Ball-Type Fuel Element

In initial tests conducted to determine feasibility of fabrication of fuel balls, both lead and copper shotting devices were employed. As previously reported, 5 the general crucible design developed was 

The experimental ball tower apparatus used is shown pic-torially in Fig. 61 a sectional view is shown in Fig. 62. All equipment that contacts NaK is of AISI Type 347 stainless steel most other elements are of brass or ceramics. A stainless steel anti-spatter shield, which is a small inverted cone with a l/z-in. diameter hole in the apex, is used over the quench tank. The ceramics system rests on a Nichrome ring stand. Water cooling is provided for the base of the Vycor furnace tube gasket and the cover plate. A fishing-reel pawl and screw mechanism drives the tantalum stopper rod. This arrangment provides a uniform speed for the stopper rod throughout its period of travel. 

Vacuum pressures are measured by a Pirani gauge and a McLeod gauge. The melt temperature is measured from an optical pyrometer through a quartz prism and through a quartz sight glass into an Alundum well which rests on the inside bottom of the crucible. NaK temperatures are determined by thermocouples in capillary wells welded into the NaK pots and quench tank. 

After reaching shotting temperature, the vacuum valve was closed and helium brought into the system to a pressure of about 1 psig. 

NaK was then forced from the lower pot into the quench tank up to approximately 1 in. from the top. The NaK in the quench tank next was heated to temperature. The stopper rod reciprocating automatic drive was finally switched on (unless operated manually), and the shotting process proceeded automatically until the stopper rod piston had forced all of the melt out of the nozzle. After the NaK had cooled to room temperature, it was forced back into the lower hold pot through a small screen at the base of the quench tank. The system was then opened and cleaned of NaK with ethyl alcohol and water rinses. The balls were taken from the bottom of the quench tank through the hex nut sealing device. 

---