Management of Radioactive Waste

Unlike other hazardous materials, radioisotopes are invulnerable to degradation by external chemical or physical processes. Dilution of these atoms into the air, landfill or bodies of water simply moves them from one location to another. The only mechanism whereby radioisotopes can be eliminated from the environment is by radioactive decay.

To minimize the environmental impact of radioisotope disposal, the following guidelines must be strictly followed. These guidelines are enforced by law and are administered by the Atomic Energy Control Board (AECB). Detailed accounting of all disposal of radioisotopes is required. Each radioisotope poses a unique degree of risk to people and the environment. Therefore the AECB has set out isotope disposal limits that vary with the associated degree of hazard.

Classification of waste

1. Solid waste includes
   1. Non-hazardous items such as gloves, tissues, pipette tips, bottles, bench paper, etc. Solid waste bound for landfill may not contain biohazardous or toxic material.
      
   2. Biohazardous or animal waste including whole or parts of dead animals contaminated with radioisotopes. Animal waste or biohazardous waste must be incinerated.
   
   
2. Liquid waste includes
   
   1. Aqueous: water-soluble, non-toxic chemicals
   2. Organic: non-soluble and/or flammable and toxic materials. Liquid scintillation fluid falls under this category.
   3. Corrosive materials.
   
   
3. Gaseous waste
   Includes radioactive gases such as tritium or carbon dioxide released during an experiment.
   
   
4. Other
   Any unusual waste not listed above.

All radioactive waste is considered part of the radioisotope inventory and consequently it is necessary to keep a permanent record of disposal for each isotope. An isotope disposal record sheet shall be kept near the decay area, sink, fume hood or approved disposal containers and shall include the date, isotope, activity, and user s name. All users must fill out the appropriate sheet when disposing of radioactive waste.

Methods of disposal
There are 6 basic ways to dispose of radioactive waste:

1. Storage until the activity has decayed.
2. Landfill for non-toxic, non-biohazardous solid garbage.
   Limits: 1.0 SQ per kilogram solid garbage.
3. Sewer for water soluble waste.
   Limits: 0.01 SQ per litre after dilution.
4. Storage and appropriate disposal or organic and corrosive liquids.
   Limits: 0.01 SQ per litre after dilution.
5. Gaseous waste to the environment.
   Limits: 0.001 SQ per cubic meter of air.
6. Shipment to controlled burial areas for high activity radioactive waste.

1. Storage of waste for decay

   Isotopes with a half life of less than 90 days (32P, 35S) may be held for decay until acceptable disposal guidelines are met. As a general rule, holding for ten half lives will ensure that all the isotope has decayed to an acceptable level. Aqueous liquid waste containing short-lived isotopes should be held for decay rather than immediately diluting into the sewer system.

   Radioactive waste will be held in the isotope laboratory in appropriately shielded containers such that exposure of workers to the radiation field is less than 2.5 Sv per hour (0.25 mR/hr). Each container must be labelled with the initial holding date, the isotope and activity, the user s name and the anticipated disposal date. Once the isotope has decayed to the acceptable level the waste may be treated as ordinary solid or liquid (aqueous, organic or corrosive) waste and disposed of accordingly. The disposal sheet should then be placed in the isotope log book.

2. Solid waste (back to Methods of Disposal)

   Solid waste containing non-toxic materials and low levels of radioactivity shall be sent to landfill. Solid waste includes such items as gloves, tissues, syringes, bottles, bench covering, etc. Use a cardboard box double lined with plastic bags. Sharp objects such as syringes, glass pipettes, etc. Should be packaged in an appropriate sized can or paid before disposal in the box. The weight of the filled box should not exceed 5 kg.

   Solid waste must contain less than or equal to 1 SQ per kilogram and emit less than 2.5 Sv per hour (0.25 mR/hr) at the surface of the container. By ensuring the disposal guidelines are met, the radiation in the box does not pose a health hazard to any individual who may be required to handle it. It may therefore be disposed of as regular garbage. There should be no markings, tape or labelling indicating that the box contains very low levels of radioactivity. Boxes containing glass waste should be appropriately labelled as GLASS WASTE.

   The isotope disposal sheet should then be placed in the radioisotope log book. It is essential to ensure that there is full and complete documentation of all quantities of radioactivity disposed of as solid waste.

   Biohazardous or radioactively contaminated animal parts must be incinerated. Do not autoclave waste that has been radioactively contaminated.

3. Liquid wastes: (back to Methods of Disposal)

   The disposal limit for radioactive liquid waste is 0.01 SQ per litre.

   1. Aqueous

      If possible, aqueous waste should be held in sealed containers until the radioactivity has decayed. For large volumes or long-lived isotopes, disposal of aqueous solutions via the sanitary sewer is permissible.

   2. Organic and corrosive materials:

      All waste organic solvents and corrosive liquids, contaminated or not, shall be collected in corrosion resistant containers of volumes not to exceed 5 litres. Glass or other breakable containers should not be used. Chlorinated organic compounds should be kept in separate containers. Liquid waste containers should be placed in a tray with an absorbent pad to control accidental spillage.

      Each container should be labelled with the type of organic or corrosive waste, the isotope and the activity present in the container. A running tally of radioactivity added to the container should be kept and when full, the total activity in the container should be verified by counting a sample:

      Total activity = in waste

      (Net CPM of sample x total volume of waste x 10-6Ci) / (Efficiency of counter x volume of sample x 2.2)

      or in SI units

      Total activity = in waste

      (Net CPM of sample x total volume of waste x 1 Bq) / (Efficiency of counter x volume of sample x 60)

      Liquid scintillation vials must be emptied into appropriately labelled corrosion resistant containers. An estimate of the activity present may be obtained by keeping tack of the net CPM for each vial as counted during your experiment.

      Total activity in waste = (Sample CPM-background CPM)

      (Net CPM in all vials x 10-6 Ci) / (Efficiency of counter x 2.2)

      Liquid scintillation fluid will be treated as organic waste and, provided the disposal limit of 0.01 SQ/1 is maintained, can be disposed of an non-radioactive waste. Keep scintillation fluid containing short-lived isotopes (32P and 35S) separate and in an appropriately shielded location, and allow them to decay before disposal.

      The vials themselves, when empty, may be disposed of as solid waste, as long as the disposal guidelines for radioactive solid waste (1.0 SQ/kg) are met.

4. Gases and Aerosols (back to Methods of Disposal)

   Procedures for which there is a potential to emit radioactive gases, aerosols or dust shall be performed in an absorbent paper-lined fume hood. For radioactive material that may be discharged to the atmosphere via fume hoods, the disposal limit is 0.001 SQ per cubic meter of air at the point of discharge, averaged over a one week period.

5. High Activity Waste (back to Methods of Disposal)

In situations where the activity to be disposed of exceeds the solid waste disposal guidelines and the half-life of the isotope precludes holding the material for decay, the material may be sent for burial in Chalk River, Ontario. The appropriate containers for this are new, empty 1 gallon paint cans, available from most commercial paint stores. Minimize the volume of waste placed in cans...the shipping is very costly. Cans should be used for items such as stock solution vials containing unused radioisotope, columns and heavily contaminated glassware from iodination procedures and "hot spots" only cut out of heavily contaminated bench paper. The activity of all isotope waste placed in the can must be documented.

Record Keeping

The Atomic Energy Control Board requires that each licensed laboratory maintain accurate and up-to-date records of all radioactive sources.

Purchasing

The acquisition of radioisotopes is strictly regulated by laws which require the possession of a license prior to obtaining any radioisotopes. At TRU the RSO will maintain a central record of all radioisotopes purchased or donated and in what quantities. Authorized Users must place their isotope requests with the RSO. A copy of the invoice will be forwarded to the users to keep in the Isotope Usage log book.

Usage

For every stock vial of isotope purchased, a usage record must be maintained. Every time you remove an aliquot from the stock vial you must record your name, the date, and the activity removed on the "Isotope Usage Sheet" for that vial. These sheets will be kept in a special log book in the lab. At the end of your experiment, you must account for all of the isotope removed in terms of amounts disposed of into liquid, solid and gaseous waste, or held for decay.

Disposal

All radioactive waste is considered part of the radioisotope inventory and consequently it is necessary to keep a permanent record of disposal for each isotope. An isotope disposal record sheet shall be kept near the decay area, sink, fume hood or approved disposal containers and shall include the date, isotope, activity, and user's name. All users must fill out the appropriate sheet when disposing of radioactive waste.

Contamination Control: Monitoring for contamination by wipe testing and direct reading (if appropriate) must be performed at the end of each working day in which radioactive materials were used. The results of these tests must be kept in the log book, even if no contamination is found. Records must be kept for a period of three years for inspection by the AECB.