The US Defense Advanced Research Projects Agency (DARPA) is pursuing a new generation of compact nuclear power sources that could provide electricity to military equipment for years or even decades without conventional recharging.
Through its Rads to Watts program, DARPA is funding seven teams to develop advanced radiovoltaic power systems. The technology could eventually support applications ranging from battlefield communications and remote sensors to satellites and equipment deployed at forward military locations.
The program seeks to overcome two major obstacles associated with portable nuclear power: heat and weight.
Conventional nuclear reactors and radioisotope thermoelectric generators (RTGs) produce significant heat while generating electricity. Managing that heat requires additional equipment, increasing the size and weight of the overall power system and limiting its usefulness for portable applications.
DARPA program manager Tabitha Dodson identified heat management as one of the principal challenges preventing nuclear energy systems from becoming more easily transportable.
How Radiovoltaic Nuclear Batteries Work
Radiovoltaic technology approaches nuclear power generation differently.
Rather than first converting radioactive energy into heat, a radiovoltaic device uses semiconductor materials to transform energy released through radioactive decay directly into electricity.
The principle has similarities to photovoltaic solar cells. Solar panels use semiconductor materials to convert incoming photons into electrical energy, while radiovoltaic devices capture energy released by radioactive particles.
Removing the intermediate heat-conversion stage could allow engineers to build significantly smaller power sources capable of operating in environments where conventional batteries face limitations.
The concept, however, creates another engineering challenge: radiation itself can gradually damage semiconductor materials.
More energetic radioactive particles potentially offer greater power output, but they can also degrade or destroy the materials responsible for converting their energy into electricity. DARPA’s program is therefore examining both radioactive sources and semiconductor technologies capable of balancing power density with long operational life.
Seven Teams Exploring Different Technologies
The Rads to Watts program includes seven prime performers pursuing different solutions to the problem.
City Labs is working with tritium, a radioactive isotope that produces relatively low-energy beta particles. Its approach seeks to increase power density by placing more tritium within a smaller volume while maintaining the durability of the power cell.
Other participants are investigating higher-energy radioactive sources alongside advanced materials designed to tolerate stronger radiation.
BWXT, working with Johns Hopkins University, is developing a system based on alpha particles. The team is studying radiation-resistant semiconductor materials that could withstand sustained exposure while producing useful levels of electrical power.
Artificial intelligence is also playing a role in the research. The BWXT-led effort is using computational methods to examine large numbers of potential crystal structures before promising materials are selected for physical testing.
Avalanche Energy Takes Different Approach
Avalanche Energy is also investigating alpha radiation, but its concept introduces an intermediate material to protect the semiconductor.
Instead of allowing high-energy alpha particles to strike the semiconductor directly, the design uses a liquid-metal absorption layer. Energy deposited in the metal can then be transferred in a form that is easier for the semiconductor system to convert into electricity.
The approach could help address one of the fundamental problems facing high-power radiovoltaic devices: obtaining more energy from radioactive material without rapidly damaging the power-conversion components.
Strontium-90 System Also Under Development
Another team, led by Morgan State University in partnership with Project Omega, is pursuing a beta-powered system using strontium-90.
Strontium-90 provides higher-energy beta radiation than tritium, potentially enabling greater power output while introducing more demanding material requirements.
The project is also drawing on artificial intelligence, with Northrop Grumman supporting simulations intended to identify semiconductor materials capable of surviving prolonged radiation exposure.
Project Omega founder Staff Sheehan suggested that successful technology could eventually produce battery-like power sources capable of operating for around 30 years.
At larger scales, similar systems could potentially provide alternatives to diesel generators used at forward military installations, while extremely small versions could be integrated directly into electronic hardware.
DARPA Targets Higher Power Density
According to Dodson, technologies being developed under the program have already demonstrated power densities of at least 10 watts per kilogram, which she said represents roughly two to three times the efficiency of traditional RTGs.
DARPA believes considerably higher performance may ultimately be achievable, with the program targeting technologies in the range of approximately 10 to 100 watts per kilogram.
The participating teams are expected to finalize prototype power cells during a 15-month development period. The most promising designs would then advance to a nine-month endurance phase.
Those tests will examine whether the systems can continue operating despite prolonged exposure to their own radioactive sources and challenging external environmental conditions.
Potential Military Applications
If the technology proves practical, its military implications could be significant.
Modern forces depend heavily on electrical power for communications, surveillance equipment, navigation systems, unmanned platforms, sensors and computing hardware. Supplying that equipment in remote locations can require batteries, fuel deliveries and supporting infrastructure.
A compact power source capable of functioning reliably for years could reduce some of those logistical requirements, particularly for systems deployed in inaccessible or hostile environments.
Space-based military systems could also benefit because satellites and other spacecraft require reliable power sources capable of operating for extended periods without maintenance.
DARPA’s immediate objective is not simply to demonstrate the physics behind radiovoltaics but to develop a system durable and powerful enough for practical use. Following prototype development and endurance testing, the agency aims to identify at least one technology suitable for transition toward larger-scale military deployment.
The Rads to Watts program remains in the development stage, meaning the technologies should not yet be viewed as replacements for conventional military batteries or generators. If researchers overcome the challenges of radiation damage, power density and manufacturing, however, radiovoltaic power could provide the US military with a new class of compact, exceptionally long-lasting energy sources.