Francesco Venneri

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 burnup capabilities of the deep burn modular helium reactor analyzed by the Monte Carlo continuous energy code MCB

In the future development of nuclear energy, the graphite-moderated helium-cooled reactors may play an important role because of their valuable technical advantages: passive safety, low cost, flexi ...

Comparison of accelerator-based with reactor-based nuclear waste transmutation schemes

Abstract An overview of the most significant studies in the last 35 years of partitioning and transmutation of commercial light water reactor spent fuel is given. Recent Accelerator-based Transmutation of Waste (ATW) systems are compared with liquid-fuel thermal reactor systems that accomplish the same objectives. If no long-lived fission products (e.g., 99 Tc and 129 I) are to be burned, under ideal circumstances the neutron balance in an ATW system becomes identical to that for a thermal reactor system. However, such a reactor would need extraordinarily rapid removal of internally-generated fission products to remain critical at equilibrium without enriched feed. The accelerator beam thus has two main purposes (1) the burning of long-lived fission products that could not be burned in a comparable reactors margin (2) a relaxing of on-line chemical processing requirements without which a reactor-based system cannot maintain criticality. Fast systems would require a parallel, thermal ATW system for long-lived fission product transmutation. The actinide-burning part of a thermal ATW system is compared with the Advanced Liquid Metal Reactor (ALMR) using the well-known Pigford-Choi model. It is shown that the ATW produces superior inventory reduction factors for any near-term time scale.

Project Deep-Burn: Development of Transuranic Fuel for High-Temperature Helium-Cooled Reactors

The helium-cooled, graphite-moderated Very High Temperature Reactor (VHTR) has become the centerpiece of the U.S. Department of Energy’s (DOE) Next Generation Nuclear Plant (NGNP) program. The NGNP program aims to construct a VHTR prototype, with the participation of industry, by the year 2021.Copyright

Disposition of Nuclear Waste Using Subcritical Accelerator-Driven Systems: Technology Choices and Implementation Scenarios

Los Alamos National Laboratory has led the development of accelerator-driven transmutation of waste (ATW) to provide an alternative technological solution to the disposition of nuclear waste. While ATW will not eliminate the need for a high-level waste repository, it offers a new technology option for altering the nature of nuclear waste and enhancing the capability of a repository. The basic concept of ATW focuses on reducing the time horizon for the radiological risk from hundreds of thousands of years to a few hundred years and on reducing the thermal loading. As such, ATW will greatly reduce the amount of transuranic elements that will be disposed of in a high-level waste repository. The goal of the ATW nuclear subsystem is to produce three orders of magnitude reduction in the long-term radiotoxicity of the waste sent to a repository, including losses through processing. If the goal is met, the radiotoxicity of ATW-treated waste after 300 yr would be less than that of untreated waste after 100 000 yr. These objectives can be achieved through the use of high neutron fluxes produced in accelerator-driven subcritical systems. While critical fission reactors can produce high neutron fluxes to destroy actinides and select fission products, the effectiveness of the destruction is limited by the criticality requirement. Furthermore, a substantial amount of excess reactivity would have to be supplied initially and compensated for by control poisons. To overcome these intrinsic limitations, we searched for solutions in subcritical systems freed from the criticality requirement by taking advantage of the recent breakthroughs in accelerator technology and the release of liquid lead/bismuth nuclear coolant technology from Russia. The effort led to the selection of an accelerator-driven subcritical system that results in the destruction of the actinides and fission products of concern as well as permitting easy operational control through the external control of the neutron source.

Accelerators address nuclear waste problems

If the world is to continue using nuclear-generated electricity, the problem of radioactive waste disposal must be addressed. Permanent storage of long-lived waste from nuclear power stations is an issue that generates public concern, scientific uncertainty and political pressures. One alternative is to investigate ways of reducing the intensity and lifetime of the radioactivity of the waste so that it can be buried safely almost anywhere.

The physics design of accelerator-driven transmutation systems

Nuclear systems under study in the Los Alamos Accelerator‐Driven Transmutation Technology program (ADTT) will allow the destruction of nuclear spent fuel and weapons‐return plutonium, as well as the production of nuclear energy from the thorium cycle, without a long‐lived radioactive waste stream. The subcritical systems proposed represent a radical departure from traditional nuclear concepts (reactors), yet the actual implementation of ADTT systems is based on modest extrapolations of existing technology. These systems strive to keep the best that the nuclear technology has developed over the years, within a sensible conservative design envelope and eventually manage to offer a safer, less expensive and more environmentally sound approach to nuclear power.

Accelerator-driven Transmutation of Waste

Taking advantage of the recent breakthroughs in accelerator technology and of the natural flexibility of subcritical systems, the Accelerator-driven Transmutation of Waste (ATW) concept offers the United States and other countries the possibility to essentially eliminate plutonium, higher actinides, and environmentally hazardous fission products from the waste stream destined for permanent storage.

SOLUTAL SEPARATION UNDER CENTRIFUGATION

ABSTRACT We report on experiments and numerical simulations of the centrifugal separation of solutes in aqueous solutions. The experiments are measurements of solutal concentrations in binary and ternary aqueous mixtures of seven different salts subject to centrifugal accelerations of between 57,000g and 200,000g. The evolution of the concentration profiles are measured and the sedimentation coefficients are determined. We compare our experimentally determined coefficients with those predicted by the Svedberg relation. Our numerical simulations of the diffusion and sedimentation dynamics of centrifugation agree well with the experiments and constitute a basis for a nonequilibrium centrifugal separation scheme.

Conceptual design of a thorium target for molten salt transmutation systems

A spallation target constructed of thorium metal has been designed for applications using molten‐salt as the target coolant. The design consists of an array of wire‐wrapped, hastelloy‐clad, thorium rods in which a parabolic void region is introduced in the upper regions. Each target rod is approximately 1 m in length, 3.1 cm in diameter, and has a clad thickness of 0.05 cm; 140 rods are arranged in a triangular lattice with a pitch of 3.2 cm, which results in a cylindrical target configuration with a radius of 20 cm and an estimated yield of 17 neutrons/proton for 800 MeV protons.