NNC is developing a system to remove a sodiumpotassium alloy used as a coolant at the Dounreay fast breeder reactor. One option is to drain the water- and air-sensitive NaK alloy from the reactor system and deal with the residues using NNC's water vapour nitrogen (WVN) process.
After draining, the remaining coolant coats all the exposed steel surfaces within the system and forms small pools. It must be removed and converted to hydroxide, which can then be flushed out with water, without generating excess hydrogen.
NNC's WVN process passes low-concentration water vapour carried by nitrogen over contaminated surfaces. The rate of hydrogen production, which indicates how much contaminant remains, is measured using two Systech 542 programmable gas analysers.
The process is being run at test scale at NNC's Warrington site to determine operational parameters and carry out other tests before the process is scaled up.