Wednesday, June 19, 2019

A New Tool to Address ‘Single Point Vulnerabilities’

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Nuclear Plant Operators Use EPRI Database to Mitigate Vulnerable Components That Can Cause Costly Shutdowns

In a nuclear power plant, a single point vulnerability (SPV) is a component or subcomponent that, if failure occurs, can cause a reactor or turbine to trip and the plant to go offline. Among plants built in the 20th century, about 1% of components are SPVs, with most in the turbine-generator side (not the reactor side) of the plant. For example, if the setpoint of a relay in the main power system drifts too low, the generator could trip, which in turn could cause the turbine to trip. While many SPVs are known to plant operators, others are unrecognized or inadequately mitigated. To minimize the risk of an SPV failure, operators may enhance operational procedures or conduct additional inspections, testing, and preventive maintenance.

Preventing SPV-related shutdowns and eliminating SPVs are vital to safe, reliable plant operations. Shutdowns as a result of equipment failure can be costly. Repair of an easy-to-fix component may require a three-day shutdown at a cost of about $3 million in lost generation revenue.

To prevent unnecessary shutdowns, utilities are using EPRI’s new Single Point Vulnerability Analysis Tool to identify SPVs in their plants along with actions to eliminate or mitigate them. The tool draws on a database of SPV data provided by the industry—including identified vulnerabilities, mitigation designs and costs, and successful elimination strategies. Users can compare SPVs in their facilities with SPVs in other plants and learn how those plants mitigated them.

The tool enables users to organize and plot data by plant system, plant design, and component type. It alerts EPRI technical staff to newly identified component vulnerabilities, which prompts research to address them. Because engineers at different plants often use different names for the same components and systems, EPRI incorporated a common information model that helps users find relevant SPVs.

SPV comparisons on the reactor side are most beneficial when made between plants with similar designs—and the tool enables such comparisons. On the turbine/generator side, plant operators and engineers can compare across different designs and still gain insights about their facilities.

For example, consider nuclear plants A and B with similar designs. If plant A shares all its information on SPVs and successful mitigations in the database, plant B can verify that it has identified the same SPVs and that it is using the best mitigation strategies. If plant B has listed an SPV that plant A has not listed, Plant A may have already eliminated that SPV, and plant B may want to consider plant A’s elimination strategy.

In 2010, the U.S nuclear power fleet reported 77 scrams (emergency reactor shutdowns). In 2017, there were just 38 scrams. This significant reduction was driven by an industry focus on SPV identification, labeling, elimination, and mitigation. In 2015, EPRI issued an SPV guide that plant personnel have used for process improvements.

Previously unrecognized SPVs caused half of the scrams in 2017, pointing to the benefits of ongoing action to address SPVs. Indeed, this is why EPRI created the tool—to facilitate collaboration among plant personnel.

To help make the database comprehensive, EPRI and the Institute of Nuclear Power Operations (INPO) recently created a system that prompts plant operators to flag SPV-related scrams as part of their scram reporting requirements to INPO.

Along with the tool’s release, EPRI plans to provide training to help utilities characterize the technical aspects of their plants’ vulnerabilities. A better understanding of what causes vulnerabilities in the first place is needed before an appropriate mitigation strategy can be developed.

The tool is available for use by utilities in the United States and Mexico, and EPRI staff are working with utilities in Canada and China to enter their data. Utilities in United Arab Emirates and South Africa have expressed interest in using the tool.

The industry’s knowledge of SPVs and their impacts is maturing, but operators are still on a learning curve. The industry can continue to improve by sharing information through the tool.

EPRI Technical Experts:

Jacquelyn Fraedrich, Mark Woodby