Moderator Tank

A proton beam of 1 mA produces about 3-6·1016 high energy spallation neutrons per second, which are slowed down to thermal energy in the moderator. The cylindrical moderator tank of about 2 meters in diameter is surrounded by a light water reflector jacket. The tank contains inserts for the horizontal extraction of cold and thermal neutrons via neutron guides and beam tubes on the ground floor level. The moderator is enclosed by 7000 tons of steel bulk shielding, which is cooled by a light water cooling system and surrounded by the outer target block structure of heavy shielding concrete.

Thermal neutrons are extracted to the experimental areas in 4 sectors of the target block. Every sector has two beam tubes, leading the thermalised neutrons to different expriments. Heavy water for moderation and cooling was preferred to light water because of its smaller cross section for neutron capture, resulting in a higher efficiency of neutron thermalisation.