Ljubljana TRIGA MARK II Research Reactor (R3)

The 250 kW TRIGA Mark II research Reactor at the J. Stefan Institute in Ljubljana began operation in May 1966. It is a light water reactor with solid fuel elements in which the zirconium hydride moderator is homogeneously distributed between enriched uranium. Therefore the reactor has the large prompt negative temperature coefficient of reactivity, the fuel also has very high retention of radioactive fission products. The reactor core is a cylindrical configuration with an annular graphite reflector.

The experimental facilities include a rotary specimen rack, a central incore radiation thimble, a pneumatic transfer system, and pulsing capability. Other experimental facilities include two radial and two tangential beam tubes, a graphite thermal column, and a graphite thermalizing column. At the steady state power of 250 kW the peak flux is 1E13 n/cm2 in the central test position. In addition, pulsing to about 2000 MW is usually provided giving peak fluxes of about 2E16 n/cm2 sec.

The main areas of present neutron beam utilization are:

• Neutron radiography (NR), using thermal, resonance and fast neutrons,
• Neutron-induced autoradiography (NIAR) using Solid State Nuclear Track Detectors (SSNTDs) and various other autoradiographic techniques,
• Development and applications of neutron activation analysis,
• Irradiation of biological and medical samples with fission neutrons from the U-235 thin fission plate in the dry exposure cell,
• Fuel management studies for the power reactor,
• Research in solid state physics by neutron scattering,
• Experimental exercises within the scope of training of technical personnel from the Nuclear Power Plant at Kr"sko (Slovenia)

Besides this research, in the TRIGA Reactor due to the rather low neutron flux mainly the short lived radioactive isotopes are produces and which are used for medical and industrial applications. Isotopes being produces are the following:

• Technetium-99m and Fluorin-18 are produced routinely for diagnostic purpose (nuclear medicine)
• For different industrial application the routine production of Sodium, Bromine, Zinc and Cobalt is carried out.

On average, the reactor operates around 4000 hours per year and about 4000 samples are irradiated for the nuclear chemistry laboratory and other users. In 1992 and 1993 the reactor was completely renewed (instrumentation, some mechanical parts, wiring, etc.)

Picture: During the last two years (1992-1993) the TRIGA Reactor was completely reconstructed and converted to the pulse mode operation when during the short neutron pulse a few hundred megawatts power is released. This is demonstrated by a strong Cherenkov radiation (see picture).

Contact: Prof. Dr. Gvido Pregl