Part 1 of 2 Parts
“The Advanced Test Reactor (ATR) is a research reactor at the Idaho National Laboratory, located east of Arco, Idaho. This reactor was designed and is used to test nuclear fuels and materials to be used in power plants, naval propulsion, research and advanced reactors. It can operate at a maximum thermal power of 250 MW and has a "Four Leaf Clover" core design (similar to the Camunian rose) that allows for a variety of testing locations. The unique design allows for different neutron flux (number of neutrons impacting one square centimeter every second) conditions in various locations. Six of the test locations allow an experiment to be isolated from the primary cooling system, providing its own environment for temperature, pressure, flow and chemistry, replicating the physical environment while accelerating the nuclear conditions.”
The ATR also plays an important role in keeping commercial nuclear power plants running longer and in developing new and safer reactors to mitigate climate change. Sean O’Kelly is associate lab director in charge of ATR. He said, “ATR is an absolutely beautiful reactor. There has never been one like it on the planet.”
The ATR is the most powerful test reactor of its kind, producing two hundred and fifty megawatts of power at full output. China has a similar test reactor that produces one hundred and twenty-five megawatts. Belgium’s test reactor can produce one hundred megawatts and the Oak Ridge National Laboratory in Tennessee has a test reactor that can produce eighty-five megawatts.
“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, 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.” Wikipedia
O’Kelly said that the more power your test reactor has, the more that fuels and materials can be tested to their limits. He added that, “You don't want fuel that is designed for 100 megawatts, and the first time you go to 103 megawatts, it fails. You build a safety margin in, and we have to test to that safety margin.” The ATR has what O’Kelly describes as the ability to maintain “a constant gradient of neutron flux throughout the core. ATR has this constant curvature of flux, so the experimenters have a fixed power and they know exactly what the power is in that region.” He said that other test reactors can be more difficult for experiments because the environment is changing during the experiment.
The ATR is configured in order to run multiple tests simultaneously. Some of the prime testing slots face a decade-long waiting for the opportunity to run experiments. Other testing slots are booked in advance. The ATR is unique because instead of turning heat into energy like commercial nuclear power reactors, the ATR produces neutrons so new materials and fuels can be tested to see how they are affected by a high-radiation environment. The ATR has a unique cloverleaf design which includes a core that is surrounded by beryllium metal to reflect the neutrons.
Please read Part 2