Mitsuaki Yamaoka

An Axially and Radially Two-Zoned Large Liquid-Metal Fast Breeder Reactor Core Concept

A new core concept that has advantages over conventional homogeneous cores in neutronics characteristics such as power peaking factor, burnup reactivity loss, and reactivity response to the movement of control rods in earthquakes has been evolved. Two options of the new core concept are feasible. One is the so-called axially heterogeneous core, with the internal blanket placed at the lower part of the core. The other concept is similar to the conventional homogeneous core, but has two different plutonium-enriched zones in the axial as well as in the radial direction, so it is a hybrid type of the conventional homogeneous core and the axially heterogeneous core. The new design concept is described and the way that the core characteristics are improved by the chosen key parameters is shown.

Comprehensive analysis of passive safety test phase IIB in the fast flux test facility

Power Reactor and Nuclear Fuel Development Corporation (PNC), using computer codes developed and/or modified at PNC, has analyzed the Phase IIB passive safety test (PST) proposed for the Fast Flux Test Facility (FFTF). Major interests of PST are understanding core bowing and mitigating extremely low probRbility accidents. It is confirmed that the PNC code system is applicable to all aspects of the FFTF Phase IIB PST program. Results of the pretest analysis indicate that the proposed Phase IIB PST in FFTF can be devised to provide very useful data for validation of the analytical models that treat reactivity feedback effects due to core bowing. Recommendations to the test program are also made

An application of metal fuel cycle technology toward self-consistent nuclear energy system (SCNES) concept

A fast reactor core and fuel cycle concept has been discussed for Self-Consistent Nuclear Energy System (SCNES) concept. This paper discussed loading material candidates for long-lived fission products (LLFPs) and LLFPs burning capability. Some of LLFPs were possible to be loaded in metal of the generated form. The potential for LLFP-confinement in the reactor system is discussed along with metallic fuel cycle concept. The proposed fuel cycle scheme is a successful candidate for SCNES concept.

Intra-pellet neutron flux distribution measurements in LWR critical lattices

We have developed inexpensive and easy-handling measurement methods on intra-pellet neutron flux. A foil activation method with metallic foils, which were fabricated by punching out technique and etching technique to reduce fabrication error and positioning error, was used for the intra-pellet neutron flux distribution measurement. The developed method was applied to measure intra-pellet neutron flux distributions in a reduced–moderation light water reactor (LWR) lattices, and uncertainty of the distributions was estimated to be 1% to 2%. Measured values were analyzed with a continuous energy Monte Carlo code. Comparison of measurements and analyses revealed that the developed method is useful for the validation of an advanced fuel design method considering neutron behavior in fuel pellets.

Physics Benchmark Experiments and Analysis for Reflector-Control-Type Small Fast Reactors at TOSHIBA Nuclear Critical Assembly

New physics benchmark experiments were successfully accomplished in order to study the basic characteristics of a reflector controlled small reactor 4S and to validate core design methods using Toshiba NCA critical facility. The experience gained through the analyses provides rationality of nuclear design methodology and nuclear library. Continuous Monte Carlo transport calculation method using JENDL3.2 enables core designers to predict reflector control characteristics with high reliability. Prediction accuracy for burn-up characteristics is needed for further design activity.

Experimental Study on Reactivity Worth of Burnable Poison in Ultra-Long Life, Small LMR

Experimental study using an LWR-type critical assembly, NCA, has been conducted on the reactivity worth of the burnable poison (BP) that is employed in a small reactor, 4S, for achieving an extremely long core life. The experimental BP is composed of natural gadolinium oxide (Gd2 O3 ) mixed in polyethylene. Three types of BPs are prepared: polyethylene without Gd, polyethylene with Gd/H ratio of 0.015at% and 0.943at%. Reactivity worth of each BP assembly is measured through change in critical water height. Power profile of fuel rods and flux profile are also measured. Analyses are conducted with a Monte-Carlo code, MCNP.Copyright

Investigation of failed fuel detection and location using a flux tilting method in a fast breeder reactor

Detection and location of failed fuel in a liquid-metal fast breeder reactor (LMFBR) are very important both for safety and availability. When a fuel failure is detected, it is desirable to identify the failed subassembly quickly to reduce plant shutdown time. The flux tilting method is expected to effectively identify the defective subassembly. The feasibility of the flux tilting method is investigated for an LMFBR with a 100-MW (electric) homogeneous core. A numerical simulation is performed to estimate the viability of the flux tilting method, and a combination of the flux tilting method and the sipping method is found to be very effective in identifying the failed subassembly. In this paper a functional scheme for a computer-aided failed fuel detection and location system is discussed as part of a future on-line support system.

An Axially Multilayered Low Void Worth Liquid-Metal Fast Breeder Reactor Core Concept

A new core concept with a negative sodium void reactivity coefficient has evolved. The core is composed of two core layers in the axial direction. The core layers are separated by an internal blanket, the central region of which comprises a neutron-absorbing material such as boron carbide or tantalum. Consequently, the two core layers are completely decoupled as regards neutronics, leading to an effective increase in neutron leakage from the core region when sodium is voided. This design is expected to be free from the disadvantages of a large core radius, as seen in a conventional spoiled core such as a pancake core. In this paper the design is described in detail, and its application to a 300-MW (electronic) metal fuel core and to a 450-MW (electric) minor actinide burned core is given as an example.

Development of Uranium-Free TRU Metallic Fuel Fast Reactor Core

A TRU-burning fast reactor cycle associated with a uranium-free trans-uranium (TRU) metallic fuel core is one of the solutions for radioactive waste management issue. Use of TRU metallic fuel without uranium makes it possible to maximize the TRU transmutation rate in comparison with uranium and plutonium mixed-oxide fuel because it prevents the fuel itself from producing new plutonium and minor actinides, and furthermore because metallic fuel has much smaller capture-to-fission ratios of TRU than those of mixed-oxide fuel. Also, adoption of metallic fuel enables recycling system to be less challenging, even for uranium-free fuel, because a conventional scheme of fuel recycling by electrorefining and injection casting is applicable.

Void reactivity evaluation by modified conversion ratio measurements in LWR critical experiments

We have developed a void reactivity evaluation method by using modified conversion ratio measurements in a light water reactor (LWR) critical lattice. Assembly-wise void reactivity is evaluated from the “finite neutron multiplication factor”, k*, deduced from the modified conversion ratio of each fuel rod. The distributions of modified conversion ratio and k* on a reduced-moderation LWR lattice, for which the improvement of negative void reactivity is a serious issue, were measured. Measured values were analyzed with a continuous-energy Monte Carlo method. The measurements and analyses agreed within the measurement uncertainty. The developed method is useful for validating the nuclear design methodology concerning void reactivity.