Radioactive waste disposal | The Daily Star
12:00 AM, August 29, 2013 / LAST MODIFIED: 10:49 PM, August 28, 2013

Radioactive waste disposal

Once a nuclear reactor becomes operational, significant amount of radioisotopes develop within the fuel elements from nuclear transmutations. After a time, the concentration of radioisotopes increases to the point where the fuel is considered “spent” and is replaced with fresh fuel. These radioisotopes constitute nuclear waste. They are highly radioactive and decay into other nuclei in the course of time. During decay, the waste will produce ionizing radiation which can kill a person within seconds if he/she stood unshielded within a few meters of the spent fuel.
The potency of a radioisotope is determined by its half-life, the time it takes for the radioactivity to decrease by a factor of two. It takes about ten half-lives for a radioisotope to be considered safe.
The isotopes produced in a nuclear reactor include every element from zinc to the lanthanides. Many of them are either non-radioactive or have short half-lives. Their disposal does not pose any problem as they become harmless in a short time.
The disposal of radioisotopes that have medium half-lives is a problem of immense magnitude. They will remain hazardous for hundreds of thousands of years. Two of the most troublesome and dangerous nuclear waste to dispose of are strontium-90 and cesium-137, both with half-lives of about 30 years. They are extremely hot in the radioactive sense and require isolation for about 300 years (TDS 4-20-13). Even more troublesome are the actinides produced in the spent fuel. One of them, plutonium-239 with a half-life of 24.360, will remain dangerous for at least 243 thousand years! Plutonium has received a great deal of publicity because of its toxicity and its potential as a material for nuclear bombs.
The problem of nuclear waste disposal looms large over Bangladesh because at a recently concluded seminar in Dhaka, a senior official of Rosatom, the Russian agency that will build the nuclear power plant at Rooppur, stated that as per existing law, Russia cannot import nuclear waste from other countries just for the purpose of disposal (TDS 6-10-13). The official also denied the existence of a written waste management agreement with Bangladesh. According to the Norway based Bellona Foundation however, Rosatom “gave its new customer a verbal guarantee” that the most dangerous high-level radioactive waste from the Rooppur plant will be transported back to Russia.
By law, Russia is allowed to import spent nuclear fuel for either reprocessing or long-term storage, but only from reactors of Russian origin. If the fuel is accepted for storage, at the end of the contracted period the fuel owner would have to choose between taking back the spent fuel, extending the storage, or giving consent to reprocessing. Rosatom was perhaps embarrassed to disclose that Russia lacks the technical capabilities to reprocess waste generated in VVER-1000 reactors, the ones that will be built at Rooppur.
Rosatom is “seriously misleading its Bangladeshi partners,” notes Bellona. If this is true, then Bangladesh will have to deal with the problems associated with radioactive waste management.
To date, no country has come up with a sure-fire way of safely storing radioactive waste for longer than 50 years. The problem won't disappear soon, even though nuclear power industry is on the decline.
Currently, spent nuclear fuel from power reactors is stored underwater in spent fuel pools adjacent to the power plants. It is held in these pools for periods ranging from a few years to decades. During this period, the water cools the radioisotopes and shields the environment from the radiation. At the end of the cooling period, the spent fuel rods are placed in steel canisters surrounded by a “heavy shielding shell” of reinforced concrete and stored on-site or in a centralised facility. But on-site storage is not considered a viable long-term solution.
Most experts believe that emplacement of spent fuel containers into geological repositories could reliably prevent the escape of radioactive materials to the biosphere for at least several thousand years. But the long-term stability required of an appropriate storage site poses unique engineering, social, and political problems simply because the half-lives of most of the radioisotopes are so large that periods ranging from tens of thousands to up to a million years are required to minimise releases of the contained radioactivity into the environment.
Hannes Alfvén, a Nobel physicist, wrote: “The geologic deposit must be absolutely reliable as the quantities of poison [spent fuel rods] are tremendous. Moreover permanently guarded storage requires a society with unprecedented stability.”
In the United States, the hope for a permanent nuclear waste site has been focused on the inside of Yucca Mountain in Nevada. But technical, geological, and political issues kept postponing the repository's opening. Some observers believe that it may never open because scientists discovered numerous active earthquake fault lines near the site.
As a nation with a history of socio-political problems, can Bangladesh have a society with unprecedented stability? Is the geology of Bangladesh suitable for an underground repository where radioactive materials can be stored safely for hundreds of thousands of years? Does Bangladesh have the technology and expertise to build a cost-effective, low-risk repository? What precautions will be taken to avoid theft of plutonium? The transportation of radioactive waste from the reactor site to the repository will also present problems no less difficult than those in the permanent disposal process. After all, the potential for vehicular accident in Bangladesh is significantly high.
After more than half a century of nuclear power, waste management has been characterised by split and misplaced responsibilities and improper substitution of short-term for long-term goals. Practically all stakeholders agree that radioactive waste generated by existing reactors must be disposed of before constructing new reactors. The Bangladeshi government should, therefore, make a rational judgment whether nuclear power plant should be built at Rooppur to produce enormous quantities of lethal wastes before a safe method for handling has been fully developed.

The writer is a Professor of Physics at Fordham University, New York.

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