A new diffuser/permeator design has been proposed for a new Savannah River Site tritium project. The use of a single heaterwell in the center of the shell had raised concerns that the Pd/Ag coils may be shielding radiative heat transfer to the walls thus reducing Pd/Ag tube temperatures near the shell below the recommended minimum operating temperature.
The diffuser was fitted with thermocouples to measure shell temperatures during testing. Tests were run with the shell evacuated, helium Feed flows of 0, 1000, and 2000 sccm; Bleed pressures ranging from 0 to 203 kPa, and heater temperatures of 650, 675, and 700°C. Hydrogen permeation tests were run with two hydrogen/helium mixtures and Feed rates to simulate 1st and 2nd stage diffuser operations.
Approximately 20 hours were required to bring the diffuser from ambient temperature to steady-state conditions. For tests with a heater temperature of 675°C and no hydrogen flow, helium flow rate and pressure had little impact on the measured shell temperatures, the thermowell temperature, roughly 415°C, and altered heater output by only 11 watts. Conversely, controlling the thermowell temperature to 415°C during hydrogen permeation tests increased heater power output, lowered heater temperature, and increased shell temperatures. The tests showed the diffuser can perform its intended function with reasonable assurance that the Pd/Ag tubes were within the recommended temperature range.