Overall heat transfer characteristics were measured for film-wise free-convective condensation of CO_2-steam mixture and air-steam mixture upon a cooled horizontal tube. The test tube is of stainless steel and 25.4mm outer diameter. The range of non-condensable gas fraction was 10-55 wt%. First, method of obtaining mean temperature of tube surface was studied. Heat transfer characteristics of CO_2-steam mixture were examined under decompressed condition, and compared with those of air-steam mixture. Influence of ambient pressure upon heat transfer characteristics was also examined. Finally, the rate of heat transfer degradation by the non-condensable gas was evaluated.
A study has been performed for a small molten salt power reactor operated with Th-U fuel cycle, and nuclear characteristics of the reactor are evaluated using latest codes and cross sections. Nuclear characteristics of the reactor core are analyzed by using SRAC95 (a standard reactor analysis code), with 30 group cross section data from JENDL3.2 (nuclear data file). Burn up characteristics of the reactor are estimated by using SRAC95 and ORIGEN2 (a code to calculate the build up and decay of radioactive materials), assuming that the fuel salt is reprocessed once in every 6 years, and graphite moderator are replaced in every 15 years. From the present study, the following results have been obtained. (1) Fuel conversion ratio of the reactor is about 0.92, and the reactor can be operated feeding only 8% fossile material of LWR case. (2) Build up of dissolvable fission products is low enough not to cause chemical problems or precipitation troubles, even after 40 years operation. (3) Regarding long-lived radioactive waste, this reaetor produces only 10% minor actinides amount of LWR case.
Interaction between liquid droplets under breakup in gas stream was investigated experimentally, to obtain basic knowledge for developing numerical simulation model of twin-fluid liquid atomization. Pair of inline water droplets was dropped into air stream passing through an orifice, and breakup processes of droplets were observed using a high-speed video camera. When dimensionless distance between droplets was larger than about 3, each droplet broke up as a single droplet. However the upstream droplet affected breakup behavior of the downstream droplet when dimensionless distance was small. There are three representative types of interaction. Critical condition for the interaction was investigated and the mechanism of interaction was discussed. Experimental data on droplet acceleration were compared with numerical results based on drop drag and breakup model. It was shown that the conventional numerical model could not estimate acceleration as well as deformation of droplets accurately when droplet number density was high.
Burnup characteristics of a fast-spectrum chloride molten salt reactor (Cl-MSR) are studied to utilize the trans-uranium element (TRU) and depleted uranium effectively. The fuel salt used is a mixed salt of NaCl, CaCl2, UCl3 and TRUCl3. This fuel salt is expected to have a solidification temperature of about 530℃ and a heavy metal solubility of about 30 mol％. When the uranium inventory is 66.0 tons and the reprocessing rate is 18.3 liter/day, the fuel conversion ratio of Cl-MSR becomes about 1.0 after 16 years of reactor operation supplying both 238U and TRU. After that, Cl-MSR can continue to operate on 238U supply only and can confine TRU in its primary loop for a long period of time without increasing or decreasing its amount. By using TRU and depleted uranium currently existing in Japan, 14 Cl-MSRs can continue to generate 14 GWe electricity for more than 1,000 years. These burnup characteristics of Cl-MSR are analyzed by SRAC2006 with SRACLIB-JDL40.
A short wave was observed on the interface of liquid jet which was injected from the coaxial dual nozzle into a co-current gas stream. This wave promoted the breakup of liquid jet. To clarify the inception mechanism of the short wave, the internal instability of liquid jet flow was analyzed numerically. It was shown that the short wave was mainly due to the internal disturbance within liquid jet which rose from the internal instability. The effect of liquid injection velocity ratio, the diameter ratio of the coaxial dual nozzle and the liquid properties upon the instability were examined numerically. Finally, it was found that the breakup of the coaxial liquid jet could be controlled by appropriate adjustment of these parameters.
Distinct element method (DEM) proposed by Cundal and Strack is useful for simulating behavior of particle beds. However, the results of the simulation differ from the experiment in general Although the rolling friction should be taken into account, it is usually ignored in the existing DFM, so that for instance, a single particle rolling on a horizontal plate keeps unreally constant velocity without deceleration. This paper proposes to take account of the rolling friction generated by the elastic hysteresis of particles in the existing DEM. A particle bed in a rotating horizontal cylinder is chosen as a testing model for the numerical simulation to examine the DEM improved in this paper by introducing the rolling friction. The present DEM can explain the rolling, cascading and cataracting flow modes of the particle bed, while the existing DEM cannot do except the rolling mode.
A study is performed on a molten salt fast reactor (MSFR) of 1.5 GWe output. The reactor is started up by using transuranium elements reprocessed from spent fuel of a BWR. The fuel salt of the reactor is the mixed fluoride salt NaF–KF–UF4–TRUF3, which is reprocessed almost continuously by an oxide-precipitation process during the reactor operation. By performing calculations using the nuclear analysis code PIJ–BURN in SRAC2006 and the nuclear data file of JENDL–3.3, the following results are obtained. (1) The burn-up characteristics of the reactor are mainly determined by the uranium inventory (Uinv) in the reactor and the reprocessing cycle (Lrep), which is the time interval necessary to reprocess all the fuel salt in the primary loop. (2) A large Uinv and short Lrep enhance the breeding performance of the reactor. (3) The period necessary to keep the radioactive waste under control will be about 400 years in the case of Lrep longer than 400 efpd. (4) Power stations consisting of 20 MSFRs (total output of 30 GWe) can operate for 600 years by utilizing 14,000 t of uranium obtained from the spent fuel of LWRs in Japan.
This paper performed the transient core analysis of a small molten salt reactor in the case of blockage accident. The emphasis is that the numerical model developed in this paper takes into account the interaction between fission reaction and fuel salt flow. The model consists of two group diffusion equations for fast and thermal neutron fluxes, balance equations for six-group delayed neutron precursors and energy conservation equations for fuel salt and graphite moderator. The results of transient analysis in the case of blockade accident are as follows ; (1) neutron multiplication factor hardly changes, (2) the outlet temperature of fuel salt decreases 10 K, and (3) fuel salt and graphite temperatures largely increase at the blockage point, but lower than fuel salt boiling temperature and the molten temperature of the reactor vessel.
