[en] Structural heat-resistant alloys in JAERI-VHTR are being considered for use in a 40 atm circulating helium environment at 1,000₀C. Characterization of corrosion, creep and fatigue behavior of the heat-resistant alloys under service conditions is necessary to evaluate the durability and predict the life of the reactor structures. Various material tests were performed in a high temperature, ambient pressure and low flow rate helium environment. In the future test will be run under high temperature, high pressure and high flow rate conditions. Much technical experience and many engineering developments concerning the test facilities for performing material tests under a controlled environment were obtained through performing these tests. Technical problems on the helium loop, corrosion test equipment, creep test facilities and fatigue test facilities are described. Also counter measures developed for those problems are shown. Various schemes are compared and discussed in accordance with the need for increasing the mass flow and specimen size for future tests. (author)