When a nuclear reactor is in a critical state, the neutrons released in each fission trigger an average of exactly one additional fission. If the average number of additional fissions triggered rises above one, the reactor enters a supercritical state in which the fission rate and the power output grow very rapidly. A reactor in a critical state has a power output of 25 kW. The reactor then enters a supercritical state in which each fission triggers an average of 1.01 additional fissions. The average time for the neutrons released by one generation of fissions to trigger the next generation of fissions is 1.2 × 10-8 s. How much time elapses before the power output from a single generation of fissions grows to 3300 MW (roughly the normal output of a commercial reactor)? |
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