Facilities
The TRIGA Mark II nuclear reactor facility is composed of specialized parts and systems that support reactor operations. Together, these interconnected components provide a safe, versatile environment for learning and discovery across nuclear engineering and the sciences.
In-Core/In-Pool Irradiation Facilities
The in-core and in-pool irradiation facilities include a well in the reflector around the core, central thimble, fuel spaces, pool, a pneumatic "rabbit" sample transit system and small penetrations in the upper grid plate. Ex-core irradiation facilities include penetrations from the edges of the core to the experiment floor surrounding the reactor shielding, a section of graphite accessible from the experiment floor, a section of graphite accessible under water and a neutron source. Gamma only irradiation is possible following operating the reactor at high power then inserting samples in the spaces in and around the core. Total dose is dependent on an exposure rate that varies with time as e(-λ*t), with λ determined from experimental data.
Fast neutron, thermal neutron and gamma radiation values normalized per Watt reactor power are tabulated in the table.
| Facility |
Thermal Neutron Flux |
Fast Neutron Flux |
Gamma Dose Rate |
| Central Thimble | 3.3 x 107 | 3.9 x 107 | 1.0 x 10-1 |
| Penultimate Fuel Ring | 1.6 x 107 | 2.6 x 107 | 6.0 x 10-2 |
| Outer Fuel Ring | 1.7 x 107 | 1.4 x 107 | 6.0 x 10-2 |
| Reflector Well | 7.2 x 106 | 6.0 x 106 | 1.6 x 10-2 |
| Pool Outside Reflector | 2.7 x 106 | 2.7 x 105 | 1.8 x 10-3 |
| Pool Above Core | 1.4 x 106 | 4.4 x 105 | -- |
The graphite reflector around the reactor core has a 10 inch deep well about 3 inches from the core, allowing for a large number of samples to be placed in a high neutron flux.
The highest neutron flux in the core is available in the center at the mid-plane. An aluminum liner positions samples in the "central thimble." The central thimble (1.33 inches in diameter) extends 7.5 inches below the bottom of the reactor core, but a spacer holds samples at the core midplane.
The facility has a dry tube that can be positioned in any space normally occupied by fuel or the neutron source. The tube is configured with an S-bend to limit radiation streaming from the core. The currently available tube was constructed to deliver fast neutrons to samples.
Spaces around the core are authorized for use in sample irradiation. Neutron irradiation of relatively large samples (as opposed to the 1.25 & 1.33 in spaces of other core sites) is possible.
A helium driven pneumatic system can be installed if needed to support research using very short-lived radioisotopes. Samples sizes up to 0.5 inches in diameter and 2 inches long can be inserted in the "rabbit" system and delivered to the neutron activation analysis laboratory.
Small holes penetrate the upper grid plate between fuel positions to support in-core measurements.
The ex-core irradiation facilities include beam ports and two graphite filled irradiation facilities (thermal column and thermalizing column).
Four cylindrical tubes provide beams of neutron and gamma radiation for a variety of experiments. One of the beam ports penetrates the core reflector, so that fission-energy neutron and gamma radiation can be extracted into the volume of the piercing beam port or out to the experiment floor. Another beam port is tangentially extracted from the outer reflector surface providing a lower neutron energy and reduced core gamma radiation beam. The remaining beam ports are radially oriented to the center of the core one of which is equipped with a highly oriented pyrolytic graphite monochromator for selecting neutron energy.
The thermal column contains a 4 ft3 column of graphite with access by opening either a shield door or smaller stringer access plug. The graphite column is composed of 4 in2 stringers 50 inches long. A 2 in thick lead curtain is on the stringer end nearest to the core for reducing gamma streaming into the thermal column. The column container walls are lined with boral to reduce capture gammas from the surrounding concrete.
On the opposite side of the core from the thermal column is a facility known as the "thermalizing column." The thermalizing column exits the reactor shielding underwater in the "bulk shield tank." The thermalizing column is 2 ft2, and contains (from the core to the bulk shield tank) 8 in of graphite, 2 in of lead, a 19 in void space, and 24 in of graphite.
Californium 252 spontaneously fissions, providing a significant source of high energy neutrons. Two Cf-252 sources are available for various activation, imaging, and neutron detection research efforts.
The facility maintains a Cs-137 panoramic irradiator for experiments and calibrations related to personnel dosimetry.