William C. Sailor

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.

Long-term uranium supply estimates

Abstract We address the long-term uranium supply from first principles, summarizing estimates of the abundance of uranium in the crust of the earth as a function of concentration and accessibility. Defining the supply curve as a functional relationship between the cumulative quantity of uranium extracted and the cost of extracting the next unit of uranium, we note that a supply curve requires a crustal abundance model plus a correlation between ore grade and extraction cost. Surveying a number of supply curves that appear in the literature, we observe that while estimates vary widely (we observe an order of magnitude difference in forecasts of the quantity of uranium available at

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

100/kg U or less), they generally reflect expectations that uranium availability will be significantly greater than the Red Book numbers imply. Furthermore, by comparison with historical data for more than 40 other minerals, we show that the assumption of time invariance when formulating a supply curve is not borne out by experience. In fact, the price of most other minerals has decreased with time as well as with cumulative quantity extracted. Neither the Red Book nor the other supply curves we survey explicitly accounts for the unit-based technological learning that fosters this behavior.

Civilian Nuclear Cooperation and the Proliferation of Nuclear Weapons

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.

Preliminary Investigation of Actinide and Xenon Reactivity Effects in Accelerator Transmutation of Waste High-Flux Systems

In his article, Matthew Fuhrmann challenges the conventional wisdom about the relationship between civilian nuclear cooperation and nuclear weapons proliferation.1 The literature on nuclear proliferation focuses on the demand side and explains decisions to acquire nuclear weapons on the basis of security threats, hegemonic ambitions, national identity, or related factors.2 The role of civilian technical nuclear cooperation is generally discounted as a motivating factor in the acquisition of nuclear weapons capabilities. Fuhrmann argues that there is a causal connection between peaceful nuclear cooperation and proliferation and that civilian nuclear assistance over time increases the likelihood that states will initiate nuclear weapons programs. The implications of the notion that civilian nuclear technology promotes nuclear proliferation are disturbing, because they lead to the conclusion that the central bargain of the nuclear nonproliferation regime—namely, access to civilian nuclear technology in return for the renunciation of nuclear weapons—is not viable and that instead the Nonproliferation Treaty (NPT) might be a vector for the spread of nuclear weapons technology. The central thesis of Fuhrmann’s article seems implausible. Nuclear proliferation is exceedingly rare. One hundred eighty-nine states are members of the NPT, including ave nuclear states. There are only four states that are not members of the NPT and that have nuclear weapons. Of the four, the last one to make the decision to go nuclear and that received civilian nuclear assistance started its nuclear program in 1972. North Korea went nuclear in the absence of civilian nuclear assistance.3 Belarus, Kazakhstan, Correspondence: Nuclear Cooperation and Proliferation

Direct irradiation of long‐lived fission products in an ATW system

The possibility of an unstable positive reactivity growth in an accelerator transmutation of waste (ATW)-type high-flux system is investigated. While it has always been clear that xenon is an important actor in the reactivity response of a system to flux changes, it has been suggested that in very high thermal flux transuranic burning systems, a positive, unstable reactivity growth could be caused by the actinides alone. Initial system reactivity response to flux changes caused by the actinides and xenon are investigated separately. The maximum change in reactivity after a flux change caused by the effect of the changing quantities of actinides is generally at least two orders of magnitude smaller than either the positive or negative reactivity effect associated with xenon after a shutdown or startup. In any transient flux event, the reactivity response of the system to xenon will generally occlude the response caused by the actinides. The capabilities and applications of both the current actinide model and the xenon model are discussed. Finally, the need for a complete dynamic model for the high-flux fluid-fueled ATW system is addressed.

Neutronics and engineering design of the aqueous-slurry accelerator transmutation of waste blanket

The feasibility of directly irradiating five long‐lived fission products (LLFPs: 79Se, 93Zr, 107Pd, 126Sn, and 135Cs, each with a half‐life greater than 10,000 years), by incorporating them into the target of an Accelerator Transmutation of Waste (ATW) system is discussed. The important parameters used to judge the feasibility of a direct irradiation system were the target’s neutron spallation yield (given in neutrons produced per incident proton), and the removal rate of the LLFP, with the baseline incineration rate set at two light water reactors (LWRs) worth of the LLFP waste per year. A target was constructed which consisted of a LLFP cylindrical ‘‘plug’’ inserted into the top (where the proton beam strikes) of a 30 cm radius, 100 cm length lead target. 126Sn and 79Se were each found to have high enough removal rates to support two LWR’s production of the LLFP per year of ATW operation. For the baseline plug geometry (5 cm radius, 30 cm length) containing 126Sn, 3.5 LWRs could be supported per year (at 75% beam availability). Furthermore, the addition of a 126Sn plug had a slightly positive effect on the target’s neutron yield. The neutron production was 36.83±.0039 neutrons per proton with a pure lead target having a yield of 36.29±.0038. It was also found that a plug composed of a tin‐selenide compound (SnSe) had high enough removal rates to burn two or more reactor years of both LLFPs simultaneously.The feasibility of directly irradiating five long‐lived fission products (LLFPs: 79Se, 93Zr, 107Pd, 126Sn, and 135Cs, each with a half‐life greater than 10,000 years), by incorporating them into the target of an Accelerator Transmutation of Waste (ATW) system is discussed. The important parameters used to judge the feasibility of a direct irradiation system were the target’s neutron spallation yield (given in neutrons produced per incident proton), and the removal rate of the LLFP, with the baseline incineration rate set at two light water reactors (LWRs) worth of the LLFP waste per year. A target was constructed which consisted of a LLFP cylindrical ‘‘plug’’ inserted into the top (where the proton beam strikes) of a 30 cm radius, 100 cm length lead target. 126Sn and 79Se were each found to have high enough removal rates to support two LWR’s production of the LLFP per year of ATW operation. For the baseline plug geometry (5 cm radius, 30 cm length) containing 126Sn, 3.5 LWRs could be supported per year (a...

Actinide and xenon reactivity effects in ATW high flux systems

A conceptual target and blanket design for an accelerator transmutation of waste system capable of transmuting the high-level waste stream from 2.5 light water reactors is described. Typically, four such target-blanket designs would be served by a single linear accelerator. The target consists of rows of solid tungsten rod bundles, cooled by heavy water and surrounded by a lead annulus. The annular blanket, which surrounds the target, consists of a set of actinide-oxide-slurry-bearing tubes, each 3 m long, surrounded by heavy water moderator. Heat is removed from the slurry tubes by passing the slurry through an external heat exchanger. Long-lived fission products are burned in regions that are separate from the actinides. Using the Monte Carlo codes LAHET and MCNP, a conceptual design for a beam current of 62.5 mA/target of 1.6-GeV protons has been developed. Preliminary engineering analyses on key system components have been performed. A preliminary layout of the concept and the associated primary-heat transport subsystems was developed, demonstrating a multiple-containment-boundary design philosophy.

PRIVATIZING GOVERNMENT OPERATIONS A SYSTEMS APPROACH

In this paper, initial system reactivity response to flux changes caused by the actinides and xenon are investigated separately for a high flux ATW system. The maximum change in reactivity after a flux change due to the effect of the changing quantities of actinides is generally at least two orders of magnitude smaller than either the positive or negative reactivity effect associated with xenon after a shutdown or start‐up. In any transient flux event, the reactivity response of the system to xenon will generally occlude the response due to the actinides.