Control of Radioactive Materials

• References: The Principles of Radioactive

Waste Management, IAEA (1995) K. R. Rao, Radioactive waste: The

problem and its management, Current Science, vol. 81, no. 12, 25 December (2001), pp: 1534-1546

Chapter 9: Control of Radioactive Substances, in Practical Radiation Protection in Healthcare, CJ Martin & DG Sutton (eds.), Oxford (2002).

Transport Index

• The number given indicates the maximum radiation level (in mrem/hr) at a distance of one meter from the external surface of a package or container. (Readings in mSv/hr are multiplied by 100 to get mrem/hr.) For example, a TI of 3 (as shown above) would indicate that, at one meter from the labelled package, the radiation intensity that can be measured is no more than 3 mrem/hr (0.03 mSv/hr).

• If the radiation level at one meter from a package is found to be higher than the specified value, a radiation authority should be consulted. The package contents might have shifted, shielding might have been breached, or an error might have occurred in packaging or labelling.

Introduction

• Regulation on procurement, possession, use, transport, disposal of radioactive materials is necessary to safeguard society from potential harmful effects of radiation.

• “to deal with radioactive waste in a manner that protects human health and the environment now and in the future without imposing undue burdens on future generations”. (Principles of Radioactive Waste management, IAEA, (1995)

Answer TRUE or FALSE

• Hospitals are allowed to dispose 1GBq per month of Tc-99m radioactive waste into the drainage system. T/F

• Kr-81m gaseous waste may be released without need for authorisation. T/F

• Records not needed if limits not exceeded. T/F

Waste Disposal/Waste Management?

• Waste disposal is discarding waste with no intention of retrieval.

• Waste management means the entire sequence of operations starting with generation of waste and ending with disposal.

What is Radioactive Waste?

• Any waste that contains or is contaminated with radioactive materials .

• Inevitable by-product from use of unsealed radioactive materials.• Produced during the generation of nuclear power, use of

radioactive materials in industry, research and medicine.• May be in gaseous, liquid or solid forms; form dictates their

disposal methods, liquids and solid wastes should be separated.• All radioactive waste, regardless of form, should be separated by

isotope.• Waste must be managed starting from the time it is declared as

waste.• Waste disposal must be documented: the location and activity.

Principles of Radioactive Waste Management

1. Protection of human health2. Radioactive waste shall be managed in such a way as to

provide an acceptable level of protection of the environment3. Protection beyond national borders4. Protection of future generations5. Burdens on future generations6. National legal framework7. Control of radioactive waste generation8. Radioactive waste generation and management

Interdependencies9. Safety of facilities

Classification of Radioactive Waste

• High Level Waste (HLW): Nuclear Industry (from fuel reprocessing/spent fuel), long-lived radionuclides especially alpha emitters

• Intermediate Level Waste (ILW): NORM (radium), nuclear industry

• Low Level Waste (LLW): long-lived radionuclides, containment for a few hundred years

• Very Short-Lived Waste (VSLW): medical uses/research facilities

• Very Low Level Waste (VLLW): do not require radiation protection measures

• Exempted Waste (EW)

Exemption Orders

• liquid waste: In UK, hospitals are allowed to dispose to the drainage system up to 1 GBq Tc-99m and 500 MBq of any other radionuclides per month.

• Gaseous waste containing only radionuclides with T½ less than 100 seconds (e.g. Kr-81m) may be released without need for authorisation.

• Sources used for testing instruments activities less than 200 kBq may be disposed off to landfill sites.

• Records must be kept to show limits are not exceeded.

Medical Radioactive Waste

• At medical facilities, radioactive materials are used in numerous diagnostic and therapeutic procedures for patients. During these procedures, test tubes, syringes, bottles, tubing and other objects come into contact with radioactive material.

• Some of the radioactive material remains in the objects, contaminating them.• In medical research, laboratory animals are sometimes injected with

radioactive material for research purposes. The animal carcasses containing the radioactive material become low level radioactive waste and must be handled appropriately.

• Hospitals may store waste containing radioactive material with short half-lives until it decays to background radiation levels for ultimate disposal with non-radioactive medical waste.

• Waste containing longer-lived radioactive material is stored or sent to a low-level radioactive waste disposal facility.

Aqueous Liquid Waste

• Radioactive waste in aqueous solution or solid matter in suspension (water) may be discharged to the drainage system – Liquid waste from hospitals: urine/faeces from patients undergoing

nuclear medicine procedures, include large quantities of Tc-99m– Separate toilets equipped with special delay tanks for in-patients

undergoing therapy with I-131 or other radiopharmaceuticals– Smaller amounts of waste from preparation of radiopharmaceuticals,

unused preparations which are usually discharged into sinks designated for this

• Large amounts of water should be poured to reduce radionuclide concentration to below 1MBq/litre.

Gaseous waste

• Kr-81m: not necessary due to short T½ 100 seconds• Xe-133: need to be vented out through exhaust pipe to avoid

gas re-entry into occupied areas• Tc-99m DTPA aerosols: usually trapped by the dispensing

equipment• I-125 iodine vapour: hazard from volatilisation during

iodination can be overcome by working in fume cupboards/ BSCs.

Solid waste

• Hospital solid wastes fall into 3 categories:– Clinical waste: articles become contaminated with liquid

radiopharmaceuticals• Syringes, empty vials, needles, paper tissues, disposable gloves• Biological materials such as human and animal tissues, blood, swabs, dressings,

– Special waste: possess properties requiring treatment as special waste• Highly flammables, toxic, carcinogenic, corrosive, irritant • Biological samples containing viable disease-causing microbial organism • Liquid scintillants for beta counting

– Decayed sources: sealed sources will eventually become waste• Activity has decayed, no longer suitable• Design lifetime no longer safe to use• Damaged source• Radionuclide generators becomes waste when activity fallen below useful level,

preferably to be returned to supplier/producer

Approaches for Radioactive Waste Disposal

• If the concentrations of radioactive elements are largely short-lived, then one would resort to what is referred to as ‘delay and decay’ approach; that is, to hold on to such a waste for a sufficiently long time that the radioactivity will decay in the meanwhile. After waiting ~10 half-lives, the waste can usually be disposed like normal refuse.

• For radioactive materials in aqueous or gaseous form, a second approach is to ‘dilute and disperse’ so that the final concentration of radionuclides becomes acceptably low. – Used for majority of waste from unsealed radionuclides used in medicine and

research. It is diluted to acceptable levels and then discharged to the environment.

• For long-lived solids, the only approach that is possible is to ‘concentrate (confine) and contain’ the activity.– Stored in repository– Return sources to supplier

Concentrate & Contain

• The waste is collected and converted into a form such that when placed in a repository, it will retain the radionuclides until the activity has decayed or at least the leakage of radionuclides does not give rise to unacceptable concentrations in the environment.

• In order to carry out concentrating the waste (generally the sludge), chemical precipitation, ion exchange, reverse osmosis and natural or steam evaporation, centrifuging, etc. are resorted to. The resulting solids are highly concentrated in radioactivity.

Record Keeping for Radioactive Waste

• Up-to-date record is kept of all activity on site and all disposals made.– Amounts of liquid waste discharged via designated sinks– Liquid waste from patients : equal to those administered or

percentage – Estimates of amounts of gaseous released– For solid waste: activities being used and corrections to allow for

decay prior to disposal

Summary

• Records must be kept to show limits are not exceeded.

• Regulation/guidelines on procurement, possession, use, transport, disposal of radioactive materials is necessary to safeguard society from potential harmful effects of radiation.