The 9th Symposium on Accelerator Science and Technology, Tsukuba, Japan1993

Application of High Intensity Accelerator to Nuclear Engineering
Motoharu Mizumoto
Japan Atomic Energy Research InstituteTokai-mura, Naka-gun, lbaraki-ken, Japan, 319-11
Abstract
Many advances have been made in accelerator technology
during the past decade such as intense beam acceleration, highefficiency accelerating structure and RF source, improved beamhandling technique and so on. These progresses will make itpossible to apply the accelerator technology for new applications
in various nuclear engineering fields. The objective of this talk isto present new nuclear energy researches by use of theaccelerators, which can be realized only through the close
cooperation between experts of nuclear engineering and accelerator
technology.
I. Introduction
In nuclear engineering, almost all the types of acceleratorssuch as linear accelerator, Van de Graaff, cyclotron andsynchrotron have been extensively used to build up the data bases
for the nuclear data measurements, material sciences and isotope
productions. In addition to the handling of radiation andradioactive material, accelerators have many common technologies
to the nuclear engineering including precision machinery, computercontrol, beam diagnostics, high voltage power supply, radio
frequency source, high vacuum and so on. The technologies related
to the target which is bombarded by intense beam such as heattransfer and fluid, radiation shielding, neutronics calculation andradiation damage are of particular importance in both fields. The
relationship of these technologies is shown in Fig. 1.

Accelerator

placed on the waste depository can be substantially moderated. ·The Japanese Atomic Energy Commission concluded in1988 to strengthen the research and development on partitioningand transmutation of nuclear wastes of minor actinides and longlived fission products. The Science and Technology Agency
formulated a national program called OMEGA (Options Making
Extra Gains of Actinides and Fission Products). The accelerator
based transmutation system using the spallation reaction by highenergy proton beam is one of the options in the studies 1• As
compared with usual nuclear reactors, an accelerator based systemdoes not require a critical condition, and therefore it has thesignificant advantage of large criticality safety margin. The thermal
power of the subcritical core can be easily controlled by adjusting
the power of accelerated beam.
The technical and economic success of future fusion
reactors will depend on the endurance and availability of materials
suitable for the severe radiation environment. It is important toestimate the mechanical properties of material under high intensity
radiation fields, particularly, neutron field. It is, however, difficult
to extrapolate from low dose irradiation, due to non-linear effects
in the evolution towards end-of-life conditions and due to theabsence of a guide line theory. Irradiations in high flux reactors
and fast reactors are not valid for fusion conditions. It is generally
understood that only accelerator based neutron source can provide
the necessary source strength with the required neutron energy
distribution. Therefore, the availability of an accelerator based
neutron source is mandatory for a reliable prediction of thetechnical and economical feasibility for fusion reactor.
One of the most important devices, which contribute to theproduction of high temperature plasma in the tokamak type fusion,is the neutral beam injection (NBI) heating system. It shoulddeliver high power hydrogen or deuterium neutral beams to theplasma. The performances of the system are dependent on thedevelopment of positive ion source/accelerator which can produce
an ion beam current of tens of amperes at the beam energy of theorder of 100 keV

Nuclear Engineering
Fig. 1 Common Technologies for Accelerator and Nuclear
Engineering
In order to make nuclear technologies steady progress inpower generation and utilization of radiation, the effort has been
directed toward the following two major targets. One is thedevelopment of safer nuclear reactor and new alternative energy
resources. The other important aspect is to establish the radioactive
waste management technology. In the spent fuel of the nuclear
power reactor, minor actinides (MA: Np, Am and Cm) must be
isolated from the human living area for long period, because some
MA have long half lives exceeding 104 years. If the MAs aretransmuted to stable or short life nuclides, the technological burden-I-These three fields (nuclear transmutation, intense neutron
source and neutral beam injection) will be discussed in thispresentation as the examples where accelerator technologies will
be used for the nuclear engineering.
II. Nuclear Transmutation SystemA. Solid Target/Core System
Fig. 2 shows a conceptual flow diagram for an accelerator
based solid target transmutation system in combination with asubcritical reactor. The high energy proton beam of 1 GeV classand several tens of rnA bombards the tungsten target and produces
intense neutrons caused by spallation reaction and subsequentfission. The target and fuel assembly in the reactor are similar tothat used for the common fast breeder reactor with the sodiumcoolant. Nuclear spallation reactions and the following particle
transport processes are simulated using the intra-nuclear cascadecode and a three dimensional Monte Carlo transport codes. This
concept makes use of fast neutron flux, because most of MA
nuclides are only fissionable above the several hundred keVregion. Thermal hydraulics calculations are also performed toassure that the fuel and the cladding temperature stay below themaximum allowable temperature.
to Grid146 MWe

100 NWe

Proton Seam
1.5 GeV.39 rnA.

Fig.2 A Concept of Accelerator-Driven Actinide Transmutation
Solid Target/Core System
From the calculations for the proton beam with an energyof 1.5 Ge V and a beam current of 39 rnA, the system cantransmute the MAs produced by nearly ten LWR (Liquid WaterReactor). As a by-product, the maximum thermal output powersof 820 MW are obtained. This system also produces excess electric
power of about 246 MW, a part of which can be used to operate
the proton accelerator. Table 1 summarizes the operating conditions and characteristics of this accelerator transmutation system.
Table 1. Operating Conditions of the Accelerator-Driven
Transmutation Solid Target/Core System
Proton beam energy
Proton beam current
Actinide inventory

katNo. of neutrons
No. of fission (>15MeV)(<15MeV)
Neutron flux:
Mean neutron energy
BurnupMaximum temperature
OutputFuel
Clad

1.5 GeV
39mA
3160 kg
0.89
40 n/p0.45 f/p
100 f/p
4x1015 n/cm2s
690 keV
250 kg/y(8%/y)system based on the consideration about actinide solubility. The
system is calculated to have a power output of 1660 MW. In themolten-salt system, the most difficult heat removal problem
appears in heat exchanger. If the design condition had followed aconventional approach with external type heat exchanger, removalof 800 MW thermal power would require the total fuel volume
much larger than >10 t Of actinides. Highly efficient heatexchangers are essential in the molten-salt system to reduce thetotal volume of the primary loops.
Recently, the Los Alamos National Laboratory (LANL) has
being proposing an another unique molten-salt system, called theAccelerator Transmutation of Nuclear Waste (ATWt. The LANL
concept uses the extremely high thermal neutron flux of the orderof 1016 n/cm2s. Iii such a high thermal flux, actinides can betransmuted effectively by so-called two-step reaction (Actinides
capture neutrons and then fission with competition of short halflife 13 decay). Major advantages of this concept are that it can alsotransmute fission products effectively, and it can operate with avery small radioactive inventory. The system consists of a 150 rnA
class accelerator, a liquid lead (or lead-bismuth flowing target),and a surrounding heavy-water blanket. Actinide and fission
products are loaded in the heavy-water blanket. Most difficult
problems of the ATW system are radiation damage in target
container material, processing and separation chemistry due to theextremely high neutron flux.
C. Accelerator Development
The high-intensity proton linear accelerator (ETA:Engineering Test Accelerator) with an energy of 1.5 GeV andaverage current of 10 rnA has been proposed by JAERI5• Various
engineering tests will be performed using a high intensity
accelerator for the transmutation system before actual plant has
been constructed. The need for the development of such a highintensity proton linear accelerator (ETA) should be stressed for that
purpose. Nuclear spallation reactions with high energy proton
beams wi11 also produce various intense be3Jlls, that can be utilized
for other nuclear engineering applications. Those include materialsciences, radio isotope productions, nuclear data measurements andother basic sciences with proton, neutron and other secondary
beams in addition to nuclear waste transmutation.
The conceptual layout of the Engineering Test Accelerator(ETA) is shown in Fig.3. Iii the case of high intensity accelerator,
it is particularly important to minimize beam losses to avoid

473 °C890 oc528 ocB. Molten-Salt Target/Core System
Another advanced option for an accelerator-based nuclear
waste transmutation system3 is molten-salt target system. The main
advantage of molten-salt system is the capability of the continuous
on-line separation of fission products and spallation products fromthe fuel. Furthermore, process of actinide fuel fabrication is not
required. Although this system offers several attractive features forthe design of transmutation system, the actinide in the primarymolten-salt loops other than the core region occupies a
considerably large amount of the total inventory compared to thesolid system.
A preliminary conceptual design study is performed on an
800 MWt chloride molten-salt core/target which is chosen for thedamage and activation of the accelerator ~tructures. Because thebeam quality and maximum current are mainly determined by thelow energy portion of the accelerator, the accelerator (BTA) withan energy of 10 MeV and average current of 10 rnA is designed
and will be built as a first step in the ETA development6•7•
The accelerator cavities and rf system for high 13 structures
dominate the construction cost for ETA. The conceptual andoptimization studies for the ETA are performed concerning properchoice of operating frequency, energy configuration, type of high
13 structure based on the beam dynamics and mechanicalengineering considerations. RF source aspc;cts on the trade-offs
between large and small amplifiers are being investigated.
ill. Intense Neutron Source for Fusion Material Test

A proposal is made o~ a version of the D + Li (the FMITtype) neutron source called ESNIT (Energy Selective Neutron
Irradiation Test Facility) for resolving complex neutron energy
dependence in irradiation effects on materials8 • Attractive featuresof an accelerator-based source are the flexibility of controlling thequality and quantity of neutrons and the closer accessibility to insitu type experiments, which are essential for the studies withspecific neutron environments. The maximum fluence of about 0.5-2-

Engineering Test Accelerator (ETA)
LOWER ENERGY PARTHIGHER ENERGY PART

Basic Technology Accelerator (BTA)..........................................................
JiON SOURCEJ

JHIGH BETA ACCELERATOR STRUCTURE!

.................................................................
Fig.3 A Conceptual Layout of ETA and BTA
initiative to evaluate the neutron source requirements and theof a typicaldamagecreatecanwhich- 1
technologies for the next step fusion reactor DEMO. The muchcandidate fusion reactor material by around 10 dpa (displacement
intensive scheme called IFMIF (International Fusion Materialper atom).
Irradiation Facility) have been proposed with two deuteron beams.
Since the primary purpose for the ESNIT is the fusion
The beam would be generated by accelerator module capable ofreactor materials test, the peak energy of the neutron spectrum
delivering up to 250 rnA each with a total delivered current of 500
should be around 14 MeV. However, the neutron spectrum
rnA to 1A10 •contains a broad, high energy tail, and the basic research in theeffects of such components is the main object of the ESNIT. Thus,
IV. Neutral Beam Injection for Fusion Reactor
the deuteron energy is chosen 40 MeV to enhance the high energy
tail component and can be varied and selective with the 5 MeV
In the fusion device, one MeV class NBI system plays anstep.
important role in the plasma heating and the plasma current drive
The ESNIT injector section has three types of ion source,
for the steady state operation of the tokamak 11 • The role of thea low energy beam transport line and a radiofrequency quadrupole
high energy and high power ion source/accelerator in the fusion
negativedeuteron,linear accelerator (RFQ). It supplies positive
research becomes much more important. Charged particle beams
deuteron and hydrogen molecular ion beam. Typically a de D+
can not be injected into the plasma because of the strong magnetic
heam and a low duty pulsed D- beam are injected simultaneously.
field for plasma confinement. Hence, the ion beams must beThe most important issue for the accelerator system is to produce
converted into the plasma without being deflected by the magnetic
the well controlled and stable neutron field at the irradiation
fields. The high energy neutral particle If, D0, 'J'l injected into thevolume for a long period, several months to a year. Some ofplasma are ionized by the collisions with the plasma injection andspecifications of the preliminary design of the accelerator concept
electrons.
of the ESNIT are given in table 29 •The NBI system for the existing large tokamak such as
JT60 and the JET can deliver hydrogen or deuteron neutral beams
Table 2. Preliminary ESNIT Specifications
with the energy of 50 - 140 keV and injection power of 10 - 30
MW and contribute to the increase of plasma temperature up to 10Main characteristics-30 keY. These NBI systems utilize positive ion source which can120MHz
Frequency
produce 30 - 60 A of hydrogen or deuterium ion beams. The high10,15,20,25,30,25,30 MeV
Exit energy
energy ions contribute also to the direct fusion reaction whose50mA(cw)
Average current
effect improves the fusion gain. The neutral beams contribute toIon source
the supply of the fuel, the deuteron or tritons, in the core of the60mA max
D•!D-!H\plasma.
75keV
Output energy
lltmmmrad
Emittance(90%)
V. Summary
RFQ structure
2MeV
Exit energy
Recent advances in the accelerator technology appear to>90%
Transmission
make practical high intensity accelerators with the average beam
<1.5 kilpatrik
Max surface fieldcurrent up to the range of 100 rnA. Important applications of such
D1L
accelerators include nuclear waste transmutation and high intensity
1- 1.5McV/m
Field gradientneutron sources for material researches. The same technology can<0.01J1NmBeam spill
be applied to the Neutral Beam Injection for fusion plasma
RF sourceheating. The problems, which are still solved and developed, wouldlMW/unit x 9 set
Powerbe an activation by beam spill, stable and high current ion source
4.3SMW
Required power
development, high power RF source and heat removal in target andaccelerator structure. The necessary technologies for these
The International Energy Agency (lEA) is also taking anx1023

n/cm 2/year-3-problems are common to those in nuclear engineering fields. Highintensity accelerator will be realized in collaboration between
accelerator and nuclear engineers and will open up various newpractical and attractive research areas.

Acknowledgement
The author would like to thank Dr. Y. Kaneko and Dr. T.
Hiraoka for their encouragement and support in the present work.
He is also indebted to all the collaborators in Accelerator
Engineering Laboratory and Nuclear Spallation Study Group for
valuable discussions and suggestions.

References(1). Y. Kaneko, "The Intense Proton Accelerator Program", The
2nd Int. Symp. on Advanced Nuclear Energy Research, Mito,
1990, p 25.
(2). T. Takizuka et a!., "Conceptual Design Study of an
Accelerator-based Actinide Transmutation Plant with Sodiumcooled Solid Target/Core", the 2nd OECD/NEA Information
Exchange Meeting on Partitioning and Transmutation of Actinides
and Fission Products, ANL, Argonne, 1992
(3). H. Katsuta et a!., "A Continuous Transmutation System forLong-lived Nuclide with Accelerator-Driven Fuel Targets", ibid.
(4). E.D. Arthur, "A New Concept for Accelerator Driven
Transmutation of Nuclear Wastes", Fusion Technology vol.20(1991) 641-647.
(5). M. Mizumoto et a!., "High Intensity Proton Accelerator for
Nuclear Waste Transmutation", 1992 Linear AcceleratorConference Proceedings, 1992 August 24-28, Ottawa, Canada,C.R.Hoffman Editor, AECL-10728, p.749-751. (1992)(6). Y. Okumura et a!., "Development of A High Brightness Ion
Source for the Proton Linear Accelerator (BTA) at JAERI", ibid.
p.645-647(7). K. Hasegawa et a!., "Design Study on An RFQ for The BasicTechnology Accelerator in JAERI", ibid. p.314-316(8). K. Noda et a!. , "Capability of Energy Selective Neutron
Irradiation Test Facility (ESNIT) for Fusion Reactor Materials
Testing and the Status of ESNIT Program", Journal of NuclearMaterials, 191-194 (1992) 1367-1371(9). M. Sugimoto et a!., "Accelerator System for the Energy
Selective Neutron Irradiation Test Facility (ESNIT)", Journal ofNuclear Materials 191-194 (1992) 1432-1436(10). G.P. Lawrence et al., "A High-Flux Accelerator-Based
Neutron Source for Fusion Technology and Materials Testing",
Journal of Fusion Energy, Vol.8 Nos. 3/4, 201 (1989)(11). Y. Ohara, "Fusion Reactor Development Using High PowerParticle Beams", The 2nd Int. Symp. on Advanced Nuclear
Energy Research, Mito, 1990, p 120.

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