The ILL high-flux reactor

The Institut Laue-Langevin was founded by an agreement between France and Germany signed on January 19, 1967, joined shortly afterwards by the United Kingdom as third partner; today it has thirteen member countries. Its reactor, first critical in 1971, produces no isotopes and tests no materials: it exists to deliver neutrons to instruments. With 58.3 MW thermal it reaches a flux of 1.5 × 10¹⁵ neutrons per square centimeter per second, among the highest in the world.

The design is singular: a single annular fuel element of uranium aluminide plates enriched to 93%, replaced whole at the end of each cycle, submerged in a heavy-water tank that moderates and reflects the neutrons, inside a light-water pool. Beam tubes lead from the tank to a hot graphite source and two liquid-deuterium cold sources, which shift the spectrum toward faster or slower neutrons depending on the experiment, and to a network of neutron guides feeding about 40 instruments: diffractometers, spectrometers, reflectometers and small-angle scattering machines for condensed matter, magnetism, chemistry and structural biology.