TRIGA MARK II Nuclear Reactor Facility

Kansas State University

Table of Contents

• Introduction
• Facility Description
• Control and Measurement
• Safety
• Tate Laboratory
• Services

The TRIGA reactor is fueled with a uranium alloy initially enriched to 2O% in the isotope U-235. The enriched uranium (8.5% of the fuel by weight) is homogeneously combined with a zirconium-hydride moderator (hydration ratio 1.7) and clad with O.OO51 cm thick stainless-steel to form the cylindrical fuel elements. Click here to see a cross-sectional view of a typical fuel element. Graphite sections sandwiching the uranium-zirconium-hydride fuel form part of the reflector. Upper and lower fittings on the fuel elements permit their proper positioning in the 91-hole grid plates. The core consists of approximately 78 fuel elements and 5 graphite elements. Click here to see core map Surrounding the core is a 30.4 cm thick, annular graphite reflector. Click here to see a cutaway view of the reactor. The reactor may be operated in steady-state mode with a maximum (thermal) power of 25O kW or may be operated in high-power, short-duration pulses with maximum power of 250 megaWatts (MW) with a duration of approximately 35 milliseconds. The maximum steady-state thermal flux is 1 X 1O^13 neutrons/cm^2-sec and the maximum thermal fluence per pulse is 4 X 10^14 neutrons/cm^2.

The control and most of the measurement instrumentation are located in a console in the reactor control room adjacent to the reactor bay. The reactor power is controlled by the positioning of three boron-loaded control rods, which occupy three locations in the grid plates. Click here to see a cutaway view of the reactor. The shim and the regulating rods are made of aluminum-clad boron carbide and are motor driven with maximum withdrawal rates of approximately 5 mm/sec. The third rod, used for pulsed operation and made of aluminum-clad borated graphite, is pneumatically operated and can be ejected from the core in about 0.1 second. The reactor power is monitored by four neutron detectors located radially near the outer edge of the graphite reflector. A fission chamber is used to monitor the start-up range (1 mW-1 W). Boron-lined compensated ion chambers are used to monitor the entire operating range (O.01 W-25O kW, steady state), and a boron-lined uncompensated ion chamber is used to monitor the power range (1% to 1OO% of full power and the pulse power). Thermocouples located in several fuel elements serve as monitors for the fuel temperature, which is not allowed to exceed 450 degrees celcius. Other instruments provide information about the operating condition of the reactor and its associated systems.

Uranium-zirconium-hydride was chosen for the TRIGA fuel because of its inherent safety features. This fuel has the important property that its prompt temperature coefficient of reactivity is negative and large. This means that the neutron multiplication rate decreases instantly as the fuel temperature rises and that this decrease is very sensitive to the increase of the temperature. Since an increase of reactor power increases the fuel temperature, power excursions are limited by the nature of the fuel. Thus, human, electronic, or mechanical operations are not required to guarantee the safety of the reactor. Further to prevent an inadvertent overpower operation, a number of automatic shutdown circuits (scram circuits) are incorporated into the reactor console. The shim and regulating rods are connected to their drive motors via electro- magnetic couplings. When an abnormal console indication occurs (as, e.g., one indicating an excessive power level or an excessive temperature) the scram circuits interrupt the power to the electromagnets. The rods then fall back into the core and thereby shut down the reactor. Radiation monitoring for personnel safety is accomplished by the use of numerous Geiger counters, ion chambers, scintillation detectors, air monitors, film badges, and other devices.

Pulsing

Since increases in reactor power are self-limiting by the nature of the uranium- zirconium-hydride fuel, it is safe to intentionally send the reactor on large power excursions (pulses). This is accomplished by:
1. bringing the reactor to criticality at low power (typically 10O Watts) by withdrawing the shim and regulating rods as needed and then
2. rapidly ejecting the pulse rod from the core.
These high-power, short-duration pulses are useful for transient radiation- effects studies and for the investigation of short-lived radioisotopes. An observer watching a high-power pulse from atop the reactor witnesses a display of awesome beauty from the dazzling blue glow caused by Cerenkov radiation.

Shielding

The reactor core is located 4.9 m below the top of a 2.0 m diameter aluminum tank filled with high purity water. Click here to see a vertical cross section of the reactor. The water allows easy access to and provides excellent visibility of the core by persons on the reactor bridge at the top of the tank. The water also serves as shielding to protect persons on the bridge from radiation produced in the vicinity of the core. Radial shielding is provided primarily by about 2.4 m of concrete surrounding the reactor tank at the level of the core. Click here to see a horizontal cross section of the reactor.

Cooling

The core is cooled primarily by natural convection of the reactor tank water. Some of the reactor tank water (maximum--110 gal/min) is pumped through the tube side of a tube-and-shell heat exchanger for cooling. The water (maximum--10 gal/min) is purified in a parallel clean-up loop. A small cooling tower located just outside the reactor bay is used as needed to cool the water which passes on the shell side of the heat exchanger.

Experimental Facilities

Rotary Specimen Rack

The rotary specimen rack (RSR), located in the graphite reflector close to the reactor core, consists of 40 specimen tubes in which up to 80 standard cylindrical sample containers (approximately 2.5 cm diameter by 9 cm long) can be placed and irradiated simultaneously. Click here to see a cutaway view of the reactor. Most routine irradiations are performed in the RSR. Samples are readily loaded and retrieved via a loading tube which connects the RSR to the reactor/bridge. Examples of materials commonly irradiated are geological samples, agricultural samples, biological samples, and other source materials for radioisotope production.

Central Thimble

A water-filled tube 3.3 cm inside diameter, extending from the reactor bridge through the center of the core is used to perform irradiations at the center of the reactor core, where the neutron flux is highest. Click here to see a horizontal cross section of the reactor . Click here to see a cutaway view of the reactor. Other in-core irradiation chambers are available for special irradiations requiring primarily epithermal neutrons or 14 MeV neutrons.

Beam Ports

Four 20 cm diameter beam tubes extend from the graphite reflector through the biological shielding to ports conveniently located 91 cm above the reactor bay floor. Click here to see a vertical cross section of the reactor . Click here to see a horizontal cross section of the reactor. These tubes provide well-collimated neutron beams for experimental investigations. Three of the tubes are radial, i e , they are directed toward the center of the core, and one is tangential, i e , it is directed toward the graphite reflector to provide a thermalized neutron beam with a low gamma-ray contribution. One of the radial ports is a source for fast neutrons. The graphite reflector has a void between the inner end of this beam tube and the core so neutrons traveling outward from the core encounter minimal moderating material in the direction of the fast port.

Columns

Two large columns extend from the reflector outward through the reactor tank wall. Click here to see a vertical cross section of the reactor . Click here to see a horizontal cross section of the reactor. The graphite thermal column has a 122 x 122 cm cross section and extends from the reflector through the tank wall and the concrete shielding to a movable concrete door, which can be retracted on railroad tracks for access to the outer face of the column. This thermal column is designed for use whenever a highly thermalized neutron flux or a large-area neutron beam is required. The thermalizing column, consisting mostly of graphite and air, extends from the reflector through the tank wall and concrete shielding to the bulk shielding tank, a 2.4 x 2.7 X 3.7 m tank of high-purity water in which samples too large or otherwise unsuitable for insertion into the reactor tank are irradiated.

Pneumatic Trsnsport System

The pneumatic transport system, which consists of metal tubing, a blower, and assorted valves, can transfer a sample container (called a rabbit) from the reactor core to a remote laboratory within several seconds. The terminus of the transport system at the reactor end occupies one grid-plate location in the outer ring of the core. Click here to see a cutaway view of the reactor. The transport system is most useful for the investigation of irradiated samples which contain short-lived radioisotopes, it is especially advantageous when used with the pulsing feature of the reactor.

The Tate Neutron Activation Analysis Laboratory (NAAL), named for C.C.Tate (a distinguished service alumnus and benefactor of KSU), is located in Ward Hall on the campus of KSU. The primary function of the laboratory is to perform qualitative and quantitative analyses of samples by the use of gamma-ray and x-ray spectrometry. The laboratory is used extensively in connection with the TRIGA reactor facility to perform neutron activation analysis on a wide variety of samples. The principal radiation detectors in use are lithium-drifted germanium (Ge-Li) and intrinsic germanium detectors for gamma-ray and X-ray measurements. The energy distributions of the X rays and gamma rays are accumulated and displayed by multi-channel pulse height analyzers. Click here to see a Gamma-ray energy distribution. The processing power and operating flexibility of the pulse height analysis systems of the Tate NAAL may be enhanced by microcomputers interfaced to the multi channel analyzers. Digital magnetic tape recorders permit large-quantity data storage and data transfer to the computing facilities at the KSU Computing Center for further processing. Various electronic modules are available for the assembly of specialized measurement systems.

Tours and Lectures

Tours of the TRIGA Nuclear Reactor Facility,the Tate Neutron Activation Analysis Laboratory, and the Nuclear Engineering Department are available, by appointment, to members of the general public as well as to high school, college, and university groups. Associated lectures can be provided also.

Reactor Experiments

Limited reactor operating time can be provided to college and university groups for the performance of reactor experiments, which can be either standard experiments (such as control rod calibration, approach-to-critical, flux mapping, etc ) or experiments designed especially for the outside users.

Irradiations

Service irradiations, mostly of small samples of neutron activation analysis, are commonly performed for outside users. Irradiations are also performed for radiation effects studies, neutron radiography, isotope production and others. Due to the reactor's extensive experimental facilities, nearly all noncommercial requests for service irradiations can be accommodated.

Information and Arrangements

For further information concerning reactor services or to arrange for reactor use, contact the Director, KSU Nuclear Reactor Facility, Department of Nuclear Engineering.

Neutron Activstion Anslysis

Complete or partial, qualitative or quantitative neutron activation analysis can be performed either by outside users or by Department of Nuclear Engineering personnel. Users need not necessarily visit the Reactor Facility to have analyses performed. For more information or to arrange for services contact the Director, Tate Neutron Activation Analysis Laboratory, Department of Nuclear Engineering.

Nuclear Radiation Measurements

The Nuclear Engineering Department has extensive facilities to assist outside users with specialized radiation measurement problems. The instruments most likely to be of interest to external users are the photon spectrometers, the liquid scintillation spectrometer system, the alpha/beta proportional counter systems, and the thermoluminescent dosimeter sytems. For further information contact the Head, Department of Nuclear Engineering.

Radiation Standards Laboratory.

A modern Radiation Standards Laboratory is the focal point for nuclear instrumentation research emphasis is placed upon instrument design, calibration, and testing as well as methods development in the areas of data acquisition and data analysis. The Laboratory contains a medium energy gamma-ray calibration facility, a beta-particle calibration facility, and a neutron calibration facility with either a bare or heavy-water moderated Cf-252 source. All sources are calibrated by the Physikalisch-Technischen Budensanstalt (beta particles) or have calibrations traceable to the U S National Bureau of Standards (gamma rays and neutrons).

Cobalt-60 Irradiations

A kilo-curie, 3.7 liter, gamma irradiation cell, which delivers a dose rate of approximately 50 krad/h, is available for a wide variety of radiation-effects studies. For more information or to make arrangements for use contact the Director, KSU Nuclear Reactor Facility, Department of Nuclear Engineering.

Educational Services

Formal course work in nuclear engineering, leading to Bachelor of Science, Master of Science, and Doctor of Philosophy degrees, is available in the Department of Nuclear Engineering. Programs may also be developed through the KSU Division of Continuing Education. For detailed information consult the Head, Department of Nuclear Engineering.