〔56〕高速炉の吸収・制御材

A review is presented of the IAEA-IWGFR Specialists' Meeting on the "Development and Application of Absorber Materials for Fast Reactors" which was held at Dimitrovgrad, USSR, June 4-8, 1973. At the meeting, attention was given mainly to the choice of absorbing materials for the control elements of fast reactors, to the design of absorbing rods and tests of their performance.About two thirds of the sessions were devoted to the oldest established and the most promising absorber-B4C. The pre-irradiation properties of B4C are considered to be fairly thoroughly known already. Good agreement has been seen on the results of compatibility studies. On the other hand, the irradiation behavior of B4C-specially swelling and He release-stimulated brisk discussion among the participants in respect of the appreciable discrepancy discerned in the results obtained so far and the possible explanations given therefore. Development of the vented control rod is being actively undertaken in most of the countries.Tantalum and Eu2O3 attracted attention as promissing alternatives to B4C. There arises problems, however, on the compatibility of these two materials in the presence of Na. Another difficulty foreseen in the use of Ta rods is cooling during reactor shut-off. For Eu2O3, phase stability should be an important problem for future study.