Steady State Analysis of Small Molten Salt Reactor : Effect of Fuel Salt Flow on Reactor Characteristics

The Molten Salt Reactor (MSR) is a thermal neutron reactor with graphite moderation and operates on the thorium-uranium fuel cycle. The feature of the MSR is that fuel salt flows inside the reactor during the nuclear fission reaction. In the previous study, the authors developed numerical model with which to simulate the effects of fuel salt flow on the reactor characteristics. In this study, we apply the model to the steady-state analysis of a small MSR system and estimate the effects of fuel flow. The model consists of two-group neutron diffusion equations for fast and thermal neutron fluxes, transport equations for six-group delayed neutron precursors and energy conservation equations for fuel salt and the graphite moderator. The following results are obtained: (1) in the rated operation condition, the peaks of the neutron fluxes slightly move toward the bottom from the center of the reactor and the delayed neutron precursors are significantly carried by the fuel salt flow, and (2) the extension of residence time in the external-loop system and the rise of the fuel inflow temperature show weak negative reactivity effects, which decrease the neutron multiplication factor of the small MSR system.・rights：日本機械学会・rights：本文データは学協会の許諾に基づきCiNiiから複製したものである・relation：isVersionOf：http://ci.nii.ac.jp/naid/110004820225

Fluid Motion and Heat Transmission in a Horizontal Liquid Layer Heated Locally from Free Surface

Heat transfer from a heated wire and a heated vertical plate, located just below a liquid surface, was studied experimentally. The curve representing the heat transfer coefficient as a function of the temperature difference between the heaters and a cooled tray could be divided into four parts. The range of each part depended strongly upon the size of the heaters, the depth of the tray and the liquid properties. The mechanism of heat transfer from the heaters in each part was discussed. The following observations were made. In the first part, where the temperature difference was the smallest, convective heat transfer was obscured by conduction. The heat transfer was mainly due to natural convection in the second part, and was mainly due to Marangoni convection in the fourth part. The third part could be considered as a transition regime. Furthermore, it was found that the transition was suppressed by the meniscus of the liquid surface which was in contact with the heaters.・rights：日本機械学会・rights：本文データは学協会の許諾に基づきCiNiiから複製したものである・relation：isVersionOf：http://ci.nii.ac.jp/naid/110002981408

A road map for the realization of global-scale thorium breeding fuel cycle by single molten-fluoride flow. Energy Conversion and Management 49

Abstract For global survival, we need to launch a rapid regeneration of the nuclear power industry. The replacement of the present fossil fuel industry requires a doubling time for alternative energy sources of 5-7 years and only nuclear energy has the capability to achieve this. The liquid metal cooled fast breeder reactors (LMFBR) have the best breeding criteria but the doubling time exceeds 20 years. Further, the use of plutonium in these systems has the potential of nuclear proliferation. The Thorium Molten-Salt Nuclear Energy Synergetic System [THORIMS-NES], described here is a symbiotic system, based on the thorium-uranium-233 cycle. The production of trans-uranium elements is essentially absent in Th-U system, which simplifies the issue of nuclear waste management. The use of 233 U contaminated with 232 U as fissile material, instead of plutonium/ 235 U makes this system nuclear proliferation resistant. The energy is produced in molten-salt reactors (FUJI) and fissile 233 U is produced by spallation in Accelerator Molten-Salt Breeders (AMSB). This system uses the multi-functional ''single-phase molten-fluoride" circulation system for all operations. There are no difficulties relating to ''radiation-damage", ''heat-removal" and ''chemical processing" owing to the simple ''idealistic ionic liquid" character of the fuel. FUJI is size-flexible, and can use all kinds of fissile material achieving a nearly fuel self-sustaining condition without continuous chemical processing of fuel salt and without core-graphite replacement for the life of the reactor. The AMSB is based on a single-fluid molten-salt target/blanket concept. Several AMSBs can be accommodated in regional centers for the production of fissile 233 U, with batch chemical processing including radio-waste management. FUJI reactor and the AMSB can also be used for the transmutation of long-lived radioactive elements in the wastes and has a high potential for producing hydrogen-fuel in molten-salt reactors. The development and launching of THORIMS-NES requires the following three programs during the next three decades: 0196-8904/$ -see front matter