Accelerator-driven systems

Bowman, C. D. Accelerator-Driven Systems for Nuclear Waste Transmutation, Ann. Rev. Nucl. Part. Sci. 48, 505 (1998). 

RTF (1997). Accelerator driven systems. 3 pp.. Royal Institute of Technology, Stockholm, Website http //www.neutron.kth.se/introduction/. 

Recently much attention has been given to the accelerator driven systems, burning in inert matrices, and the use of thorium to burn plutonium. The concept of a closed nuclear fuel cycle was traditionally considered as transmutation (burning) of only plutonium and recycled uranium, with minor actinides (neptunium, americium, curium) destined for final geological disposal. But as time goes on, a new understanding is emerging reduction of the quantity of actinides would ease requirements for final repositories and make them relatively less expensive. 

FIG. 19.4. Neutron spectra of some chain reacting systems and a proposed accelerator driven system. The abscissa shows neutron flux times energy on an arbitrary scale. 

Preliminary studies on lead-bismuth and lead cooled reactors and ADS (accelerator driven systems) have been initiated in France, Japan, the United States of America, Italy, and other countries. Considerable experience has been gained in the Russian Fedaration in the course of development and operation of reactors cooled with lead-bismuth eutectic, in particular, propulsion reactors. Studies on lead cooled fast reactors are also under way in this country. 

For solving this task the works on mastering the new nuclear technology using accelerator-driven systems are carried out. The main stimulus for developing this technology is Pu and minor actinides blanket subcriticality that eliminates the prompt neutrons runaway nuclear accident. 

GROMOV, B.F., TOSHINSKY, G.I., STEPANOV, V.S., "Use of Lead Bismuth Coolant in Nuclear Reactors and Accelerator-Driven Systems", (Nuclear Engineering and Design, 1997) Vol.173,207-217. 

The investigation of safety and more particularly of severe accident conditions is important for accelerator driven systems (ADS). Subcritical ADS could be of particular interest for the actinide transmutation from the safety point of view, because fast reactors with Neptunium, Americium and Curium have a much smaller fraction of delayed neutron emitters (compared to the common fuels and U), a small Doppler effect and possibly a positive coolant void coefficient. This poses a particular problem of control since the fraction of delayed neutrons is essential for the operation of a nuclear reactor in the critical state. In addition, the IRC presented in the past a review of accelerator-driven sub-critical systems with emphasis on safety related power transients followed by a survey of thorium specific problems of chemistry, metallurgy, fuel fabrication and proliferation resistance. 

The calculated Loss-of-Flow and reactivity accidents were described and estimates of the behaviour of a lead-cooled fast system and that of thermal ADSs with a circulating fuel/salt mixture were described in the chapter on ADS safety in the IAEA State of the Art (SOAR) report on accelerator-driven systems which will soon be published. 

To overcome these problems various concepts of accelerator driven systems aiming at the transmutation of actinides and long lived fission products have been proposed in the recent past. The JRC presented a review of accelerator-drivai sub-oitical systems with emphasis on safety related power transients followed by a survey of thorium specific problems of chemistry, metallurgy, fuel fabrication and proliferation resistance. 

Such fission potentials might also have practical relevance. The possibility of transmutation of nuclear waste and the production of energy by accelerator-driven systems is under consideration. Accurate fission potentials are needed, particularly in the actinide region, to predict the fission cross sections for these applications. 

The aim of the present improvement work on the PUREX process is to make the separations more selective and to create effluent streams of high purity. Thus, modifications are performed to make neptunium end up in a fraction for later transmutation in a reactor or accelerator-driven system. This can be achieved by a better control of redox conditions in the process. Today neptunium is partially co-exlracted with plutonium and uranium. There are also suggestions to withdraw product streams with Tc and respectively, i.e., long-lived nuclides that might be of interest for transmutation. 

Abstract The chapter is devoted to the practical application of the fission process, mainly in nuclear reactors. After a historical discussion covering the natural reactors at Oklo and the first attempts to build artificial reactors, the fimdamental principles of chain reactions are discussed. In this context chain reactions with fast and thermal neutrons are covered as well as the process of neutron moderation. Criticality concepts (fission factor 77, criticality factor k) are discussed as well as reactor kinetics and the role of delayed neutrons. Examples of specific nuclear reactor types are presented briefly research reactors (TRIGA and ILL High Flux Reactor), and some reactor types used to drive nuclear power stations (pressurized water reactor [PWR], boiling water reactor [BWR], Reaktor Bolshoi Moshchnosti Kanalny [RBMK], fast breeder reactor [FBR]). The new concept of the accelerator-driven systems (ADS) is presented. The principle of fission weapons is outlined. Finally, the nuclear fuel cycle is briefly covered from mining, chemical isolation of the fuel and preparation of the fuel elements to reprocessing the spent fuel and conditioning for deposit in a final repository. 

In the following, the PWR will be discussed in some detail, followed by a brief discussion of the similar BWR. The RBMK and FBR will be presented as quite different possibilities. Finally, the accelerator-driven system (ADS) will be outlined as an attractive possibility for the future. 

Schematic sketch of the target assembly and core of an accelerator-driven system (ADS) (Bowmann et al. 1992)...

Although some of the long-lived fission products have thermal neutron capture cross sections suitable for transmutation in reasonable irradiation times, others do not and would require reactors with very high neutron fluxes to reduce inventories significantly. As a result, dedicated reactors with large thermal fluxes and/or dedicated accelerator-driven systems... 

The options for burning TRU include both thermal and fast critical reactors and thermal and fast-spectrum subcritical accelerator-driven systems (ADSs). O Figure 61.5 is a schematic of one of many possible transmutation schemes involving both aqueous partitioning and nonaqueous partitioning. 

Accelerator driven system (subcritical, hard spectrum, and high neutron flux)... 

For the AFC to be most effective and reduce the inventory of minor actinides at a reasonable rate, dedicated devices that produce a hard or fast neutron spectrum will be required. Such devices include the advanced liquid metal reactors (ALMRs), a fast reactor configured to operate as an actinide incinerator rather than breeder and accelerator-driven systems (ADSs). Fast reactor technology discussed earlier in this chapter is relatively mature whereas the development of ADS is in its infancy. Accelerator-based waste transmutation programs are ongoing in France, Japan, USA, and CERN. 

For an in-depth comparison of fast reactors and accelerator-driven systems for transmutation of actinides and long-lived fission products, see (OECD/NEA 2002). For more information on accelerator transmutation of waste (ATW) program in the USA, see refs. Jarvinen et al. (1992), LANE (1999), and DOE (2001). 

OECD/NEA (2002) Accelerator-driven systems (ADS) and fast reactors (FR). In Advanced nudear fuel cydes a comparative study, NEA Press, Paris Persson G, Wingefors S, Liljenzin JO, Svantesson I (1984) Radiochimica Acta 35 163... 

Ignatiev, V.V. 2003. Molten Salt Fuels for Nuclear Waste Transmutation in Accelerator Driven Systems. Review of National Accelerator Driven System Programmes for Partitioning and Transmutation. In Proceedings of an Advisory Group Meeting, Taejon, Republic of Korea. 

Abbreviations ADS Accelerator Driven System FP Fission Products MA Minor Actinides MOX Mixed oxide NPP Nuclear Power Plant UNF Used Nuclear Fuel... 

Oxide, metal alloy and inen matrix fuels and targets containing MA and Tc are fabricated, at a laboratory scale, and scheduled for irradiation. Concepts of nitride and molten salt fuels have been proposed for the advanced transmutation systems, e.g. actinide burners and accelerator driven systems. 

Several transmutation devices are being considered, such as fission reactors and accelerator driven systems. 

Beside LWRs and fast reactors, accelerator driven systems are getting increasing interest. The increase of proton currents by two orders of magnitude from the present level is a very challenging task. Further research is needed to clarify which accelerators with good transmutation rates could be used in the future. 

It is possible to use the SVBR reactor as a sub-critical blanket of a proton accelerator driven system for transmutation of long-lived radioactive waste [XIX-10]. 

XXV-2] GROMOV, B.F., et al.. Use of lead-bismuth coolant in nuclear reactors and accelerator-driven systems. Nuclear Engineering and Design, 173, pp. 207-217 (1997). 

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