JOIN USScientists succeed in making N-waste less toxic
In what may be a pathbreaking step in disposing of radioactive wastes generated by nuclear power plants, Indian scientists and engineers have successfully separated actinides—the most toxic component in nuclear waste—from the bulk waste material, reducing its life from close to 20,000 years to about 300 years.
“This means wastes will not be left for future generation for thousands of years to deal with,” Srikumar Banerjee, former chairman of Atomic Energy Commission, said on the sidelines of centenary session of the Indian Science Congress. “Tarapur Nuclear Power Plant has set up a large-scale unit to chemically filter out toxic minor actinides.”
The initial success, if replicated on a large scale in all the existing and upcoming nuclear power plants, would make handling of nuclear waste safer. A deep geological repository, however, will still be needed for safe keeping the nuclear waste inside vitrified glass matrix. But those wastes will be thousands of times less toxic.
Actinides are a bunch of 15 metallic chemical elements, which impart toxicity to radio-active wastes. They are some of the most dangerous radioactive poisons. If the minor actinides are “partitioned” or removed, the rest of the waste is dominated by materials having a half-life of about 30 years. So, in 10 half-lives, (300 years) they will have negligible activity. The partitioned minor actinides can then be “transmuted” or burned in Fast Breeder Reactors (FBR) or in Accelerator Driven Systems (ADS), the Department of Atomic Energy had stated in an affidavit in the Supreme Court.
“At some point of time, we will have to burn minor actinides in one of our fast reactors. The first FBR will be operational in an year or so. A number of such reactors are in the pipeline,” Banerjee said.
Disposing of radio-active waste has been a major issue raised by the anti-nuclear activists in India as the country has a different strategy in this regard compared with the US. Since all the spent fuel contain materials suitable for recycling, India reprocesses almost 97 per cent of spent fuel.
Each nuclear power plant has an underwater storage pool for storage of spent fuel named “spent fuel storage bay.” The 97 per cent is made re-usable through a chemical “reprocessing”. Since almost the entire spent fuel is recycled, Indian nuclear scientists—bereft of any large domestic uranium source—consider spent fuel as a resource rather than waste.
But the remaining 3 per cent spent fuel is not reusable and consists of various fission products and minor actinides, which have a long half-life of lakhs of years and make nuclear wastes poisonous.
The separation of actinides is a major problem even for the developed countries because of the long-term hazard of many actinides, but is also due to the regulatory requirements associated with actinides waste disposal, which are different from those associated with other radioactive wastes.