Monitoring the reactor core is vital to safe and efficient operations of a nuclear power plant.

Since the early 1990’s, Framatome Cogema Fuels (FCF) and Framatome SA in France have worked to develop an advanced fixed incore monitoring system to complement the installed moveable incore monitoring systems in Electricité de France (EDF) power plants. In 1996, two fixed rhodium incore detector assemblies, specially developed by FCF
to fit in the installed instrument guide thimbles, were installed in the Golfech 2 unit in France. These assemblies have operated successfully and provided the basis for going forward with a full system of rhodium incore assemblies, instrumentation and software. The complete system is
called MARINE.

MARINE, Marge Améliorée Reconstituée à partir d’une Instrumentation Nucléaire Evoluée, translated to mean, “improved margin reconstituted with advanced nuclear instrumentation,” is a complete system of incore detector assemblies, instrumentation and displays working together with software to enhance core-monitoring capability. MARINE features very small-diameter incore assemblies that operate in the flux thimble tubes of a W- or Framatome-type reactor. Since only 16 core locations are monitored with MARINE, the installed moveable incore detector system can continue to operate and monitor the remaining 42 core locations with its moveable fission chambers. Thus, the fixed and moveable systems can operate together in a complementary manner. The fixed incore system provides continuous monitoring inside the reactor core, including monitoring during power transients. The moveable incore system, which can only be operated about every 30 days, continues to produce a very accurate axial flux map at steady-state conditions.

Improved core monitoring with MARINE helps to provide additional core margin to accommodate modern, more aggressive fuel-load patterns. It can also help the utility maneuver through power transients more quickly.

FCF and Framatome plan to build the first MARINE system in France for use in EDF plants. FCF’s part is to supply the 16 rhodium incore detector assemblies. MARINE’s successful operation may open the way for installation at additional EDF reactors.