9.2.1 Uranium-Loaded ADS Experiments

KUCA comprises two solid polyethylene-moderated thermal cores designated A and B and one water-moderated thermal core designated C. The A-core is mainly used for experiments of ADS basic research. The three cores are operated at a low mW power in the normal operating state; the maximum power is 100 W. The constitution and the configuration of the cores can be altered easily, and the coupling with the conventional Cockcroft-Walton type accelerator and with the FFAG accelerator has allowed conducting experiments separately with the use of 14 MeV neutrons from deuteron-tritium fusion reactions and 100 MeV protons with the heavy metal target, respectively.

m Normal fuel (3/8"P36EU)| I | Fe + polyethylene □ Polyethylene reflector H Void x3 + Fe + polyethylene © Control rod И Polyethylene + boron (10wt%)

Safety rod |_b^ Voidx 3 + polyethylene + boron (10wt%)oid

© Neutron source (Am-Be) Ш Voidx 1 + polyethylene (FC Fission chamber | s | Voidx 3 + polyethylene

UIC detector □ Aluminum sheath

I F ‘I Partial fuel (3/8"P14EU) О 1’ty3He detector SV SV Fuel (3/8"P32EU) О 1/2"ф BF3detector

T ungsten target

The A-core (Fig. 9.1) employed in the ADS experiments was essentially a thermal neutron system composed of a highly enriched uranium fuel and the polyethylene moderator/reflector. In the fuel region, a unit cell is composed of the highly enriched uranium fuel plate 1/16 in. thick and polyethylene plates 1/4 in. and 1/8 in. thick (Fig. 9.2). The SV assembly is composed of a

5.8 x 5.08 x 5.08 cm center void region, 32 fuel unit cells, and the polyethylene blocks. In these ADS experiments, three types of fuel rods designated as the normal, partial, and special fuel SV were employed. For reasons of the safety regulations for KUCA, the heavy metal target was located not at the center of the core but outside the critical assembly. As in the previous ADS experiments with 14 MeV neutrons,

the introduction of a neutron guide and a beam duct is requisite to lead the high — energy neutrons generated from the heavy metal target to the center of the core as much as possible. In the uranium-loaded ADS experiments, the proton beam parameters were 100 MeV energy, 0.01 nA intensity, 30 Hz pulsed frequency, 100 ns pulsed width, and 80-mm diameter spot size at the tungsten target (100 mm diameter and 9 mm thick). The level of the neutron yield generated at the target was around 1.0 x 106 1/s by the injection of 100 MeV protons onto the tungsten target.