ML23219A029
| ML23219A029 | |
| Person / Time | |
|---|---|
| Issue date: | 08/15/2023 |
| From: | NRC/NMSS/DFM/FFLB |
| To: | |
| Shared Package | |
| ML23219A024 | List: |
| References | |
| Download: ML23219A029 (1) | |
Text
IROFS Risk-Informed Prioritization Tool used for Fuel Facility Construction Inspections Fuel Facilities Construction Oversight Workshop - August 15, 2023
Purpose Risk-informed inspection planning tool that will provide input into the construction inspection plan and provide inspectors insights into how to prioritize inspections of Items Relied On For Safety (IROFS).
This planning tool is only one tool in developing inspection plans.
Conceptual Design
- Same fundamental methodology for inspection prioritization used for previous construction projects that streamlines and has evolved from previous lessons learned
- Uses an accident sequence paradigm of the facility to understand total risk
- Uses risk information from the applicants Integrated Safety Analysis (ISA) Summary (i.e., accident sequences and IROFS)
Information Sources
- Risk information comes from the ISA Summary
- Provides a list of the accident sequences, their likelihood, and their consequences.
- Provides a list of the IROFS and associates the IROFS with accident sequences.
- Risk is evaluated based on the sequences considering both the likelihood and the consequences.
- The risk calculation is limited by the level of detail in the ISA Summary
Input - Phase 1: IROFS IROFS input table derived from ISA Summary and dependent upon level of detail.
IROFS Number Control Type (Passive, Active, or Admin)
Components Safety Function Description PPB2-CRIT1 passive hopper, outlet, and gasket Hopper and outlet design prevent UO2 leaks with a double gasket at the outlet PPB2-CRIT2 administrative N/A Two sample measurements by two persons to ensure contents are dry before transfer to hopper, prevents the introduction of water to the blender PPB2-CRIT3 administrative N/A Posting excluding water from the blender room PPB2-CRIT4 passive piping, drains, and roof Double piping, floor drains, and roof integrity prevents water accumulation in the blender room PPB2-SUMP active DP cell and pump Water level in the blender room is measured with a DP cell, when level is too high a sump pump drains water from the blender room floor PPB2-VENT active enclosure, fans, filters, detectors, and isolation vents The blender is within a ventilated enclosure. Fans are active to ensure the enclosure is at a negative pressure. The fan ducts include HEPA filters to catch any released powders. A radiation detector near the HEPA filter signals if there is a radiological release, which will isolate the enclosure.
PPB2-INRT passive smoke detector, Ar/N2 tanks, piping and nozzles, enclosure, and isolation vents Smoke detection leads to inert gas fire suppression system actuation. The system isolates the ventilated enclosure and pressurized tanks of Argon and Nitrogen gas inject gas into the enclosure through nozzles.
Input - Phase 2: Accident Sequences The accident sequence (not IROFS) is used to assess risk. The accident sequence input table is derived from ISA Summary contents and dependent upon level of detail.
Sequence Name Initiator Likelihood Index Consequence Category IROFS PPB2-NCS-1
-2 3
PPB2-CRIT1 PPB2-CRIT3 PPB2-CRIT4 PPB2-SUMP PPB2-NCS-2
-2 3
PPB2-CRIT1 PPB2-CRIT3 PPB2-CRIT4 PPB2-SUMP PPB2-NCS-3
-1 3
PPB2-CRIT3 PPB2-CRIT2 PPB2-RAD-1
-2 2
PPB2-CRIT1 PPB2-VENT PPB2-SMC-1
-3 3
PPB2-CRIT3 PPB2-CRIT4 PPB2-SUMP PPB2-SMC-2
-3 2
PPB2-VENT PPB2-FLD-1
-2 3
PPB2-CRIT1 PPB2-SUMP PPB2-FLD-2
-3 3
PPB2-CRIT1 PPB2-FIR-1
-2 2
PPB2-INRT PPB2-VENT
Methodology Outline
- IROFS associated with each accident sequence
- Calculates risk-informed importance score based on likelihood and consequence indices
- Ranks IROFS according to the risk-informed importance score Input Tool
Limitations
- Risk-informed importance score is calculated by approximating the risk associated with each IROFS o Importance Score provides the approximate importance of IROFS to other IROFS. The importance score only gives the order of magnitude of the result.
- Ranking amongst IROFS is important in informing priority during inspection. Numerical values of the scores should not be construed as important in and of themselves.
Next Steps How Will Results Be Used
- One input to the construction inspection plan for construction inspections
- Determine the risk-informed sample sizes and, if necessary, adjust the sample size providing greater flexibility
- Consolidate construction inspection efforts thereby reducing overlap/redundancies
- Focuses communications with applicant regarding IROFS changes/updates that may potentially impact construction inspections
Questions?