Why is the spent fuel from nuclear power plants dangerous?
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.
When the uranium-235 (U-235) nucleus absorbs a neutron, it can fission to barium-144, krypton-89, and three neutrons.
If the ‘debris’ (barium-144 and krypton-89) 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.
It 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.
Nuclear waste is highly radioactive and needs to be stored in facilities reinforced to prevent leakage and/or contamination of the local environment.
How can they be stored safely with minimum human contact?
Handling the spent fuel is the main challenge.
It is hot and radioactive.
It needs to be kept underwater for up to a few decades.
Once it has cooled, it can be transferred to dry casks for longer-term storage.
All countries with long-standing 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.
Nuclear power plants also have liquid waste treatment facilities.
Small quantities of aqueous wastes containing short-lived radionuclides may be discharged into the environment.
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 high-level 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 can’t be used to fuel
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 are countries with major nuclear power programmes storing nuclear waste?
Once spent fuel has been cooled in the spent-fuel pool for at least a year.
It can be moved to dry-cask 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.
The upside here is long-term 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 non-fissile material in spent fuel.
It’s another way to deal with the spent fuel.
Here, the material is chemically treated to separate fissile material left behind from the non-fissile 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 weapons-usable (different from weapons-grade) plutonium.
The IAEA has specified eight kilograms of plutonium in which plutonium-239 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.
Does India have nuclear waste reprocessing plants?
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.
COMMENTS