Benefits of PRISM:

Appendix R

  • Create/evaluate logic used to demonstrate Safe Shutdown capability
  • Quick visual review for impacts of proposed changes and ‘What If’ scenarios for Safe Shutdown

    • NFPA 805

  • Create/ evaluate logic used to demonstrate Nuclear Safety Capability Assessment and Non-Power Operations
  • Quick visual review for impacts of proposed changes and ‘What If’ scenarios for the Nuclear Safety Capability Assessment
  • Evaluate success paths and level of redundancy for fire areas, or scenarios

    • Fire PRA

  • Create and store scenarios to support risk evaluations, evaluate scenario results to understand direct failure impacts, indirect failures and levels of redundancy
  • Quick visual review for impacts of proposed changes and ‘What If’ scenarios for Fire PRA and Safe Shutdown
  • Fault Tree solution export to various quantification engines. Creates flag files for all scenarios in any desired format (i.e. CAFTA, WinNUPRA)
  • Evaluate success paths and level of redundancy for compartments, zones or scenarios
  • Ability to combine losses to determine system impacts to support the Fire PRA multi-compartment analysis

    • Security and Beyond Design Basis Events

  • Ability to combine losses to determine system impacts to support security strategies, beyond design basis events and alternate compensatory measures

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    Figure 1: Electrical Distribution of a Typical Plant Diagram. Diagram depicts a plant’s one-line diagram built with logic including off-site power, Emergency Diesel Backup, alternate cross-ties, DC control power and the ability to visually credit recovery actions for success.

     

     

    Figure 2: Display of PRISM Inputs and Outputs. FPRA cables routed through the plant are linked to PRA Basic Events. As a fire scenario is selected, the failed Basic Events are exported for quantification

     

     

    PRISM makes a Difference:

    • PRISM can visually depict logic in a format that is familiar to the plant
      • Electrical diagrams (Figure 1) are made to look like plant one-line diagrams; system diagrams are set-up to mimic existing plant flow diagrams (Figure 5)
    • PRISM logic is easy to modify
      • Plant modifications or ‘What If’ scenarios performed through a graphical drag-n-drop, copy-paste routine.
    • Logic is easy to validate due to the visual diagram user interface
    • PRISM is easy to customize
      • New windows with different views can combine existing logic catered to each individual plant
      • Makes custom what-if scenario evaluations and reports easy to generate
    • Identify spurious operation concerns, LOCA scenarios, over-current trip concerns, secondary fires, maloperations, recovery actions, cable re-routes/ raceway fire wraps; add/remove equipment from service

     

     

    Figure 3: Color Codes Define the Diagram Logic; Visual review of a one-line diagram or system flow diagram can pinpoint failures and where to focus attention on risk.

     

     

    Figure 4: Zoomed-in View of Electrical Diagram. The Back-up Generator Auto-loads (GREEN breaker) when Normal power is unavailable (ORANGE breaker) to the Bus.

     

     

    Using PRISM Logic to determine a success path for a credited system: For a system with built-in redundancy for success, PRISM aides in determining the most suitable flow path. Figure 5 indicates power/control to the pump and all associated valves including two credited manual actions. Figure 6 confirms that adequate instrumentation is available to the steam generator (degraded). Figure 7 identifies that at least one successful Flow Path is available for each unit.

     

    Figure 5: System Review. View pumps, valves, instrumentation, and support systems to determine which flow paths can be successful.

     

     

     

     

    Figure 7: Logic Check; Review multiple system flow paths to determine minimum success or redundant success paths to reduce risk.
    Figure 6: Instrument Logic indicating “minimum” or “DEGraded” instrumentation available; increase in plant risk.

     

     

    Figure 8(LEFT): Normal and Alternate power supplies. The Normal power supply breaker is failed due to direct cable damage but the Alternate power supply breaker is available.
    Figure 9(RIGHT): Once the manual action is credited, logic is updated to reflect power availability to the credited instrument.

     

     

    Review Options for Safe Shutdown Strategy

    Credit operator manual actions or propose plant modification to credit components for a success path.

    In a given scenario, power unavailable to 3 valves affects a success path to a required system for Safe Shutdown. Direct cable damage fails breaker (RED); power to Panel and components below the breaker become unavailable (Orange) based on logic ties. Operator manual actions are available (Fuchsia HEP flag) to credit the safety system.
    Solution #1, Recovery Actions: Provided the actions are low risk due to location and timing to perform the actions, the decision was made to credit the manual actions for success of the safety system. The color of each valve (Blue) indicates that manual actions were credited.
    Solution #2, Plant Modification: After reviewing the single cable damage to the breaker, it was determined that protecting the cable would provide the best reduction of risk. A plant modification was performed to protect the raceway containing the cable, thus protecting the breaker and power to the panel.

     

    The correct solution for any given scenario will always be based on the facts for each individual case. The risk of performing the action must be compared to the cost of eliminating the problem with a plant change. PRISM does not calculate risk vs. cost, but it is a valuable tool used to provide a visual depiction that will benefit the decision making process.