SCRAM/Down-Power Vulnerability Assessments

Reducing the probability of unplanned plant transients

Vulnerabilities as a result of design deficiencies can lead to unplanned down-powers and reactor emergency shutdowns, or SCRAMs. Latent vulnerabilities pose a significantly greater risk to nuclear stations than obvious or active vulnerabilities due to the fact that identification of a latent vulnerability may not occur until it causes a plant event. Vulnerability assessments offer one method to identify latent issues and subsequently reduce the probability of unplanned plant transients.

The Challenge

Identify vulnerabilities for unplanned down-powers and SCRAMs

MPR performed assessments for multiple utilities identifying latent vulnerabilities for unplanned down-powers and SCRAMs. The goal of these assessments is to reduce the number of plant trips and enhance plant reliability, generating capacity, and nuclear safety, as well as proactively prepare for NRC inspections (e.g. NRC 95-001 inspection). MPR also performed extensive evaluation of components and systems of specific concern for the evaluated plants, such as implementation of the Extended Power Uprate (EPU), pump seal issues, or low system pressures.

The Solution

Review pump signals and recommend changes

To provide a comprehensive assessment, MPR reviewed key pump trip signals (downshifts), for pumps that can cause a plant SCRAM or down-power, and identified any signal that can trip a pump from a single source. MPR recommended changes to the trip logic to replace or revise pump trip signals with time delays or operator actions. Past SCRAM/down-power events are reviewed to identify any gaps in the actions to prevent recurrence, and industry operating experience (OE) is reviewed to identify any missed opportunities. MPR provides various design, procedural, and/or programmatic recommendations to address the vulnerabilities.

The Results

Assessments that actively address areas of concern and enhance plant performance

MPR’s SCRAM/Down-Power Vulnerability Assessments provide nuclear plants with solutions to proactively address areas of concern and to enhance plant performance. MPR offers an independent, honest assessment with the necessary technical rigor across multiple disciplines. This allows MPR to identify long-standing issues that may have become a part of normal plant operation, but can cause consequential SCRAMs. The key component of these assessments is the identification of unknown vulnerabilities. MPR not only identifies these vulnerabilities, but also provides actionable recommendations with a technical basis.

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