Radioactive solid nuclear wastes: select the recommended disposal method used in practice to isolate long-lived radionuclides safely from the biosphere.

Introduction / Context:
Nuclear facilities and some medical or industrial processes generate radioactive solid wastes that may remain hazardous for decades to millennia. The aim of disposal is to keep radionuclides isolated from people and ecosystems over the relevant time scales. This question asks which method aligns with established practice for high-integrity isolation.

Given Data / Assumptions:

• Waste is radioactive solid material, not low-hazard general refuse.
• Objective is long-term isolation rather than volume reduction alone.
• Compliance with multi-barrier containment concepts.

Concept / Approach:
Safe radioactive waste disposal relies on engineered and natural barriers. Incineration or pyrolysis are thermal volume-reduction techniques that are appropriate for combustible non-radioactive wastes or certain low-level streams after robust off-gas controls, but they do not constitute final isolation for long-lived nuclides. Deep or secure underground burial using robust containers and backfill, often in geologically stable formations, provides the required long-term containment.

Step-by-Step Solution:

Verification / Alternative check:
Repository designs use multiple barriers such as waste forms, containers, backfills, seals, and the host rock to minimize migration.

Why Other Options Are Wrong:
High-temperature incineration: not a final isolation method and creates radioactive off-gas issues.
Pathological incineration: a term for biomedical wastes, not suitable as a final method for radioactive solids.
Pyrolysis: thermal treatment without assured long-term containment.

Common Pitfalls:
Equating volume reduction with safe disposal; overlooking the necessity of geological stability and engineered barriers for long-lived waste.

Final Answer:
Underground burial in concrete containers