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THE DESIGN AND PERFORMANCE OF THE JET IONISATION CHAMBERS FOR USE WITH TRITIUM

1993; American Nuclear Society; Linguagem: Inglês

10.1016/b978-0-444-89995-8.50222-8

0748-1896

C. Caldwell-Nichols, J.L. Hemmerich, R. Lässer, P. Milverton,

Nuclear reactor physics and engineering

JET has developed and tested two original designs of ionisation chambers for use in the JET Active Gas Handling System (AGHS) for detecting tritium. They will be used in two main applications, the detection of tritium inside the secondary containments of the main AGHS components and in tritium process control applications. They satisfy several criteria for use in the AGHS including being demountable, UHV compatible and able to be baked in-situ to remove the memory effect typical of ionisation chambers used with tritium. Two sizes of chamber have been produced, one of about 570 cc active volume primarily to detect tritium-in-air up to 2 Ci/m3, and a second of about 15 cc active volume for use in process control in streams of up to 100% tritium. The chambers are of open wall construction and are mounted from standard Conflat flanges fitted with multi-pin feedthroughs which carry the electrical signals and also power for the heated collector for decontamination. The performance of these chambers and the efficacy of the electrical heating as a means of decontamination was confirmed during tests at TSTA at Los Alamos. The same devices and associated electronics were also used to detect tritium in the JET vacuum backing line during the first JET tritium experiment. In this mode the 3He+ ions created as tritium decays are collected to give a signal proportional to the tritium content of the exhaust gases. Two chambers were installed in the Gas Collection System for the experiment. They made important contributions to the safe and efficient operation of the recovery system, the inventory measurements of the tritium recovered from JET and studies of tritium recycling from the first wall of the torus. The response to varied pressures and gas mixtures experienced is complex, but these devices will be used in later tritium experiments at JET on a routine basis in this mode.