closeEnergy Development Case Study
MPR Associates Qualifies Commercial Static Exciter Component for Use in Safety Systems in the Nuclear Industry
Challenge
While a client assignment often includes product development, MPR also works with clients to identify ways to enhance or modify an existing product to expand market share or industry reach. Such is the case with client Basler Electric. MPR serves as Basler’s sole representative and engineering consulting firm for nuclear utilities. MPR's scope of work on this project was to evaluate one of the company's existing commercial products and determine its suitability for nuclear safety-related use.
The product in this case is part of a static exciter. Basler Electric's microprocessor-based reference adjuster, RA‑70, is a low burden, variable resistance controller that provides superior performance and reliability over a conventional motor-operated potentiometer (MOP), sometimes called a motor-operated controller (MOC). The nuclear industry uses static exciters as a key part of emergency diesel generators, which provide power under all circumstances, allowing for safe shutdowns of nuclear power plants even if the power grid has failed. MPR took the existing device and qualified the commercial device that Basler Electric provides so that it could be sold to the nuclear industry for safety-related applications.
Meeting the regulatory expectations of the U.S. Nuclear Regulatory Commission (NRC) was one of the primary challenges of the project. Because RA‑70 was built as a commercial device, there was no documentation showing how the device met the safety expectations of the nuclear industry. There were no quality assurance records for the device. MPR engineers reviewed the software in the device and performed extensive testing to verify that the device was acceptable.
Approach
For more than 10 years, MPR and the Electric Power Research Institute (EPRI) have been generating guidance for using digital equipment in the nuclear industry. Part of that guidance deals with acceptance of commercial products for safety related use. MPR applied that guidance on this Basler Electric product.
Before this series of testing, the MPR project team evaluated Basler’s records of the product's software, design processes used on the software, and the software design in the RA‑70. Using industry guidance that MPR wrote and recently revised for EPRI, called a Critical Digital Review (CDR), MPR evaluated RA‑70. From the CDR, the team implemented a set of compensatory actions to bring the design records and process up to regulatory expectations.
Testing the RA‑70’s qualifications in three critical categories, including seismic, environmental and electromagnetic compatibility (EMC), was part of the approach that MPR took. Seismic testing verified that the MOC would continue to operate correctly during, and after a severe (design-basis) earthquake. Environmental testing verified that the MOC would continue to operate during, and after exposure to high and low temperatures and humidity that could occur while the device is in use. EMC testing demonstrated that the RA‑70 had some issues with susceptibility to electromagnetic noise, emitted by other components. MPR found that the RA‑70 does not emit enough interference to disturb other components located close to the product.
Solution
MPR’s review of the software showed that additional software testing was not necessary. MPR’s experts conducted peer review of the RA‑70 software and generated appropriate design documents to describe the software. This was sufficient to meet the quality assurance expectations and requirements of the regulator, as described in 10 CFR 50 Appendix B.
MPR’s EMC testing indicated that the design had vulnerabilities to external noise sources. As a result, MPR shielded the device and added EMC filtering to eliminate the EMC issues. Knowledge of the possible issues with EMC led MPR’s experts to start with this approach, rather than discovering this at the end of testing. The MPR approach dramatically decreased the testing time and expenses, by having the device pass all tests on the first try. The MPR-designed shield and filtering demonstrated acceptable results for all qualification tests.
Benefits
Through review, documentation, appropriate design, testing and product redesign, MPR generated a new, high quality MOC replacement product that Basler and MPR are currently marketing to the nuclear industry. Initial response to the first safety-grade RA‑70 is being well received in this niche market of MOP/MOC replacements.