Answer to Question #8516 Submitted to "Ask the Experts"

Category: Radioactive Waste Disposal — Disposal

The following question was answered by an expert in the appropriate field:

A new radiation oncology facility is being built that includes a vault with lead-lined walls. What, if anything, must be done with the lead lining at the end of the useful life of the equipment? If the lining is not required to be removed, can the room be used for other nonradiation purposes? I understand there is a salvage value for the lead. Are there any decommissioning procedures?

Normally, concrete is the material of choice for vault shielding due to its low cost and low activation potential, but the required thickness to achieve an equivalent shielding effectiveness is much greater. In some cases there is simply not enough room for a concrete shield, so lead and/or high-density concrete is used to shrink the overall dimensions of the vault.

When lead is used as a primary component of the radiation shield for a linear accelerator vault, it is likely that there will be induced radioactivity (activation) in the lead due to the neutron fields present during operation of the linear accelerator. How much radioactivity there will be at the end of the useful life will depend on the energy of the accelerator beam, the amount of time it is pointed at a particular location, distance between the accelerator head and the closest wall, and finally the thickness of lead used. I would recommend a consultation with a qualified medical or health physicist who can provide a more specific recommendation. Disposal costs for activated lead can be quite high because it will be classified as a mixed waste.

If the linear accelerator beam energy is below 15 MV, then the potential for activation of lead in the shielding walls is greatly reduced. In a situation where lead is used only in the maze entrance door, then the potential for activation is fairly limited and will likely not be an issue at the end of the useful life.

Roger Moroney, CHP
Answer posted on 14 September 2009. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.