Under which set of regulations are fitness for duty requirements outlined?

The correct choice is based on the fact that 10 CFR 26 specifically addresses fitness for duty requirements within the context of nuclear regulatory regulations. This part outlines the standards and protocols that organizations must follow to ensure that employees are physically and mentally capable of performing their duties without posing a safety risk to themselves or others.

Furthermore, 10 CFR 73.56 complements this by detailing additional security and safeguards measures that relate to access control, further underscoring the importance of fitness for duty in a secure environment.

The other options reference parts of the Code of Federal Regulations that do not specifically relate to fitness for duty. By focusing on the correct regulations, one can understand the comprehensive safety culture and regulatory framework that governs the fitness of individuals in sensitive and safety-critical positions, particularly within the nuclear sector.