The New Emergency Core Cooling (NECC) system for the National Research Universal (NRU) reactor

The New Emergency Core Cooling (NECC) system is the penultimate of seven major safety upgrades being implemented at the National Research Universal (NRU) Reactor in Chalk River. The NECC upgrade was designed to improve the original systems for core cooling in the event of an unisolable failure within the primary cooling circuit. The NECC upgrade ensures that water is automatically made available to the emergency cooling circuit pumps in the event of a break. Reactor core cooling is achieved from the discharge of these pumps which distribute emergency coolant to the individual fuel rods. Heated water from the vessel returns to the heat exchangers within the emergency cooling circuits for heat removal to the secondary coolant. The NECC upgrade significantly improves protection for a wide range of Loss Of Coolant Accidents (LOCAs) through the use of design features such as component redundancy, automatic initiation and hazard qualification. The introduction of the NECC upgrade combined with previous improvements in liquid confinement capability provide a closed loop system that ensures stable long term reactor core cooling. CATHENA (Canadian Algorithm for THErmalhydraulic Network Analysis) analysis was performed to assess the NECC upgrade and to validate the design for credible leak scenarios. (author)