Radioactive wastes and their management

Introduction

Radioactive materials are one of the most toxic materials in the environment. The term radioactivity is readily used in various fields and is closely linked with the disciplines such as nuclear physics, nuclear energy and nuclear medicine.  The procedures conducted in these areas generate wastes due to the usage of radioisotopes as raw materials. The most commonly used radioisotope is the technetium-99 (Tc-99) which accounts for about 80% of all nuclear medicine procedures as well as  85% of all the diagnostic scans in the field of nuclear medicine globally.

 

Radioactivity

Radioactivity is the phenomenon where a radioactive element or group of radioisotopes generate some by-products called radioactive rays. The SI unit of radioactivity is the Becquerel (Bq), named after Henri Becquerel. One Bq is defined as one decay or disintegration or transformation per second. Radioactive rays are seriously potent as they disturb the cellular composition of animals, plants and human beings. Radioactive rays allow the DNA to undergo mutation which can cause irreversible damage to the genes.  Therefore, one should carefully exercise proper universal precautions while managing radioactive wastes. A partly processed radioactive material is called a radionuclide which needs to be completely decayed otherwise, they harm the living organisms. However, the decay takes more time, hence they must be processed by using some manual techniques. The time that radioactive waste must be stored depends upon the type of waste and the lethality of radioactive isotopes. To understand this, we should know about the half-life of a radioisotope. Half-life is half of the time required to decay given radioactive element and it varies between different elements. 

 

 

Radioactive decay

It is otherwise known as radioactive disintegration, nuclear decay, radioactivity, or nuclear disintegration. It is the process by which an unstable atomic nucleus loses energy by radiation over a specified duration. The materials having unstable nuclei are considered highly radioactive. Radioactive decay is a gradual process and is divided into 3 types; alpha decay, beta decay, and gamma decay, all of which involves emitting one or more dangerous radioactive particles called photons. Alpha decay is the outcome of emitting an alpha particle from its nucleus. On the other hand, beta-decay is divided into 2 types;  Beta-minus decay and beta plus decay. Beta minus decay is when the nucleus emits an electron and an antineutrino which in turn changes a neutron to a proton. Beta-plus decay occurs when the nucleus emits a positron and a neutrino in process, as a result, a proton is changed into a neutron. In the case of gamma decay, a radioactive nucleus first decays by the emission of an α or β particle. Ultimately, the daughter nucleus is left in a non-excited state which progressively gets decayed into a lower energy state by emitting a gamma-ray photon.

 

 

Radioactive materials and radioactive wastes

Radioactive material is generally indicated as NORM-Naturally occurring radioactive materials (NORM). They consist of industrial by-products containing rich radioactive elements. The most common radioactive elements are uranium, thorium and plutonium which produces some decay products such as radium and radon. The most common radioactive waste contains hazardous radioactive material generated after the nuclear power generation, nuclear treatments and nuclear explosion. 

 

 

Classification of radioactive wastes

Radioactive wastes are divided into Very low-level wastes (VLLW), low-level wastes(LLW), intermediate-level wastes(ILW) and the high-level wastes(HLW). VLLW is the term used when the waste contains radioactive materials of not more than 7 giga-becquerels per tonne, and are generally harmless. Low-level waste (LLW) on the other side possesses radioactive content not exceeding  12 giga-becquerels per tonne and are accountable for 90% of all the radioactive wastes. Intermediate-level waste (ILW) is more potent as it generates about  2 kW/m3 of heat. Furthermore, ILW comprises some resins, chemical sludges, and metal fuel cladding that makes up 7% of the volume and has 4% of the radioactivity of all radioactive waste. High-level waste (HLW) produces the decay heat of >2kW/mand is accountable for  95% of the total radioactivity.

 

 

 

 

Effects of radioactive materials

Radiation emission cannot be noticed by a naked eye nor can be felt by heat hence it is very difficult to sense the leakage. Radiation can cause genetic changes by altering DNA, RNA, and chromosomes. The ultimate effect is the induced mutation that causes irreversible errors in the genetic material. Short-term effects of the radioactivity are nausea, vomiting, loss of hair, uncontrolled loose motion, bleeding, damage to the most essential organs such as intestine, brain, skin and ultimately person dies. The prolonged mutation may cause cancer and cell death. Children suffering from radiation hazard are more prone to low levels of intelligence, disabilities and more importantly, they are retarded.

 

 

Radioactive material waste management strategies

 

The principles of radioactive waste management focus on limiting the exposure doses, achieving high levels of radiological protection and ensuring proper disposal system in place to reduce the exposure. Radioactive waste management is the process involving systematic storage, treatment, and proper disposal of a variety of wastes. The most common radioactive wastes include radioactive liquids, airborne wastes, and solid effluents released due to nuclear industrial operations. Most of these wastes are loaded in the corrosion-resistant containers and tightly sealed before they are being transported to their respective disposal sites. Depending upon the lethality, quantity, nature,  and the half-life of the isotope, a number of approaches being used while doing this. They must first be segregated and stored at 3 levels. The short-lived waste can be stored near-surface, some intermediate-level waste and strong wastes must be buried through a deep burial and it is highly important that the storage of nuclear waste after sufficient pre-treatment should be done in tight, thick and shielded containers. These containers are then buried between rocky areas at about 500 meters deep into the earth.

 

 

PPE s( Personal protection equipment

Radioactive wastes can be properly processed without harming ourselves by taking some precautions by using PPE (personal protective equipment’s) such as a special apron, thick gloves, eyeglasses etc,

 

 

 

Questions

  1. What are radioactive wastes? Mention the most common radioactive wastes. 
  2. What are the medical uses of radioactivity?
  3. What is radionuclide? Explain the treatment of radionuclides.
  4. Explain about radioactive decay.
  5. Classify radioactive wastes.
  6. Explain the effects of radioactive materials
  7. Brief about radioactive material waste management strategies.

 



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