Final answer:
The primary concern associated with radioactive waste from nuclear power stations is Harmful effects for thousands of years (Option C). It remains hazardous to human health and the environment for thousands of years.
Step-by-step explanation:
The main concern with radioactive waste from nuclear power stations is the long-term harmful effects.
This is because the radioactive materials, such as spent reactor fuel and uranium mill tailings, remain dangerous over extremely long periods due to their long radioactive half-lives.
These materials can pose significant health risks to humans, as well as environmental hazards.
High-level radioactive waste such as used nuclear reactor fuel must be stored with multiple containment methods, including cooling by water and later in special containers.
Managing the long-term storage of this waste is a complex challenge that still lacks a permanent resolution.
Moreover, the potential for contamination of air, water, and food, and risks associated with uncontrolled nuclear reactions heighten these concerns.
Hence, the correct answer is Option C.