Molten salt reactor neutronics data released
08 July 2016
Transatomic Power Corporation has released technical information on the design of its molten salt reactor (MSR), which it says offers multiple advantages over existing generation technologies.
The technical white paper issued by the Cambridge, Massachusetts-based company outlines how its 1250 MWth reactor design - the TAP MSR - uses the properties of its liquid fuel to increase fuel utilization while decreasing the overall amount of waste produced.
Transatomic published the white paper after the US Department of Energy awarded it a $200,000 grant under its Gateway for Accelerated Innovation in Nuclear (GAIN) Nuclear Energy Voucher pilot program. The funding will enable the company to perform high-fidelity modelling of the design in partnership with Oak Ridge National Laboratory (ORNL). The reactor technology on which the TAP MSR is based was first demonstrated at ORNL in the 1960s.
Leslie Dewan, Transatomic's CEO, said the current design is the result of years of open, clearly communicated scientific progress. "Our research has demonstrated many-fold increases in fuel efficiency over existing technologies, and we're really excited about the next steps in our development process," she said.
Fuel utilization - or burnup - is defined as the thermal energy extracted per unit mass of heavy metal in nuclear fuel, typically expressed in units of gigawatt-days per tonne of heavy metal. The higher the burnup, the more energy is extracted from the fuel and the less waste is produced. However, in conventional light-water reactors using solid fuel, burnup is limited by the build-up over time of fission products inside the fuel which in turn affect the thermal conductivity of the fuel itself. The increased temperature and radiation-induced swelling over time threaten the integrity of the fuel rods, while the build-up of neutron-absorbing fission products over time reduces the system's reactivity.
Unlike solid fuel, liquid fuel has no long-range structure to be damaged, does not experience significant volumetric swelling, and avoids fission product poisoning through continuous fission product removal. This means it can potentially reach higher burnups. Transatomic's white paper presents qualitative studies into these properties based on software modelling studies.
The studies found that the TAP MSR design allows for more than twice the fuel utilization of conventional light water reactors by exploiting the properties of the liquid fuel through the continuous removal of fission products and the ability to vary the geometry of the reactor core. Using fuel enriched to 5% uranium-235 - the maximum enrichment level readily available for low-enriched uranium in the existing nuclear fuel supply chain - this increased efficiency leads to a waste reduction of about 53%. For uranium enrichments up to 20%, the waste reduction reaches 83%.
Dewan said the issue of nuclear waste presented two "big-picture" steps to be overcome: reducing the rate at which waste is produced, and designing reactors capable of extracting the remaining energy in the waste to achieve a 'net-negative' waste profile, where a reactor produces less waste than it takes in.
Transatomic chief technology officer, Mark Massie, said the calculations showed that its design would clear the first hurdle. "Even under the current fuel supply chain, which doesn't enrich fuel past 5% U-235, we still reduce annual waste production by over 50%," he said.
Subsequent design work will focus on maximizing the energy extracted from used nuclear fuel to achieve a net-negative profile. The work will include developing new tools to model other reactor physics phenomena, and completing the overall design of its nuclear power plant, Transatomic said.
The TAP MSR's architecture is based on inventions developed by Dewan and Massie at the Massachusetts Institute of Technology Department of Nuclear Science. The duo founded Transatomic Power in 2011.
Researched and written
by World Nuclear News