Page 124 - Neutrons for Sciences and Society

Neutrons for Science
The above table (taken from a booklet prepared by Franco Franzetti for the twentieth anniversary of the ILL) gives all the features of the reactor and shows that the exceptional amount of power to be removed from the core requires a very special design. This core, derived from that of the Oak Ridge High Flux Isotope Reactor (HFIR), was conceived and calculations were made by Louis Brégeon. It is in the form of a cylinder and consists of
an assembly of long (80 cm) and thin (1.27 mm) curved plates between which the coolant circulates (see Fig. 5.6). The fuel element is highly enriched 235U. The central hole, which in the Oak Ridge reactor is used to place material for irradiation, is
used here to house the control rod yielding the best conditions for neutron beam production.
This raised the problem of the supply of enriched uranium. Germany, of course, had no enrichment plant. France had one at Pierrelatte built for military use, but the cost of this uranium was prohibitive. It was necessary to seek provision from the USA. At that time the USA did not have very strict export regulations for highly enriched uranium (usable for making a bomb). An agreement was made with the USA for the purchase of the fuel, and the ILL reactor could be started up without any problems. We shall see later that the later introduction of a more rigorous regulatory regime has posed serious problems for the ILL.
It should be noted that the characteristics of this reactor are much more stringent than those of reactors for producing electricity. The power density in the core is at least an order of magnitude larger than pressurised water reactors and three orders greater than gas cooled graphite reactors.
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