Vacuum Drying of the Pickering A Units 1 and 2 Primary Heat Transport Systems

Abstract

The Primary Heat Transport Systems (PHTS) of Pickering Units l and 2 were vacuum dried, after draining, to reduce the tritium exposure to the crew re-tubing these units from residual water in the pressure tube.

A vacuum drying system was designed as a temporary attachment to the lower portion of the PHTS consisting, basically, of the system between the headers. The lower portion of the PHTS was isolated from the upper portion (which included the boilers etc.) and connecting systems, via approximately 100 valves and some tube crimping.

With heat provided by the moderator, end shields and feeder cabinet heating, the residual water in the PHTS was boiled off under a vacuum of 6KPa(a), provided by the vacuum pumps.

On unit l, approximately 19 Mg of 17% isotopic D₂O was recovered over a nine day period. Approximately 13.3 Mg of 8% isotopic D₂O was recovered over six days on unit 2.