Final answer:
The Permit RSO initiates a written request for disposal instructions for radioactive materials, ensuring safety and regulatory compliance.
Step-by-step explanation:
The individual who initiates a written request for disposal instructions is typically D. the Permit RSO (Radiation Safety Officer). The Permit RSO is responsible for maintaining the safety and compliance of the facility's use of radioactive materials, which includes the appropriate and legal disposal of radioactive waste. The waste generator, who creates the waste, has the responsibility to notify the Permit RSO when waste is ready for disposal. The RSO then evaluates the waste and provides the necessary disposal instructions following regulatory guidelines.