March/April 1997
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March/April 1997 |
by Walter E. Carey
Oh mgosh! Were done with this place! Now weve got to get rid of it! Why didnt we think of this before?!! This is the panicky scenario sometimes visualized when the word decommissioning is uttered. Actually, decommissioning isnt new, nor should it present a particularly alarming prospect. Decommissioning simply means removal of a facility from operation and operational regulation. It has been used in many venues, including naval operations and various commercial pursuits. Current interest is generated by concern for the fate of nuclear power stations. Since many of these are located in the Great Lakes basin, the question naturally arises: "Is the basin ready for this?"
There is already a considerable body of experience with shutting down such facilities. In the United States, 16 older plantshave been permanently removed from service. Most of them were used for multiple purposes such as training, research or demonstration of a particular design concept. All of them produced commercial electric power. They operated at power levels from five to 265 megawatts, averaging 60 megawatts. Each has been decommissioned using one of three methodologies: dismantling, mothballing or entombment. All of the lessons learned from these efforts are available for application to the 1,000 megawatt plants that are currently being operated.
Of course, decommissioning is always preceded by any necessary decontamination. This cleanup is performed within a set of stringent regulations and independent inspections. Frequently associated only with nuclear power, decontamination and decommissioning are equally applicable to research laboratories, medical clinics and manufacturing plants. Still, power reactors will be the major source of radioactive material resulting from decommissioning. They also generate the most apprehension, whether justified or not. For both reasons, the remainder of this article deals with several issues associated with decontamination and decommissioning in the context of nuclear power stations. These issues are: What do we do with the waste? How do we get it from hither to yon? When will it happen? Whos going to pay for it? How clean will we be afterwards?
W a s t e
Decommissioning results in radioactive waste. The waste falls into one of two categories, depending on how radioactive it is. High level waste consists almost entirely of used fuel from nuclear power plants. Virtually everything else is classified as low level waste. Depending on how much radioactivity is involved, the waste must meet special packaging, shielding and physical form requirements before being accepted at a licensed disposal facility. Do centralized disposal facilities currently operate within the Great Lakes basin? No, except for a limited site at West Valley, New York. In the United States, responsibility for low level waste disposal, other than wastes from the Departments of Energy and Defense, has been assigned to the states, either individually or as multi-state compacts. U.S. reactors operating in the basin are either in states belonging to the Midwest Compact, or in the states of New York and Michigan, which are proposing to "go it alone." The Midwest Compact selected Ohio as host of the compacts initial disposal facility. The site selection project is already underway in these states. Focus readers should know that one of Ohio's site selection criteria stipulates that the facility shall not be located in the Lake Erie coastal area.
Where high level waste is concerned, Canada and the United States will each have a single, federal disposal site. A probable location for the U.S. site is Yucca Mountain, Nevada. While Canada does not yet have a specific location designated, site selection procedures are included in the document Environmental Impact Statement on the Concept for Disposal of Canada's Nuclear Fuel Waste.
Will there be enough room, once suitable sites are designated? A reasonable estimate of the volume of radioactive waste resulting from each nuclear plant decommissioning is 17,000 cubic meters (600,000 cubic feet). That's one Canadian football field dug just over three meters (nine feet) deep. Or, using a longer-handled shovel, a U.S. football field four meters (12.5 feet) deep. I think we can find the necessary space. Please don't misunderstand. Disposal facilities will not just be a hole in the ground. They will be engineered structures incorporating barriers to material leakage, shielding against radiation and extensive monitoring systems.
Transportation
Even though were confident that we can provide disposal space, we still must have methods of moving material from the decommissioning site to the disposal site. The material can be moved by rail, barge or truck. All three have been used in previous decommissioning efforts. As an example of the effort required to move the material, consider using trucks. In fact, just use medium-sized trucks with cargo space that is approximately six feet high, six feet wide and 12 feet long. Given the 17,000 cubic meters (600,000 cubic feet) estimate from the previous section, it would require about 1,400 truck loads to move the entire decommissioned plant. If the decommissioning process took five years, a not unreasonable estimate, 280 truck loads would move each year. That is about one truck per working day. Our current highways should handle it.
What about radiation exposure, or material loss, during the shipment? Highly radioactive material, such as used fuel, will be shipped in special casks that have been severely tested before being certified for use. U.S. regulations require a spent fuel shipping cask to be dropped nine meters (30 feet) onto reinforced concrete covered by steel plate. It is then dropped one meter (40 inches) onto a pointed steel bar. If it doesn't give up, it is engulfed in an 800° Celsius (1,475° Fahrenheit) fire for 30 minutes and then immersed in one meter (three feet) of water for eight hours. If it is still undamaged, it is immersed in 15 meters (50 feet) of water for another eight hours.
Other methods of risk reduction include advance approval of routes, communications monitoring of shipments, use of escorts and prior arrangements with local officials. These precautions have resulted in an exemplary safety record for shipment of radioactive material for many years.
Timing
The load placed on transportation and waste disposal capabilities will depend on when the existing plants are decommissioned. If they were all decommissioned at the same time, our resources could be stretched. But they didn't all begin operation at the same time, so it is unlikely that they will be decommissioned at the same time. Thus, the demands on waste disposal and transportation systems will be distributed and manageable.
Another major factor is the difference between license lifetime and system lifetime. U.S. plant licenses are good for 40 years. But major component replacement experience indicates that system lifetimes may be longer than 40 years. If a longer system life is indeed technically and economically feasible, then decommissioning efforts can be further spread out over time.
Cost
How much will it cost? That's a tough question. The answer depends on when decommissioning occurs and the methodology adopted. Will things cost more or less in 10, 20, 30 years? Will we have devised more efficient techniques? Will we dismantle, entomb or mothball the plants? And how clean is "clean?"
A study published in 1983 estimated that it could cost from $3 million to $40 million (in 1980 U.S. dollars) to either entomb or mothball a light water reactor. Either approach would require an additional, annual maintenance and surveillance cost of up to $300,000. The study also estimated the cost of dismantling a plant to be $120 million. A subsequent 1988 report estimates the range for all options, including ongoing surveillance and maintenance, to be from $180 million to $225 million.
Who will cover the cost is much more certain than the cost itself. The licensees will. After getting stiffed for several unbudgeted, nonreactor decommissioning projects, the U.S. Nuclear Regulatory Commission established a requirement that all licensees must have a decommission funding plan. Naturally, the encumbered money will come from payment for the goods and services provided.
How Clean is Clean?
One of the "hottest" topics concerned with site restoration projects is acceptability of cleanup standards. It is the subject of conferences, symposia and public debates. The decisions made about this topic will significantly impact all of the issues presented previously.
We know we cant achieve a "zero radiation" area. That's physically impossible. Current regulatory objectives seek to reduce residual radioactivity to levels "indistinguishable from background." Is this objective sufficient? Is it reasonable?
Answers will come from continued discourse among all the stakeholders. Hopefully these discussions will have an appropriate mix of prudence, passion, politics, professionalism, reason, logic, knowledge and feasibility. These are not totally incompatible.
And So ... ?
And so we arrive back at the initial question. Is the Great Lakes basin ready for this coming decommissioning effort? I think so.
Walter E. Carey is associate professor emeritus at Ohio State University and a member of the International Joint Commissions Nuclear Task Force. For more information, contact the author in care of Ohio Sea Grant, 1541 Research Centr, 1314 Kinnear Road, Columbus, Ohio 43212-1194.
sommaire
Le déclassement nest pas chose nouvelle; il ne devrait pas non plus présenter de perspective alarmante. Il a été utilisé dans bien des domaines, notamment des opérations navales et diverses entreprises commerciales. Les préoccupations actuelles concernent le sort réservé aux centrales nucléaires. Étant donné quun grand nombre de ces stations se trouvent dans le bassin des Grands Lacs, il convient de se poser la question suivante : «Le bassin est-il prêt pour cela?»
Il existe déjà une expertise considérable dans la fermeture de ce genre dinstallations. Aux États-Unis, 16 vieilles centrales ont déjà été mises hors-service de façon permanente. La plupart dentre elles étaient utilisées à des fins multiples comme la formation, la recherche ou la démonstration dun concept particulier. Elles produisaient toutes de lélectricité à des fins commerciales et avaient une puissance allant de 5 à 265 mégawatts, avec une moyenne de 60 mégawatts. Elles ont toutes été déclassées à laide dune des trois méthodes suivantes : démantèlement, mise sous surveillance ou mise en tombeau. Toutes les leçons apprises grâce à ces efforts peuvent sappliquer aux centrales actuelles de 1000 mégawatts.
«Le bassin est-il prêt pour les activités de déclassement?» - «Je crois que oui.»
Revised: April 14, 1997
Maintained by Kevin McGunagle,
mcgunaglek@ijc.wincom.net