Kyoto University Research Reactor

Kyoto University Research Reactor (KUR) is a light-water moderated tank-type reactor operated at the rated thermal power of 5 MW. The core consists of plate-type fuel elements using about 20% enriched uranium and graphite reflector elements. KUR is operated by using four shim rods and a regulating rod; those are made of the stainless steel containing boron. The core is constructed at the bottom of the aluminum core tank with the size of 2-m diameter and 8-m depth, which is filled with light-water.

KUR is widely used for the experimental studies in physics, chemistry, biology, engineering, agriculture, medicine etc. Since its first criticality in 1964, it has been successfully operated for over than 40 years, and has served as one of the most useful inter-university research reactors in Japan.

By reflecting the accident of TEPCO’s Fukushima-Daiichi Nuclear Power Plant which occurred in March 11th 2011, the safety review of KUR has been performed to confirm the integrity for the loss of all power supply and cooling function. Moreover, we have been working on the safety enhancement of KUR by setting up the additional safety equipments etc. to achieve the higher level of safety.

Kyoto University Research Reactor
Kyoto University Research Reactor


Experimental Facilities in KUR

1) Hydraulic Conveyer
The neutron irradiation equipment is positioned at the center of the reactor core, and the sample can be irradiated for 70h (one week) at maximum with an aluminum capsule in a thermal neutron flux of 8.2 x 1013 n/cm²/s, which is the highest neutron flux in the KUR. The tube is used for the irradiation of high-dose and the isotope production of highly specific activity.
2) Pneumatic Tubes
There are three pneumatic systems, Pn-1, Pn-2 and Pn-3, for the neutron irradiation with a polyethylene capsule. The irradiation position is in the graphite reflector beside the core and thermal neutron fluxes are 1.9 x 1013, 2.8 x 1013 and 2.3 x 1013n/cm²/s for the three systems, respectively. The irradiation time is limited to shorter than one hour.
3) Slant Exposure Tube
Large-size samples can be irradiated using the slant tube with a thermal neutron flux of 3.9 x 1012n/cm²/s. The irradiation position is at the outside of, and adjacent to, the graphite reflector.
4) B-1:Filtered Beam Hole
An iron-filtered beam facility was installed in the beam hole B- 1 with an iron-filter of 45 cm in thickness and an aluminum filter of 35 cm in thickness to obtain quasi-monochromatic neutrons near 24keV. The characteristic neutron spectra were studied by a transport calculation and also by measurements using a spherical proton recoil counter and activation foils. The neutron flux at 24 keV was estimated to be about 6.8×106n/cm²/s behind the filters. The absorbed doses just behind the filters and the position at 50 cm behind the filters were about 1 Gy/h and about 0.05 Gy/h, respectively.

Heavy Water Neutron lrradiation Facility

The Heavy Water Neutron Irradiation Facility (HWNIF) was updated in March 1996, mainly for an improvement in boron neutron capture therapy (BNCT). The main purposes of the updating were as follows: (i) an improvement in the safety and maintainability of the facility, (ii) an improvement in the performance for BNCT utilizing both thermal and epi-thermal neutrons, and (iii) the realization of BNCT clinical irradiations during full-power continuous KUR operation.
This facility has a heavy water tank of approximately 2 m3 adjacent to the KUR core. In the heavy water tank, an aluminium-heavy water mixture (Al/D2O=80/20 in volume percent), and a neutron-energy spectrum shifter of heavy water whose thickness changed from 0 to 90cm, are installed in order from the core side. Outside of the spectrum shifter, two thermal neutron filters of 1mm-thick cadmium plate are installed. The energy spectrum of the neutron beam can be controlled from almost pure thermal to epi-thermal within five minutes by remote control under a continuous reactor operation.
After the updating, the KUR Advanced Irradiation System for BNCT was organized. Clinical irradiation utilization under the full-power continuous KUR operation can be performed by employing both a Radiation Shielding System consisting of a shielding door and an irradiation room, and a Remote Carrying System for a patient. The safety and utility of the facility are kept by the Safety Observation System.
As of the end of July 2018, 510 BNCT clinical irradiations have been performed, namely, 254 for brain tumours, 193 for head and neck tumours, 27 for malignant melanomas, 44 for lung tumours, 10 for liver tumours, and 19 for tumours of the other body-parts, using the three standard irradiation modes of thermal-neutron, mixed-neutron and epi-thermal neutron.

Heavy Water Neutron lrradiation Facility
Heavy Water Neutron lrradiation Facility

KUR Neutron Guide Tube

When low energy neutrons are incident on a nickel mirror evaporated on an optically flat glass, total reflection occurs below the critical angle which is a function of the reflecting material and neutron wavelength. The long neutron guide tubes utilizing the total reflection of the nickel mirror were constructed in E-3 as the first neutron guide tube in Japan, for extracting thermal neutrons to a distant wide experimental hall of 10 meters away from the reactor. The nickel/titan supermirror composed of layers whose thickness are varied gradually layer by layer, has a reflective angle larger than the total reflection angle and reflects neutrons with a wavelength range shorter than the nickel mirror. The supermirror guide tube in B4 is the first one in the world. The neutron flux at the exits are  2 x 106n/cm²/s (E3 for prompt gamma-ray analysis for BNCT), 5 x l07n/cm²/s(B4 for neutron imaging), 5 x 107n/cm²/s(CN-2 for SANS) and 2 x 107n/cm²/s(CN-3 for neutron reflectometry and neutron device development).

Slow Positron Beam System (B−1)

The Slow Positron Beam System provides positron beams through the electron-positron pair-creation reaction with reactor γ-rays for materials analysis by positron annihilation spectroscopy. Positrons with energies of about 10 eV generated at the source position are extracted and fed into the beam line, accelerated up to 30 keV before irradiating samples. Positrons recombine with electrons and emit two γ-rays each of 0.511 MeV. Positron lifetimes and Doppler broadening can be measured from the emission time and the energy dispersion of annihilation γ-rays. It is well known that when positrons annihilate at atomic-scale vacant spaces such as vacancies and voids, positron lifetimes get longer and also Doppler broadening is influenced. It is possible to obtain information of vacant spaces based on these phenomena.

Neutron Imaging Facilities (E-2 & B-4)

Neutron imaging can be performed using thermal neutrons generated in the Kyoto University Research Reactor (KUR), which has two irradiation port; E-2 port and B-4 guide tube room. E-2 port is located in the reactor room of the KUR, which has relatively large field of view (ϕ15mm) with the thermal neutron flux of 3.2×105n/cm2s. This port is mostly utilized to obtain the static images including 3-D computed tomography. B-4 neutron guide tube facility has the world’s first super mirror neutron guide tube. The thermal neutron flux of B-4 port is 5×107n/cm2s at 5MW thermal power of the KUR and it is possible to apply not only for static image acquisition but also for dynamic imaging using a high speed camera combined with an image intensifier.B-4 guide tube room is equipped with a stabilized DC power supply (max. 20 V, 1200 A) and a cooling water unit for boiling two-phase flow researches. Furthermore, X-ray imaging system has been installed for complementary use to neutron imaging.
Boiling two-phase flow loop at B-4 guide tube room

Material Controlled lrradiation Facility

This facility has an improved control capability of irradiation conditions, such as irradiation temperature and atmosphere. The irradiation temperature of specimen is between 340K and 773K. The neutron flux is 9.4 x 1012n/cm²/sec (E>0.1MeV) and 3.8×1013n/cm²/sec (all). The maximum size of specimen is Ø38mm x 60mm. The photo is the specimen loading chamber.
Material Controlled lrradiation Facility
Material Controlled lrradiation Facility

On-Line Isotope Separator (T-1 Through Tube)

The On-Line Isotope Separator (ISOL) is an apparatus used to study short-lived nuclides produced by thermal neutron fission reaction. A target of 93% enriched 235U is irradiated by a thermal-neutron flux of 3 × 1012 n/cm²/s and produced fission fragments are transported to an ion source by a gas-jet within a few seconds. The ionized activities are extracted from the ion source and accelerated up to 30 keV. They are electromagnetically focused and mass-separated to form a chemically pure atomic beam of the nuclides to be studied.
In this system, a surface ionization ion source is employed to ionize efficiently alkali elements (Rb, Cs), alkali-earth elements (Sr, Ba) and light rare-earth elements (La, Ce, Pr, Pm and Nd). The RI beams thus obtained are used to study the nuclear structure by nuclear spectroscopy, and to apply nuclear methods to solid state physics by, e.g., a perturbed angular correlation (PAC) technique. A post accelerator is equipped to implant the RI ions with the kinetic energy of up to 200 keV.

On-Line Isotope Separator
On-Line Isotope Separator


Small-angle neutron scattering (SANS) is an experimental method to analyze nanostructure and frequently used for various materials such as polymers, micelles, proteins, metals, and magnetic materials. A SANS instrument equipped with a multilayer monochromator, a 3He two-dimensional detector, and a transmission monitor is installed at CN-2. Compared to a neutron velocity selector used at general SANS instruments, the multilayer monochromator is compact, highly stable, and easily maintained. The wavelengths of 0.3 nm and 0.46 nm are available. A magnetic field of 0.5 T can be applied to the sample. The data acquisition system operates in an event-recording mode, which enables flexible data reduction.


Quasi-Monochromatic Neutron Beam Tube No.1

Iron (Fe) has a deep minimum (~0.4 b) in the neutron total cross section at 24.3 keV. As a result, neutrons near to the minimum are efficiently transmitted through thick Fe-filters, as a neutron window. Quasi-monochromatic neutrons near to 24 keV can be obtained by applying this property from a continuous spectrum in a reactor. Thick Fe-filters have been installed in beam tube No.1 (B-1) of the Kyoto University Research Reactor (KUR). By making reactor neutrons penetrate through Fe-filters of 45cm in total thickness mixed with aluminum (Al) filters of 35cm in total thickness, a Fe-filtered neutron beam at 24 keV has been extracted. The following characteristics have been achieved: (1) The neutron flux of the Fe-filtered neutrons at 24 keV is about 8 x 106n/cm²/s at the deepest position of the B-1 tube, and (2) the gamma-ray dose is about 1 Gy/h. At the irradiation position of 46 cm behind the filters, the neutron flux is about 5 x 105 n/cm²/s, the gamma-ray dose about 0.023 Gy/h and the absorbed dose 0.055 Gy/h. This facility is very useful for fundamental studies in, biology, medicine, physics, engineering, detector/dosimeter calibrations and so on.