Denis Beller

The U.S. accelerator transmutation of waste program

Abstract A national project to develop a future capability to separate actinides and long-lived fission products from spent fuel, to transmute them, and to dispose off the remaining waste in optimal waste forms has begun in the United States. This project is based on the Accelerator-driven Transmutation of Waste (ATW) program developed during the 1990s at Los Alamos National Laboratory, and has its technological roots in several technologies that have been developed by the multi-mission laboratories of the U.S. Department of Energy (DOE). In the Fiscal Year 1999 Energy and Water Appropriation Act, the U.S. Congress directed the DOE to study ATW and by the end of FY99 to prepare a “roadmap” for developing this technology. DOE convened a steering committee, assembled four technical working groups consisting of members from many national laboratories, and consulted with several individual international and national experts. The finished product, “A Roadmap for Developing ATW Technology – A Report to Congress,” recommends a five-year,

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

281 M, science-based, technical-risk-reduction program. This paper provides an overview of the U.S. Roadmap for developing ATW technology, the organization of the national ATW Project, the critical issues in subsystems and technological options, deployment scenarios, institutional challenges, and academic and international collaboration.

A roadmap for developing ATW technology: System scenarios & integration

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.

Conceptual design and neutronics analyses of a fusion reactor blanket simulation facility

A roadmap has been established for development of ATW Technology. The roadmap defines a reference system along with preferred technologies, which require further development to reduce technical risk, associated deployment scenarios, and a detailed plan of necessary R&D to support implementation of this technology. The potential for international collaboration is discussed which has the potential to reduce the cost of the program. A reference ATW plant design was established to ensure consistent discussion of technical and life cycle cost issues. Over 60 years of operation, a reference ATW plant would process about 10,000 tn of spent nuclear reactor fuel. This is in comparison to the current inventory U.S. of about 40,000 tn of spent fuel and the projected inventory of about 86,000 tn of spent fuel if all currently licensed nuclear power plants run until their license expire. The reference ATW plant was used together with an assumed scenario of no new nuclear plant orders in the U.S. to generate a deployment scenario for ATW. In the R&D roadmap, key technical issues are identified, and timescales are proposed for the resolution of these issues. A key recommendation is that, in the first year of any ATW program, trade studies intended to confirm technology choices and optimization of design be conducted. These studies will then be used to define future R&D. International collaboration will be important in this endeavor.

Integral Neutron Multiplicity Measurements from Cosmic Ray Interactions in Lead

Abstract : A new conceptual design of a fusion reactor blanket simulation facility has been developed. This design follows the principles that have been successfully employed in the Purdue Fast Breeder Blanket Facility (FBBF), because experiments conducted in it have resulted in the discovery of deficiencies in neutronics prediction methods. With this design, discrepancies between calculation and experimental data can be fully attributed to calculation methods because design deficiencies which could affect results are insignificant. Inelastic scattering cross sections are identified as a major source of these discrepancies. The conceptual design of this FBBF-analog, the fusion reactor blanket facility (FRBF), is presented. Essential features are a cylindrical geometry and a distributed, cosine-shaped line source of 14 MeV neutrons. This source can be created by sweeping a deuteron beam over an elongated titanium-tritide target.

A roadmap for the development ATW technology: Systems scenarios and integration

Sixty element 3He neutron multiplicity detector systems were designed, constructed and tested for use in cosmic ray experiments with a 30‐cm cube lead target. A series of measurements were performed for the cosmic ray configuration at ground level (3 meters water equivalent, mwe), in the St. Petersburg metro tunnel (185 mwe), and in the Pyhasalmi mine in Finland (583 and 1185 mwe). Anomalous coincidence events with charged cosmic ray particles at sea level produced events with 100–120 neutrons due possibly to the total disintegration of the Pb nucleus. These events were also detected at 185 mwe, but the particles causing such disintegration are currently unidentified. We present examples of preliminary data from the various measurements and discuss future plans for underground experiments including possible searches for Weakly Interacting Massive Particles (WIMP, dark matter).

The Need for Nuclear Power

As requested by the US Congress, a roadmap has been established for development of ATW Technology. The roadmap defines a reference system along with preferred technologies which require further development to reduce technical risk, associated deployment scenarios, and a detailed plan of necessary R and D to support implementation of this technology. Also, the potential for international collaboration is discussed which has the potential to reduce the cost of the program. In addition, institutional issues are described that must be addressed in order to successfully pursue this technology, and the benefits resulting from full implementation are discussed. This report uses as its reference a fast spectrum liquid metal cooled system. Although Lead-Bismuth Eutectic is the preferred option, sodium coolant is chosen as the reference (backup) technology because it represents the lowest technical risk and an excellent basis for estimating the life cycle cost of the systems exists in the work carried out under DOEs ALMR (PRISM) program. Metal fuel and associated pyrochemical treatment is assumed. Similarly a linear accelerator has been adopted as the reference. A reference ATW plant was established to ensure consistent discussion of technical and life cycle cost issues. Over 60 years of operation, the reference ATW plant would process about 10,000 tn of spent nuclear reactor fuel. This is in comparison to the current inventory of about 40,000 tn of spent fuel and the projected inventory of about 86,000 tn of spent fuel if all currently licensed nuclear power plants run until their license expire. The reference ATW plant was used together with an assumed scenario of no new nuclear plant orders in the US to generate the deployment scenario for ATW. In the R and D roadmap, key technical issues are identified and timescales proposed for the resolution of these issues. For the accelerator the main issue is the achievement of the necessary reliability in operation. To avoid frequent thermal transients and maintain grid stability the accelerator must reach levels of performance never previously required. For the target material the main technical choice is between solid or liquid targets. This issue is interlocked with the choice of coolant. Lead-Bismuth eutectic is potentially a superior choice for both these missions but represents a path with greater technical risk. For the blanket metal fuel has been selected. The reference method of processing of spent fuel from LWRs to provide the input material for ATW is chosen to be aqueous because of the large quantity of uranium that needs to be brought to a state that it can be treated as Class C waste. Again this is the path of least technical risk although the pyrometallurgical option will be pursued as an alternative. Processing of the fuel after irradiation in ATW will be undertaken using pyrometallurgical methods. The transmutation of Tc and I represents a special research issue and various options will be pursued to achieve these goals. Finally the system as a whole will need optimization from a reactivity and power control perspective. Varying accelerator power is feasible but can lead to overdesign of the accelerator; other options are movable control rods, burnable poison rods, and adaptations of the fuel management strategy.