Mock-Up to Simulate Pipe Freezing in Shutdown Cooling Rooms

Abstract

In order to repair/replace isolation valves in the Shutdown Cooling (SDC) Rooms inside the Reactor Vault, three ice plugs are required to provide the necessary isolation. An attempt was made in 2001, but the ice plugs formed could not provide work protection for the replacement of the isolation valve as the jackets were not full and there was no Liquid Nitrogen (LN2) visible at the jacket vents.

The mock-up was carried out using new hoses and arrangement, which allowed LN2 to arrive at the freezing jackets 32 minutes from the start. Within 125 minutes of the first LN2 observed at the jacket, the first ice plug (10") was called and the second ice plug (8") was formed 78 minutes later, while maintaining the first ice plug. Both ice plugs were successfully called within 4 hours and 42 minutes from the first start of the LN2. This mock-up also measured the amount of LN2 required to maintain the two ice plugs being 20% lower than the OP&P limit of 250 kg/h.