Question

fill in the blanks with the terms that complete the sentences about nuclear power plants. without a critical \boxed{} of fissionable material, a nuclear reaction cannot be sustained. the turbine is powered by \boxed{}. done

Explanation:

For the first blank: In nuclear physics, a critical mass of fissionable material is required to sustain a nuclear chain reaction. Mass is the correct term here as it refers to the minimum amount of fissionable material needed.
For the second blank: In a nuclear power plant, the heat generated from the nuclear reaction (fission) is used to produce steam, and this steam powers the turbine. So the turbine is powered by steam.

Answer:

First blank: mass
Second blank: steam