Critical Mass Experiments

Critical Mass Experiments with Plut> onium Nitrate Solutions, E. D. Clayton, R. C. Lloyd, and W. A. Reardon (GE-HAPO). 

Experience has shown plant start-ups to be difficult and that it takes time for capacities to reach critical mass. 

Students who pursue Joint degrees are often required to take a heavier course load and may or may not find the experience isolating as it is can be difficult to establish a home department. For this reason, it is important that schools work to develop a critical mass of students pursuing the Joint degree to ensure a sense of community for their students. At the same time, this path may... 

Compared with other subjects, chemistry is commonly believed to be more difficult, at least at the introductory level. There is some justification for this perception for one thing, chemistry has a very specialized vocabulary. However, even if this is your first course in chemistry, you already have more familiarity with the subject than you may realize. In everyday conversations we hear words that have a chemical connection, although they may not be used in the scientifically correct sense. Examples are electronic, quantum leap, equilibrium, catalyst, chain reaction, and critical mass. Moreover, if you cook, then you are a practicing chemist From experience gained in the kitchen, you know that oil and water do not mix and that boiling water left on the stove will evaporate. You apply chemical and physical principles when you use baking soda to leaven bread, choose a pressure cooker to shorten the time it takes to prepare soup, add meat tenderizer to a pot roast, squeeze lemon juice over sliced... 

Despite that frightening experience, Frisch wanted to work with full critical masses to determine by experiment what Los Alamos had so far been able to determine only theoretically how much uranium Little Boy would need. Hence his daring proposal ... 

Experiments at Los Alamos determined the critical masses of U235 and Pu239. Adding U235 cubes to a subcritical assembly within blocks of beryllium tamper measurably increased neutron flux. 66. The Los Alamos Tech Area. 

This paper presents the results obtained with the ERANOS calculation scheme and data for several major parameters of the Super-Phenix start up core (CMP) including the critical mass, the control rod reactivity worth, the power map distribution, the burn up reactivity swing and the Doppler feedback. Agreement of calculation results with experiment are very satisfactory agreement within 100 pcm for the critical mass, less than 5% discrepancy on control rod worth, a residual radial gradient of less than 5% the radial power map, an discrepancy less than 10% on the reactivity swing, and a full agreement on the Doppler constant. 

A2.1.3 Besults and Dincnssion. Experiments were performed with DjO, beryllium, and H O reflectors to find (1) critical mass, (2) neutron distributions, and (3) values of control rods, cavities, etc., in terms of fuel. Various ratios of A1 to HjO were used. These experiments served as a check on the theoretical calculations of critical masses under the same conditions. The values for the critical mass found in both theory and experiment are compared in Table A2.A. 

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. 

Critical-Mass Measurements on Beryllium-Reflected, Enriched-Uranium, Spherical Systems, by O. Kolar and H, R. Ralston (VCBL-L). A scries of critical mass determinations has been made for spherical beryllium reflected systems. Cores were enriched (93.17S U-235) uranium spheres ranging in mass from 10.6 to 32.6 kg. The corresponding reflector thicknesses were 20.3 to 2.2 cm. All results were nonnalized to a core density of 18.6 g/cc. Some Los Alamos data are included for completeness and have been similarly normalized. These two sets of experiments were found to be in good agreement. The experiments and results arc discussed, together with the fit to the experimental data obtained with the spherical Si, 5-group code in use at UCRL. 

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