Calibrating a Vacuum Ionization Gauge for Hydrogen Using a Frit-Type Plugging Meter

Abstract

The hydrogen meter leak detectors at the Experimental Breeder Reactor II (EBR-II) are periodically checked with a vacuum ionization gauge to see if the leak detectors are calibrated. The gauge, which measures equilibrium pressure, requires an equation to convert the gauge pressure to the hydrogen concentration in sodium. The original equation

H, ppm = 10.30 * (P_g, Torr)^1/2

is derived from Sievert’s law with adjustments for gauge sensitivity to hydrogen and thermal transpiration effects. EBR-II experience has shown that the Sievert’s law equation has not been reliable in accurately determining the hydrogen concentration in sodium. It is also difficult to determine the hydrogen gauge sensitivity, which can change with time. EBR-II has developed a new equation over a hydrogen range of 0.063 to 0.230 ppm,

H, ppm = 0.016 + 10.10 * (P_g, Torr)^1/2,

by using a frit-type plugging meter to determine the hydrogen concentration when an equilibrium pressure measurement is done. With sodium hydride as the predominant impurity, the impurity saturation temperature (plugging temperature) measured with the plugging meter can be used to calculate the hydrogen concentration. Measuring the equilibrium gauge pressure and plugging temperature at various hydrogen impurity levels provides the data to accurately calibrate the vacuum ionization gauge without measuring or estimating the gauge sensitivity, gauge temperature, or Sievert’s law constant.