A Post-Fukushima Look at Assessing Flood Hazards

Baltimore, Maryland

Society of Women Engineers Annual Conference

WE 13 October 24-26, 2013

A Post-Fukushima Look at Assessing Flood Hazards

by

Kit Y. Ng

October 24 Lightning Talk Session

CIVIL GOVERNMENT SERVICESMINING & METALSOIL, GAS & CHEMICALS POWER

Overview

Fukushima Nuclear Accident - A Few Key Facts

Fukushima Lesson Learned and NTTF Recommendations

US Regulatory Actions

Impact to US Nuclear Fleet

Status of Flooding Reevaluation

Flooding Reevaluation Expectations

Fukushima Nuclear Accident – Key Facts March 11th@ 2:36 pm local

Magnitude 9.0 Earthquake 231 miles NE of Tokyo, 5th Largest Since 1900

First of Seven Tsunami Waves Arrived 41 Minutes Later

© Bechtel | 3

Fukushima Nuclear Accident – Key Facts

© Bechtel | 4

Source: NRC NRR April 2011 Presentation on Fukushima

Fukushima Nuclear Accident – Key FactsPlant Response - Earthquake

© Bechtel | 5

Earthquake - Automatic Shutdown of Units 1, 2 & 3 (SCRAM – Emergency Shut down)

Peak acceleration measured at Fukushima Daiichi was 0.561g horizontal and 0.308g vertical at Unit 2

Exceeded the design basis acceleration of 0.447g horizontal for Units 2, 3 and 5.

Offsite Power Lost

Emergency Diesel Generators Started for Backup AC Power


Fukushima Nuclear Accident – Key FactsPlant Response – Tsunami (41 minutes Later)

© Bechtel | 6

Maximum Tsunami Runup Height at 46 to 49 ft

> 18.7 ft Design Basis Tsunami Height by over 27 ft

> El 32.8 ft Plant Grade

Loss of Emergency Diesel Back-up Power in Units 1 to 5 - Station Black Out (SBO)

8 -10 hours Later Station Batteries Depleted (Loss of DC Power)

One Unit 6 Emergency Diesel Generator left to cool Units 5 & 6 reactors and spent fuel pools

Seawater Intake Damaged and Non-functional

Loss of Ultimate Heat Sink to All Units

Unable to Monitor Units 1 – 4 Spent Fuel Pools or Restore Cooling Flow


Fukushima Nuclear Accident – Key FactsPlant Response – Tsunami (41 minutes Later)

© Bechtel | 7

No Core Cooling for Units 1 to 3

Steam Driven Injection Pumps for Units 1 to 3 Failed

Core Damage Started in Unit 1, then on Units 2 & 3

Pressure Built Up inside Containment due to Increasing Temperature

Containment Could Not Be Vented Successfully

—Due to High Dose Rates and Lack of Contingency Procedures for Operating the Vent System W/O Power

—Lack of Prestaged Equipment such as an engine-driven air compressor

Hydrogen Explosions: Units 1 to 4 Containment Structures Damaged

Loss of Primary & Secondary Containments Resulted in Ground-Level Releases of Radioactive Material


Fukushima Nuclear Accident – Key Facts

© Bechtel | 8

Source: INPO 11-005 November 2011 Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station

Post Fukushima Regulatory Actions - 2011

March 11 – NRC Operations Center to Monitor Tsunami Risk in US and Support Response Efforts

March 18 – NRC reminded Post-9/11 additional emergency equipment

March 23 – Resident inspectors re-examine Post-9/11 emergency equipment

April 1 – NRC Appointed Near Term Task Force (NTTF) on Fukushima Lessons Learned

April 29 - Resident inspectors examine severe accident management procedures and training at U.S. nuclear power plants per TI2515/184

May 11 - NRC requires nuclear power plants to provide information on post-9/11 emergency equipment, as well as how the plants ensure strategies to use the equipment remain effective over time (Bulletin 2011-01)

June 6 - NRC reports on areas for improvement regarding U.S. nuclear power plants’ Severe Accident Management Guidelines (SAMG)

© Bechtel | 9


July 12 – NRC NTTF Report on Lessons Learned from Fukushima Issued. Concluded that U.S. Plants are Operating Safely and Provided 12 Broad Recommendations for Enhancing Reactor Safety (SECY–11-093)

—Clarifying the Regulatory Framework - Defense-in-depth & Risk Considerations

—Ensuring Protection – Reevaluate/Upgrade Design-basis Seismic & Flooding

—Enhancing Mitigation –

—SBO Mitigation; Reliable Hardened Vent

—Hydrogen Control & Mitigation; SPF Makeup & Instrumentation

—Onsite emergency response Capabilities

—Emergency Operating Procedures, Severe Accident Management Guidelines, Extensive Damage Mitigation Guidelines

—Strengthening Emergency Preparedness -

—Emergency plans Address Prolonged SBO & Multi-unit Events

— Improving the Efficiency of NRC Programs - Reactor Oversight Process

© Bechtel | 10

Post Fukushima Regulatory Actions - 2011 September 9 - NRC staff presented 6 NTTF Recommendations that

should be Initiated Without Delay (SECY–11-0124)

October 3 - NRC staff proposed three tiers of prioritization for the NTTF recommendations (SECY-11-0137)

October 18 - The Commission approved the NRC staff’s proposal to implement recommendations described in SECY-11-0124 within five years, by 2016

December 15 - The Commission approves the staff’s proposed prioritization of the Near-Term Task Force recommendations described in SECY-11-0137

© Bechtel | 11


Tier 1 Recommendations

2.1 Seismic and flood hazard reevaluations

2.3 Seismic and flood walkdowns

4.1 Station blackout (SBO) regulatory actions

4.2 Equipment covered under Title 10 of the Code of Federal Regulations (10 CFR) 50.54(hh)(2)

5.1 Reliable hardened vents for Mark I and Mark II containments

7.1 SFP instrumentation

8 Strengthening & integration of emergency operating procedures, severe accident management guidelines, extensive damage mitigation guidelines

9.3 Emergency preparedness (EP) regulatory actions

© Bechtel | 12


Tier 2 Recommendations

7 SFP makeup capability (7.2, 7.3, 7.4, and 7.5)

9.3 Emergency preparedness regulatory actions (the remaining of Recommendation 9.3, except for Emergency Response Data System (ERDS) capability to be addressed in Tier 3

© Bechtel | 13


March 12 – NRC issued three Orders and a Request for Information Letter to the nation's 104 operating reactors:

—Order EA-12-049 Modifying Licenses with Regard to Requirements for Mitigation Strategies for Beyond-Design-Basis External Events

—Order EA-12-050 Reliable Hardened Containment Vents—Order EA-12-051 Reliable Spent Fuel Pool Instrumentation—50.54(f) RFI Letter on Recommendations 2.3 Seismic/Flooding Walkdown, 2.1

Sesimic/Flooding Reevaluation and 9.3 EP Actions

May 31 – Endorsed flooding walkdown guidance & seismic walkdown guidance

— Issued guidance to Assess emergency preparedness communications and staffing—Endorsed EP assessment guidance

July 13 – NRC outlined plans for implementing the longer-term "Tier 2" and "Tier 3" recommendations (SECY-12-0095)

August 30 – NRC issued implementation guidance to enable U.S. nuclear power plants to achieve compliance with each of the Orders

© Bechtel | 14

Impact to United States Nuclear Fleet

104 Reactors at 65 Sites

35 BWR Units

69 PWR Units

~1/3 Coastal Plants

~2/3 River Plants

© Bechtel | 15

NTTF 2.1 Flooding Hazard Reevaluation Scope

Phase 1

—Reevaluation per Present-Day Data, Standard, Methodology and Regulatory Requirements (1 - 3 Years after 50.54(f) RFI Letter )

Phase 2

— Integrated Assessment (2 Years after Flooding Reevaluation)

© Bechtel | 16

1/201311/2012 ~ 1/2013 to

~1/2015

1/2014 to

1/2016

1 to 3 years from Request

Within 2 years

60 days 3/12/2012

External Event Flooding Mechanisms

© Bechtel | 17

NA = Not Applicable; C = Cold Region

Flood Hazard Evaluation Methodology Changes

Present-Day Requirements Consistent with New Plant Licensing Requirements (ESP/COLA)

Guides and Standards: some new and some revised – RG1.59, RG1.102, RG1.206, SRP-0800, NUREG/CR-7046, ANS 2.8/1992; ISG on Storm Surge, Tsunami and Seiche; New ISG on Dam Break

Technical Approach – remains primarily deterministic

Technology/Methodology – advanced from engineering judgments and simplified analytical hand calculations to 1D, 2D and 3D computational models

Flood Source Data

– Updated meteorological data such as Probable Maximum Precipitation– Updated hurricane data such as Probable Maximum Hurricane parameters– Updated tsunami source data

© Bechtel | 18

Source Data Updates

Topography – LiDAR data, USGS DEM database

Bathymetry – sonar survey (e.g., NGDC Coastal Relief Model, Global Relief Models - ETOPO database)

Submarine Tsunami Sources - Sea floor imagery (e.g., GLORIA); NUREG/CR-6966; USGS Tsunami Studies; extensive geological literature search

Tsunami runup - NOAA database

Sea level changes - NOAA NOS tidal station database

Historical Storm - NOAA NCDC climatic data, NEXRAD

Flood Discharge – USGS Stream Gage database

Watershed Delineation – USGS NHD Watershed Tool

Ice and Snow – NOAA Ice and Snow Database

Dam – USACE National Dam Inventory

© Bechtel | 19

Source Data Updates

© Bechtel | 20

Source Data Updates

© Bechtel | 21


Coastal Sites:

– Expect to require tsunami evaluation and modeling– Expect to require 2-D storm surge modeling – Expect to require consideration of sea-level changes

Streamside Sites:

– Probable Maximum Flood evaluation to consider higher hydrograph peaking factors per NUREG 7046; zero initial rainfall loss

– Sensitivity of Manning’s n, constant rainfall losses– Upstream dam failure evaluation (seismic/hydrologic/sunny day)– Downstream (Ultimate Heat Sink) dam failure as a result of upstream flooding– Consider blockages of drainages during local intense precipitation

© Bechtel | 22


Coastal Plants

Storm Surge still level increases by 2 ft to 5 ft

– Newer generation storm surge models vs 1-D model– Long-term sea level rise– Updated Probable Maximum Hurricane parameters

Tsunami levels increases by 12 ft to 14 ft

– Conservative runup estimates vs engineering judgment (no tsunami level was derived for operating plants)

© Bechtel | 23


Streamside Plants

River flooding level changes from -4 ft to +10 ft

– Updated NOAA HMR PMP values– Higher Resolution Topographic Data– Lower Rainfall Loss and Higher Peaking Factor– More Conservative Manning’s n values

Upstream dam failure level changes from -5 ft to +15 ft

– Selection of Breach Models– Changes in Dam inventories and Inflow Estimates– Adoption of more conservative but simpler computational approach for dry sites

© Bechtel | 24

Next Phase - Interim Measures and Integrated Assessments

Apply when Reevaluated Flood Hazards Exceed Current Design Basis

Need to Consider Other Associated Flood Hazards– Hydrostatic and Hydrodynamic Forces– Debris Loading; Sediment; Erosion– Flood Duration; Warning Time– Combined Effects of Multiple Flood Mechanisms

Higher Flooding Hazards Expected for Most Plants– Options: Protection vs Mitigation

Integrated Assessment – A New Process - Regulatory/Industry Guidance is being developed

Industry Group Task Force Involvement – NEI/EPRI/INPO/Utilities/Vendor

Peer Review Requirements; Human Performance Factor

3 Approaches: – Scenario Based; Margin Based; Probabilistic Risk Assessment

© Bechtel | 25

Questions?

Email for Further Questions

[email protected]

© Bechtel | 26

mailto:[email protected]

Engineering

A Post-Fukushima Look at Assessing Flood Hazards