How is nuclear waste generated?

How is nuclear waste generated?

Subject: Science and tech

Section: Nuclear science/energy 

Context:

• Recently, India loaded the core of its Prototype Fast Breeder Reactor (PFBR) vessel, bringing the country to the cusp of stage II — powered by uranium and plutonium — of its three-stage nuclear programme.

What is nuclear waste?

• Nuclear waste refers to the radioactive byproducts resulting from the fission process in nuclear reactors, where neutrons bombard nuclei of specific elements like uranium-235, causing them to split and release energy along with new elements that cannot undergo further fission.
• These non-fissionable elements, such as barium-144 and krypton-89, along with spent fuel that contains radioactive fission products and elements produced through neutron absorption and radioactive decay, constitute nuclear waste.
• This waste is highly radioactive and necessitates containment in specially designed-facilities to prevent leakage and environmental contamination.

How do we handle nuclear waste?

• Handling nuclear waste primarily involves managing spent fuel, which is both hot and radioactive. Initially, this spent fuel is stored underwater for cooling, potentially for decades.
• Post-cooling, it is transferred to dry casks for long-term storage. Countries with significant nuclear power programs, such as the U.S., Canada, and Russia, have accumulated large quantities of spent fuel, necessitating storage solutions that ensure isolation from human contact for periods extending far beyond the history of modern humans.
• Additionally, nuclear power plants process liquid waste, which can involve discharging treated water with short-lived radionuclides into the environment, as seen with Japan’s treatment and discharge from the Fukushima plant into the Pacific Ocean. Depending on the hazard level, other liquid wastes are managed through evaporation, chemical precipitation, absorption on solid matrices, or incineration.
• For high-level liquid waste containing most fission products from the fuel, vitrification is employed to transform it into a stable glass form for storage.
• In India, due to the reprocessing of spent fuel to extract uranium and plutonium for use as fuel, the remaining fission products present in the liquid waste pose additional accident hazards and require secure storage.

How is nuclear waste dealt with?

• Nuclear waste is managed through several methods:
• Dry-Cask Storage: After cooling in a spent fuel pool for a minimum of a year, spent fuel is moved to dry-cask storage. It’s placed inside large steel cylinders, surrounded by inert gas, sealed, and then housed in steel or concrete chambers for safety.
• Geological Disposal: As proposed by some experts, this method involves sealing the waste in special containers and burying it underground in stable geological formations like granite or clay. This method aims for long-term isolation from human activities, though there’s a concern about potential exposure from disturbances such as digging.
• Reprocessing: This technology separates fissile material (usable in further nuclear reactions) from non-fissile material in spent fuel through chemical processes. Reprocessing aims to increase fuel efficiency and reduce waste, but it requires extensive protection due to the hazardous nature of the materials handled. A significant issue with reprocessing is that it produces weapons-usable plutonium, necessitating strict international regulations.

How does India handle nuclear waste?

• In India, nuclear waste is managed through facilities in Trombay, Tarapur, and Kalpakkam, with each serving specific functions ranging from producing plutonium for reactors and weapons to processing spent fuel from various reactor types.
• According to a 2015 report, the management of low and intermediate-level waste is conducted onsite at nuclear power stations, with comprehensive monitoring for radioactivity around these areas.
• Challenges have been noted regarding the efficiency and capacity factors of reprocessing facilities, as well as potential complications from the varied waste produced by different reactor types, such as the PFBR (Prototype Fast Breeder Reactor).

Issues associated with nuclear waste encompass environmental, operational, and financial challenges:

• Environmental Concerns: Historical instances, like the Asse II salt mine in Germany, illustrate the risk of nuclear waste contaminating water resources, including groundwater. This case underscores the environmental hazards and the extensive efforts and costs required for decontamination, estimated between €5 billion and €10 billion over about 30 years.
• Operational Risks: The Waste Isolation Pilot Plant (WIPP) in the U.S. demonstrated the potential for “unknown unknowns” when an accident in 2014 released radioactive materials into the environment, despite the facility being operational since 1999 with a license for millennia-long storage. This incident revealed significant maintenance failures.
• Uncertainties in Waste Treatment: Questions remain regarding the effectiveness of vitrification plants at reprocessing facilities and the amount of high-level and intermediate-level liquid waste yet to be vitrified, indicating uncertainties in managing liquid waste.
• Siting and Ethical Issues: Efforts to locate repositories for nuclear waste have frequently failed across different countries, raising concerns about environmental injustice and the ethical dilemma of exporting nuclear waste. The principle that those benefiting from nuclear power should also bear its disposal costs is a significant ethical consideration.
• Financial Implications: Managing nuclear waste imposes considerable costs on the nuclear power sector. An analysis of a hypothetical 1,000 MWe nuclear power plant operating at a 70% capacity factor for 30 years revealed that waste management costs account for a significant portion of total expenses. The front-end cycle, operation waste management, and decommissioning, along with the back-end fuel cycle, contribute to the overall costs, imposing an estimated $1.6-7.1 per MWh of nuclear energy generated.

Source: TH