How is nuclear waste generated?
Why is the spent fuel from nuclear power plants dangerous? How can they be stored safely with minimum human contact? How are countries with major nuclear power programmes storing nuclear waste? Does India have nuclear waste reprocessing plants?
The story so far:
ecently, India loaded the core of its longdelayed Prototype Fast Breeder Reactor (PFBR) vessel, bringing the country to the cusp of stage II — powered by uranium and plutonium — of its threestage nuclear programme. By stage III, India hopes to be able to use its vast reserves of thorium to produce nuclear power and gain some energy independence. But the largescale use of nuclear power is accompanied by a difficult problem: waste management.
RWhat is nuclear waste?
In a fission reactor, neutrons bombard the nuclei of atoms of certain elements. When one such nucleus absorbs a neutron, it destabilises and breaks up, yielding some energy and the nuclei of different elements. For example, when the uranium235 (U235) nucleus absorbs a neutron, it can fission to barium144, krypton89, and three neutrons. If the ‘debris’ (barium144 and krypton89) constitute elements that can’t undergo fission, they become nuclear waste.
An important source of nuclear waste is the fuel itself. “The spent fuel contains all the radioactive fission products that are produced when each nucleus … breaks apart to produce energy, as well as those radioactive elements, … produced when uranium is converted into heavier elements following the absorption of neutrons and subsequent radioactive decays,” M.V. Ramana, the Simons Chair in Disarmament, Global and Human Security at the School of Public Policy and Global Affairs, University of British Columbia, wrote in a 2018 paper.
Nuclear waste is highly radioactive and needs to be stored in facilities reinforced to prevent leakage and/or contamination of the local environment.
How do we handle nuclear waste?
Handling the spent fuel is the main challenge — it is hot and radioactive, and needs to be kept underwater for up to a few decades. Once it has cooled, it can be transferred to dry casks for longerterm storage. All countries with longstanding nuclear power programmes have accumulated a considerable inventory of spent fuel. For example, the U.S. had 69,682 tonnes (as of 2015), Canada 54,000 tonnes (2016), and Russia 21,362 tonnes (2014). Depending on radioactivity levels, the storage period can run up to many millennia, meaning “they have to be isolated from human contact for periods of time that are longer than anatomically modern Homo sapiens have been around on the planet,” Dr. Ramana wrote.
Nuclear power plants also have liquid waste treatment facilities. “Small quantities of aqueous wastes containing shortlived radionuclides may be discharged into the environment,” International Agency for Atomic Energy (IAEA) scientist V. Tsyplenkov wrote in a 1993 feature. Japan is currently discharging, after treatment, such water from the Fukushima nuclear power plant into the Pacific Ocean. Other such waste, depending on their hazard, can be evaporated or “chemically precipitated” to yield a sludge to be treated and stored, “absorbed on solid matrices” or incinerated.
Liquid highlevel waste contains “almost all of the fission products produced in the fuel”. It is vitrified to form a storable glass. “The vast majority of the radioactivity in the waste from [pressurised heavywater reactors of stage
The Power Reactor Fuel Reprocessing plant (PREFRE) and Advanced Fuel Fabrication Facility (AFFF) at Tarapur.
I] … can’t be used to fuel the PFBR,” Dr. Ramana said of India’s situation in an email to The Hindu. “Only uranium and plutonium can be used as fuel. Because India reprocesses its spent fuel, these fission products will have to be stored, at least for a while, in the form of liquid waste, which poses accident hazards.”
How is nuclear waste dealt with?
Once spent fuel has been cooled in the spentfuel pool for at least a year, it can be moved to drycask storage. It is placed inside large steel cylinders and surrounded by an inert gas. The cylinders are sealed shut and placed inside larger steel or concrete chambers.
Some experts have also rooted for geological disposal: the waste is sealed in “special containers”, to quote Dr. Ramana’s paper, and buried underground in granite or clay. The upside here is longterm storage away from human activity, although some studies have pointed to the risk of radioactive material becoming exposed to humans if the containers are disturbed, such as by nearby digging activity.
Reprocessing — the name for technologies that separate fissile from nonfissile material in spent fuel — is another way to deal with the spent fuel. Here, the material is chemically treated to separate fissile material left behind from the nonfissile material. Because spent fuel is so hazardous, reprocessing facilities need specialised protections and personnel of their own. Such facilities present the advantage of higher fuel efficiency but are also expensive.
Importantly, reprocessing also yields weaponsusable (different from weaponsgrade) plutonium. The IAEA has specified eight kilograms of plutonium in which plutonium239 accounts for more than 95% to be the threshold for “safeguards significance”. It tightly regulates the setting up and operation of these facilities as a result.
What are the issues associated with nuclear waste?
In 2013, Der Spiegel reported on
engineers’ years’ long effort to access the Asse II salt mine, where “thousands of drums filled with nuclear waste” had been kept for “over three decades”. The effort — a decontamination project — was prompted by mounting public concerns that the waste may have contaminated water resources (including groundwater) in the area. The newspaper said it was likely to cost “somewhere between €5 billion and €10 billion” and around 30 years, to decontaminate the waste. Dr. Ramana also used the case of the Waste Isolation Pilot Plant (WIPP) in the U.S. to illustrate the issue of “unknown unknowns”. The facility has been operational since March 1999 with a licence to store waste for a few millennia. “For long, WIPP had been held up as a model for how radioactive wastes should be dealt with,” Dr. Ramana wrote. But in 2014, an accident at the site released small quantities of radioactive materials to the environment, revealing serious failures in its maintenance.
He expressed concerns to The Hindu about uncertainties with treating liquid waste: “How well have the vitrification plants at reprocessing plants functioned? How much liquid waste — high level and intermediate level — is yet to be vitrified?”
“Almost all countries that have tried to site repositories have experienced one or more failures,” he wrote. He also highlighted “normative problems with the idea of exporting nuclear waste, including the environmental injustice inherent in the exports of such hazardous materials, and the ethical argument that those enjoying the benefits of nuclear power should also incur the costs”.
What does waste-handling cost nuclear power?
In the 1993 feature, Dr. Tsyplenkov considered a nuclear power plant of 1,000 MWe capacity “operating at a capacity factor of 70% for 30 years”.
They estimated “the waste management at the front end of the cycle leads to about 10% of the total waste management cost. Of this, about onethird is due to the management of
depleted uranium as a waste. The management of wastes from power plant operation accounts for about 24% of the costs and 15% is due to power plant decommissioning. The remaining 50% of costs is associated with the back end of the fuel cycle.”
In the final estimate, they added, waste management imposed a cost of $1.67.1 per MWh of nuclear energy.
How does India handle nuclear waste?
According to a 2015 report of the International Panel on Fissile Materials (IPFM), India has reprocessing plants in Trombay, Tarapur, and Kalpakkam. The Trombay facility reprocesses 50 tonnes of heavy metal per year (tHM/y) as spent fuel from two research reactors to produce plutonium for stage II reactors as well as nuclear weapons. Of the two in Tarapur, one is used to reprocess 100 tHM/y of fuel from some pressurised heavy water reactors (stage I) and the other, commissioned in 2011, has a capacity of 100 tHM/y. The third facility in Kalpakkam processes 100 tHM/y.
Also in 2015, Jitendra Singh, the Minister of State for the Prime Minister’s Office (among other portfolios), said in the Rajya Sabha: “The wastes generated at the nuclear power stations during the operation are of low and intermediate activity level and are managed at the site itself.”
He added they are treated and stored in onsite facilities, that “such facilities are located at all nuclear power stations”, and that the surrounding area “is monitored for radioactivity”.
The IPFM report also said the PFBR’s delays suggested the Tarapur and Kalpakkam facilities “must have operated quite poorly, with a combined average capacity factor of around 15%”.
Dr. Ramana also said in his email, “If and when the PFBR starts functioning and spent fuel from it is discharged, that will bring its own complications because it will have a different distribution of fission products and transuranic elements.”