ML23219A029

IROFS Risk Informed Prioritization Final

ML23219A029
Person / Time
Issue date:	08/15/2023
From:	NRC/NMSS/DFM/FFLB
To:
Shared Package
ML23219A024	List: ML23219A025 ML23219A026 ML23219A027 ML23219A028 ML23219A029 ML23219A030
References
Download: ML23219A029 (1)

Text

IROFS Risk-Informed Prioritization Tool used for Fuel Facility Construction Inspections

Fuel Facilities Construction OversightWorkshop - 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.

Control Type IROFS Number (Passive, Active, Components Safety Function Description or Admin)

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

The blender is within a ventilated enclosure. Fans are active to ensure the PPB2-VENT active enclosure, fans, filters, detectors, and enclosure is at a negative pressure. The fan ducts include HEPA filters to catch isolation vents any released powders. A radiation detector near the HEPA filter signals if there is a radiological release, which will isolate the enclosure.

smoke detector, Ar/N2 tanks, piping and Smoke detection leads to inert gas fire suppression system actuation. The PPB2-INRT passive nozzles, enclosure, and isolation ventssystem 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.

Initiator Consequence Sequence Name Likelihood Category IROFS Index

PPB2-NCS-1 -2 3 PPB2-CRIT1PPB2-CRIT3 PPB2-CRIT4 PPB2-SUMP

PPB2-NCS-2 -2 3 PPB2-CRIT1PPB2-CRIT3 PPB2-CRIT4 PPB2-SUMP

PPB2-NCS-3 -1 3 PPB2-CRIT3PPB2-CRIT2

PPB2-RAD-1 -2 2 PPB2-CRIT1 PPB2-VENT

PPB2-SMC-1 -3 3 PPB2-CRIT3PPB2-CRIT4 PPB2-SUMP

PPB2-SMC-2 -3 2 PPB2-VENT

PPB2-FLD-1 -2 3 PPB2-CRIT1PPB2-SUMP

PPB2-FLD-2 -3 3 PPB2-CRIT1

PPB2-FIR-1 -2 2 PPB2-INRT PPB2-VENT Methodology Outline

• IROFS from ISA Summary

• IROFSassociated witheach accident sequence

• Calculates risk-informed importance score based onlikelihood and consequence indices

• Ranks IROFS according to the risk-informed importance score 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 constructioninspection 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?