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18-Env-B5 Industrial & Hazardous Waste Management · May 2017

Question 17 of 19: Managing Treatment and Disposal of Liquid Radioactive Wastes

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

Reference texts: Nemerow & Dasgupta, Industrial and Hazardous Waste Treatment, 2nd ed.; Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery, 5th ed.; Davis & Cornwell, Introduction to Environmental Engineering, 6th ed.; LaGrega, Buckingham & Evans, Hazardous Waste Management, 2nd ed.; CCME, Guidelines for the Management of Biomedical Waste in Canada (1992); Canadian Environmental Protection Act (CEPA), 1999; Canadian Nuclear Safety Commission (CNSC) regulations on radioactive waste under the Nuclear Safety and Control Act; provincial hazardous waste regulations (e.g. BC's Environmental Management Act and Hazardous Waste Regulation).

Question 17: Managing Treatment and Disposal of Liquid Radioactive Wastes (4 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Liquid radioactive waste management is regulated in Canada by the Canadian Nuclear Safety Commission (CNSC) under the Nuclear Safety and Control Act, and follows a hierarchy driven primarily by the waste's radionuclide content and half-life:

  1. Minimize volume at source. Segregate genuinely contaminated liquid from clean process/cooling water at the point of generation so only the truly radioactive fraction needs specialized management.
  2. Decay-in-storage for short-lived isotopes. Low-level liquid waste containing short-half-life isotopes (e.g. medical isotopes such as I-131 or Tc-99m) is held in shielded, secure storage tanks until activity decays to background/clearance levels (typically 10 half-lives), after which it can be discharged or disposed of as ordinary waste.
  3. Concentration and volume reduction. For longer-lived or higher-activity waste, use ion exchange, evaporation, or reverse osmosis to concentrate the radioactivity into a small volume of solid or sludge, leaving a large volume of dilute effluent that can be discharged within regulatory release limits.
  4. Immobilization/solidification of the concentrated fraction. Solidify the concentrated radioactive residue (cementation or vitrification) to produce a stable solid waste form suitable for interim licensed storage.
  5. Licensed long-term storage or disposal. Short/intermediate-lived solidified waste goes to a licensed storage facility pending decay or transfer; long-lived, high-level waste ultimately requires a deep geological repository (the approach being developed in Canada by the Nuclear Waste Management Organization, NWMO).
  6. Monitoring, licensing and record-keeping govern every step, with the CNSC requiring documented activity measurements, release limit compliance, and a full chain-of-custody record from generation to final disposal.