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Risk-Informed Technical Specification Task Force Initiative 7 (PSAM-0015)

Excerpt

Technical Specifications (TSs) address configuration control by specifying time limits for equipment out of service, and actions, generally leading to plant shutdown, when the out-of-service times are exceeded. TSs are primarily based on deterministic design basis accidents, and do not explicitly consider the plant risk impact as a factor in the action requirements. The nuclear industry has achieved substantial gains in plant capacity factors over the last decade through reduced planned outage duration and increased use of on-line maintenance. Plant maintenance generally involves temporary impacts on equipment availability that are balanced by increased reliability. A risk-informed plant configuration control provision was added to the Maintenance Rule (MR) requiring risk assessment and risk management prior to performance of both on-line and shutdown maintenance.

It is recognized that the configuration control requirements of TSs (deterministic) and the MR (risk-informed) may be in conflict; however, the licensee is required to comply with both, resulting in limitations on configuration control flexibility that does not necessarily ensure plant safety. To address the incompatibilities between these methods, the nuclear industry embarked on a series of risk-informed TS initiatives under the auspices of the Nuclear Energy Institute's Risk-Informed TS Task Force (RITSTF). There are currently eight identified initiatives, which are briefly described. However, the purpose of this paper is to discuss the purpose, evolution, technical rationale, and status of Initiative 7, which addresses the impact on system operability from degraded non-TS equipment.

This paper discusses the efforts related to Initiative 7, which addresses the impact on system operability from degraded non-TS equipment. Initiative 7 is discussed initially from a broad perspective briefly covering the entire scope of design features and then from a subset of design features commonly called “barriers,” which is the primary focus of the paper. Design features include snubbers, (which are treated as an individual effort), and other structures/components not currently in TSs such as doors/hatches, lead shielding, monitoring equipment, ventilation panels, insulation, etc.

The paper focuses on the subset called Initiative 7a, which is confined to barriers which are defined as doors, walls, floor plugs, curbs, hatches, mechanical devices, or other devices, not explicitly described in TSs. The paper presents the technical rationale to justify a new Limiting Condition for Operation, LCO 3.0.9, showing that removal of a barrier for certain initiating events presents a low plant risk condition and therefore any supported system LCOs are not required to be declared not met solely for the reason of the barrier being removed for up to a maximum of 30 days.

A summary of the implementation guidance is provided that outlines the process to be followed to use new LCO 3.0.9 and how that process uses the current Maintenance Rule program that currently exists at each licensee plant. Finally, a summary of the current status of Initiative 7a is presented. Availability to implement the new LCO 3.0.9 is expected in 2006.

  • Summary/Abstract
  • Introduction
  • RITSTF Initiatives
  • Initiative 7 — Broad Overview
  • Purpose
  • Technical Rationale
  • Implementation Guidance
  • Current Status/Future Activies
  • Acknowledgments
  • References

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