ENERGY SPENT IN DECOMMISSIONING

This article first appeared in the NDR July 2012 issue, pg 38, by author Dr. Michele Laraia.

 

Image 1: Using gravity to  dismantle Yankee Rowe NPP and drop debris to the ground.
Image 1: Using gravity to dismantle Yankee Rowe NPP and drop debris to the ground.

Quite recently, I was taken aback when somebody asked me about the energy (e.g. Mwh or Petajoules, PJ) spent to demolish a NPP, and the innuendo was that the decommissioning-related energy could be comparable with the construction of the same NPP, and even to the energy generated by that plant. I must admit I had no answer to offer on the spot. And yet, I realized soon that this is an argument used at times by the anti-nuclear groups. Was this really a loaded question? I decided to launch an enquiry among my colleagues and friends and I am glad to share the results with you.

Answers soon flooded my PC. One simple answer, which captures the essence of the issue (thanks, Tom!) is that the energy required to decommission a NPP is far less than that required to construct one. Individual components need to be manufactured in shops distributed throughout the country (or imported from other countries), requiring electrical power for machining and welding; associated lighting, heating and cooling of the shops is also required. Materials for construction must be trucked or rail shipped from all parts of a country (or other countries). In construction, all materials need to be raised into position with cranes, forklifts, electric hoists, etc. There is an extensive amount of electric welding required to connect the millions of meters of piping to the components, then to inspect the welds (using electronic techniques) which also requires lighting to set up the equipment and see the inspection operation.

Construction typically can take 10 years or more of energy to light, heat and cool buildings not only being constructed, but those needed for temporary office and warehouse space as well. In addition, energy is consumed while running the systems for at least one year to debug electronic systems, check operation of pumps, valves, heat exchangers, tanks (for leakage), turbines, generators, diesel-generators, condensates systems, etc. Excavation for buildings involves soil or bedrock removal by bulldozers and cranes, as well as the transport of the material off-site for disposal. Concrete used for construction must be trucked in to the site, mixed onsite and pumped or poured into place.

By comparison, decommissioning uses to the maximum extent possible the weight of the buildings to implode them to the ground (see image on the right), and then muck out the rubble with front-end loaders. Systems are cut in larger sections than when they were installed, using oxyacetylene torches, plasma torches or shears to segment them for containerization for disposal. Lighting needs are minimal, for such work. Certainly, underwater cutting of the vessel internals, and then segmentation of the vessel requires energy, but such operations have been demonstrated to take one year or less, whereas installation of the same would take two or more years. Once containerized, the waste material needs to be trucked or rail shipped for disposal, a much less energy-consuming process than constructing the individual components from multiple locations in the country. Some of the demolished concrete can be used for fill of below-grade voids, rather than shipped off-site. Generally, a smaller amount of backfill soil would need to be imported to the site for grading and landscaping.

Another way of looking at this (thanks, Paul!) is that a typical LWR produces say 1000MWe for about 90 percent of the year. It is inconceivable that decommissioning operations—the energy intensive parts of which are cranes, front loaders, trucks, etc.—would use this much power almost continuously. A big piece of plant may have a 1000 kW engine – even a big railway loco is only about 20 MW, and that is used for a very short time in decommissioning. I would guess decommissioning is using, on an average basis, much less than 0.1 percent of the energy the plant would have produced over the same period. And active decommissioning takes five years against several decades of operation.

In a physicist’s approach to decommissioning (thanks, Ian!) we are lifting a large mass and transporting it to a disposal site. Let’s assume that we raise the total mass for disposal through 100 m and then transport it to a site 1000 km away at a speed of 100 km/h. To estimate the energy used for segmenting the removed mass one could multiply the lifting energy by a factor of 2. Finally, an energy efficiency of 20 percent for the tools used can be assumed. (Of course all these figures can be disputed, but an order of magnitude is needed to see where we are.)

Comparing decommissioning-related energy to the energy generated by an EPR with a design life of 60 years, we get a ratio of 0.01 percent. The transport distance is the main factor. In Europe we can assume a smaller distance so the above ratio becomes less than 0.01 percent.
A Finnish colleague (thanks, Harri!) reported on a detailed calculation for the decommissioning of the Loviisa power plant. According to this study, the energy needed is 0,44 PJ (=123 GWh) (1 TWh = 3.6 PetaJoule, PJ) in total for the eight years decommissioning time. The lifetime power production will be about three-and-a-half orders of magnitude higher.

Figures provided by the World Nuclear Association (WNA)[1] are, respectively, 6 PJ for the energy spent in decommissioning and 3024 PJ as total output, which gives a ratio of 0.2 percent.

The Loviisa figure is lower in comparison to the figures from WNA sources, since the Finns have certain advantages in respect to decommissioning, such as an onsite radioactive waste repository.

In summary, it is clear that the energy spent to decommission a nuclear plant is a small fraction of the energy spent during the construction and a tiny fraction of the energy generated by that plant.

About the Author:
Dr. Michele Laraia is the former IAEA Nuclear Decommissioning Team Leader, and a chemical engineer by background. He obtained his degree at the University of Rome. From 1991 to 2011, Laraia worked at the IAEA, Waste Technology Section, as Unit Leader responsible for decontamination and decom­missioning of nuclear installations, closeout of uranium mining and milling sites, and environ­mental restoration. His tasks included drafting and preparation of technical reports and other docu­ments, organization of international conferences and seminars, and the management of technical cooperation projects with developing countries, either on a national or regional scale.
From 1975 to 1991, he worked at Italy’s Regulatory Body (ENEA/DISP) in the capacity of reviewer of ra­dioactive waste management systems, and since 1982 as licensing manager of decommissioning projects. During the 1982-1991 period, under his management, seven small research reactors and other nuclear fuel cycle facilities were dismantled in Italy and their sites returned to other uses. In other plants, modifications to license conditions were implemented to achieve a safe storage state was granted to Gorigliano NPP.

Dr. Laraia currently offers consultant services. To contact him, email: Michele.laraia@ndreport.com.

References:
[1] The World Nuclear Association, http://www.world-nuclear.org/info/inf11.html