JAIF Report Details Economic Impact of Nuclear Power Plants

The U.S. Department of Energy (DOE) has approved two capacitor development milestones for Zap Energy under the Milestone-Based Fusion Development Program. These approvals cover a detailed design for a pulsed power capacitor engineered for the repetition rate and operating lifetime required in a fusion power plant, and a prototype capacitor designed, manufactured, and tested by Zap Energy.

These milestones indicate advancements in long-life capacitor design and the U.S.-based manufacturing capabilities necessary for large-scale production of these components. Pulsed power, delivered by high-voltage capacitor banks, is a critical technology for various fusion energy approaches, including Zap Energy’s sheared-flow-stabilized Z pinch. Developing capacitors that can operate at high repetition rates over billions of pulses is a step toward commercial fusion power plants.

Commercial Fusion Requirements

Zabrina Johal, CEO of Zap Energy, stated that commercial fusion requires reliable, repeatable, and power-plant-scale operation of technologies surrounding the fusion core. She noted that pulsed power is a critical enabling technology, and these milestones demonstrate progress toward the long-life, high-repetition-rate systems needed for commercial fusion plants, while also building manufacturing capability within the United States.

Pulsed power capacitors store electrical energy and release it in rapid bursts. In pulsed fusion, these bursts help drive fuel into extreme conditions for fusion reactions. While commercial units are typically rated for about 100,000 pulses, a commercial power plant operating for 20 years at 10 pulses per second would require individual capacitors to withstand approximately 6 billion pulses.

Capacitor Specifications and Testing

Zap Energy's detailed design is for a 35-kilovolt, actively-cooled capacitor rated for 50,000 amps of peak current, projected to last 6 billion pulses. It incorporates self-healing metallized polypropylene film, which degrades gradually, and uses multiple capacitor sections in series to reduce the voltage seen by the film. Integrated active cooling enables continuous operation at 10 pulses per second.

The prototype is a compact, 2.8-pound epoxy-potted capacitor using the same multi-section winding approach. Zap Energy performed the winding, arc spraying, assembly, potting, and testing in-house, cycling the unit hundreds of times at 8 kilovolts and over 7,000 amps. Its capacitance remained stable within 0.25% throughout the test campaign, exceeding all prototype milestone criteria.

Supply Chain and Future Development

Ryan Umstattd, Zap’s VP of Federal Programs, explained that a goal of the DOE Milestone Program is to support the fusion supply chain across various fusion approaches and establish new U.S.-based manufacturing. He added that while long-lifetime, high-repetition-rate capacitors will eventually be needed by the thousands in fusion power plants, the initial step involves developing designs, manufacturing techniques, and qualification standards.

These approvals followed a review by an independent panel of experts convened by the DOE. Zap Energy's next steps include testing the designs to higher voltages, longer lifetimes, and with voltage reversals for implementation in future Zap fusion power banks.

The MARVEL (Microreactor Applications Research Validation and Evaluation) microreactor project has achieved several key milestones as researchers prepare for initial startup tests. The primary coolant system (PCS) arrived at the Idaho National Laboratory (INL) in mid-September, completing its fabrication and delivery. This component is crucial for the microreactor to achieve criticality, a stable nuclear chain reaction necessary for full operation. The PCS will be integrated with the reactor's other systems at INL's Transient Reactor Test Facility, with criticality anticipated in December.

The PCS is designed to circulate heat during operation, using a sodium-potassium alloy as a coolant. This alloy remains liquid at room temperature and efficiently transfers heat at high reactor temperatures without requiring pressurization. The MARVEL microreactor employs a two-loop natural circulation system for thermal energy transfer. Its core consists of 36 solid fuel rods, each containing five uranium hydride fuel meats, arranged in a hydrogen-moderated, beryllium-reflected configuration. Fission heats 120 kg of eutectic sodium-potassium (NaK) alloy in the primary loop, which then transfers heat to four secondary loops containing eutectic gallium–indium–tin (eGaInSn) liquid metal via four intermediate heat exchangers (IHXs). Each secondary loop connects to a commercial Stirling engine, generating 5 to 7 kWe, for a total output of up to 20 kWe. The system operates entirely by natural circulation, eliminating the need for pumps. The primary circuit is enclosed in a stainless steel 316H vessel, rated to ASME Section III Division 5 standards. Active reactivity control is managed by rotating beryllium oxide drums clad with neutron-absorbing boron carbide, while a central insurance absorber (CIA) rod provides shutdown capability. The reactor also features passive decay heat removal.

Prior to the PCS delivery, the Idaho Operations Office of the Department of Energy (DOE) approved MARVEL's final documented safety analysis (FDSA). This safety document authorizes a dry criticality configuration, which will generate data to serve as a national benchmark for reactor physics. Dry criticality refers to the critical condition achieved with near-zero power generation, thus not requiring coolant. Abdalla Abou-Jaoude, the MARVEL microreactor lead, expressed satisfaction with both the PCS fabrication and the DOE approval, which facilitates progress toward initial criticality. Doug Gerstner, a nuclear safety engineer at INL, noted that the documented safety analysis represents years of engineering and safety analysis, validating the risk-informed methodology developed by the team. John Jackson, national technical director for the DOE Microreactor Program, acknowledged the dedication of the MARVEL team, INL leadership, and DOE in reaching this milestone.