N.T. Kazakovsky, E.L. Koira, A.I. Vedeneev
RFNC-All-Russian Research Institute of Experimental Physics
Sarov, Russia
G.L. Saksagansky, D.V. Serebrennikov
D.V. Efremov Scientific Research Institute of Electrophysical Apparatus
St. Petersburg, Russia
Features of the test facility and results of the experimental research into tritium impact on the physico-mechanical and vacuum characteristics of the ITER cryosorption panel mock-ups are presented. ITER pumping is based on impurities condensation on LN2 baffle and co-adsorption of hydrogen isotopes and helium on activated charcoal coated panels maintained at ~5K.
The test facility includes a vacuum system, a tritium generator (uranium bed), a box for mock-up exposure to tritium, a thermostat system in the box at cryogenic (LN2) and higher temperatures, and vacuum gauges. Small fragments of cryosorption panels (mock-ups) put into box were tested. After pumping, a box was filled with tritium and was raised to 80-300K. Temperature (T), pressure (p) and exposure duration of tritium (t) were chosen on the basis of similarity to real operation conditions of cryopanels in the ITER primary pump system. Critical features of the sorptional layer are were before and after exposure to tritium.
The studies were conducted with the mock-ups produced at the Research Center in Karlsruhe. The mock-ups were made of a stainless steel 316 LN plate, 80x15x1 mm of size, covered by Thermoguss 2000 glue with incorporated sorbing (activated charcoal) CHEMVIRON SCI or CFF30. Check mock-ups glue-covered but without sorbent were also investigated.
The mock-ups were subjected to tritium at temperatures ranging between 78-300K and [pt] < 1010 Pa-sec. Two holding modes in tritium were chosen: T=78K, p=9x104 Pa; T=298K, p=2x104 Pa. Following the exposure to tritium and subsequent degassing, the mock-ups were subjected to thermal cycling (50 cycles) according to following scheme: 10 cycles-ten minutes exposure at 300K with subsequent immersion in liquid nitrogen, each tenth cycle-heating to 460K followed by plunging in LN2. The tritium inventory of the mock-ups after their regeneration at room and elevated temperatures was estimated using calculation and experimental techniques.
For comparison of experimental results and analysis of physico-chemical processes in the samples, the following operations were performed: pre- and post-holding of mock-ups in tritium: sample mass measurements; microstructural analysis; measurement of glue microhardness; X-ray phase analysis of "glue-sorbent" composition; determination of the mock-up sorption capacity.
The results of these studies will be used while choosing optimal structure and technology of cryosorption panels for ITER.