No power, no operator, no problem: Argonne test facility simulates nuclear reactors to explore next-generation nuclear safety systems
Data generated at the facility validates computational models and guides the design of nuclear reactors
image: Matthew Jasica is a member of a small team conducting large-scale experimental testing of reactors and their components at the NSTF.
Credit: (Image by Argonne National Laboratory.)
To create safe and efficient nuclear reactors, designers and regulators need reliable data consistent with real-world observation. A facility at the U.S. Department of Energy’s (DOE) Argonne National Laboratory simulates aspects of a nuclear reactor under a wide range of conditions to accelerate the development of next-generation reactors and safety systems. Next-generation nuclear energy is a key component of energy plans that will help the nation meet its clean energy goals.
Designed as a half-scale model of a real reactor system, Argonne’s Natural Convection Shutdown Heat Removal Test Facility (NSTF) enables large-scale experimental testing of reactors and their components. In particular, the facility explores the performance of passive safety systems, which can cool a reactor without any human intervention or power.
“This type of open science is critical for the advancement and long-term operation of the next generation of nuclear power plants.” — Argonne Nuclear Engineer Matthew Jasica
The NSTF program generates data of the highest caliber, qualified to the level of National Quality Assurance-1 (NQA-1), a national standard for quality assurance in the nuclear industry. This data is shared with vendors and regulators to validate computational models and guide licensing of new reactors and components.
“The NSTF was carefully designed to ensure the physics observed inside the facility represents the physics involved with a real, full-scale reactor,” said Matthew Jasica, a nuclear engineer in Argonne’s Reactor Safety Testing and Analysis group. “We receive requests for data from industry stakeholders and the Nuclear Regulatory Commission to ensure that the output from their models reflects the real world.”
When a nuclear reactor is shut down — either a normal shutdown or during an accident — the reactor core is still generating heat. This is called decay heat. Decay heat needs to be removed to ensure that the reactor fuel is maintained within its specifications. Reactor plants are equipped with heat removal systems that are designed to handle decay heat. These systems often rely on the action of an operator or some other physical input, such as a pump that requires electricity to work.
In the event those active safety systems fail, passive safety systems can act as a backup. They don’t require any electricity, switch-flipping, wheel-turning or other input to operate. Instead, they are always on or standing by, ready to remove heat from the reactor using natural forces, such as gravity and the convection of heat, as soon as reactor conditions demand it. The NSTF is currently testing a type of passive safety system called a water-based reactor cavity cooling system.
There is no actual nuclear fuel at the NSTF. Instead, the heat produced by a reactor core is simulated by exposing a large steel plate to powerful electric heaters. The rest of the facility resembles a real reactor vessel cavity more closely. On the other side of the steel plate, pipes filled with filtered tap water run through an insulated cavity.
Hot water naturally rises, so as the reactor core heats the pipes in the cavity, the water begins to circulate through the pipes. The heat is whisked away with the water as it travels around a large, vertical closed loop of pipes and tanks. The water in this type of loop does not interact with the material in the nuclear reactor; it contains no radioactive material or waste.
“Part of the appeal of passive safety systems is their relative simplicity,” said Jasica. “But there are open questions for designers about what might happen in edge cases — those rare instances that still need to be accounted for in their designs.”
For example, when the reactor core gets hot enough, the water in the pipes will start to boil as designed. Boiling can cause challenges including pressure waves and fluid loss. It is also a complex and chaotic process to model. Small deviations in the thermal conditions and system configuration can cause dramatically different performance outcomes.
“We are generating large, high-quality datasets under different conditions, from normal operation to accident scenarios, to make sure the nuclear industry has the best possible understanding of how small changes affect decay heat removal,” said Jasica.
NSTF researchers test the system thoroughly, making one change at a time and observing the system’s response. Examples of tests include running the system with blockages in different areas of the pipes, or with different water levels in the tanks. The team has even worked with industry stakeholders to simulate — based on their own reactor plant design and models — an extended, real-world scenario where active cooling is suddenly lost.
Originally built at Argonne in the 1980s, the NSTF has tested a series of reactor technologies and configurations. In 2005, the program began exploring air-based passive safety systems. This work led to a patent by Darius Lisowski, NSTF’s group manager of reactor safety testing and analysis, for a weather cap device that protects sensitive exhaust systems from wind-induced downdrafts. The program shifted to its present water-based configuration in 2018.
“Our facility is always responding to the evolving needs of the nuclear industry,” said Jasica. “This type of open science is critical for the advancement and long-term operation of the next generation of nuclear power plants.”
This work is supported by DOE’s Office of Advanced Reactor Technologies.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology by conducting leading-edge basic and applied research in virtually every scientific discipline. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.
The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.