The Beckman 7C Thermal Cell (Hydrogen Monitor) Experiments Page: 1

                                
1. Introduction

Small scale laboratory experiments were conducted at the IRC (INEL
Research Center) on a Beckman model 7C thermal conductivity cell under
various sample input conditions. The purpose of the experiments was to
provide a better understanding of the response of the hydrogen monitor
during the Power Burst Facility (PBF) Severe Fuel Damage (SFG) tests. The
main objective of the experiments was to identify conditions others than
increased hydrogen concentration that would produce a positive output
signal similar to that observed late in the PBF SFD 1-4 test. Such a
signal occurred during the argon gas cooling of the bundle, a time period
when little or no hydrogen was expected. To meet the test objective, the
effects of flowrate, gas composition, temperature, water aerosol, steam,
and the humidity content of the input sample were studied. Both steady
state and transient type experiments were performed to understand the
monitor response under varied conditions. The results of these
experiments are summarized in this report.
Section 2 presents the general experiment design and equipment
layout. The functional characteristics of the Wheatstone bridge are also
identified. Section 3 discusses the steady state 'dry' (without the
addition of water to the input gas stream) experiments and reports the
results of the monitor output voltage as a function of gas composition,
and flow rate. The steady state 'wet' (with water moisture) test results
are  presented in Section 4, and the water aerosol test results are
reported in Section 5. The transient experiment results are summarized in
Section 6 and the main conclusions of the report are listed in Section 7.
Finally, the impact of these experiments on the interpretation of the SFD
test data is discussed in Section 8.
2. Experiment Design
A functional diagram of the Wheatstone bridge used in the thermal
conductivity analyzer is shown in Figure 1. During all experiments, the
bridge power supply, as recommended by engineers at Beckman Industrial,
was set at 67.9 mA (as measured at room temperature). This curre t
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