Alan Baxter

Deep-Burn: making nuclear waste transmutation practical

Abstract In the Deep-Burn concept, destruction of the transuranic component of light water reactor (LWR) waste is carried out in one burn-up cycle, accomplishing the virtually complete destruction of weapons-usable materials (Plutonium-239), and up to 90% of all transuranic waste, including the near totality of Neptunium-237 (the most mobile actinide in the repository environment) and its precursor, Americium-241. Waste destruction would be performed rapidly, without multiple reprocessing of plutonium, thus eliminating the risks of repeated handling of weapons-usable material and limiting the generation of secondary waste. There appears to be no incentive in continuing the destruction of waste beyond this level. An essential feature of the Deep-Burn Transmuter is the use of ceramic-coated fuel particles that provide very strong containment and are highly resistant to irradiation, thereby allowing very extensive destruction levels (“Deep Burn”) in the one pass, using gas-cooled modular helium reactor (MHR) technology developed for high-efficiency energy production. The fixed moderator (graphite) and neutronically transparent coolant (helium) provide a unique neutron energy spectrum to cause Deep-Burn, and inherent safety features, specific to the destruction of nuclear waste, that are not found in any other design. Deep-Burn technology could be available for deployment in a relatively short time, thus contributing effectively to waste problem solutions. Extensive modeling effort has led to conceptual Deep-Burn designs that can achieve high waste destruction levels (70% in critical mode, 90% in with a supplemental subcritical step) within the operational envelope of commercial MHR operation, including long refueling intervals and the highly efficient production of energy (approximately 50%). To the plant operator, a Deep-Burn Transmuter will be identical to its commercial reactor counterpart.

The application of gas-cooled reactor technologies to the transmutation of nuclear waste

Abstract Nuclear waste from commercial power plants contains large quantities of plutonium, other fissionable actinides, and long-lived fission products that pose long-term safe storage problems. Along with materials from weapons decommissioning programs, they are also a proliferation concern. Based on current levels of global nuclear power generation, it is estimated that by 2015 there will be more than 250,000 tons of spent fuel worldwide. This waste will contain over 2,000 tons of plutonium. (There is also more than 100 tons of plutonium becoming available from disarmament programs.) The disposal of this nuclear waste from commercial and defense programs has become a significant environmental and political issue. Long-term uncertainties are hampering the acceptability of a geologic repository for spent fuel in the U.S. The greatest concerns are with the potential for radiation release and exposure from the waste, and the possible diversion of fissionable material. The development of high-power accelerators has brought up the possibility of a technological solution to the problem. This is the so-called accelerator transmutation of waste (ATW), in which an intense beam of protons is used to produce a large, high-energy neutron flux in a spallation target. The target is surrounded by a multiplying medium of the plutonium and actinide waste, which is destroyed by neutron fission and capture. This paper describes the application of gas-cooled technology to the ATW, which can result in the elimination of weapons-useful material in the waste in one pass, without intermediate reprocessing, along with at least an order of magnitude reduction in the amount of reactor-generated transuranic (TRU) waste. Repository heat loads and the radio-toxicity of the waste are dramatically reduced. The process provides a waste form that is highly resistant to corrosion. It is also passively safe and does not produce mixed waste. The use of gas-cooled nuclear technology also provides maximum flexibility in the transmutation approach, and can allow the use of a direct-cycle gas-turbine generator power conversion system to produce electricity with 47% efficiency. Economic analyses suggest that gas-cooled transmutation systems are economically viable and would attract private investment for deployment.

Conceptual Design of the NGNP Reactor System

In May 2010, General Atomics (GA) was awarded a contract by the U.S. Department of Energy (DOE) under the Next Generation Nuclear Plant (NGNP) project to develop the conceptual design for a steam-cycle modular helium reactor (SC-MHR) demonstration plant. The SC-MHR is a graphite-moderated, helium-cooled reactor that is designed to produce steam for industrial applications and/or electricity production using a Rankine cycle. The SC-MHR operates with a thermal power level of 350 MW and a coolant outlet temperature of 725°C. This paper provides an overview of the conceptual design of the SC-MHR reactor system (RS), including assessments of core performance in the areas of reactor physics and power distributions, temperature/flow distributions, fuel integrity, and fission product release.Copyright