Nuclear Waste Transmutation Research Articles

Progress in fusion-driven hybrid system studies in China

The fusion-driven hybrid reactor studies have been performed for nearly 20 years in China to seek for early application of fusion energy. The overall progress is presented, including that in conceptual designs and related R&D activities of fusion-fission hybrid reactors for fissile nuclear fuel breeding or so-called fusion-driven sub-critical systems for both nuclear waste transmutation and fuel production. The further prospect of fusion-driven hybrid systems is given.

Multicavity proton cyclotron accelerator

A mechanism for acceleration of protons is described, in which energy gain occurs near cyclotron resonance as protons drift through a sequence of rotating-mode ${\mathrm{TE}}_{111}$ cylindrical cavities in a strong nearly uniform axial magnetic field. Cavity resonance frequencies decrease in sequence from one another with a fixed frequency interval $\ensuremath{\Delta}f$ between cavities, so that synchronism can be maintained between the rf fields and proton bunches injected at intervals of $1/\ensuremath{\Delta}f$. An example is presented in which a 122 mA, 1 MeV proton beam is accelerated to 961 MeV using a cascade of eight cavities in an 8.1 T magnetic field, with the first cavity resonant at 120 MHz and with $\ensuremath{\Delta}f\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}8\mathrm{MHz}$. Average acceleration gradient exceeds 40 MV/m, average effective shunt impedance is $223\mathrm{M}\ensuremath{\Omega}/\mathrm{m}$, but maximum surface field in the cavities does not exceed 7.2 MV/m. These features occur because protons make many orbital turns in each cavity and thus experience acceleration from each cavity field many times. Longitudinal and transverse stability appear to be intrinsic properties of the acceleration mechanism, and an example to illustrate this is presented. This acceleration concept could be developed into a proton accelerator for a high-power neutron spallation source, such as that required for transmutation of nuclear waste or driving a subcritical fission burner, provided a number of significant practical issues can be addressed.

SCANDAL - A Facility for Elastic Neutron Scattering Studies in the 50–130 MeV Range

Recently, a large number of applications involving high-energy (> 20 MeV) neutrons have become important. Examples are development of spallation sources, transmutation of nuclear waste, fast-neutron cancer therapy, as well as dose effects for airflight personnel and electronics failures due to cosmic-ray neutrons.Elastic neutron scattering plays a key role for the understanding of all these areas. The most important reason is that it allows a determination of the optical potential, which plays a decisive role in every microscopic calculation including neutrons in either the entrance or exit channel. In addition, the elastic cross section is also the largest of the individual partial cross sections contributing to the total cross section.A facility for detection of scattered neutrons in the energy interval 50–130 MeV, SCANDAL (SCAttered Nucleon Detection AssembLy), has recently been installed at the 20–180 MeV neutron beam facility of the The Svedberg Laboratory, Uppsala. It is primarily intended for studies of elastic neutron scattering, but can be used for the (n,p) t and (n,d) reaction experiments as well.The performance of the spectrometer is illustrated in measurements of the (n,p) and (n,n) reactions on 1H and 12 C at 96 MeV.

Neutron Cross Section Measurements at the Spallation Neutron Source

With the prospect of construction of the Spallation Neutron Source (SNS) at ORNL, and the fantastic high neutron flux, new, up to now impossible, experiments seem to be feasible in the fields of applied nuclear physics and astrophysics. These experiments will supply crucial neutron-induced cross section data for radionuclides, which are badly needed by many applied physics programs. The SNS will be uniquely suited for measuring the cross sections of interest to nuclear criticality safety, accelerator transmutation of nuclear waste (ATW), and heavy element nucleosynthesis for astrophysics. Because the sample sizes required at current facilities are usually too large for practical measurements, scarce information of these cross sections is available. Using the high neutron flux at the SNS will allow these measurements to be made with samples about 40 times smaller than at the next best facility. The large reduction in sample size at the SNS will result in orders of magnitude reduction in background from the radioactive samples and make them much easier to produce; hence, a much wider range of samples will be accessible for measurement at the SNS than at any other facility.

The Neutron Total Cross Section of 129I below 1 keV

Although the isotope 129I is known to be an important fission product of conventional nuclear power plants, only few measurements describe its properties in the resonance region 1,)2,)3 mainly because of sample procurement and handling problems. In order to improve nuclear data for nuclear waste transmutation purposes, time-of-flight measurements (TOF) of the total cross section of 129I have been performed in the energy range from 0.14eV up to 100keV at the white neutron source GELINA of the Institute of Reference Materials and Measurements (IRMM) in Geel, Belgium.The neutron resonance shape fitting program REFIT 4) was used to determine the energy E0, the radiative width Γγ and the neutron width Γn of the resonances.

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral of the 166mHo(n, γ167Ho Reaction using a Two-Step Irradiation Technique

The thermal neutron capture cross section (a0) and the resonance integral (I0) of 166mHo have been measured as data for the transmutation of nuclear waste. Samples of 166mHo were made by the neutron irradiation of 165Ho. Two metallic foils of 165Ho were irradiated for 2 weeks and two others for 3 weeks at the Kyoto University Reactor. A high purity Ge detector was employed for activity measurement. The samples irradiated were cooled for 3 months to reduce the activity of 166gHo. One of the samples irradiated for 2 weeks was irradiated again with Cd cover sheets and the other one without a Cd cover sheet. For the samples irradiated for 3 weeks, the same irradiation was performed. The 167Hon uclei were produced at the second irradiation via the neutron capture of 166mHo and the double neutron capture of 165Ho. The amount of 167Ho via the double capture was estimated from the difference between the data of 2 week irradiation and 3 week irradiation, and corrected. The reaction rate to produce 167Ho from 166mHo was analyzed by Westcott's convention. A resonance at 0.274 eV was considered in the analysis. The results obtained were 3.11±0.82kb for the a0 and 10.0±2.7 kb for the Ia of 166mHo.

Design study of lead-bismuth cooled ADS dedicated to nuclear waste transmutation

Research and development on nuclear waste transmutation are being carried out with a special emphasis placed on dedicated accelerator-driven systems at the Japan Atomic Energy Research Institute under the Japanese OMEGA Program. The reference accelerator-driven system design employs eutectic lead-bismuth as spallation target material and coolant. The fuel for the subcritical core is minor-actinide mononitride. The system consists of a 1.5GeV, 14mA proton accelerator and an 800MWt subcritical core with an effective neutron multiplication factor of 0.95. The transmutation rate of minor actinides is approximately 250 kg/y at 80% load factor. The design has salient features that the coolant inventory is large due to the tank-type configuration, the temperature rise through the core is relatively low, and the power conversion is operated on a saturated steam turbine cycle. These features make the plant response to a beam trip slow and much less demanding.

Partitioning and transmutation studies at JAERI both under OMEGA program and High-Intensity Proton Accelerator Project

At the Japan Atomic Energy Research Institute (JAERI), active and comprehensive studies on partitioning and transmutation (P&T) of long-lived nuclear waste from the reprocessing processes of spent fuel has been carried out under the OMEGA program. Studies at JAERI include a design study of dedicated transmutation systems both of an MA burner fast reactor (ABR) and an accelerator-driven subcritical system (ADS), and the development of a high intensity proton accelerator as well as the development of partitioning process, nitride fuel fabrication/dry separation process technologies and nuclear data studies. During the course of studies, JAERI developed the concept of the double-strata fuel cycle, in which a dedicated system is used for transmutation. Comparing the various transmutation systems, such as thermal neutron spectrum or fast neutron spectrum systems, power reactors or dedicated systems, from the viewpoints of reactor physics, nuclear fuel cycle and socio-technical issues, it was concluded that the ADS is the best option for transmutation of minor actinide(MA). JAERI, therefore, decided to concentrate its R&D efforts on the development of ADS and related technologies. One of the goals of R&D is to provide a basis for designing demonstration facilities of ADS, aqueous partitioning process and nitride fuel fabrication and dry separation technologies. As the initial step toward this purpose, the construction of an ADS experimental facility is planned under the High-Intensity Proton Accelerator Project which JAERI and the High Energy Accelerator Research Organization (KEK) are jointly proposing since 1998. The paper discusses the some of the results of P&T studies and the outline of the High-Intensity Proton Accelerator Project under which ADS experimental facility will be constructed.

Monte Carlo studies of accelerator driven systems: energy and spatial distribution of neutrons in multiplying and non-multiplying media

The LAHET code system is used to study the behaviour of the spallation neutrons resulting from the interaction of 2.5GeV/c protons with a massive lead target within a large (∼32m3) lead and graphite moderating environments. The spatial and energy distribution of the neutrons with presence and absence of a fissile material in Accelerator Driven Systems (ADS) are investigated.It is shown that the energy spectra of the neutrons in graphite and lead moderators are very different and such difference is expected to result in noticeable differences in the nuclear waste transmutation abilities of the ADSs that use graphite and lead for neutron moderation and storage.

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

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

High intensity ECR ion source (H+, D+, H−) developments at CEA/Saclay

Source of light ions with high intensities The (SILHI) source has been producing proton beams since 1996. The first aim is to produce up to 100 mA cw beams at 95 keV for the injector of protons for high intensity demonstrator. This prototype is developed by a CEA/DSM–CNRS/IN2P3 collaboration for applications such as accelerator driven systems for nuclear waste transmutation, production of radioactive ion beams, or secondary particles. To measure installation reliability, continuous 5 day long runs have been performed. In October 1999, a 99.96% availability was achieved with a single short beam off and a 103 H uninterrupted beam. A new extraction system leads to lower beam losses and higher LEBT transparency. SILHI now produces a 95 keV–130 mA total beam with a proton fraction higher than 80%. Up to a 157 mA (247 mA/cm2) total cw beam has been extracted. The new EPICS control system, electromagnetic interference hardened devices and automatic control procedures now allow us to do longer runs. To analyze the reliability of these upgrades, a 4 week test was planned. In the framework of the International Fusion Material Irradiation Facility project CEA participation, 135 mA–95 kV deuteron pulsed beams were produced. Extraction simulations and recent SILHI results are also presented. In addition, a new test bench has been recently developed to analyze H− beam production.

A Fusion Neutron Source Driven Sub-Critical Nuclear Energy System: A Way for Early Application of Fusion Technology

This paper proposes a sub-critical nuclear energy system driven by fusion neutron source, FDS, which can be used to transmute long-lived radioactive wastes and to produce fissile nuclear fuel as a way for early application of fusion technology. The necessity and feasibility to develop that system in China are illustrated on the basis of prediction of the demand of energy source in the first half of the 21th century, the status of current fission energy supply and the progress in fusion technology in the world. The characteristics of fusion neutron driver and the potential for transmutation of long-lived nuclear wastes and breeding of fissile nuclear fuel in a blanket are analyzed. A scenario of development steps is proposed.

129I targets for studies of nuclear waste transmutation

Nuclear incineration of long-lived fission products and minor actinides is being investigated as an alternative means of reactor waste disposal. 129I is of particular interest because of its long half-life and high mobility in the environment. Lead iodide targets of 129I for neutron capture cross-section measurements were prepared from 210 l fuel reprocessing waste solution containing 1.3 g l −1 iodine and other fission products. The iodine was separated by oxidation to I 2 and extraction into chloroform, reduction to iodide by sodium sulphite and re-extraction into an aqueous phase. Iodide was precipitated using lead nitrate and dried. The chemistry was carried out batch-wise using 400 ml starting solution each time and recycling the chloroform. An extraction efficiency of about 90%, determined by γ-ray spectrometry, was achieved.

The Pb–Bi cooled XADS status of development

In 1998, the research ministers of France, Italy and Spain have decided to set up a group of advisors for the definition of a common R&D European platform on accelerator driven systems (ADS). The advisors in turn, have established a Technical Working Group (TWG), chaired by Professor Carlo Rubbia, and now extended to the most part of the European Union member countries, in order to identify the critical technical issues for which R&D is needed. The recommendations of the TWG, included in the recently issued document `A European roadmap for developing ADS for nuclear waste incineration' [April 2001] clearly indicate the need to design and operate, approximately in 12–15 years, an XADS at a sufficiently large scale to assess the feasibility of an industrial ADS for transmutation of nuclear waste. The European Community, through the 5th Framework Program, has launched a large program on partitioning and transmutation. This program which includes R&D and preliminary design will constitute a reference for the choice of the technical solutions to be pursued forward during the 6th Framework Program. In Italy, since early 1998, the ENEA (National Research Organization for Innovative Energy), INFN (National Institute for Nuclear Physics), CRS4 (Research Institute) and Ansaldo have set up a team, led by Ansaldo, to design an 80 MWth XADS. The results obtained so far allow a consistent XADS configuration to be outlined. The main issues investigated and the associated solutions adopted are concisely described in the paper.

Spallation neutron production and the current intra-nuclear cascade and transport codes

A recent renascent interest in energetic proton-induced production of neutrons originates largely from the inception of projects for target stations of intense spallation neutron sources, like the planned European Spallation Source (ESS), accelerator-driven nuclear reactors, nuclear waste transmutation, and also from the application for radioactive beams. In the framework of such a neutron production, of major importance is the search for ways for the most efficient conversion of the primary beam energy into neutron production. Although the issue has been quite successfully addressed experimentally by varying the incident proton energy for various target materials and by covering a huge collection of different target geometries --providing an exhaustive matrix of benchmark data-- the ultimate challenge is to increase the predictive power of transport codes currently on the market. To scrutinize these codes, calculations of reaction cross-sections, hadronic interaction lengths, average neutron multiplicities, neutron multiplicity and energy distributions, and the development of hadronic showers are confronted with recent experimental data of the NESSI collaboration. Program packages like HERMES, LCS or MCNPX master the prevision of reaction cross-sections, hadronic interaction lengths, averaged neutron multiplicities and neutron multiplicity distributions in thick and thin targets for a wide spectrum of incident proton energies, geometrical shapes and materials of the target generally within less than 10% deviation, while production cross-section measurements for light charged particles on thin targets point out that appreciable distinctions exist within these models.

Application of ion beams to nuclear waste issues:: evaluation of nuclear ceramics

Oxide ceramics are promising matrices for nuclear waste immobilization or transmutation. The most important issue concerning these materials is the investigation of their physico-chemical properties with respect to safety criteria. This paper shows the potentiality of ion beams for the evaluation of ceramics as nuclear waste matrices. Several items are concerned. The different sources of radiation damage occurring in the reactor and during the storage term may be simulated by irradiation of the matrix with a variety of ions in a wide energy range. The doping of the material with foreign species produced by radioactive desintegration may be performed by ion implantation of stable or radioactive isotopes. The modifications induced in the matrices may be characterized by nuclear microanalysis techniques using medium-energy light ion beams. Examples relative to these various items are provided.

MEGAPIE, a 1 MW pilot experiment for a liquid metal spallation target

Megawatt pilot target experiment (MEGAPIE) is an initiative launched by Commisariat à l'Energie Atomique, Cadarache (France) and Forschungszentrum Karlsruhe (Germany) together with Paul Scherrer Institut (Switzerland), to demonstrate, in an international collaboration, the feasibility of a liquid lead bismuth target for spallation facilities at a beam power level of 1 MW. Such a target is under consideration for various concepts of accelerator driven systems (ADS) to be used in transmutation of nuclear waste and other applications world wide. It also has the potential of increasing significantly the thermal neutron flux available at the spallation neutron source SINQ for neutron scattering. SINQ's beam power being close to 1 MW already, this facility offers a unique opportunity to realize such an experiment with a reasonably small number of new ancillary systems. The paper describes the basic features of the experiment and its boundary conditions, the technical concept of the target and underlying research carried out at participating laboratories.

NEUTRON FLUCTUATIONS IN TRADITIONAL AND ACCELERATOR DRIVEN REACTORS

Classical particle transport, such as the diffusion and slowing down of neutrons in a multiplying system, is a random process. As a result, the number of neutrons in the system, or the number of detector counts, is a random number. Because of the branching property of the cascade, i.e. producing two or more neutrons in the fission process, correlations will exist between the neutrons in the system. This will lead to non-trivial statistics in the cascade, which, among others, carries information on the dynamical properties of the system. Neutron fluctuations have thus been used for a long time to measure either nuclear physics parameters such as the effective delayed neutron fraction, or the so-called multiplication constant, which describes the criticality properties of the system. In addition to the above described inherent random property of the particle transport in steady-state systems, another possibility of neutron fluctuations arises in systems whose properties fluctuate in time. This type of noise is observed in systems with high power. The reason for neutron fluctuations, that is neutron noise, is the fluctuations of the reactor material. There is boiling of the coolant, vibration of various components such as control rods, the core barrel etc., which all will lead to parametric excitation of the neutron noise. In this paper we shall however mostly deal with the neutron noise in low power systems, i.e. with inherent fluctuations of the neutron transport process, and the case of power reactor noise will only be touched upon. The neutron noise in low power systems has received a renewed strong interest recently, due to the appearance of a new concept, the so-called accelerator driven systems (ADS). An ADS is a subcritical reactor, driven by a strong external source, which utilizes spallation. The advantages of such a system is that it has excellent operational safety properties (a criticality accident is practically impossible), can utilize fertile nuclides as fuel such as thorium or U-238 easier than traditional reactors (hereby having access to more abundant fuel reserves as the current reactors), and finally, on the long run and with proper design, it would produce less high-level nuclear waste. As a matter of fact, an ADS can incinerate more waste than it produces, so it can also be used primarily for transmutation of nuclear waste with energy production as a by-product. In an ADS, however, the statistical properties of the neutron source are different from those of the classical radioactive sources that were used in the development of the theory in the past. A radioactive source emits one neutron at a time, and thus all source neutrons are independent (they obey Poisson statistics). In a spallation source, on the other hand, a large number of neutrons are produced in each spallation event, and the number of neutrons generated is a random number. Thus the source neutrons are correlated. In addition to time correlations, energy correlations may exist between spallation neutrons even if the neutron energies in a single spallation even are independent. This fact will be illustrated i the paper. All of the above mentioned (i.e. time and energy) correlations will influence the statistics of the neutrons in an ADS and thus they need to be accounted for.

MYRRHA: A multipurpose accelerator driven system for research & development

SCK·CEN, the Belgian Nuclear Research Centre, in partnership with IBA s.a., Ion Beam Applications, is designing an ADS prototype, MYRRHA, and is conducting an associated R&D programme. The project focuses primarily on research on structural materials, nuclear fuel, liquid metals and associated aspects, on subcritical reactor physics and subsequently on applications such as nuclear waste transmutation, radioisotope production and safety research on sub-critical systems. The MYRRHA system is intended to be a multipurpose R&D facility and is expected to become a new major research infrastructure for the European partners presently involved in the ADS Demo development. Ion Beam Applications is performing the accelerator development. Currently the preliminary conceptual design of the MYRRHA system is under way and an intensive R&D programme is assessing the points of greatest risk in the present design. This work will define the final choice of characteristics of the facility. In this paper, we will report on the status of the pre-design study as of June 2000 as well as on the methods and results of the R&D programme.

Proton-induced production of residual radionuclides in lead at intermediate energies

Integral excitation functions for the production of residual nuclides are basic quantities for the calculation of radioactive inventories of spallation targets in spallation neutron sources and in accelerator-driven devices for energy amplification or for transmutation of nuclear waste. We present comprehensive measurements of such data for the proton-induced production of residual nuclides from lead for proton energies between 64.8 MeV and 2.6 GeV. About 2000 individual cross-sections for 127 reactions were determined by means of off-line γ-spectrometry. The phenomenology of excitation functions which exhibit clearly distinguishable reaction modes like multi-fragmentation, three different types of asymmetric and symmetric fission and deep spallation is discussed. The experimental data are compared with calculations based on an intranuclear cascade/evaporation model in form of the LAHET code system. Together with earlier model exercises this comparison demonstrates the necessity for further improvements of models and codes if medium-energy activation cross-sections for applications shall be reliably predicted by theory. Today, experimental investigations remain indispensable.