A Simple Method for Control Rod Worth Evaluation with Diffusion Codes

To present a simple method for calculating the worth of control rods in multiregion reactor cores, the well model approximation is applied to the finite difference diffusion code. The results of calculation are compared with experimental results obtained on the ōzenji Critical Facility, and also with calculations using transport equivalent constants. With its simplicity, the method proposed is accurate enough to suffice amply for most cases where only the reactivity is the end result sought, although the application of this method is limited to control rods inserted in the core region, and gives no information about the detailed neutron flux distribution around the control rod.     

Sodium Vapor Deposition,on Simulated Model of LMFBR Rotating Shield Plug Annulus, (I)

Experimental study was made to investigate the controlling factors on the vapor deposition rate on reactor operational shield plug annulus, which is exposed to the vapor entrained cover gas during reactor operation. Two simulated test assemblies having annuli were made for this purpose and were installed into a small test vessel. In the experiment, the average deposition rates on the annular walls of the test assemblies were measured for various pool temperatures, and their dependents upon such parameters as pool temperature, T_s (or the saturated vapor pressure P_s at pool surface), cover gas pressure P_g , and temperature drop ΔT_a across cover gas, were studied.

The results revealed that the dominant controlling factor was the vapor pressure P_s at pool surface. Dependent of the average deposition rate φbar_d. upon the above parameters was simply expressed by: φbar_d=Bσp_sD_sΔT_G , where, σ_s is the saturated vapor concentration at pool surface, D_s , the vapor diffusion coefficient, and B the proportional constant.

To these experimental results, the previously published evaporation rate data and the theoretical evaporation rate equation based on Epstein & Rosner's theory were reviewed. Then correlation between the deposition and the evaporation rates was discussed.     

Incipient Boiling of Sodium in an Annular Channel Heated by a Single-Pin with Blockage

Abstract

In simulation of partial failure affecting a fast breeder core, experiments on sodium boiling were performed in a single vertical channel of annular cross section (15 mm I.D.), indirectly heated by high flux heater pin (6.5 mm O.D., 60 cm heating length) and provided with a blockage disk (11mm O.D., 1mm thick, obstructing 42% of the channel area). The experimental conditions were; Pressure of cover gas: 1.0 kg/cm² abs., Heat flux: 0–80 W/cm², Flow rate of sodium: 1–4/l min.

The results revealed that the degree of incipient boiling superheat is reduced to a fraction of the value obtained previously for direct joule heating under similar conditions, and that, consequently, the intensity of pressure pulses is correspondingly reduced. On the other hand, the incipient boiling superheat increases, together with the extent of its scattering, with rising intensity of the heat flux.

Local boiling was observed to precede the onset of bulk boiling, causing small pressure spikes to be detected by all three pressure sensors installed along the test channel. The pressures evaluated from the measured velocities of the liquid sodium column based on single-bubble model were compared with the measured pressure signals, and a fairly good agreement was obtained.     

Development of Reflux Vapor Trap for Sodium Cooled Fast Breeder Reactor, (I)

With the view of obtaining basic data required for designing durable reflux vapor traps of high performance for use in sodium-cooled FBR's, experiments were conducted to (a) select a suitable packing, and (b) to examine the effect brought on trapping performance by changing the gas flow rate, packing material, packing density and trap outlet temperature. The results indicated that:

(1) As trap packing, plane weave stainless steel mesh proved to ensure lower pressure drop through trap.

(2) Using the plane weave mesh packing, and with the trap outlet temperature kept at 130°C, the reflux vapor trap efficiency was found to exceed 99.6% in the range of vapor trap gas velocity below 1.3 m/s, and packing density below 0.07 g/cc. The efficiency decreased at outlet temperatures above 130°C.     

Experimental Studies of the Enhanced Heat Transfer from a Heating Vertical Flat Plate by Ionic Wind

The effects of the ionic wind on the heat transfer rate from a heated vertical flat plate are described. The ionic wind is induced by three different types of discharge, corona discharge, dielectric barrier discharge （DBD） and dc glow discharge. The heat transfer coefficients for the heated copperplate under free convection conditions with and without an ionic wind are obtained by measuring the temperature and the heating power of the copper plate. It has been proved that the convective heat transfer coefficients increase by several times with the help of the ionic wind. With the ionic wind induced by a uniform dc glow discharge, the heat transfer coefficient of the heated copper plate is highly enhanced compared with those induced by a corona discharge or DBD. With the use of DBD, the breakdown voltage is increased significantly, which is helpful in avoiding a breakdown when heat transfer is enhanced by the ionic wind. In addition, it makes the application of the ionic wind much safer.     

A Brief Study on the Ignition of the Non-Thermal Atmospheric Pressure Plasma Jet from a Double Dielectric Barrier Configured Plasma Pencil

To understand the self sustained propagation of the plasma jet/bullet in air under atmospheric pressure, the ignition of the plasma jet/bullet, the plasma jet/bullet ignition point in the plasma pencil, the formation time and the formation criteria from a dielectric barrier configured plasma pencil were investigated in this study. The results were confirmed by comparing these results with the plasma jet ignition process in the plasma pencil without a dielectric barrier. Electrical, optical, and imaging techniques were used to study the formation of the plasma jet from the ignition of discharge in a double dielectric barrier configured plasma pencil. The investigation results show that the plasma jet forms at the outlet of the plasma pencil as a donut shaped discharge front because of the electric field line along the outlet’s surface. It is shown that the required time for the formation of the plasma jet changes with the input voltage of the discharge. The input power calculation for the gap discharge and for the whole system shows that 56% of the average input power is used by the first gap discharge. The estimated electron density inside the gap discharge is in the order of 1011cm-3 . If helium is used as a feeding gas, a minimum 1.48×10-8C charge is required per pulse in the gap discharge to generate a plasma jet.     

Vibratory Compaction of Uranium Dioxide, (II) Compaction of Sol-Gel UO2 Powder with a Pneumatic Vibrator

Vibratory compaction was studied making use of a pneumatic vibrator to pack sol-gel UO₂ powder in a thermal reactor type fuel canning tube. It is shown that the pneumatic vibrator utilized is superior to the commonly used electrodynamic vibrator from the view point of easy operation and high attainable density. Compared with the latter type, the pneumatic vibrator is less restrictive in the range of mesh size composing each fraction of the starting powder, and good results could be obtained with a powder with coarse, medium and fine fractions respectively having mesh ranges of 4–6 (60%), 20–65 (20%) and ?200 (20%).

The selected operational conditions are: vibration frequency; 300 cpm, driving air pressure; 3 kg/cm² and duration of operation; 10 min.

Fuel rods of 100cm length compacted in these conditions with sol-gel UO₂ (particle density: 96%T.D.) attained a bulk density of 88.2±0.2% T.D. with an axial density distribution as uniform as ±3% T.D.     

Estimation of Hot Wire Temperature of Thermal Diffusion Column by the Pressure Change after Turning on Electricity

A simple method was proposed for estimation of the temperature of the hot wire of the thermal diffusion column. The method is based on Boyle-Charle's law between the pressure change before and after turning on electricity and the radial temperature distribution which is determined by the thermal conductivity of the charged gas. The hot wire temperatures estimated by the present method agree well with those measured directly by the thermocouple and those measured through the glass window by the radiation pyrometer whose correction dial of emissivity was calibrated by the thermocouple. Separative analyses incorporated with the present temperature of the hot wire temperature predicted well experiments for nitrogen isotope separation. The present method is applicable for experiments with continuous feed and draw-offs, if the temperature distribution in the radial direction is not effectively affected by the feed and draw-offs.