design and Qualification

of Structures, Systems and Equipment (SS&E) by

• Analysis • Shake Table Testing


TECTONIC PLATE BOUNDARY


Plates


Method of circles


Different types of Faults


Failures During Earthquake

• Buildings, RCC, Steel Structure

• Tanks, Vessels, Piping, Ducting & their supports, Valves

• Battery banks & their connectors, Transformers, CircuitBreakers, Ceiling panels, Lighting fixtures, Mercuryweighted Relays


Damages to Buildings

Failure due to discontinuity in 5th Floor

Failure of Steel Frame Structure due to large ductile deformation


Damages to Buildings

Full view Close View

Failure of Steel Column and Concrete Column


Failure of u-bolts of piping system

Failure of flange joints of piping system


Failure of Hanger supports of piping system

Thermal Power India-II, Dec 2007Failure of pump casing connected to rigid pipe

Deformed but not totally failed pump casing


NUCLEAR POWER PLANTS IN INDIA OLDER GENERATION PLANTS • TAPS-1&2 : 2x165 Mwe BWR • RAPS-1&2 : 1x100 and 1x220 Mwe PHWR • MAPS-1&2 : 2x220 Mwe PHWR Since 1975, NPC has qualified in house Fourteen NPPs for Seismic Resistance • NAPS-1&2 : 2x220 Mwe PHWR • KAPS-1&2 : 2x220 Mwe PHWR • KAIGA-1,2,3&4 : 4x220 Mwe PHWR(4 under construction)• RAPS-3,4,5& 6 : 4x220 Mwe PHWR (5&6 under constru.)• TAPS-3&4 : 2x540 Mwe PHWR • PFBR : 1x500 Mwe PFBR (under construction) Kudunkulam -1&2 : 2x1000 Mwe VVER (Russian Design) Under construction


The Seismic Qualification of Overall Plant begins with • Evaluation of Local Earthquake Environment

• Free Field Site specific Response Spectrum • Free Field Time History

• Generation of Floor Response Spectra and Floor Time

Histories to be used for the qualification of the floormounted systems and equipment


Seismic Qualification of Overall Plant (Contd …) • During the site selection stage itself, it is seen that

• No capable fault exists within a radius of 5 Km • Site is not in Zone –V as per Seismic Zoning Map of

IS-1893


Seismic Qualification of Overall Plant (Contd …)

• Evaluation of Local Earthquake Environment

• Geological and Seismological Studies areconducted within a radius of 300 Km.

• Satellite imagery of the site is prepared delineating

the lineaments. This work is done by NationalRemote Sensing Agency, Dehradun


Seismic Qualification of Overall Plant (Contd …)

Generation of Design Basis Ground Motion for SSE

• Based on • Peak Ground Acceleration • Spectral Shape


Peak Ground Acceleration

• The Peak Ground Acceleration is calculated using Maximum

Potential of the Region, which is moved on to an active faultclosest to the site by using the acceleration Attenuation lawfor the site specific soil condition

• The maximum potential (M) of the region is calculated by

using the maximum historical/recorded earthquake within aradius of 300 Km of the site and adding one intensityequivalent

• The epicentral distance (D) which is the minimum distance

between the active fault and the site and depth of focus (H) • Using M, D & H and the attenuation law, the PGA for the site

is derived


DGRS – Deterministic Method


ESTIMATION OF PGA

•The PGA for a site is estimated by Mc-Guire (1978) Attenuation relation:

•PGA = 0.0306 exp(0.89 M) .Rh-1.17 exp(-0.20S)

•where M is the Magnitude of Design earthquake

•Rh is the Hypocentral Distance

•S is the soil condition (S=0 for Rock and 1 for soil)

Thermal Power India-II, Dec 2007: ZERO PERIOD ACCELERATIONS FOR DESIGN EARTHQUAKES AT INDIAN NPPs: ZERO PERIOD ACCELERATIONS FOR DESIGN EARTHQUAKES AT INDIAN NPPs


Derivation of Spectral Shape

• Spectral shape of the Response spectrum is based on no. of time histories recorded on similar geological and seismological condition as that of the plant site.

• A minimum of 25 earthquake records are used.

• First, the spectra are normalized by the respective PGA value of the record.

• This is to say that, after normalization, the spectral ordinate at any frequency is nothing but the Dynamic Amplification Factor (DAF) of the PGA at that frequency.


Response Spectra for 1st TH

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Response Spectra for 2nd TH

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Time History plot of 1st TH

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Time History plot of 2nd TH

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• After normalization, mean and standard deviation (sigma) from all the records is calculated at each frequncy.

• The mean plus one standard deviation ordinates which has a confidence of 84% non exceedance, is taken as the design spectral shape.


SMOOTHENING OF SPECTRA

• The mean+sigma spectral shape (DAF) as derived from the records is not smooth and has many kinks;

• Therefore, it is first smoothened on a log-log plot of acceleration versus frequency.


Shape of Response Spectrum (DAF) for KAPP-3&4 (5% damping)

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Site Specific Ground Motion

• The smoothened spectral shape is then multiplied by the site specific design PGA value to get the Design Basis Ground Motion (DBGM)

• The DBGM is derived separately for each damping values viz. 1%, 2%, 3%, 4%, 5%, 7% and 10% damping.


A typical DGRS for SSE for various values of damping

Earthquake Design Ground Motion Response Spectrum (1 to 10% Damping, SSE, Horizontal)

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Spectrum Compatible time history

• Acceleration time history is generated compatible to site specific ground response spectrum which is used for generation of floor response spectra


Plot of spectrum compatible Time History for DBGM

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Generation of Design Basis Ground Motion for OBE

• Generally, the PGA for OBE is taken as half of the SSE

PGA, however, the spectral shape is same for both OBEand SSE.


Generation of Input motion for analysis of

Structures, Systems and Equipment mounted on Civil Structures

• Using Spectral Compatible Time Histories

• Analysis of Civil Structures

• For design by Response Spectra Method • Generation of Floor Time Histories and Floor

Response spectra by time history analysis method


Generation of Floor Response Spectra • In the past, stick models prepared using beam elements were

used for performing the time history analysis and to generatefloor time histories and floor response spectra.

• Now, Finite element models prepared using shell elements

are used for generation of floor time histories and floorresponse spectra.


FE Model of Building


FE MODEL OF TURBINE BUILDING

Thermal Power India-II, Dec 2007Concept of Generation of Response Spectra


Raw & broadened floor response spectra and ground response spectrum for SSEfor 2% damping.


Seismic Qualification of Over all plant required

• Identification of Structures, Systems and Equipment to beseismically qualified

• Design of Equipment from seismic consideration

Thermal Power India-II, Dec 2007Schematic of Indian PHWR Plant


Seismic Qualification of Over all plant requires • Identification of Structures, Systems and Equipment

(SS&E) to be seismically qualified • Design of SS&E from seismic consideration


Identification of the systems required for Seismic Qualification • Safety Systems (SS)

which perform the following functions

• Safe S/D of the plant • maintaining long term S/D • Decay Heat removal • Containment of Radioactivity

• Safety Support Systems (SSS) which supports the above functions • Systems which supports SS & SSS


For seismic design of a Nuclear Power Plant

• It is essential that the buildings which houses the equipment & the plant equipment

Viz. Mechanical – Tanks, vessels, Heat exchangers reciprocating equipment, rotating equipment viz. pumps, compressors

Electrical – Low & medium voltage switch gear, battery banks, diesel-generator,transformer, battery charger & circuit breaker

C&I – Control panels

are designed for earthquake resistance


• Failure in Mechanical equipmentviz. piping systems, tanks, vessels, heat exchangers, pumps, valves which form the pressure boundary of the system can lead to leak of the radioactive liquid of the system

– As such there is a need to design these systems & equipment with proper anchorage, so that the systems structural and pressure boundary integrity is maintained


• Failure in Electrical systemviz., diesel generator, battery banks will not provide the final electrical power which is required for the control of the plant

- The power from Diesel generator & battery banks is required if the electrical power from the grid which is guaranteed to be lost during a large magnitude earthquake


• Failure of Control & Instrumentation systemsviz., the malfunction in the relays, contactors, switches on the instrumentation panel may lead to spurious signal being generated leading to an action which may be damaging to the functioning of the plant & may lead to unsafe condition.


• The Civil structures, Mechanical, Electrical & Instrumentation and control (I&C) equipment in nuclear industry are designed for earthquake resistance at the design stage itself.

• The mechanical, electrical & I&C equipment in a nuclear power plant are designed by the method of Analysis & Testing


Seismic Qualification by Analytical Method

• Finite Element Analysis

• Time History Method • Response Spectrum Method

• Equivalent static load Coefficient Method


Qualification of SS&E against the earthquake acceleration

Acceleration results into

- stresses

- displacement


Resultant stresses in the SS&E for a load combination of DW, operating loads with earthquake are used to qualify the SS&E for the stresses being less than the allowable value (limiting value) as per the relevant code/standard

Civil - ACI-318, 349; IS 456,

Mechanical - ASME-Section III Div. 1, Subsection,NB,NC,ND for pressure vessel & piping ASME section III div.-1 sub-section NF andIS-800 for supports.


Qualification by limiting value of stress & displacement as a design criteria by

Analytical method

It is possible for SS&E which are passive in nature and which can be easily modelled by finite element method and are qualified based on the stress and displacement as limiting value

- Pressure vessel- Piping- Civil structures

Thermal Power India-II, Dec 2007FE MODEL OF CALANDRIA-END SHIELD ASSEMBLY


FE MODEL OF RE-CIRCULATION PIPING SYSTEM


Service Building

FE Model of Reactor and Service Building


General Procedure followed in carrying out Seismic Analysis

• Finding out the Frequencies and Mode shapes • Determination of modal displacements

• Determination of other modal responses (stresses,

strains, forces & moments)

• Determination of final displacements, forces and moments


Find the response of different elements of the structures, systems or equipment (SS&E) to a given

response spectrum

1st: Calculate the mode shapes and frequencies of the SS&E :

This is done by solving the following equation for the eigen vectors and eign values

[ [K] - ω2n[M]} {Øn} = 0

where

[K] - Stiffness Matrix

ωn - natural frequency of the nth mode

[M] - Mass matrix

Øn - Eign vector of nth mode

ONLY significant modes up to 33 Hz are generally determined.


MODE SHAPES

FIXED BEAM

CANTILEVER BEAM

SIMPLY SUPPORTED BEAM


2nd Step

Determine the maximum model displacements w.r.t. the supports

This is done as follows:

{Øn}max = PF {Øn} Sa/ ωn2

{Øn}max - Max. displacement vector for nth mode

PF - model participation factor for the nth mode given by

- {Øn}T [M] {I}/ {Øn} T [M] {Øn}

Sa - value of acceleration in a acceleration response spectrum corresponding to ωn and design damping


3rd Step

Other responses such as stress, strain, moment, shear

can be calculated from the {Øn}max displ.

• For a mode in each orthogonal direction

4th Step

Compute the maximum response at a given d.o.f. for all modes and combine them

• by SRSS/closely spaced modal combination method for each orthogonal direction

• Combine the directional response by SRSS to get complete response


Checking of SS&E for qualification

• The resulting seismic responses shall be combined with the responses due to dead weight load and other operating load

• Check for the allowable stresses as per code for qualification


Equipment Anchorage • Traditionally Supported Against Friction • Equipment shall be properly anchored

• Embedment Anchorage • Expansion Anchor Bolt

• Heavy Equipment shall be mounted on separate foundation

separate from the structure • If equipment is mounted on higher elevation the foundation

Shall be rigid


Tanks

• Proper Anchorage

• Provide Full Penetration Weld Between Shell & BottomPlate

• Avoid abrupt changes in thickness of shell

• Design Shell-Head junction for buckling againstcompression


Failure of tanks

• Traditionally heavy equipment like large storage tanks were secured to the foundation by friction i.e. self standing. For such tanks, major damages in the past earthquakes have occurred because of

– sliding or – overturning

• For seismic resistance, tanks are secured to the foundation by providing anchorage in the form of cast in place bolts. The bolts should be designed for the earthquake resultant forces, otherwise the bolt threads can get damaged or the bolts can get uprooted.


Figure 1 : Sliding of tank, San Fernando Earthquake, California,1971


Overturning of tank, Kern country earthquake, California, 1952


Damage to anchor bolts, Processing tower, Kern country earthquake,1952


Fig 4 : Tank shell Elephant foot bulging, San fernado earthquake, California, 1971


PIPING

In general, the piping systems have performed well during a seismic event.

• Failure of these can be extremely damaging. • Failure may cause LOCA (Loss of Coolant

Accident)• Flooding from broken lines - can severely

damage the system due to short-circuit in instrumentation & electrical components.


Pipe Failures observed in Past Earthquakes

• Nozzles between pipe and equipment • Faulty foundation of equipment or connection

At nozzle junction • Failure of Piping supports • Faulty Design • Differential Movement

• Pipe supported on Different elevations • Passing through different structures

• Cast Iron Pipes • Screwed Fittings


Majority of failure

• Majorities of the piping damages - due to a civil building falling onto a piping system

• OR • failure of a building / structure supporting the

piping system.


Other major causes

• Other major causes - due to the differential movement between the equipment and piping support

• failures in corroded and eroded pipelines.


Real Life Examples

• A piping run connected to a tank nozzle through a branch connection is shown in the next Fig.

• As the run is having a support immediately after the tee connection


During earthquake

• because of the rigidity of the piping and because of the displacement of the tank (can be because of liquefaction / failure of anchorage)

the resultant load at the tee flange connection resulted into failure of the flange joint


Failures / damages at nozzles

• Earthquake induced failures / damagesobserved at nozzles between pipes and equipment


Flexibility provided - no damage

• Wherever flexibility was provided between equipment and piping, generally no damage has occurred


• Cast iron pipe - brittle in nature• allows little deformation - before failure • failed in many instances - during

earthquake

• In recent years, steel and mild steel pipes, (ductile properties) - replaced cast iron pipes.


Support for Normal Load & EQ

• Piping systems are generally supported for normal loads == dead wt & thermal loads.

• Dead weight supports - resist only downward gravity load

• During EQ - have to resist vertical upward load & increased vertical downward load due to EQ + normal load.


Lateral Restraints

• Long continuous pipes - seldom critical for horizontal lateral EQ load, if provided with lateral restraints

• Generally, such lateral supports -provided at a spacing = 3 times the dead weight span.


Flexibility v/s seismic

• Piping system, where thermal stresses are predominant

• the need for flexibility (to accommodate thermal movement)

often tends to offset the requirement of resisting seismic loads.


In such cases, this leads to

• Use of limit stops instead of the usual seismic solid supports or

• use of mechanical/hydraulic snubbers or dampers -- permit slow thermal movement but resist rapid movement during EQ


Seismic Anchor Movement

• Valves, air filters, blower silencers, strainers -commonly included in the piping

• do affect the response of the piping system if they are independently supported i.e. not supported from the same structure

• may result in the failure of attachment e.g. failure at the valve piping weld joint


Reason of such failure

• If piping system is supported from a single structural system then (piping + support) respond as a single unit.

• If supports are taken from independent structures / from different floors of same structure results in relative displacement at the support locations will occur.


Absence of Flexibility

• If such flexibility is not provided by proper design

It will lead to failure


Relative SAM seen by piping system :

• (going from one RCC building to another RCC structure) will be < (between RCC and steel structures)

• The relative displacement between two steel structures will be still more

This should be taken into account in the design.


Corrosive fluid/erosion inside the pipe

• piping systems corrode/erode at the bend location- because of the corrosive fluid inside viz. acidic liquids, sea water, chemicals etc. or high velocity

• prone to failure during an EQ event.

• Many of the failures are observed in the past


Solution to such problems

• In such cases, it is essential that a regular in-service inspection (ISI) be carried out and

• corroded pipes are replaced if the thickness goes below allowable.


Seismic Qualification of Active Mechanical & Electrical Equipment

• Seismic Qualification by analysis may not be possible for the SS&E which are active in nature (which involve mechanical motion) and which are having close gaps & clearances between moving components

• Closure of gap and clearances can result into a possible malfunction jeopardizing the functional performance of the equipment and a seismic qualification by test is recommended for such equipment for seismic qualification


List of Active Equipment

• Reactor shutdown and control devices• Valves• Rotating equipment

Pumps, fans, blowers, motors• Reciprocating equipment

compressors, diesel generators, reciprocating pumps


Sliding of pump base


Failure of vibration isolators


Lateral seismic stops


Seismic stops for equipment mounted using vibration isolating system


The components of these equipment viz. Pumps, fans, blowers, motors, compressors, DGs, reciprocating pumps

- have close gaps/clearances between the moving and stationary components.

The components of these equipment viz. Shaft-bearings, impeller-casing, piston-cylinder, are large components and can be modelled and analysed by finite element

method to demonstrate their functional operability


To demonstrate their functional operability based on

- deflection of moving components being less than the available gaps and clearances

- reactions at the bearing being less than the bearing design load


STATIC ANALYSIS OF DIESEL ENGINE OF 2400 KW DIESEL GENERATOR

Finite element model description:

Number of elements:53185

Number of nodes: 85824

Element types: NKTP-4 (Solid elements)

Total number of valid DOFs in model: 260433

Total number of unconstrained DOFs: 259713

Total number of constrained DOFs: 720

Material properties:

Material: Steel; Mass Density: 7.8E-09 N-Sec2/mm4

Modulus of elasticity: 21000 N/mm2

Poisson’s ratio: 0.3

Thermal Power India-II, Dec 2007FE Modeling of Diesel engine- Isometric view


Side view


FE Modeling of crank shaft


FE Modeling of crank shaft bearings


However, even for these equipment qualification by testing is more reliable method to

demonstrate the functional operability.


Electrical and C&I Panels have• Relays

• electromagnetic• bimetallic- (overload relay)

• Starters-spring loaded• actuator- spring loaded• Push button (spring loaded)• beepers• recorders (spring loaded)

Most of these instruments are small in size, weight and are delicate.


A typical Over voltage Relay Type VTU


Another Typical Example of a Relay


These components have

• Close gaps/clearances• complex geometries• uncommon materials

– making it difficult to model and analyze and are to be qualified by testing on a shake table

Continued


Instrumentaion & Control and ElectricalDevices • Device Behavior should not disturb the functioning of

the system

• To continue to maintain the state of position • To change the state of Position whenever required

• Make or Break of Contact

• The contact point should not result into chatterresulting into unwanted fluctuation of current andvoltage


Functional Checks

All the functions and the operating parameters and the state of the devices are

• Prechecked• Checked during seismic test• Post checked

Checked for Relay chatter, Relay malfunction, voltage fluctuation, light indications, door opening, loosening of bolts etc.


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Required Response Spectrum (RRS) & Test Response Spectrum (TRS)

TRS

RRS

Acceleration, m/s2

Frequency, Hz


SEISMIC QUALIFICATION OF ELECTRICAL AND I & CPANELS, EQUIPMENTS AND REACTOR S/D DEVICES

With in the country we have number of shake table facilities viz., • 30 tonne Tri-axial Table at SERC, Chennai, 4m X 4m

-Vertical Actuator 4 - Horizontal Actuator-4 • 20 tonne Bi-axial Table at IIT, Roorkee, 3.5m X 3.5m -Vertical 2 - Horizontal Actuator 1 • 10 tonne Tri-axial Table at CPRI, Bangalore, 4m X 4m

-Vertical Actuator 4 - Horizontal Actuator-4

• 10 tonne Tri-axial Table at IGCAR, Chennai, 4m X 4m -Vertical 3 - Horizontal Actuator 3 • 5 tonne Tri-axial Table at SERC, Chennai, 2m X 2m • 100kg Uni-axial Tables at ECIL Hyderabad, 1m X 1m • 300 kg Uni-axial Tables at ERDA Vadodara, 0.6m X 0.6m


400V DC Switchgear TAPP-3&4


24V DC / 195A Main Battery Charger


380V Dc/ 225A Standby Battery Charger unit with 380V DC / 200A Switch Fuse Unit


220V DCDB, TAPP-3,4

Thermal Power India-II, Dec 20072000KVA, 6600/433V Dry Cast Resin Transforme


Public Address System – Common Service Rack & Power Amplifier


Compressor Panel & Air Dryer Panel


2 Tier Consol unit

Thermal Power India-II, Dec 2007Toppled Storage Batteries

Thermal Power India-II, Dec 2007Failure of Electrode of Storage Batteries


Testing of Batteries


Tubular Lead Acid Stationary Cells, KAPP


Qualification for Valve

• Structural Analysis

for Structural Integrity & Pressure Boundary Integrity

• Seismic Testing

for Function Operability


Qualification of the Valve by Seismic Loading Test

• Carried out as per Annexure-F and Appendix B of ANSI B 16.41.

• The equivalent static force to be applied at CG of the valve at the weakest section is equal to mass multiplied by

• for rigid piping and valve configuration

» 1.5 times the spectral peak acceleration of the floor response spectra


Functional Checks

• Opening or closing of valves & timing

• Operation of limit switches


CONCLUSION• The performance criteria for the structures,

systems and equipment are defined early before the design stage based on their function in relation to their contribution to plant safety.

• The Nuclear Power Plant systems and equipment are seismically qualified using state-of-the art techniques involving both seismic analysis and testing, to ensure that the nuclear power plant is capable of safely surviving an earthquake that the plant is likely to experience.

• Guidelines and criteria for meeting these qualification requirements are followed as given in various AERB, NRC, IAEA guides, ASME codes and IEEE standards etc.


Thank You

SEISMIC RESISTANT DESIGN OF NUCLEAR POWER ......Thermal Power India-II, Dec 2007 For seismic design...

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Transcript of SEISMIC RESISTANT DESIGN OF NUCLEAR POWER ......Thermal Power India-II, Dec 2007 For seismic design...