Nuclear fuel from N-waste

Since the methods of managing high level nuclear wastes are discussed again and again, I thought that it is worthwhile to recapitulate a suggestion made by BARC scientists in the late eighties. They proposed that the transuranic elements can be removed from nuclear waste.Some of them are better than normal fissile materials.

K.S.Parthasarathy





Nuclear fuel from N-waste
K.S.Parthasarathy

Many people consider management of high-level nuclear waste as a complex issue. The fuel discharged from a nuclear power reactor contains 94 per cent uranium,1 per cent transuranic elements such as neptunium, plutonium, americium and curium and about 5 per cent fission products such as caesium-137, strontium-90 etc

Transuranic elements are long lived and remain toxic for thousands of years. There is international consensus that the nuclear industry can design, construct and operate deep geological repositories to dispose of high-level waste, including transuranic elements permanently.

There may be smarter solutions. A few years ago, scientists from the Bhabha Atomic Research Centre argued that we can eliminate the stigma attached to nuclear waste and nuclear energy, if we recover some of the transuranic elements, and use them as nuclear fuel.

The study, authored by M. Srinivasan, K. Subba Rao, S Garg and P K Iyengar and presented at the 5th International Conference on Emerging Nuclear Energy Systems at Kalsruhe in July 1989 found that each and every isotope of transuranic elements is a more valuable nuclear fuel than the corresponding fissile isotopes of plutonium.

Fission products in the used fuel arise from the splitting of uranium or transuranic elements. Most of the fission products such as caesium-137 which have half-lives of a few tens of years decay relatively rapidly. In a few hundred years, the activity of fission products such as cesium-137 will be negligible.

We must keep the long-lived activity away from the biosphere for a long period because of the presence of long-lived transuranic radionuclides such as plutonium-239 (half-life 24,000 years).

If we destroy transuranic elements by some means, the long-term radiation hazard will reduce substantially; the activity will be insignificant after a few hundred years. One method is to burn them efficiently in fast reactors. Keeping the active material away for a few hundred years is feasible

If we irradiate uranium in light water reactors, at a power level of 1000 MWe for just over a month, every tonne of spent fuel, after a few years of cooling, will contain nearly 10 kg of plutonium, 0.5 kg of neptunium, 0.041 kg of curium and 0.14 kg of americium. These elements are not “wastes”. Scientists will be able to develop innovative recovery methods and fuel fabrication technologies to use these elements.

The production rate of heavy elements in the thorium-uranium-233 cycle is a million times less than those in the uranium-238-uranium-235 cycle. This is because fuels based on uranium-238-uranium-235 cycle need only two successive neutron captures to produce heavier nuclides; the urtanium-233 fuel cycle needs 7 to 8 neutron captures.

There are exotic schemes to transmute radionuclides in waste streams using novel non-fission neutron sources such as spallation targets, superconducting cyclotrons or fusion reactor blankets.

For instance, Yousry Gohar from the Argonne National Laboratory suggested that 344-MW- integrated- fusion power from deuterium-tritium plasmas for 30 years with an availability factor of 0.75, can dispose of 70,000 tons of the US inventory of spent fuel generated up to 2015. The concept eliminates the need for a deep geological repository site.

He claimed that show- casing the device which offers energy from the transmutation process to produce revenue, may help to enhance public acceptance of fusion energy.

Ultimately, the simplicity of the process and the cost- benefit criteria will prevail. BARC study is mostly theoretical. BARC scientists have developed methods to recover heavy elements on a laboratory scale

I justify referring to the 1989 Indian study now because new ways related to high level nuclear waste management are still under discussion. USA and Sweden plan to dispose of the spent fuel without reprocessing. India, France, UK and Japan will reprocess it to recover plutonium.

In 1977, Jimmy Carter halted funding for reprocessing of spent fuel. USA is now considering the revival of the programme .The proposed US policy aims to reduce the number of geologic repositories in USA to one, reuse valuable parts of the used fuel to maximize the energy from uranium ore and to recycle used fuel to minimize waste.

India’s atomic energy programme which Dr. Bhabha proposed in 1954 had all these elements!

— K.S. Parthasarathy is former Secretary, Atomic Energy Regulatory Board