The Maryland University Training Reactor (MUTR) was constructed in 1960 as a 10 kW MTR (Plate Fuel) Reactor. In 1974 the reactor was converted to a 250 kW reactor using TRIGA (Training, Research, Isotopes, General Atomics) fuel. TRIGA fuel uses Uranium Zirconium Hydride to provide special safety characteristics that make it impossible for the reactor to meltdown. The large, red, structure is the reactor biological shield which provides radiation shielding and support for the reactor pool. The MUTR is used for education and training, neutron activations, neutron imaging, and irradiation testing.
The MUTR is a pool type reactor. Water provides radiation shielding, cooling, and neutron moderation. The pool water is kept very clean by means of an ion exchange system. The reactor power is controlled by 3 boron carbide control rods. The yellow control rod drives can insert or withdraw them from the reactor core to increase or decrease the reactor power. The control rods are attached to the control rod drives by means of electromagnets. In the event of a reactor scram, the power to these electromagnets is cut and the control rods drop into the core under gravity, shutting down the reactor. Any single control rod is enough to shut down the reactor.
The reactor core is composed of bundles of TRIGA fuel elements. 3 neutron detectors and an instrumented fuel element monitor the core parameters. Forced cooling of the core is not necessary, the reactor is cooled by natural convection. The blue glow is Cherenkov Radiation, light produced by charged particles moving faster than the speed of light in water.
The reactor is controlled from the control room. Whenever the reactor is operating, an operator licensed by the Nuclear Regulatory Commission must be present.
The reactor console controls the reactor functions and displays the reactor parameters. Parameters monitored include the reactor power, reactor period, fuel temperature, pool temperature, radiation levels, and neutron detector voltages. If any of these reach a setpoint, the reactor will automatically scram. The console also includes automatic control electronics that allow the reactor to maintain a constant power level.
This board displays the layout of the reactor core including the position of fuel elements (pink), control rods (blue), neutron reflectors (gray), and experimental facilities. The pieces can be moved to reflect the status of the reactor.
One of the most common applications for the MUTR is Neutron Activation Analysis (NAA). NAA is an elemental analysis technique. Unknown samples are placed into the reactor where they absorb neutrons, making the sample radioactive. From the amount and type of radioisotopes produced, the elemental composition of the sample can be determined. NAA is sensitive to up to 74 elements in concentrations of .1 ppm or less without chemical processing and minimal sample preparation.
NAA is frequently applied in fields such as as archeology, nutrition, geology, forensics, and environmental science. Here, a vitamin is being prepared for neutron activation to test its mineral content.
Much of the work for NAA takes place in what we call the “Hot Room” as this is where the “hottest” (most radioactive) materials are handled.
NAA samples are weighed, and placed into “rabbits”. The term “rabbit” dates back to the early days of nuclear engineering and refers to a capsule used in conjunction with a pneumatic system to place a sample into a reactor core for activation or irradiation. Our rabbits are small polyethylene capsules inserted in the reactor core with a CO2 pneumatic system. CO2 is used because it does not contain argon, which will activate to radioactive argon 41.
The rabbits are inserted or removed from the reactor core from a glove box to minimize the potential for a radioactive release. The rabbit is placed into the aluminum receiver. Compressed CO2 then carries the capsule to the reactor core for a preset amount of time. At the end of the irradiation, compressed CO2 pushes the capsule back to the receiver.
Neutron activated samples can become significantly radioactive. The samples are placed in the lead cave to decay to safe levels.
Gamma Ray Spectroscopy is used to identify the radioisotopes produced by neutron activation. The spectroscopy is performed in a room away from the reactor to reduce the background radiation. The gamma ray spectroscopy is performed using a High Purity Germanium Detector (HPGe). It is capable of providing very detailed gamma ray spectrums, but must be maintained at liquid nitrogen temperatures. In the picture above, the HPGe is slightly to the right of center, with the analysis computer to the left, and the liquid nitrogen systems to the right.
The detector (silver) is inside a 4” thick copper lined lead shield to reduce the background radiation.
Each gamma ray emitting isotope emits gamma rays only of a particular energy. The HPGe is able to measure the energy of the incoming gamma rays. Each peak in the spectrum corresponds to the energy of a gamma ray being emitted by the sample. These peaks show which radioisotopes are in the sample, and can be used to determine its elemental composition.
Most of the reactor experimental facilities are accessed from the experimental floor. The reactor core is approximately waist high in relation to this level.
One of the most common applications of the nuclear reactor is neutron imaging. Neutron imaging is often used as a complementary technique to x-rays as neutrons are highly penetrating in dense materials such as lead, but very sensitive to light elements such as hydrogen and lithium. A collimated beam of neutrons emerges from the reactor thermal column and passes through the sample. Less neutrons get through the sample in regions with high neutron cross sections. After passing through the sample the neurons interact with a lithium doped zinc sulfide phosphor screen and are converted to light (regions that allow less neutrons to pass through are darker). A cooled CCD camera is used to image the phosphor screen and digitize the neutron image.
Left: A neutron image of a Lego minifigure showing neutron imaging's high sensitivity to plastics.
Right: A titanium bolt that has been partially infiltrated with hydrogen, showing the high contrast between hydrogenated and non-hydrogenated titanium. Neutron imaging can be used to measure the amount of hydrogen in materials.
This concept drawing of the reactor shows the 2 beam ports and the through tube that can be used to irradiate samples or extract neutron or gamma ray beams from the reactor. When not in use, the beam ports and through tube are shielded by large concrete plugs. The reactor thermal column, currently used for neutron imaging, is shown as well.
The MUTR displays a collection of vintage radiation detectors, and other reactor related antiques collected by Prof. Tim Koeth.
This poster from 1957 details some of the different types of reactors in use at the time. Most of the first nuclear reactors were graphite moderated.
Starting in the early 1920s, shoe fitting fluoroscopes were found in many shoe stores where they were used to x-ray customers’ feet to determine how well shoes fit. These early, unregulated devices often delivered dangerous levels of radiation and were largely regulated out of existence by 1960. This Adrian model has been rendered safe and is for display purposes only.
Top Left: A Soviet radiation detector; an identical detector could briefly be seen in HBO's "Chernobyl".
Top Right: A "Snoopy" neutron detector.
Bottom: A Precision Radiation Instruments "De Luxe Scintillator" sold during the 1950's uranium prospecting craze. A lower cost alternative from that time, "The Snooper" can be seen in the background.