Figure 1.

The effective multiplication constant, k_eff, for the geo-reactor simulation as a function of time for two different fission power levels. For the curve labeled Fission, starting with the initial isotopes and fission power listed in Table 1, the isotopes in the simulation change because of fission and radioactive decay. For the curve labeled Decay Only, starting with the initial isotopes listed in Table 1, the isotopes in the simulation change because of natural radioactive decay only; fission power is zero. A critical system is present when k_eff = 1.00.