Advanced Test Reactor - Reactor Design and Experimental Capabilities

Reactor Design and Experimental Capabilities

The ATR core is designed to be as flexible as possible for research needs. It can be brought online and powered down safely as often as necessary to change experiments or perform maintenance. The reactor is also powered down automatically in the event of abnormal experimental conditions or power failure.

Components of the reactor core are replaced as necessary every 7–10 years to prevent fatigue due to exposure to radiation and to ensure experimenters always have a new reactor to work with. The neutron flux provided by the reactor can be either constant or variable, and each lobe of the four-leaf-clover design can be controlled independently to produce up to 1015 thermal neutrons per second per square centimeter or 5·1014 fast neutrons s−1 cm−2. There are 77 different testing locations inside the reflector and another 34 low-intensity locations outside the core (see figure at right), allowing many experiments to run simultaneously in different test environments. Test volumes up to 5.0 inches (130 mm) in diameter and 4 feet (1.2 m) long can be accommodated. Experiments are changed on average every seven weeks, and the reactor is in nominal operation (110 MW) 75% of the year.

Three types of experiments can be performed in the reactor:

• Static Capsule Experiment: The material to be tested is placed in a sealed tube made of aluminum, stainless steel, or zircaloy, which is then inserted in the desired reactor location. If the tube is less than the full 48" reactor height, several capsules may be stacked. In some cases, it is desirable to test materials (such as fuel elements) in direct contact with the reactor coolant, in which case, the test capsule is not sealed.

Very limited monitoring and temperature control are available for the static capsule configuration, and any instances would have to be built into the capsule experiment (such as temperature melt wires or an insulating air gap).

• Instrumented Lead Experiment: Similar to the Static Capsule configuration, this type of experiment allows for real-time monitoring of temperature and gas conditions inside the capsule. An umbilical connects the test capsule to a control station to report test conditions. The control station automatically regulates the temperature inside the test capsule as desired by pumping a combination of helium (conducting) and neon or argon (nonconducting) gases through the capsule. The circulated gas can be examined though gas-liquid chromatography to test for failure or oxidation of the material being tested.

• Pressurized Water Loop Experiment: More complex than the Instrumented Lead configuration, this type of experiment is available in only five of the flux tubes. Test material is isolated from the primary ATR coolant by a secondary coolant system, allowing for precise conditions of a commercial reactor to be simulated. Extensive instrumentation and control systems in this type of experiment generate a large amount of data, which is available to the experimenter in real-time so that changes can be made to the experiment as required.

Research experiments at the reactor include:

• Advanced Graphite Capsule: This experiment will test the effects of radiation on several types of graphite under consideration for the Next Generation Nuclear Plant program that currently have no high-flux temperature data available.
• Advanced Fuel Cycle Initiative / Light Water Reactor: The goal of the AFCI is to transmute longer-life fuels into shorter-life ones which would be able to be used in commercial light water reactors, to reduce the amount of waste that must be stored while increasing the fuel available for commercial reactors.
• Cobalt-60 Production: The least complex of current uses of the Advanced Test Reactor is the production of the Co-60 isotope for medical uses. Disks of Cobalt-59 1 mm -diameter by 1 mm thick are inserted into the reactor (Static Capsule Experiment), which bombards the sample with neutrons, producing Cobalt-60. Approximately 200 kilocuries (7,400 TBq) are produced per year, entirely for medical uses.