TFTR vacuum system exhaust pressure control for D-T operation

For the Deuterium-Tritium (D-T) phase of High Power Pulsed (HPP) Operations in TFTR all vacuum system pumping gas effluents from the Torus Vacuum Pumping System (TVPS), Neutral Beam Vacuum System (NBVS), and Diagnostic Vacuum Systems (DVS), are routed through a Tritium Cleanup System (TCS) prior to release into the environment. The effluents are collected and held in one of two Gas Holding Tanks (GHTs), then batch processed through the Tritium Cleanup System. Low pressures (relative to the pump exhausts) are maintained in the GHT's to guard against tritium release and special precautions are taken to prevent the oil from being scavenged out of the exhaust side of the vacuum pumping systems, into the GHT's and ultimately into the Tritium Cleanup System. In order to prevent oil contamination, a pump exhaust pressure control system has been designed and installed between the mechanical pumps and the Gas Holding Tanks. This control system designated the "Vacuum Exhaust Active Pressure Control" (VEAPC), is designed to maintain all mechanical pump exhaust pressures at acceptable levels over the entire operating pressure range of the GHT's (250-750 torr). We will describe the systems active pressure control butterfly valve and the ancillary hardware and controls. In addition, we will discuss the operational performance of the system on TFTR.