DARPA Wants To Bypass the Thermal Middleman In Nuclear Power Systems

The Defense Advanced Research Projects Agency (DARPA) is exploring the possibility of directly converting radiation from nuclear reactors into electricity using radiovoltaics, a technology that could potentially revolutionize nuclear power generation by moving beyond traditional steam turbine methods. The agency is requesting information and suggestions on this topic in an RFI released on August 1st. Nuclear News reports: There's got to be a better way": Methods to convert the energy of nuclear fission reactions and the decay of radioisotopes into electricity have not evolved since the invention of radioisotope power systems and fission reactors over 70 years ago and remain unoptimized," the RFI says. They rely on thermal heat transfer, and "in each step of this indirect conversion method neutrons, heat, and energy are lost to the shielding material, working fluid, and other system materials." Advanced reactor designs that use alternative coolants, including helium, sodium, and salts, would still use what DARPA calls "heritage nuclear power conversion technology" with water and steam as the working fluids, as would the fusion power plants being planned today. Why now? Tabitha Dodson, the program manager for DARPA DSO, which is launching the RFI, told Nuclear News that "two big things" are driving the interest. "One is the extreme surge of investment in small and advanced nuclear technologies, such as in fusion and space reactors, which do not have a concurrent pairing of advanced power generation methods that doesn't involve liquid-based heat transfer," she said. "Next, there has been an order of magnitude improvement in radiation tolerance and efficiency for voltaics in recent years with encouraging performance that indicates radiovoltaics could scale up as an array usable in nuclear reactors." [...] What is the ask?: The RFI asks: "Is it possible to achieve [a] direct energy conversion nuclear power system, ranging in power from 10s of watts electric (We) to 100s of kWe?" DARPA wants information "on the potential to improve specific power greater than 1 We/kg conversion from watts-thermal per radiation emission product," and information on the potential to improve damage tolerance of the voltaic to nuclear radiation to reach an operating lifetime comparable to the life of its nuclear source, on the scale of decades. "We will learn what our boundary conditions are when respondents tell us what technologies in the field of voltaics are possible, and we'll use that to see if there is sufficient scientific rationale make a case to present for further DARPA investment," Dodson said. "I also hope people are going to start thinking about nuclear systems that use electromagnetic versus thermal-kinetic methods to harvest nuclear energetic reactions."

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