Recent Guidance Developed for Post-Fukushima Activities in the US - - PowerPoint PPT Presentation

Recent Guidance Developed for Post-Fukushima Activities in the US

Presented by Annie Kammerer January 23, 2013

Presentation Contents

• Overview of the NTTF activities
• EPRI SPID Guidance
• ISG on the NRC SMA method
• Status of Seismic Walkdowns
• NEI proposed augmented approach

2

Near Term Task Force (NTTF)

3

NTTF Activities

4

• 50.54(f) RFI Letter issued

March 12, 2012

• Enclosure 1: Seismic hazard

and risk reevaluation

• Enclosure 3 Seismic

Walkdowns

Seismic NTTF Overview

5

Ongoing Near term Long term 2.3 2.1 2.2 Walkdowns Hazard evaluation Risk evaluation Regulatory Actions 10 year update

Walkdowns to assure plants are meeting licensing basis and to look for potential seismic

• issues. Reports due November 2012. Some

equipment delayed until outage. Hazard evaluation due in 18 months for NPPs within the CEUS SSC model area. 3 years for western US NPPs performing SSHAC level 3

• studies. Plant-specific site response.

Risk results due 3-4 years after hazard. SMAs

• nly allowed for small exceedance levels.

SPRAs allowed for all exceedances, but required for large exceedances. After receiving the information from the SPRA and SMA analyses, the NRC will determine appropriate regulatory actions. Rulemaking to require a reevaluation every 10 years. 11/2012 (+outages) 9/2013 (CEUS) 3/2015 (WUS) 3 years after hazard Depends

• n findings

Rulemaking timeline

Completed except delayed equipment that requires outages

Interact with Industry

• n Hazard and Risk

Evaluation Guidance (SPID) Licensees Conduct Seismic Hazard Reevaluation NRC evaluates new hazard and near-term actions Screen & Prioritize Plants for Risk Evaluation Licensees Conduct Risk Evaluation NRC Evaluates Risk Evaluation NRC makes Regulatory Decisions as Needed * Safety Enhancements * Backfit Analysis * Modify Plant License

PHASE 1

STAGE 1 STAGE 2

PHASE 2

R2.1 Overall Approach

6

Completed September 2013 October 2013 (already doing indpendent calcs) October 2013

Seismic Response Timeline

April 2019 April 2018 October 2017 October 2016 March 2015 September 2013 March 2012

50.54(f) letter sent CEUS Hazard Report/Interim Actions CEUS Higher Priority Risk Assessment due CEUS Risk Assessments due WUS Hazard Report/Interim Actions WUS Higher Priority Risk Assessment due WUS Risk Assessments due

7

CEUS SSC Model Already Developed NUREG 2115 WUS sites must do Site-Specific SSHAC Level 3 PSHA studies

• leads to longer

start time

Seismic Response Timeline Challenges

8

• Number of plants screening into SPRA

may be higher than original estimates leading to problems with limited resources

• n both sides
• Options being considered

– NEI has proposed augmented approach (shown at the end of the presentation) – After preliminary discussions, NRC requested a white paper with details on proposal

EPRI Screening, Prioritization and Implementation Guidance (SPID)

• EPRI 1025287
• Objective was to develop

guidance to allow licensees to address the 50.54(f) letter in a uniform, technically sound and optimized way

• Publically available and

finalized November 2012

9

EPRI SPID

• NRC in the process of endorsing
• Developed through strong interaction between

Industry and NRC experts through more than a dozen public meetings

• All positions have a technical basis and

several studies were conducted to support positions

• In depth review against the ANS standard

performed to assure that the positions allow for use of SPRA for risk-informed applications

10

EPRI SPID

Some key participants

• Industry: Kimberly Keithline, Greg Hardy, Bob

Kennedy, John Richards, Kelly Merz, Divakar Bhargava, Robin McGuire, Walt Silva, Don Moore, Bob Whorton, Stewart Lewis

• NRC: Nilesh Chokshi, Jon Ake, Cliff Munson,

Bob Budnitz, Ravi Ravendra, and Annie Kammerer

• Others were involved in specific topics (see

acknowledgements page)

11

EPRI SPID

Ch1: Purpose and Approach Ch2: Seismic Hazard Development Ch3: GMRS Comparison and Screening Ch4: Seismic Hazard and Screening Report Ch5: Prioritization Ch6: Risk Evaluations Ch7: Spent Fuel Pool Integrity Evaluation

12

EPRI SPID

Appx A: Control Point Appx B: Development of Site Specific Amplification factors Appx C: Sensitivity Studies to Develop Criteria for Analyzing Rock-Founded Structures as Fixed-Base Models Appx D: Sensitivity of Computed Annual Probability

• f Failure PF to Assumed Logarithmic Standard

Deviation β Used in Hybrid Method with Capacities Defined by 1% Failure Probability Capacity C1

13

EPRI SPID

• Ch2: Seismic Hazard Development

– Uses modern PSHA with newly developed models – Provides guidance on how to develop site response factors account for uncertainties for sites with old geotechnical data (new site investigations were not required) – “approach 3” in NUREG/CR-6728 used – Site response approach provided in detail in Appendix B – Control point clarified

14

EPRI SPID

Ch4: Seismic Hazard and Screening Report

– Provides template for licensees

Ch5: Prioritization

– General information as NRC staff will develop approach

Ch7: Spent Fuel Pool Integrity Evaluation

– Significant amount of information and provides a general approach for individual NPPs. Work is on-going to find optimizations across sites.

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Seismic Flowchart

Based on chart provided in 50.54(f) letter Attachment 1

Evaluation Methods & Screening

• Current practices for hazard evaluations

– CEUS-SSC & SSHAC Level 3 for WUS to develop new hazard curves (GMRS)

• Methods for plant evaluations

– SMA or SPRA for small exceedances of SSE – SPRA for NPPs with GMRS beyond 1.3xSSE (1 to 10 Hz) – Exceedances in the high frequency range (beyond 10 Hz) to be addressed through component testing program

– Allowances for narrow band exceedances (3.2.1.2) – Allowances for very low hazard sites with exceedances in <1Hz range (addressed on an SSC basis, 3.2.1.1)

2.1 Seismic Screening

High Frequency Evaluation GMRS > SSE only at frequencies above 10 Hz Seismic PRA needed GMRS > 1.3*SSE btwn 1 to 10 Hz

2.1 Seismic Screening

Low frequency exceedance for very low hazard sites allowed to do SSC-specific margins review

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.1 1 10 100 Acceleration (g) Frequency (Hz) SSE or IPEEE HCLPF

Specific rules for narrow band exceedances are provided

SPID Positions for SPRA and SMA

• The following SPID topics apply to both SPRA and NRC

SMA

• High frequency test program
• Screening of component
• Use of the CDFM and Separation of Variables

methods for fragility curve development

• Use of existing structural models
• Scaling of in-structure response spectra
• Use of fixed-based models for soft rock sites

With the enhancements in the NRC-SMA method and use

• f the above positions the differences between SMA &

SPRA are narrowing

SPID Approach to Screening and High Frequency Exceedances

High frequency

• nly exceedances

being treated through large testing program

SPID Approach to High Frequency Exceedances

• Testing program being

conducted to demonstrate large capacities where exist (very (tables maxed out)

• EPRI Testing program

developed in consultation with NRC staff, including in 2012 workshop

• Work plan available through NRC public

meeting minutes (August or Sept 2012)

SPID Approach to High Frequency Exceedances

• Phase 1: Pilot study

– Completed in summer 2012 – Looked at multiple load types – Took sampling of different types of equipment in EPRI 1015109

• Phase 2: Production Testing

– To cover large number of components with loading informed by Phase 1 results

SPID Approach to High Frequency Exceedances

• EPRI 1015109 High-frequency equipment list

– Electro-mechanical relays (e.g., control relays, time delay relays, protective relays) – Circuit breakers (e.g., molded case and power breakers – low and medium voltage) – Control switches (e.g., benchboard, panel, operator switches) – Process switches and sensors (e.g., pressure, temperature, flow, limit/position) – Electro-mechanical contactors (e.g., MCC starters) – Auxiliary contacts (e.g., for MCCBs, fused disconnects, contactors/starters) – Transfer switches (e.g., low and medium voltage switches with instrumentation) – Potentiometers (without locking devices) – Digital/solid state devices (mounting and connections only)

SPID Approach to High Frequency Exceedances

• Also considers failure modes

– Inadvertent change of state – Contact chatter – Change in output signal or set-point – Electrical connection discontinuity or intermittency (e.g., insufficient contact pressure) – Mechanical connection loosening – Mechanical misalignment/binding (e.g., latches, plungers) – Cyclic strain effects (e.g., cracks in solder joints) – Wiring not properly restrained – Inadequately secured mechanical fasteners and thumb screw connections

SPID Approach to SSC Screening

• The components identified as “high capacity “SSCs

should be assigned capacities equal to the screening level and retained in the system model (can use tables in EPRI NP-6041- SL Rev.1, other recent refs.)

• The screening level may be set as either:

– A screening level consistent with a HCLPF capacity that is 2.5 times the RLE, or – A screening level equivalent to the HCLPF that leads to a frequency of failure on the order of 5x10-7/yr using a mean point estimate.

SPID Approach to SSC Screening

• Once the SPRA/SMA analysis has been performed, a

check must be conducted to assure that none of the following conditions exist: – A “high seismic capacity” SSC (which has been assigned a conservative HCLPF equal to the screening level) is identified as a dominant contributor to HCLPF of core damage – A high seismic capacity SSC is identified as a dominant contributor to HCLPF of large early release

(avoids a “surrogate element” problem)

SPID Approach to SSC Screening

SPID Approach to Fragility Development

• CDFM with generic βs (hybrid approach) can

be used for first pass for fragility curves (βs provided in SPID)

• For those SSCs that are determined to be the

dominant risk contributors or are risk-significant in the seismic accident sequences, estimates

• f median capacity (C50%) and variabilities (βu

and βr) should be done using the fragility or separation of variables approach and then used in the integration

• Realistic ISRS should be calculated using ASME/ANS

PRA Standard Part 10 or the guidance on the use of existing information and models provided in the SPID

• If an existing structural model is used, its attributes

should be compared to the criteria in the SPID and its applicability documented and justified. Fixed base models may be used for structures founded on rock with a shear wave velocity greater than 3,500 feet/ second (for addressing the 50.54(f) letter only)

• The use of any existing models or data should be

reviewed by an experienced structural engineer, and should be subject to peer review

SPID Approach to Structural Response

Use of Scaling of Existing ISRS

• The acceptability of scaling of responses will be based
• n:

– previously developed ISRS – shapes of the previous input response spectrum/RLE – shapes of the new RLE, and structural natural frequencies, mode shapes and participation factors

• Licensee will need to demonstrate/document that

scaling of the ISRS is appropriate for the site in their submission to the NRC. Any potential structural issues with the use of scaling should be addressed and justified in the documentation. The use of scaling and the documentation should be subject to documented peer review

SPID Approach to Structural Response

Use of Scaling of Existing ISRS

• Scaling of rock or

soil sites where the shape of the new hazard spectrum is not highly similar to the previous spectrum is not recommended without justification that demonstrates the validity of the scaling approach

SPID Approach to Structural Response

Similar Dissimilar

ISG use of NRC SMA

• NRC ISG on the NRC

SMA method

• JLD-ISG-2012-04
• Issued November 2012
• Only used for 50.54(f)

responses and only used for plants where GMRS<1.3xSSE

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Comparison of SMA Approaches

EPRI SMA NRC SMA PRA SMA Key document EPRI 6041 R1 NUREG/CR-4334 NRC ISG-20 Initiators N/A Only transients and small LOCA All relevant initiators Equipment/ systems assessed 2 success paths Fault-spaced based selection on key limited systems Fault-space based selection HCLPF calculation higher value of the lowest equipment in each path Min/max approach to sequence and plant HCLPF Through integration of sequences (or min/max) Principal uses Operating reactors when risk insights are not needed Operating reactors when risk insights are needed New reactors

Not used for any NRC Purpose Used only for 50.54(f) letter response Used only for design (PRA required before loading fuel)

Reasons for Including NRC-SMA

• Recommendation 2.1 50.54(f) letter allows it
• NRC-SMA outlined in the 50.54(f) is an enhanced

approach from the original NRC-SMA

• NRC-SMA is a fault-space based approach using PRA

system logic but limiting analysis to two seismic initiators shown to be most risk significant; transient and small LOCA

• Approach is capable of providing risk insights and suitable

for sites with lower seismic hazard. SMA is not suitable for high hazard sites

• NRC-SMA approach can be easily extended to more

detailed PRA type of analysis, if needed

Reasons for Enhancements

Reasons for the NRC enhancements for this ISG are as follows:

• To define the scope of analysis needed for information

requested in 50.54(f) letter

• To provide staff positions on the major elements of SMA
• To update references to allow use of the recent

advances in methods and guidance

• To incorporate references to applicable provisions of the

ASME/ANS standard and positions of industry (SPID) endorsed by the NRC

Outline of the ISG on the NRC SMA

• Purpose
• Basic Terms and Concepts
• Background, Overview and Issues Related

to Seismic Margin Methods

• Staff Position on Individual Technical

Issues

• Documentation
• Peer Review Attributes, Activities, and

Documentation

Staff Positions on Technical Issues

• Addition of certain containment functions and systems to assess LERF
• HCLPF capacities for core-damage and large early release sequences
• Separate analysis of HCLPF capacities of sequences with and sequences without non-seismic failures

and human errors

• Chatter analysis and treatment of high-frequency response of certain SSCs

SMA Scope 4.2

• Selection of the Review Level Earthquake
• Soil failures
• Development of in-structure response spectra
• Median seismic responses of systems and components

Ground Motion and In-Structure Response 4.3

• Enhancements to the PRA-type systems SMA model beyond those in the original guidance
• “Mission time” for the accident analysis
• Selection of the Seismic Equipment List

Systems Analysis 4.4

• Plant walkdown methodology
• Screening approach and level for of SSCs
• Fragility analysis method for evaluation of the HCLPF capacity of an SSC
• CDFM method for evaluation of the HCLPF capacity of an SSC

Fragility and Capacity 4.5

• Plant margin evaluation using the Convolution Method for sequence-level and plant-level HCLPF

capacity

• Guidance on using the “Min-Max” method for sequence-level and plant-level HCLPF capacity

SMA Integration 4.6

Key SMA Only Topics

RLE: The RLE is the envelope of the SSE and the Ground Motion Response Spectra (GMRS) over the entire frequency range. Initiating events: Transient and small LOCA with unrecoverable loss of offsite power Mission time: Extended to 72 hrs. or stable shutdown state, whichever is longer

Key SMA Only Topics

Scope of functions: Group A functions (Shutdown chain reaction plus injection-phase early core cooling) + emergency core cooling late involving recirculation and switchover phase + containment heat removal + containment over-pressure protection (early) + containment integrity (penetration &I solation) Containment structural failure modes: Need not be included

Non-seismic failures: To be included explicitly Human actions: To be included explicitly Soil failure modes: To be included as applicable Sequence/Plant HCLPF:

• Convolution approach preferred.

Max-Min approach discourage and

• nly allowed with justification.
• HCLPFs for leading sequences

separately for core damage and large release

• HCLPFs for sequences separately

with and without non-seismic failures

Key SMA Only Topics

EPRI Guidance for Seismic Walkdowns

• EPRI Guidance

1025286, “Seismic Walkdown Guidance”

• Developed through

close cooperation of EPRI and NRC experts

• Endorsed 5/31/12
• Shouldn’t be used for

any other purpose

42

Seismic Walkdowns

• Walkdowns conducted for all104 NPPs
• Due 180 days after endorsement: Nov 2012
• Resident Inspectors were trained and observed

walkdown & performed walkdowns independently

• Licensee submittals currently under review by

NRC staff and contractors

• Initial insights due February and Lessons learned

report due October 2013

• Audits and RAIs in the spring
• SARs to be issued by October 2013

43

Seismic Walkdowns

• The R2.3 walkdowns are to the current licensing

basis – short term action as 2.1 is ongoing

• 98% found items to put into the CAP
• Most items minor – not surprising as most units

have had seismic walkdowns multiple times

• Quality of program varied widely unit to unit
• The flooding walkdowns have identified issues

that challenge the licensing basis for some sites as this is the first time for this type of request

– Unachievable human actions, missing seals, etc.

44

Potential Augmented Approach for Recommendation 2.1 Seismic Evaluations

November 14, 2012

Potential Augmented Approach

Key Concepts

§ Develop new hazard curves and Ground Motion Response Spectra (GMRS) as requested in 50.54(f) letter § Perform an additional interim evaluation (limited scope, simplified deterministic evaluation) and make appropriate plant modifications by 2016* § Perform SPRA or enhanced SMA, high frequency confirmation, and spent fuel pool evaluation as needed based on comparison of GMRS to screening criteria as requested in the 50.54(f) letter but on a longer schedule

*May extend longer if outages are required.

46

Potential Augmented Approach

Schedule for Interim Evaluation and Actions

47

Interim Evaluation and Actions

Scope of Equipment

§ Include a subset of installed plant equipment needed for FLEX

– Exact list will depend on plant-specific integrated plan for FLEX (due to NRC in February 2013) – Will typically include tanks and mechanical and electrical equipment

§ Structures, other SSCs (e.g., piping, cable trays, NSSS), and two-over-one interactions would be addressed in the SPRAs or enhanced SMAs

48

Interim Evaluation and Actions

Process and Success Criteria

§ If GMRS > SSE between 1 and 10 Hz*, develop a Review Level Ground Motion (RLGM) by scaling up the SSE so that it envelopes the GMRS between 1 and 10 Hz (not to exceed 2 x SSE or 0.75g PGA) § Derive in-structure motion using existing SSE-based ISRS scaled up consistent with the RLGM § Perform HCLPF evaluations using guidance such as EPRI NP-6041-SLR1 and EPRI TR-103959 § For equipment whose HCLPF < RLGM, implement plant modifications to achieve a HCLPF > RLGM

*Consistent with SPID Section 3.2.1

49

*Screening Consistent with SPID Section 3.2.1

§ For low seismic hazard sites with exceedances only below 2.5 Hz, evaluate low frequency sensitive SSCs using GMRS. § For narrow band exceedances (as defined in 3.2.1.2), no further evaluation is necessary.

50

Example

51

Example

52

Example

53

Conceptual Timeline

54