On Variations of the Power Output in a Running Pile

Abstract. The variation of the neutron intensity is studied under various conditions. These include a sudden increase or decrease of the multiplication constant after steady operation of some length, either under the influence of spontaneous flssion or because the multiplication constant was 1 for some time. The expected operation of the limits control is also described. 

The following analysis follows quite closely that given by Ibser, Manley and Wheeler. The probability that a neutron yield, when absorbed, a radioac- 

The third column gives the decay constants in units of (1.5 x 10 sec) , the time 1.5 X 10 having been chosen as the unit of time because it represents the time between the creation of a neutron by fission and its absorption. It is unnecessary to mention that the values of Table I are subject to a considerable error. In order to have definite equations to discuss they will be adopted at face value. 

It we denote the number of neutrons by n, by sj the number of radioactive nuclei which emit a delayed neutron of the kind j, we have the equations 

The unit of time is 1.5 X 10 sec, 5 is the number of spontaneous fission neutrons during this time. Since the number of spontaneous fission neutrons is, according to Fermi and Goldhaber, about 10 per kg U and sec, the value of 5 is in a 50 ton pile 50000 x 10 x 1.5 X 10 = 750. On the other hand, n is about 4.5 X 10 ° in a 1 kW pile, S can be neglected except at extremely low power operation. 

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