Renzo Takeda

Conceptual Design of Innovative Water Reactor for Flexible Fuel Cycle (FLWR) and its Recycle Characteristics

A concept of Innovative Water Reactor for Flexible Fuel Cycle (FLWR) has been proposed based on the well-experienced Light Water Reactor (LWR) technologies. The concept aims at effective and flexible utilization of the uranium and plutonium resources through the plutonium multiple recycling by the two stages. In the first stage, the FLWR core realizes a high conversion type core concept, which is basically intended to keep the smooth technical continuity from the current LWR and coming MOX-LWR technologies without significant gaps in technical point of view. The core in the second stage represents the Reduced-Moderation Water Reactor (RMWR) core concept, which realizes a high conversion ratio over 1.0, being useful for the long-term sustainable energy supply through the plutonium multiple recycling. The FLWR is a BWR-type reactor, and its core design is characterized by the short flat core, which consists of hexagonal-shaped fuel assemblies in the triangular-lattice fuel rod configuration with the highly enriched MOX fuel and Y-shaped control rods. The cores in both stages utilize the compatible and the same size fuel assemblies, and hence during the reactor operation period, the former concept can proceed to the latter in the same reactor system, corresponding flexibly to the expected change in the future circumstances of the natural uranium resource or establishment of an economical reprocessing technology of the MOX spent fuel. Detailed investigations have been performed on the core design, in conjunction with the other related studies, and the results obtained so far have shown the proposed concept is feasible and promising.

Quench simulation analysis of a superconducting coil

Abstract A quench simulation program has been developed with the intention of identifying a quench position in a superconducting coil and it has been applied to behaviour analysis of an artificially quenched superconducting coil. The superconducting coil is a solenoidal, bobbinless, and densely wound impregnated coil with many voltage terminals, thermocouples and heaters. The propagation of a normal zone was made two-dimensional by a one-turn-heater or three-dimensional by a point-heater set in the coil. The time-spatial changes in terminal voltages and temperatures agree well with those obtained from the simulation analysis within an accuracy of ± 10 ms or ± 1 mm. If accurate thermal properties of the materials constituting the superconducting coil are obtained, identification of the quench position in the coil should be possible. Normal front velocities and effective thermal conductivities of the radial, azimuthal and axial directions are also analysed from experimental results.

A Conceptual Design of a Fuel Bundle for Extended Burnup in Boiling Water Reactors

A new design concept of a boiling water reactor (BWR) fuel bundle for extended burnup was proposed to improve the capacity factor without increasing the fuel cycle cost. Some effects, which are raised from higher burnup, such as strong pellet-cladding interaction due to enhanced fuel swelling and changes in neutronic characteristics due to increased fuel enrichment, are minimized by a reduction in the maximum fuel temperature to below 1200/sup 0/C and an increase in the moderator-to-fuel ratio. To realize these concepts, a 9 X 9 lattice design with a reduced fuel rod diameter and annular pellets was proposed. The proposed fuel bundle design offers advantages in fuel cycle improvements through extension of achievable burnup and reduction of fuel inventory. The core, loaded with the proposed fuel bundles which achieve 30% higher burnup by the full power month, has a potential for natural uranium savings of about 20% per unit power and a reduction in the amount of reprocessing of about 40% per unit power, compared with the current BWR design when coupled with other improvements such as refueling pattern optimization, natural uranium axial blankets, and spectral shift with flow control.

Man--machine communication system for boiling water reactor core management planning

A man-machine communication system has been developed for boiling water reactor (BWR) core management planning to provide a very flexible tool, which is complementary to automated optimization programs that maximize or minimize one particular performance index under certain constraints. A three-dimensional BWR simulator, which can cover a wide range of BWR operating conditions, has been developed and coupled with a graphic display serving as a main input-output controlling device. The system has been successfully applied to generate a long-term control rod programming of a BWR in which locally poisoned fuel assemblies are loaded. The time required for one cycle analysis is approximately 3 h, out of which the actual computation time is only 4 min with an average of three trials of rod pattern search per exposure step. The quick response (5 sec) and the visualized results on the screen are very helpful in understanding the complicated characteristics of the BWR core, and it is found that this kind of tool has a very great educational effect. A similar approach is expected to be applied in other fields such as core design and safety analysis, as well as in core management.

Application of the Resource-Renewable Boiling Water Reactor for TRU Management and Long-Term Energy Supply

The RBWR (resource-renewable boiling water reactor) is an innovative BWR that has a capability to breed and burn trans-uranium elements (TRUs) using a multi-recycling process. The RBWR can be used as a long-term energy supply, and it reduces the negative environmental impact that TRUs cause as they are otherwise long-lived radioactive wastes. Various design concepts of the RBWR core have been proposed. The RBWR-AC is a break-even reactor and the RBWR-TB and RBWR-TB2 are TRU burners. The RBWR-TB is designed to burn TRUs from the RBWR-TB itself and to burn almost all the TRUs by repeating their recycling. The RBWR-TB is assumed to be applied for a nuclear power phase-out scenario. The RBWR-TB2 is intended to burn TRUs from LWR spent fuels. The RBWR-TB2 is assumed to be applied for reducing the amount of TRUs to be managed in storage facilities. The RBWR cores achieve their TRU multi-recycling capability under the constraint that the void reactivity coefficient must be negative by introducing the parfait core concept. This chapter reviews details of the specific design and core characteristics of the RBWR.

Conceptual design of a highburnup fuel rod for boiling water reactors using lowdensity UO/sub 2/ pellets of an annular type

Low density UO/sub 2/ fuel pellets of an annular type are used to solve two problems related to high-discharge burnup: the enhancement of the pellet/cladding mechanical interaction, which increases cladding permanent strain, and the increase in average neutron energy due to high enrichment, which changes the core neutronic characteristics. As an example, the design concept is applied to boiling water reactor fuel rods having 57 effective fullpower months (EFPMs). The fuel pellet density and the center hole diameter are determined to be 90% TD and 3.0 mm, respectively. The cladding permanent strain of the proposed fuel rod at EFPMs of 57 can be kept lower than the current fuel rod at 36 EFPMs. The EFPMs of 36 and 57 correspond respectively to the average discharge burnups of about 30 and 50 GWd/ tonne U. With an enrichment of 4.5 wt%, the former rods provide the same neutronic characteristics as that of current rods with 2.8 wt% enrichment. Furthermore, power generation cost in the newly designed core is reduced by about 10% from present cost levels.