Research center develops nuclear battery prototype – 03/19/2024 – Science

Imagine a cell phone whose battery lasts for years and doesn’t need to be plugged in to recharge. Or a drone capable of flying indefinitely over the Amazon, recording hotspots of deforestation and illegal mining. Situations like these may soon become a reality, with the start of commercial production of new energy storage systems that use radioactive material to generate electricity uninterruptedly, for tens or hundreds of years.

One of the innovations was revealed at the beginning of the year by the Chinese startup Betavolt. The company has developed a nuclear battery that can generate energy for 50 years without needing to be recharged. The device measures 15 millimeters (mm) long, 15 mm wide and 5 mm thick and operates by converting the energy released by the decay of radioactive isotopes of nickel (Ni-63). With 100 microwatts (µW) of power and 3 volts (V) of electrical voltage, the module is a pilot project.

Betavolt plans to put a more powerful version of the battery on the market in 2025, with 1 watt (W). It has a modular function and, according to the startup, can be used in series to power drones or cell phones.

Brazil has studies in the area. A team from the Institute for Energy and Nuclear Research (Ipen), based in São Paulo, presented at the end of 2023 the first prototype of a thermoelectric nuclear battery made in the country. The operating principle of the device, also known as a radioisotope thermoelectric generator (RTG), is different from the Betavolt system: an electric current is produced from the conversion of heat generated by the disintegration of an americium isotope (Am-241). In the Chinese module, beta particles (electrons) are transformed into electrical current through a specific converter system.

The process of radioactive decay or disintegration occurs when the unstable nucleus of a chemical element transforms into the nucleus of another element, which has less energy. The process releases electromagnetic radiation and can emit particles. This phenomenon is characterized by half-life, which is the time required for half of the atoms of the radioactive isotope present in a sample to disintegrate.

“During our development, we had to design a thermoelectric generator module, responsible for converting thermal energy into electrical energy”, explains chemical engineer and doctor in nuclear technology Carlos Alberto Zeituni. He is the manager of Ipen’s Radiation Technology Center (Ceter), one of the units involved in the project — the other is the Nuclear Engineering Center (Ceeng).

The main advantage of nuclear batteries is the possibility of providing a charge over a long period of time. “A conventional chemical battery lasts five years, while a lithium battery lasts up to ten years. Nuclear batteries can last 50, 100 years or more, depending on the radioactive material used. We estimate that ours will last more than 200 years”, he says Zeituni.

Ipen did not measure the power of the module, whose electrical voltage is only 20 millivolts (mV). The next step, according to the center, is to build a version with 100 milliwatts (mW) of power, capable of controlling a remote weather station — the voltage will depend on the thermoelectric used. The research, which began two years ago, has been financed by a national company interested in commercializing the technology. By contract, your name cannot be revealed.

To create the module, Ipen researchers used 11 americium sources that were originally used in sheet thickness measuring equipment. To eliminate the risk of radioactive material leaking, the sources were stacked and encapsulated in an aluminum tube.

“The initial parameter of any nuclear project has to be safety. The battery will only be commercialized when there is a guarantee that the risk of leakage is zero. Therefore, we will use double or triple encapsulation of the radioactive material and carry out impact tests and breaking”, explains mechanical engineer Eduardo Lustosa Cabral, Ceeng researcher who participates in the project.

NASA rovers

Nuclear batteries such as those designed by Ipen and Betavolt began to be studied at the beginning of the last century. There is no commercial manufacture of these devices yet. Limited production is carried out mainly by governments of countries that dominate nuclear technology — such as the United States, Russia, France, China and England — and research centers, generally state-owned.

The technology is used in devices located in difficult-to-access places, such as lighthouses on desert islands, caves, the bottom of the sea and laboratories in the Arctic and Antarctica. In the 1970s, they were used in the health sector. “Plutonium-238 nuclear batteries were used in pacemakers, devices that monitor and regulate heartbeats, implanted in more than 300 people. There were no reports of leaks or failures”, says chemical engineer and doctor in nuclear technology Maria Alice Morato Ribeiro, Ceeng researcher and group leader.

The North American space agency NASA’s rovers use this type of technology, as well as the Voyager space probe, launched into space in 1977 — its nuclear batteries are used to rotate the solar panels that provide energy for the spacecraft. In the same vein, the device developed at Ipen will be intended for applications in remote locations.

“The use of this technology is restricted due to the manufacturing cost, the availability of raw materials and the difficulty of production, starting with the handling and encapsulation of the radioactive material”, informs Ribeiro. Great care must be taken to avoid leakage during the manufacture and operation of the device. Another difficulty concerns the fact that the entire electrical part is exposed to radiation, which can cause damage to the system. Everything needs to be very well sealed.

Tough competition

For physicist Hudson Zanin, from the Faculty of Electrical Engineering at the State University of Campinas (Unicamp) and coordinator of research that aims to develop a sodium-based battery, the work done at Ipen is promising, but it will have to overcome challenges to result in a commercial product.

“At a time when we are discussing how to move towards a 100% electric society based on renewable energy sources, which will replace fossil fuels, energy storage is a key technology. Therefore, the development of the most different types of batteries, including this one from Ipen, is important”, he states.

“The long operating time without recharging of nuclear batteries is their great advantage, but they need to evolve to increase the output voltage”, highlights the Unicamp physicist. “In addition”, he highlights, “they will face tough competition with other advanced, cheaper and already established technologies, such as lithium-iron phosphate batteries [LFP] and nickel-cobalt-manganese [NCM]”.