Atucha I Seismic Safety Evaluation Program

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International Expert’s Meeting on Protection against Extreme Earthquakes and Tsunamis in the Light of the Accident at the Fukushima Daiichi Nuclear Power Plant

(IEM3)

Paper PR28 THE SEISMIC SAFETY EVALUATION PROGRAMME

OF THE ATUCHA I (CNA-I) NPP-ARGENTINA AT THE LIGHT OF LESSONS LEARNED FROM

FUKUSHIMA DAIICHI NPP ACCIDENT Technical Session 2: Seismic and Tsunami Safety

A.R. Godoy and J.J. Johnson (James J. Johnson & Associates)

Alicia Couto and Carolina Romano (Nucleoeléctrica Argentina S.A. (NA-SA))

IAEA IEM September 2012

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Background: Atucha I

•Atucha I – PHWR (Heavy water reactor) - KWU (Germany), 357 MWe capacity; CNA I started in June 1968 and commercial operation in June 1974; 72% availability over 37 years; –Internal event PRA models; –Operator - Nucleoeléctrica Argentina S.A. (NA-SA) –No seismic design.

•Seismic Safety Evaluation Program –Needed to comply with safety evaluations against external events as a result of the Fukushima accident in Japan –In compliance with new updated international safety standards and worldwide recognized engineering practice for such assessments.

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Main Objectives of the Seismic Safety Evaluation Programme for Atucha I NPP

• Evaluate and quantify the seismic capacity of CNA-I – Ability to cope with a specified earthquake ground motion

at the site – CNA-I “as-is” conditions – Estimate the seismic safety margin defined by High

Confidence of Low Probability of Failure (HCLPF) • Take into account the lessons learned from the experience of

all recent strong earthquakes in Japan and their effects on nuclear power plants.

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Specific Objectives of the Seismic Safety Evaluation Programme for Atucha I NPP

•Demonstrate the seismic safety margin conditional on Review Level Earthquake ground motion (RLE) •Confirm no cliff edge effects exist •Identify weak links and vulnerabilities in physical and operational aspects due to seismic events. •Provide input for risk informed decision making. •Identify and prioritize possible upgrades.

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Comprehensive Five-Phase Programme

• Phase 1: Scoping Study and Preliminary Plant Walkdown ‒ Completed – November 2011

• Phase 2: Development of the Safe Shutdown Equipment List (SSEL), System Walkdown, Training Class

− SSEL for walkdown – April 2012, Final – August 2012 • Phase 3: Seismic Response and Structure Capacity

Evaluation ‒ In-progress

• Phase 4: Seismic Capability Walkdown – Screening Process – SSC HCLPF

‒ Walkdown complete – May 2012, HCLPF in progress • Phase 5: Detailed Analysis and Evaluation for Seismic

Qualification 5

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Phase 1: Scoping Study and Preliminary Walkdown: Status

• Complete 30 November 2011

• Report – Initial Issue 30 November

2011 – Living document to

incorporate additional data, e.g., success paths systems, safe shutdown equipment list

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Phase 1 – Main Results

• Assumptions for the seismic safety evaluation program of CNA I: − Methodology of evaluation: US EPRI SMA; two success

paths to safe shutdown, others; Critical relay review - Phase 5

− Review level earthquake (RLE); − Operational assumptions: loss of off-site power and no

recovery in a 72 hour period; no outside assistance; − Requirements of systems to mitigate earthquake induced

plant events: such as loss of off-site power, station blackout and small LOCA;

• Easy fixes (cabinet top bracing, raised floors, batteries/battery racks, DG flooding potential)

• Many “easy fixes” were installed during outage!!

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Phase 2: Development and Review of Safe Shutdown Equipment List (SSEL), System Walkdown, and Training Course

• Success paths • Two for safe shutdown - one mitigates small LOCA; • Containment and containment isolation; • Spent fuel cooling. • Refuelling Machine and tilting bottle (continuous operation) • Fire extinction system

• NA-SA-CNA I personnel (systems, operations and engineering staff) developed success paths (training and peer reviewed by JJJ Team)

• Safe Shutdown Equipment List (SSEL) – 627 items – In accordance with methods applied to address Fukushima issues,

e.g., European stress tests • Status – 99% complete (some refinements on-going)

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Phase 2: Development and Review of Safe Shutdown Equipment List (SSEL), System Walkdown, and Training Course

• Training Course: – Familiarity and training NA-SA staff in Seismic Evaluation

Methods (SMA and GIP) approaches for Plant Walkdown (Phase 4) and maintaining seismic capacity in the future (configuration control)

– Participants • Atucha I and II, Embalse, NA-SA Headquarters, CAREM (about 25

personnel) • Systems, engineering (civil/structural, mechanical, electrical, I&C,

etc.), operations – Completed 5- 9 March 2012 Buenos Aires (Monday – Thursday) and

Atucha site (Friday) – Training materials delivered (hard copy, electronic copy)

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Phase 3: Seismic Response and Structure Capacity Evaluation: Part 1 Seismic Response

• Seismic response – Structures and buildings housing SSEL systems and

components – Seismic demand (80% NEP conditional on RLE)

• In-structure response spectra generated at the levels required by the location of the SSEL items

• Forces/moments in structures for capacity evaluation

• Structures to be analyzed (5) • Demonstrated in many studies to be one of the most

important elements in seismic safety evaluation programmes – Excessive conservatism leads to un-needed upgrades and

modifications and may lead to mis-identification of important contributors to HCLPF or risk

– Key for fracture mechanics evaluation of RCS as in CNA-II

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Phase 4: Seismic Capability Walkdown – Screening Process

• Steps in the EPRI SMA methodology 1. Selection of Review Level Earthquake (RLE) 2. Selection of Assessment Team (6 members –

240 yrs experience) 3. Pre-walkdown and Pre-Calculation Preparation 4. Selection of Success Paths 5. Ruggedness Screening 6. Seismic Capability Walkdown

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1. Review Level Earthquake (RLE): Basis

• Spectral shape accounting for two PSHAs and procedure of US NRC RG 1.208 (ASCE 43-05) – JJJ & Associates PSHA Study – Peer Review of AECL PSHA Study

• Recommendation – enveloped response spectra for conservatism – PGA = 0.1g, – Peak spectral acceleration = 0.23g (5% damping)

• Presentation and report submitted to ARN on 14 March 2012 for review - approval May 2012

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Atucha NPP Site: Recommended and Accepted DBE/RLE

0.0000

0.1000

0.2000

0.3000

0.4000

0.5000

0.10 1.00 10.00 100.00

RLE-DBE…

Frequency (Hz)

Spec

tral

Acc

eler

atio

n (g

)

ATUCHA NPP SITE - PROPOSED ENVELOPE RLE-DBE

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6. Seismic Capability Walkdown

• Perform in-plant seismic capacity evaluation of SSEL items ‒Find and evaluate all items on the SSEL (currently 647) ‒Apply screening rules from EPRI NP-6041 Rev. 1 (note, meeting

screening rules may allow capacity verification to be for PGA=0.3g conditional on anchorage evaluation and seismic systems interaction issues)

‒Performed during outage ‒Evaluate seismic systems interaction issues ‒Document SSEL item data ‒ Status

‒ Detailed plant walkdown – 4 weeks, completed 4 May 2012 ‒ Documentation near completion ‒ HCLPF calculations on-going

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• Document SSEL item data using iPad system • Seismic Evaluation Work Sheets (SEWS) • SEWS – 27 categories of equipment/components/structural

elements • Drawings, photos, videos, field notes, etc. • iPAD data processing and storage • Uploaded to server daily

• Advantages • Consistent electronic record of walkdown results – long term

storage, printed copies, revisions for future activities • Summary Excel table yielding data for decision-making (operator,

regulator, reviewers) • Disadvantages

• Dressed out use difficult • Need additional photos from those of iPad – lighting, resolution

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• Status: • SSEL = 627 total items

• Completed data = 627 items • Acceptable = 76%, including Rule-of-the-Box • Unknown (meaning more information needed or analysis to be

performed) = 12% • Not acceptable = 12% (examples on following slides)

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6. Seismic Capability Walkdown: Observations

• Excellent cooperation and support from staff (systems, engineering, operations) – very knowledgeable

• Atucha I is very clean and appears well maintained • Mechanical equipment generally met the seismic

experience-based screening criteria • Electrical equipment needs evaluation and possible

bracing • Structures – evaluation required (secondary heat sink

building, steep slope, etc.) • Housekeeping issues

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• Piping not seismically supported – generally, judged OK based on earthquake experience data and EPRI screening guidelines

• Piping not supported at valve locations - generally, judged OK based on earthquake experience data

• HVAC ducts weak or missing supports – to be evaluated on a sample basis

• Raised floors well restrained horizontally – lack of vertical uplift restraints to be evaluated

• Connection of grout pads to floors to be evaluated, e.g., vertical tanks

• Secondary heat sink building capacity evaluation needed • Unreinforced masonry walls in vicinity of SSEL equipment to

be evaluated

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6. Seismic Capability Walkdown: EDGs potential flooding and falling hazards

Feedwater tank floor above – day tank no anchorage - block wall adjacent

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6. Seismic Capability Walkdown: To be evaluated

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iPad Data Collection

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6. Seismic Capability Walkdown: Summary from iPad Data Collection

Equipment ID No.

Equipment Description

EPRI Equip Class SEWS No. Remarks

Safety System

Success Path Building

Floor Elevation

(m)

Item Elevation

(m)

Room No.

Row/Col/ Cabinet

TB11S06 Pressure Reducing Valve GEN SEWS-25-251 Valve to reduce air pressure on quick-opening valv Reactor Building-S 0.50 2.00 1-307 TB21S06 Pressure Reducing Valve GEN SEWS-25-252 Identical to TB11S06 Reactor Building-S 0.50 1.00 1-307 TB31S06 Pressure Reducing Valve GEN SEWS-25-253 Identical to TB11S06 Reactor Building-S 0.50 1.50 1-307 HA51 Cabinet I&CP SEWS-05-002 Cabinet with Command Modules HA 1-SP01 Auxiliary Building 6.00 0.47 2-311 HA51HB53 Cabinet I&CP SEWS-05-003 Cabinet for Interlocking Logic Cards. Identical to H HB 1-SP01 Auxiliary Building 6.00 0.47 2-311 HB53RA01S04 Pressure safety valve (m AOV SEWS-13-001 Safety valve from Steam Generator 1 RA 1-SP01 Auxiliary Building 23.00 0.00 2-600 RA01S06 Motor Operated Valve MOV SEWS-14-004 Isolation Valve of the vent from Steam Generator 1 RA 1-SP01 Auxiliary Building 25.00 1.70 2-600 HB03RA02S06 Motor Operated Valve MOV SEWS-14-005 Isolation Valve of the vent from Steam Generator 2 RA 1-SP01 Auxiliary Building 25.00 1.70 2-600 HB03RA07S01 Motor Operated Valve MOV SEWS-14-006 Vent valve to atmosphere RA 1-SP01 Auxiliary Building 25.00 2.00 -600 RA07S02 Motor Operated Valve MOV SEWS-14-007 Vent valve to atmosphere RA 1-SP01 Auxiliary Building 25.00 2.00 2-600 IXION CABLE CCable DS SEWS-26-008 Cable for interconnection IX 1-SP01 CNAI - CNAII -2.00?? -2.00?? Tunnel Cabinet IXION Cabinet IXION I&CP SEWS-05-010 Cabinet for Electric Interconnection between CNAI- IX 1-SP01 CNAII 0.00 1.50 CNAII BAZ16 Switchgears MCC, LVS, MVSSEWS-01-011 Switchgear 6,6kV IX 1-SP01 CNAII 0.00 0.00 CNAII XKA -20 Diesel Generator EG SEWS-09-009 CNAII Diesel Generator IX 1-SP01 CNAII 0.00 0.00 CNAII

Equipment ID No.

BELOW ~40'?

(B)

CAP SPEC (B)

DEM SPEC (B)

CAP>DEM? (B)

EVAL OK? (C)

AUX EVAL OK? (D)

RELAY OK? ( E )

ANCHOR OK? (F)

INTER OK? (G) EQUIP OK?

Lead for same / similar?

Master for ROB? ROB with Same as Similar to

TB11S06 Yes 0.8g P SGA RLE Peak Yes Yes N/A N/A Yes Yes Yes L No TB21S06 Yes 0.8g P SGA RLE Peak Yes Yes N/A N/A Yes Yes Yes No No TB11S06 TB31S06 Yes 0.8g P SGA RLE Peak Yes Yes N/A N/A Yes Yes Yes No No TB11S06 HA51 Yes 0.8g P SGA RLE Peak Yes Yes N/A Unknown No No No L No HB53 Yes 0.8g P SGA RLE Peak Yes Yes N/A Unknown No No No No No HA51 RA01S04 No 1.2g P SGA ISRS Yes Yes N/A N/A N/A Yes Yes No No RA01S06 No 1.2g P SGA ISRS Yes Yes N/A N/A N/A Yes Yes L No RA02S06 No 1.2g P SGA ISRS Yes Yes N/A N/A N/A Yes Yes No No RA01S06 RA07S01 No 1.2g P SGA ISRS Yes Yes N/A N/A N/A Yes Yes L No RA07S02 No 1.2g P SGA ISRS Yes Yes N/A N/A N/A Yes Yes No No RA07S01 IXION CABLE C N/A N/A N/A N/A N/A N/A Yes No No Cabinet IXION N/A No No BAZ16 BAZ16 Yes 0.8g P SGA RLE Peak Yes Yes N/A Unknown Yes Yes Unknown No M XKA -20 Yes 0.8g P SGA RLE Peak Yes Yes Unknown Yes Yes Yes Unknown No No

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• 75% of SSEL items meet EPRI Screening Tables for PGA = 0.3g

• Anchorage capacity and seismic systems interaction issues – determine HCLPF

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Phase 5: Detailed Analysis and Evaluation

•High Confidence of Low Probability of Failure (HCLPF) calculations – high importance items not treated in Phase 4 due to resource limitations – refueling machine, NSSS components, etc. •Structure/building capacity evaluation •NSSS fracture mechanics evaluation for double-ended guillotine break as needed (CNA-II like analyses)

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Future Activities

• Phase 5 • Configuration Management

– Essential to maintain seismic capacity of CNA-I – Procedures to be developed

• Designs include engineering • Sign offs on new installations and replacement items –

engineering, systems, operations • Can use SEWS methodology as aid and documentation

• Containment and containment systems evaluated to seismic hazard probability of exceedance of 10-5

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Future Activities

• Geotechnical to be evaluated (steep slope – pump house and plant grade, etc.)

• Seismically- induced fire and flooding evaluation – Collaboration with CNA-I fire and flooding experts – In-building seismically induced flood (sprinkler system,

tank failures, etc.) - completed during walkdown – Yard sources of seismically induced flood – External to plant boundary flood potential – Consequences to turbine building DG flooding, etc.

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Future Activities

• Seismic instrumentation – None installed. In the process of procurement. – Shutdown and re-start decisions difficult if earthquake ground

motion is felt • Operations

– Need procedures to address occurrence of ground motion at Atucha site. IAEA SR 66 is being used.

– Training

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Questions and Answers

THANK YOU

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Atucha I Seismic Safety Evaluation Program

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