Why can't naturally occuring uranium be used in a nuclear power plant?
A. Naturally occurring uranium decays too rapidly into thorium.
B. The temperature of the uranium is too low.
C. A sustainable chain reaction requires higher concentrations of U235 than naturally occuring U contains
D. U235 undergoes fission but the U238 absorbs the extra neutrons that are produced
The correct answer is C. A sustainable chain reaction requires higher concentrations of U235 than naturally occurring U contains.
To understand this, let's break down the options:
Option A states that naturally occurring uranium decays too rapidly into thorium. This is not accurate because uranium does decay over time, but the rate of decay is relatively slow compared to the speed at which it can be used for fuel in nuclear power plants.
Option B suggests that the temperature of the uranium is too low. This is incorrect because the temperature at which uranium operates in a nuclear power plant is determined by the surrounding environment and the control mechanisms, not by the intrinsic temperature of the uranium itself.
Option C correctly explains that a sustainable chain reaction requires higher concentrations of U235 than naturally occurring uranium contains. Naturally occurring uranium consists of a mixture of two isotopes: U235 and U238. U235 is the fissile isotope, meaning it can readily undergo a nuclear chain reaction, while U238 is a fertile isotope that does not readily undergo fission. In order to sustain a nuclear chain reaction, a higher concentration of U235 is needed than what is found in naturally occurring uranium. This is accomplished through a process called uranium enrichment.
Option D states that U235 undergoes fission, but U238 absorbs the extra neutrons that are produced. This is partially correct, as U238 is indeed capable of absorbing neutrons. However, this is not the main reason why naturally occurring uranium cannot be used in a nuclear power plant. The main reason is the insufficient concentration of U235.
Therefore, the correct answer is C. A sustainable chain reaction requires higher concentrations of U235 than naturally occurring uranium contains.