The safe disposal of nuclear waste

With the coronavirus (COVID-19) pandemic highlighting the dangers from carbon emissions, and of global warming and climate change, there is now renewed focus on clean energy, especially on the civilian use of nuclear power for its capacity to supply electricity in a sustained way over a wider area than that possible through renewable sources like wind and solar.

Nuclear technology, however, naturally poses the major issue of dealing with nuclear waste in a safe and cost-efficient way. It is in this context that an American firm has recently come out with a detailed analysis on one of the few proven methods of nuclear waste management over the long term through what is known as “deep borehole disposal”.

The company, called Deep Isolation, has prepared a Post-Closure Safety Analysis (required by law in the US) for the deep borehole disposal of nuclear waste.  Deep Isolation has been working in the area of nuclear waste disposal in deep boreholes prepared by drilling into the earth’s surface. A Post-Closure Safety Analysis is designed to quantify the safety and working of the whole system of waste disposal in such a manner..

This particular safety analysis shows that spent fuel from nuclear reactors can be safely disposed off using the deep borewell method, which would allow ample compliance with the US regulatory maximum annual dose requirement for a person of potentially  (in the distant future) contaminated surface drinking water at the well over the waste at 10 millirem (mrem) per year. This figure is well within the regulatory standards laid down. The potential contamination time taken into account by the analysis starts with the sealing of the repository, includes the thermal period when the deposits are still hot, and then extends to 10 million years.

The disposal system for spent nuclear fuel includes a single or a series of deep horizontal drillholes bored into the host rocks using directional drilling technology. The individual spent fuel assemblies would be sealed inside corrosion-resistant canisters, which would then be placed in cased horizontal disposal sections of the drillholes. This disposal process begins with a vertical access hole drilled and cased from the surface. The hole and surface casings are designed to guide the drilling as well as to protect the aquifers.

From the drilling starting point, a smaller hole is drilled thereafter that gradually curves until it is horizontal. After the casing in the curved section is cemented in place, a final drillhole with a smaller diameter continues to be drilled horizontally for a few hundred meters, extending to several kilometers. The horizontal portion has a slight upward curve that provides additional isolation, and would help isolate any mechanisms that could move radioactive material upwards.

Finally, according to this study, the casing would be cemented and attached with monitoring systems, which would communicate to the surface real-time data about the repository condition through the pre-closure and evaluation periods. It also estimtes that around 10 drillholes are required to dispose of the waste from a 1,000 MW nuclear power plant (NPP) over a 30-year period.

While the concept of deep borehole disposal of spent nuclear fuel has been around for sometime, Deep Isolation, however, has been the first company to consider horizontal portions of the wells as well as the vertical ones. It is also the first to hold field demonstrations of the concept, the report of which was released in March this year.

In the very same month, it was announced in Bangladesh that Russia will take back the nuclear waste to be produced during the operation of the Rooppur Nuclear Power Plant (RNPP). Nuclear Asia reported that the Bangladesh government is preparing to revise a previously signed agreement with Russia on the management and maintenance of the RNPP with such a provision. The amended agreement will also have directions on taking Russian assistance after the full lifetime of the RNPP.

The RNPP will be operated and maintained by the Nuclear Power Company Bangladesh Ltd (NPCBL). Bangladesh Cabinet Secretary Khandakar Anwarul Islam said that with the country having no prior experience in operating and managing nuclear waste, Russia will take back the nuclear waste and dispose them outside Bangladesh. NPCBL will take over the control of the RNPP once the installation is completed. The RNPP, being constructed by Russian state atomic energy agency Rosatom, is expected to operate for a time span of 60 years and it is capable of undergoing an upgradation which will extend its life for another 40 years. The first unit of the RNPP is expected to begin operation from 2023. The reactors, turbines and other major components of the nuclear plant are being made in Russia.