2013-01-09 – Constellation Energy Nuclear Group – Severe Accident Management and Filtering Strategies in BWR Mark I and Mark II containments

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Severe Accident
Management
and
Filtering Strategies
January 9, 2013
Maria G. Korsnick
Chief Nuclear Officer
Chief Operating Officer
Constellation Energy Nuclear Group
Industry Position
* Industry supports filtration of radionuclides in
BWR Mark I & II containments to mitigate land
contamination
* Performance-based approach
– Needed for optimum filtration strategies based
on unique plant design features
– Can be implemented earlier than other options
• Filtration outside containment is not optimal
2
Layer Upon Layer of Safety Margin
A. F . 0 0
Plus On-Site
FLEX
Plus Industry
Response Capability
and Filtering
Strategy
Reioa Rspos
Centers 0
OnSt FLEX
Emergency
Response
Mitigation
Prevention
Pre-Fukushima
Emergency
Plans
SAMGs
SBO Coping
Capability
Design Basis
External Events
On-Sie FLE /
SBO Coping
Capability
Design Basis
External Events
SBO Coping
Capability
Design Basis
External Events
3
Prevent and Manage Accidents
• Protect the three barriers to fission product
release
– Fuel Cladding
– Reactor Coolant System
– Containment
” The containment is a system that must be
managed during a severe event
A passive vent filter is
no the answer
4
Managing Containment During Fuel
Damage Events
” Prevent containment failure by cooling core
debris and controlling pressure
• Filtration of radionuclides in containment
” Venting systems are only one aspect of severe
accident management
Much broader issue than
filter vs. no filter
5
Managing Containment – Water
nection
” Water is required to cool core debris to prevent
containment failure
– If containment fails, there are multiple
uncontrolled release paths
• Water will also filter radionuclides inside
containment
-Passive: suppression pool
-Active: sprays
A filter alone in the vent path will
not prevent containment failure
6
Managing Containment- Pressure
Control
” Controlled venting maintains containment
function by releasing energy
” Extends time for removal of radionuclides in
containment by deposition and filtering
• Maintain positive pressure to prevent buildup
of a combustible gas mixture
Managing containment is not a
passive function
7
Conclusions from Pilot
• Cooling core debris is essential
” EPRI filtering strategies can be reliably
implemented
” Severe accident capable vent needed
• Enhancements identified
” Operators are already trained on use of
controlled venting strategies
Performance-based
framework demonstrated
8
Examples of Identified Plant
Enhancements
” External water connection for drywell sprays
(FLEX)
” Severe accident capable vent needed from
both wetwell and drywell
” Control of vent
– Operator action or engineered control system
* Possible SAMG enhancements
– Prioritization of water injection
9
Performance – Based Approach
Reliable and effective filtering:
” External water injection
– Cool core debris
-Control drywell temperature
* Severe accident capable vent
– Control containment pressure
– Maximize suppression pool radionuclide
filtering
-Wetwell & drywell pathways
• Procedures and training
Broader approach required for managing
containment function
10
Path Forward
” Require RHVs on both the wetwell and drywell
* Revise RHV to be useable and reliable in
severe accidents (SECY Option 2)
* Ensure FLEX provides reliable water to drywell
sprays
” Finalize engineered enhancements
* Establish performance-based guidance for
implementing SECY Option 4
11
Acronyms
• BWR – Boiling water reactor
” FLEX – Diverse and Flexible Coping Strategy
* EOP – Emergency Operating Procedure
e SAMG – Severe accident management
guideline
* EPRI – Electric Power Research Institute
e RHV – Reliable hardened vent required by
EA-12-050
12