TECHNICAL ANALYSIS OF OPTIONS TO PREVENT LAND CONTAMINATION - - PowerPoint PPT Presentation

TECHNICAL ANALYSIS OF OPTIONS TO PREVENT LAND CONTAMINATION

January 9, 2013 Neil M. Wilmshurst Vice President & Chief Nuclear Officer Electric Power Research Institute

The Question…

What are the best operational strategies to prevent land contamination?

• Re-phrased question leads to

deeper understanding of the issue.

• Informs development of SAMGs

and development of other beyond design basis capabilities.

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Results published

Technical Report: “Investigation of Strategies for Mitigating Radiological Releases in Severe Accidents - BWR Mark I and Mark II Studies“ Report 1026539, September 2012

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Scope - BWR Mark I and Mk II

Spectrum of Accident Challenges (design and beyond design basis events) Core Damage Prevented Core Damage Containment Challenged Containment Not Challenged

Vent Steam No Release Heat Removal Successful No Release FLEX provides additional protection for these scenarios

Containment is Not Primary Barrier to Release

Radionuclide Release SAMGs and FLEX provide some mitigation

Containment is Primary Barrier to Release Containment Spray Containment Flood Containment Vent Filtered Vent Unfiltered Vent

Combinations of Strategies Considered

Greater than 99.99% Less than 0.01%

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Post Accident Actions

• Avoid core damage.
• If core damaged – cool damaged

core.

• If core exits vessel - protect

containment: – Cool corium – Vent when needed – Remove radioactive material from gas stream

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Decontamination Factor

(DF = 1 / fraction of cesium released)

1 10 100 1000 10000

Relative Magnitude of Contaminated Land Overall Decontamination Factor (DF)

Diminishing Benefit as DF Reaches 1000

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BWR Mark I Results

1 10 100 1,000 10,000

Overall Decontamination Factor DF = 1/Fraction of Cs Released

Without Core Debris Cooling - Eventual Breach of Containment Elements Exist in Current SAMGs and in FLEX

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BWR Mark II Results

1 10 100 1000 10000

Overall Decontamination Factor CF = 1/Fraction of Cs Released

Elements Exist in Current SAMGs and in FLEX

Lefthand bar for each category is the wetwell bypass value Right hand bar for each category is the no-bypass value 8

Significant Conclusions

• Maintain containment integrity.
• Water injection into containment

cools debris and filters potential releases: – Water spray and flood filter airborne aerosols – Cycling of vent maximizes aerosol capture and manages hydrogen

• Decontamination factor greater

than 1000 can be achieved.

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Impact on Plants

• Specific plant evaluations required.
• Plant modifications may be needed:

–Ensure post accident spray and/or flood –Wetwell and drywell vents required –Mark II pedestal drains may require protection –Possible addition of filters on plant specific basis

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Acronyms

• FLEX – Diverse and Flexible

Coping Strategy

• DF- Decontamination Factor
• SAMG – Severe accident

management guideline

• RHV – Reliable hardened vent

required by EA-12-050

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