ML19011A435
| ML19011A435 | |
| Person / Time | |
|---|---|
| Issue date: | 01/16/2019 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Nathan Siu 415-0744 | |
| Shared Package | |
| ML19011A416 | List:
|
| References | |
| Download: ML19011A435 (23) | |
Text
Level 2/3 PRA:
Beyond Core Damage Lecture 6-4 1
Key Topics
- Accident Mitigation and Emergency Response
- Level 2 PRA
- Level 3 PRA 2
Overview
Resources American Nuclear Society and the Institute of Electrical and Electronics Engineers, PRA Procedures Guide, NUREG/CR-2300, January 1983.
F.E. Haskin, A.L. Camp, S.A. Hodge, and D.A. Powers, Perspectives on Reactor Safety, NUREG/CR-6042, Revision 2, March 2002.
U.S. Nuclear Regulatory Commission, Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants, NUREG-1150, December 1990.
3 Overview
Other References D. Helton, Scoping Study on Advanced Modeling Techniques for Level 2/3 PRA, U.S.
Nuclear Regulatory Commission, May 2009. (ADAMS ML091320447)
N. Bixler, et al., MACCS Best Practices as Applied in the State-of-the-Art Reactor Consequence Analyses (SOARCA) Project, NUREG/CR-7009, August 2014.
Environmental Protection Agency, PAG Manual: Protective Action Guides and Planning Guidance for Radiological Incidents, EPA-400/R-16/001, November 2016.
R. Draxler, An Overview of the HYSPLIT Modeling System for Trajectory and Dispersion Applications, National Oceanic and Atmospheric Administration, April 7, 2018. (Available from: https://www3.epa.gov/scram001/9thmodconf/draxler.pdf)
U.S. Nuclear Regulatory Commission, Technical Study of Spent Fuel Pool Accident Risk at Decommissioning Nuclear Power Plants, NUREG-1738, February 2001.
D. Algama, et al., Consequence Study of a Beyond-Design-Basis Earthquake Affecting the Spent Fuel Pool for a U.S. Mark I Boiling Water Reactor, draft report, U.S. Nuclear Regulatory Commission, June 2013. (ADAMS ML13133A132) 4 Overview
Terminology
- Level 2 commonly used in two different ways
- Analysis starting with initiating event and ending with radiological release
- Analysis starting with plant damage (Level 1) and ending with radiological release
- Similarly, for Level 3
- Analysis starting with initiating event and ending with offsite consequences
- Analysis starting with radiological release and ending with offsite consequences
- This lecture uses latter, narrower definitions 5
Overview
Level 2 and Level 3 PRA 6
Hazards Initiating Events Plant Damage States Source Term Groups Release Categories Offsite Consequences Level 1 Level 2 Level 3 Context
A More Detailed, Historical View 7
NUREG-1150 Context
Before trip After trip 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1 day 1 week 3300 MWt 260 MWt 50 MWt 15 MWt 7 MWt Overview: Accident Mitigation Mitigation Aims Arrest core damage (cooling)
Reduce source term (scrubbing, deposition, filtration)
Prevent/delay release (isolation, venting)
Active and Passive Systems/Features Injection/recirculation, containment sump Spray, fan coolers Isolation, vent Containment and other buildings 8
Adapted from: https://www.nrc.gov/reactors/pwrs.html Accident Mitigation and Emergency Response
Overview: Emergency Preparedness and
Response
Emergency Planning Zone (EPZ)
Plume exposure pathway (~10 mile radius)
Ingestion pathway (~50 mile radius)
Emergency Classifications Notification of Unusual Event Alert Site Area Emergency General Emergency Protective Actions Sheltering Evacuation Potassium iodide Interdiction Relocation 9
Accident Mitigation and Emergency Response
EPA Protective Action Guides (PAGs)
PAG = projected dose to an individual from a release of radioactive material at which a specific protective action to reduce or avoid that dose is recommended 10 Environmental Protection Agency, PAG Manual: Protective Action Guides and Planning Guidance for Radiological Incidents, EPA-400/R-16/001, November 2016 Accident Mitigation and Emergency Response
Level 2 PRA
- Interfaces
- Level 1: plant damage states include information beyond core damage, e.g., status of RCS (temperature, pressure, integrity) and support systems
- Level 3: Source terms and other characteristics (e.g., release location, energy) relevant to consequence analysis
- Key processes
- Mitigating system response
- Severe accident progression
- Containment response
- Human and organizational response 11 Level 2 PRA
- Active Systems
- Fan coolers
- Hydrogen igniters
- Isolation
- Vents
- Analogous to Level 1 models
- Bridge trees
- Consider support, environmental conditions 12 Level 2 PRA
Severe Accident Progression Stages
- Core uncovery and heatup
- Cladding oxidation
- Fuel liquefaction and holdup
- Core slumping/relocation
- Lower head failure
- Core-coolant and core-concrete interactions PRA Challenges
- Selection of representative scenarios for system codes (e.g., MELCOR, MAAP)
- Selection of simulation end time
- Treatment of uncertainties (model and parameter) 13 NUREG/CR-6042 Level 2 PRA
Containment Response
- Severe-accident failure mechanisms
- Direct containment heating
- Fuel-coolant interactions
- Liner meltthrough
- Hydrogen explosion
- Long-term overpressure
- Other mechanisms
- External missiles
- Isolation failure
- Bypass 14 NUREG/CR-6042 Level 2 PRA
Human Reliability Analysis Complications for an already difficult analysis Performance for an extreme scenario that overwhelmed protection systems and caused core damage Guidance rather than procedures - adherence to prioritization or selection of lower-priority options?
Uncertain information; dont necessarily know what PRA scenario is occurring Need for field actions; potential effect from severe accident progression Increased challenges from multi-unit events Ex-control room organizations (Technical Support Center, offsite emergency response)
No established standard approach; important to interview emergency response staff, observe exercises 15 TEPCO photo from The Yoshida Testimony, Asahi Shinbun, 2014.
Level 2 PRA
Level 3 PRA (aka Probabilistic Consequence Assessment)
Interface with Level 2 - map source term groups to release categories 16 Level 3 PRA
Severe Accident Consequence Analysis Codes 17 Code Origin Currently Supported Gaussian Plume Trajectory Lagrangian Met.
Sampling Exposure
/Dose Counter-measures Early Health Effects Latent Health Effects Economic Impacts CRAC/
CRAC2 USA X
X X
X X
X X
CRACIT USA X
X X
X X
X X
ARANO Finland X
X X
X X
X X
CONDOR UK X
X X
X X
X X
COSYMA EU X
X X
X X
X X
X LENA Sweden X
X X
X X
MACCS USA X
X X
X X
X X
X OSCAAR Japan X
X X
X X
X X
PACE UK X
X X
X X
X
?
X X
Level 3 PRA
Atmospheric Transport Gaussian plume model based on averaging process More accurate modeling might make a difference for threshold phenomena (acute fatalities, EPA PAGs)
HYSPLIT: Gaussian puff Other considerations Weather sampling Correlation with plant conditions for Level 1 and 2 analyses 18 Level 3 PRA
MACCS Transport Illustration (Video)
Plume segments move with wind shifting from northwest to northeast Segment width depends on dispersion that has occurred due to varying weather conditions Segment length depends on wind speed 19 Level 3 PRA MACCS Video
Other Considerations
- Protective Actions
- Timing
- Compliance
- Vulnerable cohorts
- Correlation with initiator
- Disruptive events
- Non-radiological impacts
- Long-term effects
- Dose and Effects
- LNT
- Compliance 20 What can go wrong?
Level 3 PRA
Spent Fuel Pools Features Low decay heat levels, large water inventories Strong structures Concerns Outside containment Zirconium oxidation (fires)
Combined core + SFP accident Hazardous environment prior to fuel damage Initiators Loss of inventory Loss of SFP cooling Level 1 metric: fuel damage frequency U.S. studies include:
NUREG-1738 (2001)
Algama et al. (2013)
International interest 21
Comments
- Changing view on the nature of accidents
- Past emphasis
- Large, early releases => acute fatalities
- Large, late releases => cancer fatalities, other health effects
- Improved analyses + empirical experience
- Low likelihood of large early doses, avoidability of late doses
- Increased importance of: a) non-radiological effects, and b) land contamination and associated effects (psycho-social, economic)
- Increased importance of non-atmospheric pathways
- Current Level 3 analyses are inductive; deductive approaches might be needed to confirm the above 22
Thought Exercise Following the 2011 earthquake and tsunami in Japan, the Grand Duchy of Fenwick decides to hold an earthquake/flooding emergency preparedness exercise.
This an expensive and disruptive undertaking and so will be done only one time. The Exercise Coordinator says she will design the scenario to ensure that all parts of the Duchys Emergency Plan are exercised, and will develop the specific scenario elements by asking the heads of key departments (police, fire, building & safety, etc.) what they think might happen. Do you have any suggestions for her?
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