NRRPT Radioactive Waste Management & Disposal 2 — Questions and Answers
Question 1: The 'decay-in-storage' method is most applicable for radioactive waste containing isotopes with:
- Half-lives greater than 30 years
- Half-lives less than 90 days (Correct answer)
- Only gamma-emitting radionuclides
- Concentrations above Class C limits
Correct answer: Half-lives less than 90 days
Decay-in-storage is practical for short-lived radionuclides (typically half-lives ≤90 days) so the waste can decay to background levels before disposal as non-radioactive waste.
Question 2: Which treatment method is most commonly used to reduce the volume of liquid radioactive waste generated at nuclear facilities?
- Incineration
- Evaporation/concentration (Correct answer)
- Ion exchange followed by resin burial
- Centrifugation
Correct answer: Evaporation/concentration
Evaporation concentrates radioactive contaminants into a small volume of sludge or dried solids while producing relatively clean condensate, achieving high volume reduction ratios.
Question 3: What does the prohibition on 'free liquids' in LLW disposal containers require?
- All radioactive water must be treated before any disposal
- Packaged waste must not contain liquid that can drain from the container (Correct answer)
- Liquids must be solidified with a volume reduction of at least 90%
- Free liquids are prohibited only in Class B and C waste
Correct answer: Packaged waste must not contain liquid that can drain from the container
10 CFR Part 61 prohibits free-standing liquids in LLW packages to prevent leachate migration and ensure package integrity during burial.
Question 4: Cementation, bituminization, and polymer impregnation are all examples of which radioactive waste treatment process?
- Volume reduction
- Solidification/stabilization (Correct answer)
- Decontamination
- Thermal treatment
Correct answer: Solidification/stabilization
Solidification/stabilization processes immobilize radionuclides in a solid matrix, reducing leachability and improving waste form stability for long-term disposal.
Question 5: Greater-Than-Class-C (GTCC) LLW differs from Class C LLW primarily because:
- It contains only naturally occurring radioactive material
- Its radionuclide concentrations exceed Class C limits and require deeper disposal (Correct answer)
- It is generated exclusively by medical facilities
- It can be disposed of at any licensed LLW facility
Correct answer: Its radionuclide concentrations exceed Class C limits and require deeper disposal
GTCC waste has radionuclide concentrations exceeding the Class C thresholds in 10 CFR Part 61 and is not acceptable for near-surface disposal; it requires disposal in a geologic repository.
Question 6: Which regulatory framework governs the disposal of uranium mill tailings in the United States?
- 10 CFR Part 61
- 10 CFR Part 40 Appendix A and the Uranium Mill Tailings Radiation Control Act (UMTRCA) (Correct answer)
- 40 CFR Part 191
- 10 CFR Part 20 Subpart K
Correct answer: 10 CFR Part 40 Appendix A and the Uranium Mill Tailings Radiation Control Act (UMTRCA)
UMTRCA of 1978 and 10 CFR Part 40 Appendix A establish the standards and license requirements for uranium and thorium mill tailings disposal, including stabilization and groundwater protection.
Question 7: What is the primary radiological hazard associated with uranium mill tailings?
- High-energy gamma radiation from short-lived fission products
- Alpha-emitting thorium-230 and the ingrowth of radon-222 gas (Correct answer)
- Beta radiation from Sr-90 and Cs-137
- Neutron activation products in the tailings pile
Correct answer: Alpha-emitting thorium-230 and the ingrowth of radon-222 gas
Uranium mill tailings contain Th-230, which decays to Ra-226 and then Ra-222 (radon), a carcinogenic alpha-emitting gas that can migrate off-site and pose inhalation hazards.
NRRPT Radioactive Waste Management & Disposal 2
The 'decay-in-storage' method is most applicable for radioactive waste containing isotopes with: