Running On Star Power

What can generate four times more energy than a nuclear power plant and nearly four million times more energy than burning oil or coal? Fusion energy, according to the International Atomic Energy Agency. A fusion reaction happens as the result of a collision between two light atomic nuclei to form a heavier one. All of this occurs within plasma: a hot, charged gas of positive ions and free-moving electrons. In the process, large amounts of energy are released. It’s essentially the same reaction that powers our Sun, along with the rest of the stars.

Scientists at the UK Atomic Energy Authority (UKAEA) are attempting to imitate nuclear fusion as it occurs in nature, subject to extreme temperatures within the confines of a small space. The UKAEA researches fusion and related technologies to promote sustainable fusion energy in the UK. Their success depends on the fusion of deuterium and tritium (isotopes of hydrogen) to form helium and release energy as a neutron.

The effort to achieve fusion is worth the wait. When perfected, tremendous amounts of clean energy will be realized, along with some big benefits. Unlike other energy solutions, fusion relies on two plentiful, hydrogen-derived resources. Deuterium is easily extracted from seawater, and tritium can be generated inside the reactor itself. Fusion reactions, while difficult to initiate, are very easy to shut down. They’re seen as a much safer alternative to nuclear fission, which has been responsible for dangerous runaway reactions in several nuclear facilities.

Still, UKAEA scientists will have to clear some major hurdles before fusion is commercially viable. They need to address the complexities of building and maintaining a fusion machine, including the inability to rely on extensive testing, in-operation diagnostics, or periodic inspection. To be fully successful requires extensive virtual testing and predictive maintenance based on in situ monitoring in harsh environments enabled by Ansys simulation software.

Simulation builds a better fusion test rig

The primary objective for UKAEA is to build a combined heating and magnetic research apparatus (CHIMERA), or physical test rig, first. The test rig is specifically designed to test meter-scale prototype components in an environment representative of a fusion power plant. CHIMERA will simultaneously subject components under vacuum to high temperatures, high heat flux, magnetic loads, thermal cycling, and other failure modes to understand how components in a fusion reactor will behave.

The U.K. Atomic Energy Authority (UKAEA) is building a test rig of a reactor called CHIMERA and using simulations to optimize its output.

CHIMERA is currently under construction. There’s a previous history of prototyping and testing at UKAEA without the upfront simulation work — something the team is intent on changing with Ansys software. Creating the conditions to support the high temperature and pressure needed to facilitate fusion in a virtual environment was a priority. Outside of a virtual environment in the absence of simulation, iterative testing and prototyping is rendered costly and ineffective in terms of both resources and time.

To operate a test rig effectively, the team must model it and subject it to the various multiphysics loading conditions which are involved to understand how test components will behave. To this end, Michelle Tindall, Engineering Analyst, Simulation Research at UKAEA, is working towards a fusion component digital twin with the help of Ansys Twin Builder that will be used for virtual testing and monitoring of CHIMERA components within a simulation environment. By definition, a digital twin is a virtual representation of real-world entities and processes, synchronized at a specified frequency and fidelity.

Creating a system model or digital twin of CHIMERA requires the coupling of computational models with a physical counterpart (CHIMERA) that can be dynamically updated through the flow of data. Computational modeling is enabled through the simulation of various components of CHIMERA that will be considered during rig testing. Eventually, a component digital twin combining data from physical instrumentation with simulation can be used to deliver virtual, real-time diagnostics in support of future predictive maintenance of the reactor.

“We want to use simulations of CHIMERA to design our experiments and maximize the usefulness of the output to build confidence and capability in our simulation models, through calibration to tests,” says Tindall. “Only then do we get to the point where we have enough confidence in our models to conduct virtual test campaigns.”

CHIMERA Commissioning sample under test (left). Multiphysics systems simulation of CHIMERA commissioning sample under test performed by UKAEA with Ansys Twin Builder (right).

200 million degrees of virtual testing

One leading reactor design is the tokomak, a donut-shaped chamber with magnetic coils in the reactor that is instrumental in the production of controlled fusion power. The magnetic fields within a tokomak are responsible for the confinement of extremely hot plasma particles in a vacuum vessel that will ultimately combine to create energy.

An understanding of how tokamak components will fare sitting next to the plasma is a priority for the team, as the parts must be able to survive a relatively extreme environment characterized by high loads, high heat flux, and coolant loop flow. Tokomaks in the prototype power plant class involve load cases and operating conditions that can only be tested in a reactor environment.

“We’re looking at testing components, which sit inside the vacuum vessel in a tokamak, next to the plasma, which is very high temperature,” says Tindall. “It’s literally 100 million to 200 million degrees. You couldn’t have your components in contact with the plasma. In-vessel components have not yet been tested in conditions which are representative of a commercial reactor, so replicating these conditions in a virtual environment first is very important if we’re aiming to commercialize fusion energy.”

Example of temperature variation across front of commissioning sample under test due to mass flow and thermal/stress peak values obtained in Ansys optiSLang performed by UKAEA.

Closing the loop on water fluid circuit flow

At the moment, UKAEA is focusing its simulation work on a commissioning sample under test involving a water fluid circuit, which is the first component that will be placed into the CHIMERA. Commissioning is the process of enabling and verifying the operational integrity of all systems and components of power plants, research machines, and fuel cycle facilities. This process ensures all components are aligned with their original designs and meet all safety and performance criteria.

“The important thing from our perspective is that working with Twin Builder allows us to link many elements together to give us a fast-running multiphysics model that we can use to understand various outcomes,” says Tindall. “It enables the probabilistic simulation design studies and finite element analysis we wouldn’t be able to efficiently achieve with the underlying finite element models alone.”

Read the latest case study for a more details, including the use of Ansys Maxwell electromagnetic field simulation software during analysis.