Under what condition can radioactive waste be decayed in storage?

The correct choice is based on the principle of how radioactive waste management is conducted, particularly with respect to the safe decay of waste in storage. For radioactive materials with a physical half-life of less than 120 days, there is a significant benefit related to the rate at which the radioactivity diminishes.

Since the half-life is relatively short, the decay will substantially reduce the quantity of radioactive material and its associated hazard in a shorter time frame. This allows facilities to manage the waste more effectively, as waste with a shorter half-life can be monitored and eventually removed or disposed of in a safer manner once it has decayed to a minimal level of radioactivity.

While other options discuss exposure rates, which are important in assessing immediate safety and handling protocols, they do not necessarily dictate the specific timeframe for decay management that short half-life materials imply. The focus on half-life durations highlights the importance of the intrinsic property of the radioactive material itself, making this option particularly relevant for decay in storage procedures.