Abstract
The minimum mass for a critical reactor is well studied whereas the minimum heat production from a nuclear reactor has received little attention. The thermal power of a (sub)critical reactor originates from fission as well as radioactive decay. Fission includes neutron-induced and spontaneous fission. For an idealized critical core, we find that the minimum theoretical power is ER/Λ, whereas for a subcritical reactor comprising fissionable material undergoing spontaneous fission, the minimum power is dictated by subcritical multiplication. Interestingly, radioisotopic heat generation exceeds the minimum theoretical fission power for most of the fissile materials examined in this study.
Highlights
The original Chicago Pile 1 (CP-1) produced half a watt during its first operation and later 200 W [1]
It is sometimes stated casually that a nuclear reactor can operate at any power level [2,3,4]
That statement is typically directed at higher thermal power levels
Summary
The original Chicago Pile 1 (CP-1) produced half a watt during its first operation and later 200 W [1]. It is sometimes stated casually that a nuclear reactor can operate at any power level [2,3,4]. While the casual statement and the reported stable operation at milliwatts of power are motivations to determine whether there is a theoretical minimum power level, the determination of the minimum critical mass for a self-sustaining nuclear reactor is a wellstudied problem, for example, see [8,9]. In our pursuit for determining a lower limit for the thermal power of a reactor, we must recognize that heat can be generated from several sources within a core, fission and radioactive decay.
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