Toshinobu Sasa

Neutronics design for lead-bismuth cooled accelerator-driven system for transmutation of minor actinide

Neutronics design study was performed for lead-bismuth cooled accelerator-driven system (ADS) to transmute minor actinides. Early study for ADS indicated two problems: a large burnup reactivity swing and a significant peaking factor. To solve these problems, effect of design parameters on neutronics characteristics were searched. The design parameters were initial plutonium loading, buffer region between spallation target and core, and zone fuel loading. Parametric survey calculations were performed considering fuel cycle consisting of burnup and recycle. The results showed that burnup reactivity swing depends on the plutonium fraction in the initial fuel loading, and the lead-bismuth buffer region and the two-zone loading were effective for solving the problems. Moreover, an optimum value for the effective multiplication factor was also evaluated using reactivity coefficients. From the result, the maximum allowable value of the effective multiplication factor for a practical ADS can be set at 0.97. Consequently, a new core concept combining the buffer region and the two-zone loading was proposed base on the results of the parametric survey.

Corrosion–erosion test of SS316 in flowing Pb–Bi

Abstract Corrosion tests of austenitic stainless tube were done under flowing Pb–Bi conditions for 3000 h at 450 °C. Specimens were 316SS produced as a tubing form with 13.8 mm outer diameter, 2 mm thickness and 40 cm length. During operation, maximum temperature, temperature difference and flow velocity of Pb–Bi at the specimen were kept at 450, 50 °C, and 1 m/s, respectively. After the test, specimen and components of the loop were cut and examined by optical microscope, SEM, EDX, WDX and X-ray diffraction. Pb–Bi adhered on the surface of the specimen even after Pb–Bi was drained out to the storage tank from the circulating loop. Results differed from a stagnant corrosion test in that the specimen surface became rough and the corrosion rate was maximally 0.1 mm/3000 h. Mass transfer from the high temperature to the lower temperature area was observed: crystals of Fe–Cr were found on the tube surface in the low-temperature region. The sizes of crystals varied from 0.1 to 0.2 mm. The depositing crystals were ferrite grains and the chemical composition ratio (mass%) of Fe to Cr was 9:1.

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.

Accelerator-driven system for transmutation of high-level waste

Abstract The accelerator-driven transmutation system has been studied at the Japan Atomic Energy Research Institute. This system is a hydrid system which consists of a high intensity accelerator, a spallation target and a subcritical core region. In the conceptual design study, two types of system concepts, sodium cooled and lead-bismuth cooled system, are being studied. In this study, we fucus on our lead-bismuth cooled accelerator-driven transmutation system to investigate basic characteristics. The fuel compositions were optimized for efficient transmutation of minor actinide. The transmutation of long-lived fission products was also considered.

Code development for the design study of the OMEGA Program accelerator-driven transmutation systems

Abstract The Japan Atomic Energy Research Institute carries out R&D on accelerator-driven transmutation systems (ADTS) under the national OMEGA program (Options Making Extra Gains from Actinides and fission products). The code system named ATRAS was developed to analyze neutronics and burnup characteristics of ADTS. It has a unique function of burnup analysis taking into account the effect of the spallation neutron source. ATRAS consists of a hadronic cascade code, a neutron transport code and a burnup analysis code. Utility programs for fuel exchange, pre-processing and post-processing were also incorporated. The neutronics design study of a spallation target as well as the analysis of the neutronics and burnup characteristics of the sodium-cooled ADTS were performed using ATRAS.

Light Charged-Particle Production in Proton-Induced Reactions on 12C, 27Al, 58Ni, 90Zr, 197Au, and 209Bi at 42 and 68 MeV

Double-differential cross sections (DDXs) have been measured for light-charged particle production in proton-induced reactions on 12C, 27Al, 58Ni, 90Zr, 197Au, and 209Bi at incident energies of 42 and 68 MeV. The measured DDXs for 12C, 27Al, and 58Ni are compared with the LA150 evaluation. Good overall agreement is found except for the (p, xd) reaction. The dependence of total yields of secondary charged-particles on target mass number is investigated.

Neutronics study on accelerator driven subcritical systems with thorium-based fuel for comparison between solid and molten-salt fuels

Abstract Since thorium is an abundant fertile material, there is hope for the thorium-cycle fuels for an accelerator driven subcritical system (ADS). The ADS utilizes neutrons, which are generated by high-energy protons of giga-electron-volt-grade, but cross sections for the interaction of high-energy particles are not available for use in current ADS engineering design. In this paper the neutron behavior in the ADS target based on the related experimental data is clarified, and the feasibility of the ADS regarding both the molten salts (Flibe: 7LiF-BeF2-ThF4-233UF4, chloride: NaCl-ThCl4-233UCl4) and oxide ([Th, 233U]O2) fuels is examined. The difference between the experiment and the calculated result at the ADS high-energy region is discussed. In a comparison of the fuels, the time evolution of keff and the beam current in the burning period are calculated. The calculated results suggest that the ADS with solid fuel has better future prospects than that with molten-salt fuels. The ADS with Flibe molten-salt fuel tends to require a high beam current and consequently needs the installation of a metallic spallation target and the continuous removal for fission products and protactinium. In comparison with the Flibe fuel, the ADS with chloride fuel has a flux distribution that is similar to a solid fuel reactor.

Effects of Grain Size on Ultrasonic Attenuation in Type 316L Stainless Steel

A lead bismuth eutectic (LBE) spallation target will be installed in the Target Test Facility (TEF-T) in the Japan Proton Accelerator Research Complex (J-PARC). The spallation target vessel filled with LBE is made of type 316L stainless steel. However, various damages, such as erosion/corrosion damage and liquid metal embrittlement caused by contact with flowing LBE at high temperature, and irradiation hardening caused by protons and neutrons, may be inflicted on the target vessel, which will deteriorate the steel and might break the vessel. To monitor the target vessel for prevention of an accident, an ultrasonic technique has been proposed to establish off-line evaluation for estimating vessel material status during the target maintenance period. Basic R&D must be carried out to clarify the dependency of ultrasonic wave propagation behavior on material microstructures and obtain fundamental knowledge. As a first step, ultrasonic waves scattered by the grains of type 316L stainless steel are investigated using new experimental and numerical approaches in the present study. The results show that the grain size can be evaluated exactly and quantitatively by calculating the attenuation coefficient of the ultrasonic waves scattered by the grains. The results also show that the scattering regimes of ultrasonic waves depend heavily on the ratio of wavelength to average grain size, and are dominated by grains of extraordinarily large size along the wave propagation path.

Measurement of Activation Reaction Rate Distributions in a Lead Assembly Bombarded with 500-MeV Protons

Abstract Reaction rate distributions of various activation detectors such as the natNi(n,x)58Co, 197Au(n,2n)196Au, and 197Au(n,4n)194Au reactions were measured to study the production and the transport of spallation neutrons in a lead assembly bombarded with protons of 500 MeV. The measured data were analyzed with the nucleon-meson transport code NMTC/JAERI combined with the MCNP4A code using the nuclide production cross sections based on the JENDL Dosimetry File and those calculated with the ALICE-F code. It was found that the NMTC/JAERI-MCNP4A calculations agreed well with the experiments for the low-energy-threshold reaction of natNi(n,x)58Co. With the increase of threshold energy, however, the calculation underestimated the experiments, especially above 20 MeV. The reason for the disagreement can be attributed to the underestimation of the neutron yield in the tens of mega-electron-volt regions by the NMTC/JAERI code.

Measurement of Double Differential Cross Sections of Secondary Charged-Particles Produced by Proton-Induced Reactions at Several Tens of MeV

Double differential cross sections (DDXs) were measured for production of light-charged particles in proton-induced reactions on 12C and 27A1 at two incident energies of 42 and 68 MeV. The measured DDXs were in generally good agreement with LA150 evaluation, except for (p, xd) reactions. The experimental angular distributions of proton elastic and inelastic scattering from 12C showed fairly good agreement with a coupled-channels calculation based on the soft-rotator model.