Under what condition should decay-in-storage (DIS) be applied to radioactive waste?

• A. For long-lived isotopes with high activity
• B. For short-lived isotopes with half-lives allowing disposal after decay
• C. For all waste
• D. It never applies

Answer: (B)

The key idea is that decay-in-storage is used when the waste contains radionuclides whose activity will drop to acceptable levels within a practical storage period. If the isotopes have short enough half-lives, waiting allows their radiation to diminish so the waste can be disposed of or released as lower-risk material after the decay period. The required storage duration depends on the specific half-lives and the regulatory disposal or release limits, and it must be approved by the relevant authority with proper monitoring and controls during the storage.

This is why the best choice is the option describing short-lived isotopes with half-lives that allow disposal after decay. Long-lived or high-activity waste would not reliably reach safe levels in a reasonable time, so they aren’t suited to DIS. Not all waste contains suitable isotopes, and DIS is not used when it isn’t feasible to reach disposal or release criteria through decay.