New Digital Safety System Controller Approved for Nuclear Plants

The U.S. Nuclear Regulatory Commission has approved the use of Mitsubishi Electric Total Advanced Control (MELTAC) Nplus S digital safety system controllers in U.S. nuclear power plants. While new to the U.S. industry, Mitsubishi said the MELTAC system is already deployed in 38 nuclear power plants around the world, primarily in Japan and China.

MELTAC is a control and monitoring system developed from the ground up specifically for nuclear applications. It was built around a common controller for both safety- and non-safety-related plant control functions. Mitsubishi claims the system has operated for more than 30 million hours with no plant trips due to software or hardware failures. The MELTAC-N has been utilized in non-safety applications since 2001 and for safety critical control applications since 2009.

“Digital instrumentation and control system upgrades in U.S. nuclear power plants must meet strict NRC regulatory requirements. To meet these requirements, we developed a 10 CFR 50 Appendix B compliant quality assurance program (QAP) to achieve in-house control of all aspects of MELTAC Nplus S design, manufacturing, and testing,” Takahisa Kurokawa, senior general manager of Mitsubishi Electric Corp.’s Energy Systems Center, said in a press release announcing the NRC acceptance.

According to an equipment qualification summary document available on the NRC’s website, to gain NRC acceptance, equipment was required to demonstrate that it is capable of successfully performing its intended safety functions after exposure to all normal and abnormal environmental stressors. Items such as atmospheric conditions, radiation exposure, electromagnetic and radio frequency interference, and seismic disruptions had to be evaluated.

Mitsubishi intends to promote the MELTAC Nplus S controller as a solution for aging and obsolete analog or digital controllers in the U.S. market. The platform is suitable for reactor protection system, engineered safety features actuation system, reactor control system, control rod drive mechanism control system, digital rod position indication system, turbine protection system, turbine electro-hydraulic governor control system, nuclear instrumentation system, in-core instrumentation system, and radiation monitoring system applications.

Aaron Larson is POWER’s executive editor (@AaronL_Power, @POWERmagazine).