RADIATION WASTE: TOO HOT TO HANDLE?
An Interview With Dr. Rustum Roy on How To Package Nuclear Waste
by Francis Macy
Dr. Rustum Roy, Professor of Science, Technology and Society at Pennsylvania State University, was interviewed in December 1992 by Francis Macy for the Nuclear Guardianship Forum. Dr. Roy is an internationally respected research scientist who has worked extensively on the management and technologies of nuclear waste materials. He was for many years a member of the National Academy of Sciences' Committee on Radioactive Waste Management and of the Committee on Radioactive Waste Management of the National Research Council. He and his team at Penn State have authored nearly 200 scientific articles on radioactive waste including "Interactions Between Nuclear Waste and Surrounding Rock" Nature 273:216-217, 1978, which shaped all national policies on permissible repository temperatures. His book, Radioactive Waste Disposal, Pergamon Press, 1982, puts the subject of waste solidification into perspective.
You have worked for many years on technologies for isolating radioactive material from the biosphere. What do you think of the United States government policy to open a deep burial site in Yucca Mountain in Nevada by 2010 and to transport at public expense the irradiated fuel rods from our 110 commercial nuclear power stations to that permanent depository?
Everything depends on age, because the radioactivity and heat decline every year. The old rods should stay at the reactor sites for as long as possible -- at least fifty years. Time is on our side.
Some nuclear power stations are running out of space in their storage pools for irradiated rods removed from the reactors.
Of course. In five years many pools will be filled up with rods, because the U.S. government has not collected them and shipped them off for storage or disposal, as it promised the utilities it would. And it shouldn't!
How then can these highly radioactive rods be kept at the power plant sites for at least fifty years, as you urge, without risk to the neighborhood and power plant personnel?
It is not too complicated in most cases. Densification is one way -- more rods per square meter in existing pools. Another is the expansion of existing pool capacity, relatively inexpensive, using existing safety systems. And now we have a new technology for dry storage of rods. After the used fuel has been in the holding pool at the reactor, losing radioactivity and heat for some years, the rods are placed in steel or concrete casks. These specially designed casks are mounted on a concrete pad by the reactor building where they can be closely observed. Because they are sealed and naturally air-cooled, they are not dependent on a reliable source of electric power for safety, which holding pools absolutely require. The Canadians have successfully used casks for years, and a number of U.S. utilities have ordered them at approximately $500,000 to $1,000,000 each.
Should our Department of Energy proceed at this time with its preparation of Yucca Mountain for eventual storage of irradiated fuel rods and other radioactive material from commercial power plants?
No. They should forget Yucca Mountain, principally because it would create an additional nuclear graveyard without getting rid of any others.
Now a related concern. The Congress' Office of Technology Assessment concluded that radioactive waste problems from the DOE weapons complex are "among the most serious and costly to correct." DOE plans to ship small trial batches of such waste by truck to the New Mexico site of the Waste Isolation Pilot Plant (WIPP). Most of this military waste is now in liquid form. What are the real dangers of transporting it across the country through populated areas?
It is out of the question to transport nuclear waste in liquid form. Too dangerous. It must be solidified. The risk of radiation release from solidified waste in transport is relatively minor. There will be accidents, given the volume to be carried, as DOE recognizes. If a cask holding solid waste falls off a truck and breaks, the contents could (in a highly unlikely event) be splintered, but the fragments would be confined to one small area. They could be quickly gathered up. The radioactive threat would be mainly to the cleanup crew. However, most people would simply not believe that there was little danger of radioactive exposure from an accident with solidified wastes.
Are you enthusiastic about centralized deep geologic burial of military waste, as planned by DOE?
No! Absolutely not. Transport should be minimized. Any movement of active materials has its risks. In my opinion Hanford, Savannah River, Oak Ridge, and Idaho National Lab, which contain over 90% of the high-level reprocessed waste, are permanently contaminated and should be considered, therefore, as de facto permanent waste repository sites. Even transportable materials should be kept where they were generated for at least fifty years.
The actual safety record of waste handling at these sites has been rather good. The communities have long since gotten used to living with their nuclear neighbors. There is no NIMBY [Not In My Back Yard] problem.
On a visit to the Hanford nuclear production facility, I learned that 66 of the surface tanks storing highly radioactive and chemically toxic liquids are leaking their contents into the ground and water table. Also, explosive gas build-up in tanks has been noted. How would you handle the tanks?
That is a serious problem but not catastrophic. The contents of those dangerous tanks need to be stabilized. In situ solidification of liquid waste is the best means: encapsulation in concrete inside the tanks.
"My main recommendation is that
we store nuclear waste in cement packaging
on the ground at military research
and production sites where it was produced.
Likewise, on-site storage of civilian fuel rods is the way to go for
at least the next fifty years."
Do you support the government's emphasis on glassification?
Certainly not. We know from experience that it is a very expensive, unnecessarily high-tech, technologically dangerous solution that is not appropriate to some host storage environments the government has in mind. In 1982, there was a DOE decision to mimic the French technology, to be able to tell the public that the problem was "solved." Absurd! Using this rationale, a glassification plant was started at Savannah River for one billion dollars. When I was a member of a team visiting Savannah River we evaluated several scenarios for waste storage -- technologically and economically. The DOE-proposed method of transforming sludge from storage tanks at extremely high temperatures into glass blocks for transport to disposal sites in the West was thirty times more expensive than the option of storing materials on site.
So glassification is expensive. What is dangerous about it?
First of all -- the technology. You are bringing highly toxic and radioactive materials to very high temperatures in a plant which you must operate only by remote control to avoid worker exposure. There is a great danger from spillage or leakage. What do you do if a quantity of glass escapes the containers? How can you clean up a few tons of frozen glass? A second specific danger is the creation of a huge lump of glass in the melting vessel if temperatures go down for any reason. This often happens in regular glass factories. What do you do with that lump and equipment all frozen together?
Did you say that glass is inappropriate at some host sites?
That is the second disadvantage. Glass will interact with host rock and water solutions at modest temperatures. Also, some wastes are harder to glassify. In deep underground storage, the radioactive contents plus normal heat from surrounding rock at such depths would create high temperatures. Years ago we did research here at Penn State on reactions of glass at different temperatures. As a result, the governments of the U.S., Britain, and West Germany had to reduce from about 500 centigrade to about 150 centigrade the maximum temperature that could be allowed in glass packaging of radioactive waste. This means that the radioactive contents must be diluted much more with non-radioactive materials, requiring ten times more storage casks and repository size than originally estimated, and adding to the costs. In sum: Glass is unnecessary over-kill as a waste form, technologically and cost-wise. We don't need it -- so why make it?
How do you rate, then, ceramic for nuclear waste packing?
A true ceramic waste form is the cadillac version. Ceramic is much less soluble than glass by several orders of magnitude, so would be safer in many environments and could contain higher proportions of radioactive material generating heat. But it is even more complex to process than glass and more expensive, because there is, so far, less experience with it.
That leaves cement. I know you have studied it as a means of solidifying wastes that exist as radioactive liquids. How do you rate it?
Highly. We have much good research and practical experience at Oak Ridge and recently at Hanford. Cement is vastly simpler and cheaper to produce compared to glass and ceramics. You can use the basically simple technology of the cement mixer at virtually room temperatures. The product is chemically closer to many natural rocks, therefore more stable than glass. Minerals have safely contained radioactive materials in nature for eons, and we replicate that mineral environment in the cement mixture. We call this "mineral modeling from nature." What we are talking about is "super cement," whose composition and structure have been exquisitely tailored to achieve needed characteristics.
I've seen cement disintegrate in wet climates like India's.
I know. Most of that is just bad engineering. My wife, Della, who is the leading expert on radioactive waste incorporation into cement, has studied 2,000- and 4,000-year-old cement structures all over the world. The kind of cement we have in mind is actually less soluble than glass. It is as resistant to leaching of cesium and strontium as glass, and it is better than glass when it comes to leaching of plutonium and uranium.
Impressive. But what do you propose doing with radioactive liquids that have been solidified into cement? What keeps radiation from escaping the cement?
Cement is flexible. It can be cast into the form of blocks of any size. Or it can be handled as a grout, a wet paste in consistency, which easily molds to the shape of most any environment. Grout was used at Oak Ridge for the only underground disposal of radioactive material in the U.S. Some of the later work was of poor quality, which gave grout a bad name. We are now talking about a super grout made up of tailored mineral sands encapsulated in cement. Our preferred term is "low temperature ceramics," and these ceramics have won the Underwriter's Lab label of safety -- it comes from Nature. For twenty years, Penn State's laboratory has used natural minerals that contain radioactive atoms and that have survived near the Earth's surface, in wet and dry river beds and sea beaches, as the "hosts," in which we first lock up the radionuclides from the waste. Then these minerals, as a fine powder, are incorporated or encapsulated into the cement with radioactive materials, in roughly the same way that sand is mixed into the cement mixer. Grouts once poured under pressure into a natural or man-made cavity or container cannot be removed. You seal it up.
We already have 500 huge,
highly radioactive holes
in the Nevada Test Site.
These can never be moved,
changed or cleaned up.
But one of them could take
an enormous amount of grouted
radioactive defense waste
making both safer.
What sort of cavities would you fill with this grout?
One of the most interesting real options, which many might agree on, would be to "kill two birds with one stone:" We already have 500 huge, highly radioactive holes in the Nevada Test Site. These can never be moved, changed, or cleaned up. But one of them could take an enormous amount of grouted radioactive defense waste, making both safer.
I saw concrete blocks stored near the surface at Hanford.
Yes. Concrete blocks are the alternative. They can be stored in concrete cellars just below the surface or be made small enough to move or be broken up. Blocks are quite easy to monitor for radioactivity releases, temperature changes, and for removal.
If there is leakage of radioactivity from cement, what can you do about it?
The very nice thing about cement is you can patch it; you can fill in six inches or six feet under a broken part of it; and you can entomb it in another six feet on top.
This has been an eye-opening discussion. Do you have any final comments?
Yes. My main recommendation is that we store nuclear waste in cement packaging on the ground at military research and production sites where it was produced. Likewise, on-site storage of civilian fuel rods is the way to go for at least the next fifty years. In this way, waste can easily be repackaged or reprocessed in the future if the need develops. Remember that time is on our side, and haste is the biggest enemy. Nuclear waste is the opposite of tea: the longer you leave it the weaker it gets.
We need a $50 million annual national program of genuine research on radioactive waste management to study alternative strategies and produce fully engineered approaches. This could reduce by at least a factor of ten the possible cost of $250-300 billion that DOE projects for its thirty-year so-called clean-up program. In the meantime, we need to educate the public. Nothing will be accomplished unless we have a thorough program of public education, with totally open discussions, without pre-conceived notions. The Nuclear Guardianship Project has an important job to do in meeting this challenge.
Thank you for your candor, wisdom and concern.
Francis Macy is a founding member of the Nuclear Guardianship Project. He is facilitating the Hanford-Chelyabinsk Movement, a collaboration between groups at the Russian and the U.S. weapons complexes.