NUCLEAR SAFETYNo Power, No Operator, No Problem: Simulating Nuclear Reactors to Explore Next-Generation Nuclear Safety Systems

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.

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.