Control Rod Experiments

The Cd control rbds tested in these, experiments were essentially replicas of those designed for the high-flux reactor in so far as dimensions and composition are concerned. They were in. the form of hollow cylinders of square, 3K by in., cross-section and 26 in. long and were filled with water to duplicate, the conditions that will be.obtained in the case, of the high-flux reactor. 

It was also observed that the -reactivity change due to the removal of 180 g of fuel (nine tubes or a by 3)f-in. section) from a central position amounted to about 3%. 

Hydraulic studies were made to investigate the adequacy of. cooling in the reflector, safety rods, and fuel pieces. 

After completion of this mechanical program in September, 1949, it appeared that much could be learned by converting the Mock-Up into equipment for low-power nuclear experiments such as critical mass determination, ueutron-and gamma-flux measurements, and operation of the control system. These studies occupied the period Trom February, 19S0 to September, 1950. 

In an effort to keep the cost of the project at a minimum, the Mock-Up structure was designed for outdoor operation with.the enclosed space limited to the control room. The structure, illustrated in Fig. A4.A, consists of four main steel columns to support the reactor tank and a 10-ton traveling crane. The working level at the top of the tank, 22 ft above grade level, is floored. A 12-ft deep sub-pile room, IS by- IS ft is provided underneath the reactor tank. 

---

DetalM calculations on the control rod experiments are bebg performed at Karlsruhe using fliix synthesis calculations in XY/Z geometry. The results show that the reactivity of the absorbers used (Ta and B C) is generally overestimated by 9 to 18%. 

---