# Presentation: 721533

## Technical Basis for theMitigating Systems Performance Index (MSPI)

**Donald A. Dube, PhD**
**Division of Risk Assessment & Special Projects**
**Office of Nuclear Regulatory Research**
**(301) 415-5472 / dad3@nrc.gov**
**RES Seminar**
**February 28, 2006**

## “When you can measure what you

**“****When you can measure what you**
**are speaking about, and express**
**it in numbers, you know something **
**about it...”**
**	****	****- Lord Kelvin**
** **

## Seminar Overview

**Reliability Concepts**
**Regulatory Need for MSPI**
**Features of MSPI**
**PRA Quality Requirements  **

## Sponsor and Support

***Work performed for***** **
**	****Division of Inspection & Regional Support (NRR)**
***Support provided by***
**	****Idaho National Laboratory**
**	****Information Systems Laboratories**
**	****DRA and Region staff **
**	**

## Key Definitions

***Reliability:***** Probability that a device functions successfully for its specified mission time.**
**Unreliability = 1 - Reliability**
***Unavailability:***** The fraction of time that a device is out-of-service for testing and/or maintenance.**
**	**

## More maintenance increases Unavailability...

**More maintenance increases Unavailability...**

## ...but it decreases Unreliability...

## ...and there is an optimum!

## But the current Safety System Unavailability

**(SSU) Performance Indicators in the Reactor Oversight Process (ROP) account only for Unavailability...**

## 23.9 hrs/train/QTR

**23.9 hrs/train/QTR**
**Planned maintenance**

**9.2 hrs/train/QTR**
**Planned maintenance**

## 34.2 hrs/train/QTR

**34.2 hrs/train/QTR**
**Planned maintenance**

**8.8 hrs/train/QTR**
**Planned maintenance**

## 21.0 hrs/train/QTR

**21.0 hrs/train/QTR**
**Planned maintenance**

**10.7 hrs/train/QTR**
**Planned maintenance**

**19.8 hrs/train/QTR**
**Planned maintenance**

## What is MSPI ?

**What is MSPI ?**

## 			Bi ( URi – URiBL )

**MSPI = Unavailability Index + Unreliability Index**
*** ***

**For unreliability:****	****	****	**
**	****	****	****B****i**** ( UR****i**** – UR****iBL ****)**
**summed over all monitored components i***** *****in the system.  **
** ****	****The coefficients B****i**** are the component ****	****basic event Birnbaum risk-importance ****	****values taken from licensee’s PRA.**** **

## URI

**URI**

**UAI**

## Pump versus Valve? 

**...****weighted according to each B****i**

## Attributes of MSPI

**Risk-informed, performance-based.**
**Allows trade-offs between Unreliability and Unavailability to optimize system performance.**
**No penalty for on-line preventive maintenance hours up to pre-planned baseline.**
**Reflects plant-specific design and operation.**
**Addresses issues with current ROP SSU PIs.**

## Monitored Systems

| BWRs | PWRs |
| --- | --- |
| High pressure coolant injection/core spray  | HPSI (high pressure safety injection)  |
| RCIC or isolation condenser  | AFW (auxiliary or emergency feedwater)  |
| RHR (residual heat removal)  | RHR (may include containment spray) |
| EAC (emergency AC power)  | EAC |
| Cooling Water Support Systems  | Cooling Water Support Systems |

## Limitations

**	****Items to be addressed by the inspection process rather than MSPI:**
**Multiple concurrent failures**
**Conditions that cannot be discovered by normal surveillance tests**
**Failures of inactive components not accounted for in train unavailability.**

## Pilot

** ****Purpose was to:**
** ****Exercise the MSPI guidance**
** ****Perform validation & verification**
** ****Perform temporary instruction****	**** **
** ****12 months (FY2003)**
** ****20 nuclear units**

## Pilot Results

**MSPI “White” and “near-White” indicators resulted from:**
**Multiple component failures.**
**Substantial contribution from Unavailability.**
**Six recommendations implemented to refine the methodology.**
**PRA Quality requirements are needed.**

## PRA Quality Requirements

**Assure that their PRA is of sufficient technical adequacy for MSPI by:**
**(a) Resolving the A and B Facts & Observations (F&O’s) from the peer review.**
**(b) Performing a self-assessment using the NEI-00-02 process as endorsed by Appendix B of RG 1.200 for the ASME PRA Standard.**
**As alternative to (b), relying on a cross- comparison of PRAs.  **

## Slide 23

## 2

**Emergency Electrical Generators**

**2**

**3**

**4**

## Equivalent of 3 Onsite Electrical Generators

**SPAR**

**Industry**

## SPAR and Industry PRA Model Differences

**SPAR and Industry PRA Model Differences**

**Plant D Industry**

**Plant D SPAR**

## Understanding Model Differences

** ****Design Improvements**
** ****Alternate means of cooling RCP Seals**
** ****Diesel-driven air compressor**
** ****Procedure Enhancements**
** ****Cross-tie emergency AC power**
** ****Use of fire-protection system for BWR ****	****reactor vessel low pressure injection**
** ****Differing Assumptions & Methods**

## PRA Model Improvements

**Most licensees made PRA model updates to address Peer Review F&Os**
**Additionally, licensee PRA model changes to address staff identified:**
**Errors**
**Non-conservative modeling **
**Assumptions that could not be justified.**
**NRC’s SPAR model enhancements**
** ****Updated initiating event frequencies and equipment    ****	****failure rates**
** ****Addressing longstanding issues.**

## Summary

**The MSPI represents...**
**Major step forward for risk-informed performance indicators.**
**First industry-wide application using a structured process to address PRA quality.**

## Further Reading

**	****NUREG-1816, “Independent Verification of the Mitigating Systems Performance Index (MSPI) Results for the Pilot Plants.”**