ML19170A291
| ML19170A291 | |
| Person / Time | |
|---|---|
| Issue date: | 06/20/2019 |
| From: | James Drake NRC/NRR/DLP/PLPB |
| To: | |
| Drake J, NRR/DLP/PLPB, 415-8378 | |
| References | |
| Download: ML19170A291 (12) | |
Text
In-vessel Downstream Effects Compliance Discussion NRC Public Meeting June 20, 2019
Introduction
- Technical Evaluation Report determined IVDE safety significance to be low
- TRACE
- Risk Insights
- Engineering judgment
- Compliance not addressed in TER
- TER is a fleetwide analysis
- Plant-specific confirmation is needed
- Some TER assumptions are realistic and do not fully satisfy the regulatory requirements 2
10 CFR 50.46 Requirements
- Maintain core temperature acceptably low
- Remove decay heat for extended period
- Assure that most severe LOCAs are calculated
- Include limiting single failure
- Use acceptable evaluation models
- Account for uncertainties/show acceptance criteria are met with high probability
- BAP has been considered historically 3
Current Status - IVDEs
- TER is complete (ML19073A044)
- Staff is working on the concept of what plant-specific compliance should look like
- Developing staff review guidance that recognizes the safety significance of the issue while meeting the regulations
- Ideas in this presentation are not a formal position
- Intended to promote discussion amongst all stakeholders 4
Resolution Flow Chart YES
< 15 g/FA HLB NO HLSO AND tblock YES YES Very Low AFP BEFORE Resistance (B&W)
Chemical Effects NO NO Done YES UPI Design NO Debris < 17788 Fiber Limit AND SSO > 20 Min AND YES RTP < Evaluated AND AFP Resistance < Evaluated NO Plant Specific Evaluation 5
Resolution Paths
- 1 - WCAP-16793 criteria
- 2 - UPI plant with no chemical precipitation until after HLSO and tblock
- 3 - B&W plant with no chemical precipitation until after HLSO and tblock 6
Resolution Paths
- 4 - WCAP-17788 criteria
- SSO time > 20 minutes
- Fiber limit (no core inlet reduction from msplit)
- Bounded by AFP analysis (no scaling AFP/Power)
- Chemical precipitation after HLSO and tblock
- 5 - Plant Specific Evaluation 7
Plant Specific Confirmation-All Paths
- Within WCAP-17788 limit on total fiber at core inlet and in heated core
- LOCADM results meet the acceptance criteria
- Particulate debris amount reaching core prior to HLSO
- Cold-leg break (except plants that meet WCAP-16793 criteria)
- CLB fiber amount meets WCAP-17788 limit
- HLSO prior to tchem
- tblock prior to tchem 8
Plant Specific Evaluation-Discussion
- Potential to compensate for one criterion beyond analysis by demonstrating conservatism in other criteria
- SSO time
- Power Level
- AFP resistance
- Fibrous debris amount
- Possible considerations in a plant-specific evaluation
- Non-uniform flow due to radial power distribution
- Use other FA test info
- Conservatism in fiber limit determination (test and TH)
- Judicious application of credit for msplit, debris bed non-uniformity, or both 9
Plant Specific Evaluation Example
- SSO time < 20 minutes
- Compare plant power level against analyzed
- Compare AFP resistance against analyzed
- Compare realistic debris arrival timing with SSO timing
- Discuss plant core fiber amount vs. limit 10
IVDE Fiber Determination
- Use plant specific testing or similar testing
- Assume all HLB fiber arrives at core inlet or justify depletion due to CS
- For CLB, assume flow split out of the break
- Justify fiber depletion due to CS
- Fiber depletion calculations (e.g. WCAP-17788) may require load dependent penetration curves
- Adds complexity
- May require plant specific testing
- Assuming all fiber reaches core is simpler, but may be too conservative 11
Key Parameters From TER
- Initiating event frequency
- Fibrous debris
- HLSO (or equal) to dilute amounts debris, chemicals, BAP
- Minimum ECCS flow
- Chemical timing vs. AFP
- FA debris capture timing characteristics
- Chemical effects
- AFP resistance value methodology
- CLB driving head
- SSO timing
- RCS liquid mass
- Particulate debris amounts
- LOCADM 12