Darlington NGS vacuum building outage: modification to supply post-seismic makeup water to the heat transport system

The periodic stationwide outage at Darlington NGS includes removal of the Emergency Coolant Injection System from service to allow for maintenance. As a prerequisite, the station must set up a minimum 2.5 kg/s temporary makeup water supply, to help cool the fuel should a seismic event occur. This modification cannot be commissioned, as commissioning would dilute the heavy water in the Primary Heat Transport System with light water. Therefore, flow analysis is necessary to demonstrate that the required flow rate can be achieved. This paper provides details of the design, and key aspects of the supporting analysis. (author)