Neutron-physical calculation of a fresh zone in the natural nuclear reactor at Oklo

A full-scale computer model of zone 2 of the Oklo reactor with a realistic materials composition is constructed. Modem Monte Carlo programs are used to calculate the multiplication factor the excess reactivity, and the neutron flux for the fresh reactor zone 2. The calculations are performed in a wide range of variation of the zone parameters: the uranium content in the contemporary Oklo zone is varied from 35 to 55 mass% and the it,ater content from 0.355 to 455 g/cm(3). The power effect is determined. The temperature of the fresh zone is found to be 725 +/- 55 K, at which the reactor is critical and can operate in a stable manner for a long time. The power of the reactor is maintained by negative feedback. The neutron spectrum, over which the cross section of strong absorbers must be averaged, for example, Sm-149(62), in order to obtain the most accurate bounds on the possible shift of the samarium resonance as a result of a change in the fundamental constants, is found for 700 K.