S-P2-2
Accelerator-based Neutron Source and Its Application
加速器による中性子源と応用
Kazufumi Tsujimoto
辻本 和文
The Japan Atomic Eneryg Agency
2-4, Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1195, Japan
日本原子力研究開発機構 〒319-1195 茨城県那珂郡東海村白方白根2-4
Neutron beam is used for a wide variety of scientific and engineering research, such as materials and life
science, and industrial applications. There are three kinds of neutron sources: (1) isotopic neutron

source, (2) reactor sources, and (3) accelerator-based neutron sources. Recently, high intensity
spallation neutron sources with high energy proton accelerator became to offer similarcapabilities to research reactors, as well as a few extra features. In Japan, the JSNS (JapanSpallation Neutron Source) was constructed and operated at J-PARC (Japan Proton Accelerator
Research Complex). Moreover, as future utilization of spallation neutron, research anddevelopment for accelerator-driven subcritical system have been performed.
1. Introduction
The utilization of neutrons started several years
after the discovery of neutron by Chadwick. At
present, neutron beam is used for a wide varietyof scientific and engineering research, such as
materials and life science, and industrial
applications. It has been one of the key elements
of modern science and technology.
There are three kinds of neutron sources: (1)isotopic neutron source, (2) reactor sources, and (3)accelerator-based neutron sources. Isotopic source
using alpha particles emitters and beryllium, andspontaneous fission have fundamental limitations interms of the maximum intensity. So, reactor sources
and accelerator-based source are widely used forscience and industrial purposes. Although research
reactors have been utilized as intense neutron
source for a long time, high intensity spallation
neutron sources with high energy proton accelerator
recently became to offer similar capabilities toresearch reactors, as well as a few extra features. InJapan, the JSNS (Japan Spallation Neutron Source)
was constructed and operated at J-PARC (JapanProton Accelerator Research Complex).
In this paper, general description of the JSNS andacceleratod-driven subcritical system (ADS) as
future application of spallation neutron source arepresented.
2. Spallation Neutron Source and its Application
2.1 JSNS in J-PARC
The J-PARC is the multi-purpose researchcomplex, which consists of three accelerators: 181

MeV LINAC, 3 GeV RCS and 50 GeV
synchrotoron, and four major experimental
facilities: MLF, Nuclear and Particle Physics
Facility (Hadron Facility and Neutrino Facility),and Transmutation Experimental Facility [1,2].
The JSNS target station in the MLF was shown
schematically in Fig.1[3]. At the center of thestation the mercury target is set, which is designed
to accept 1-MW proton beam of 333 μA accelerated
to 3 GeV by the RCS with a pulse repetition rate of25 Hz. Mercury is selected as a target from theviewpoint of heat removal in the target vessel andneutrons yield efficiency due to its high weight
density of 13.6 kg/m3 at 300 K and high atomic
number of 80. The target system consisting of aheat exchanger, a surge tank and a compact rotatedmagnetic pump is installed on the target trolley. Thetarget vessel, a so-called cross-flow-type, consistsof multi-walled vessels to avoid the mercury
leakage into the helium vessel in the case of theTarget station
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S h tu et rs

TC yr o g e
n i c h yd r o egnra g e tv e s s el & Tor l el ysy s te m

Mercury target
Proton beamwindowTBeam duct

Target trolleyMo d e
r a to rs

Fig.1 Main components of JSNS at MLF in J-PARC

ra g e t

mercury vessel failure. Supercritical hydrogen issupplied for the three moderators through acryogenic hydrogen system. [4]Total 23 neutron beams are extracted from themoderators. The neutron beams are controlled onand off for measurement and sample exchange,respectively, by neutron beam shutters which areequipped independently for each beam line. In May
2008, the JSNS was firstly accepted the proton
beam accelerated by the LINAC and 3 GeV RCS
accelerators in the MLF. After deliberateadjustment through in-beam commissioning, theMLF was opened for users in Dec. 2008. Until
March 2011, the routine operation was carried out
with 120 kW.
2.2 Accelerator-driven Subcritical System (ADS)
Reduction of burden caused by radioactive waste
management is one of the most critical issues forthe sustainable utilization of nuclear power. The
Partitioning and Transmutation (P&T) technology
provides the possibility to reduce the amount of theradiotoxic inventory of the high-level radioactive
waste (HLW) dramatically and to extend therepository capacity. The accelerator-driven system(ADS) is regarded as a powerful tool to effectivelytransmute minor actinides (MAs) in the“double-strata” fuel cycle strategy.
The Japan Atomic Energy Agency (JAEA) has
been conducting the research and development(R&D) on ADS as a dedicated system for thetransmutation of long-lived radioactive nuclides.
The ADS proposed by JAEA [5] is a tank-typesubcritical reactor, where lead-bismuth eutectic(LBE) is used as both the primary coolant and thespallation target, as shown in Fig.2. The central partof the core is the spallation target region. In theM ovable support

Bending magnet

Proton beam

Fuel exchanger
Beam ductPrimary pum p

Steam generator

Spallation target

Reactor vessel
Subcritical core
Beam window

Core support

Fig.2 Conceptual design of LBE cooled ADS

target region, LBE is flowing from the core bottom.
It is assumed to use a super-conducting linear
accelerator delivering protons with energy of 1.5
GeV. The system is designed to generate 800 MWof thermal power.
For the core fuel, (MA,Pu)-nitride is used. As
inert matrix, zirconium-nitride (ZrN) is used withthe fuel. To minimize the burnup swing and thepower peaking, the fuel region is divided into twozones with the different initial Pu loading. The MA
inventory is about 2500 kg. Since the transmutation
rate of MA is 250 kg/yr as described before, therelative transmutation efficiency of MA is about
10 %/yr. The maximum keff during whole burnup
cycles was set to 0.97. The burnup swing in wholecycles is about 3 %k/k. The maximum beam
current is 20 mA (30 MW).
To study the basic characteristics of the ADS andto demonstrate its feasibility from viewpoint of thereactor physics and the spallation target engineering,
JAEA plans to build the Transmutation
Experimental Facility (TEF) in the second phase ofJ-PARC.
3. Conclusion
For the JSNS, after the proton beam injected
into the target in May 2008, we have learned many
lessons were learned through expected andunexpected experiences. R&Ds still are needed tosolve a sort of issues relating to unexpected results
and increase the power.
As the future application of spallation neutron,
JAEA has been promoting various R&D activities
on ADS. Items of R&D are divided into threetechnical areas peculiar to the ADS: (1)superconducting linear accelerator, (2) LBE asspallation target and core coolant, and (3)subcritical core design and technology. For thesetechnical areas, various R&D activities areprogressing in JAEA.
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