Physical Insights

An independent scientist’s observations on society, technology, energy, science and the environment. “Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop. Many passengers would rather have stayed home.” – Carl Sagan

Archive for the ‘nuclear chemistry’ Category

Researchers develop filter for nuclear waste

with 9 comments

Apologies for the thread title, we have this essentially inevitable problem where newspaper headlines aren’t always the best description of science and technology.

http://www.theaustralian.news.com.au/story/0,25197,24370728-2702,00.html

Australian researchers say they have created a low-cost material to filter and safely store nuclear waste. The potential breakthrough for the environment was made by a team of scientists from Queensland University of Technology, led by Associate Professor Zhu Huai Yong from the School of Physical and Chemical Sciences.

(Tip to NEI Nuclear Notes for finding the story.)

Prof Zhu said the discovery was particularly important as the world increased its reliance on nuclear energy.

“You have to keep nuclear waste somewhere for hundreds of years,” Dr Zhu said.

“Water is used to cool nuclear reactors and during the mining and purification of nuclear material, so waste water is a big problem.

“For example, there is a lake in the United States filled with millions of gallons of nuclear waste water.”

But if the waste was stored conventionally in lakes or steel containers, there was a danger it could leak and pollute the land around it.

Well, I’m not so sure about what he’s talking about here. I seriously hope they’re not talking about water used at nuclear generating stations as “nuclear waste”, for example – clearly Lake Anna in Virginia, for example, does not contain millions of gallons of “nuclear waste”, or anything of any radiological significance at all, for that matter.

Alternatively, perhaps they’re talking about “tailings” waste from uranium mining and extraction? I’m not sure, but in any case, I’m not particularly concerned about waste from uranium mining and extraction, since it contains naturally occurring radionuclides such as radium which occur naturally in the ground, in exactly the same amounts that they’re naturally present in the earth, which can be put right back into the earth.

Professor Zhu said the QUT team had discovered how to create nanofibres, which are millionths of a millimetre in size and can permanently lock away radioactive ions by displacing the existing sodium ions in the fibre.

“We have created ceramic nanofibres which attract and trap radioactive cations (positively charged ions), possibly forever,” he said.

“The ceramic material can last a very long time, much longer than the radioactivity of a radioactive ion.”

Ceramic was also more chemically stable than metal, could last much longer and was much cheaper to make than steel.

The ceramic nanofibres were made from titanium dioxide, a mineral found abundantly in Australia and used to colour white paint.

The fibres were mixed with caustic soda and heated in a laboratory oven to make the ceramic material.

The nanofibres, which are up to 40 micrometres in length, look like white powder to the human eye, Prof Zhu said.

“The fibres are in very thin layers, less than one nanometre in width, and the radioactive ions are attracted into the space between the layers,” he said.

“Once the ceramic material absorbs a certain amount, the layers collapse to lock the radioactive ions inside.”

It sounds like they’ve created an artificial ceramic nanomaterial based on the well-studied chemistry of perovskite materials, in this case saturated with Na+ ions, forming something like Na2Ti3O7 or Na2TiO3, perhaps.

Perovskite materials can contain all kinds of different anions – positively charged ions, usually metals – bound up inside their crystal structure. Strontium titanate and barium titanate are both well-studied materials with interesting properties. Strontium titanate is a common chemical form in which radioactive 90Sr is used when it’s packaged in sealed radioactive sources, such as the very large 90Sr sources that form the basis of 90Sr radioisotope thermoelectric generators, because it’s essentially a completely inert, insoluble solid ceramic material from which the radionuclide cannot leach, dissolve or otherwise escape.

These perovskite-type materials, and their ability to “lock up” essentially any alkali metal or alkaline earth metal, as well as transition metals, actinides and just about any metal, really, inside their crystal structure is well studied technology with regards to the disposal of radioactive waste and radioactive byproduct material, both fission products and plutonium-contaminated defence wastes, and indeed, these materials are the fundamental basis of the use of Synroc type materials for radioactive waste immobilisation.

Now, it’s difficult to speculate, based on nothing more than a newspaper report, but I’m guessing that where such a perovskite material is turned into a nanomaterial, with nanoscale structure, and loaded with sodium ions, you end up with something that is kind of like an interesting inorganic ion-exchange material. (Ion-exchange materials are of course an important part of nuclear chemistry, both for recovering and recycling nuclear materials, and decontaminating waste materials.)

If you take some waste water that is contaminated somehow, say, with nuclear fission products like 90Sr or 137Cs, (and providing it’s not economical to recover such materials for useful purposes), I suppose you can simply run it through a bed of this material, and those ions (Sr2+ and Cs+, assuming that they’re in soluble forms) become permanently substituted into the perovskite. Then, this material can be sintered, and you have the radionuclide contamination converted straight into a chemically inert, insoluble ceramic. Unlike an ion-exchange material, however, once those cations are in the material, the idea is that they will be permanently retained there.

To paraphrase Bernard Cohen, you can take this material, if you want to dispose of it, turn it into a rock, then take the rock and put it in the rock’s natural habitat, deep inside the earth.

Advertisements

A curious obituary: John W. Gofman

leave a comment »

John William Gofman M.D., Ph.D, passed away a couple of weeks ago at the age of 89. Gofman was Professor Emeritus of Molecular and Cell Biology at the University of California at Berkeley.

While a graduate student at Berkeley, Gofman co-discovered protactinium-232, uranium-232, protactinium-233, and uranium-233, and demonstrated fissionability in U-233 in both fast and thermal neutron spectra.

Post-doctorally, he continued work related to the chemistry of Plutonium, as part of the Manhattan Project. At that early period, less than a quarter of a milligram of plutonium-239 existed, but a half-milligram was urgently needed for physical measurements in relation to the MED. At the request of Robert Oppenheimer, Gofman and Robert Connick irradiated a ton of uranyl nitrate by placing it around the Berkeley cyclotron (to capture neutrons), for a total exposure period of six weeks, with operation night and day. They scaled up Gofman’s previous test-tube-sized sodium uranyl acetate process for the chemical extraction of Plutonium., dissolving 10-pound batches of the “hot ton” in big Pyrex jars, and working around the clock with the help of eight or ten others, they reduced the ton to a half cc of liquid containing 1.2 milligrams of plutonium – twice as much as expected!.

Dr. Gofman did significant work in cardiology, specifically with lipoproteins, but was best known as a figurehead of the 1970s anti-nuclear power movement.

Gofman was perhaps best known as one of the most vocal proponents of the linear no-threshold (LNT) hypothesis of radiation biology. This hypothesis posits that any dose of radiation, no matter how small, is harmful.

Curiously, for all his efforts against nuclear power, and warning of the grave risks of medical X-rays and other sources of low-dose ionsing radiation exposure in society, for all his efforts as a nuclear and radiation biology scaremonger, he did not oppose nuclear armament.

Because we live in a dangerous world,” he said in 1993, “I think the only thing you have is the deterrence value” of such weaponry.

Dr. Gofman produced a report after the April 26th, 1986 Chernobyl disaster predicting that there would be 1 million malignancies from the fallout, half of which would be fatal. 20 years later, this has not been the case, but we don’t know entirely for sure what the future will bring.

Interestingly, for somebody who worked, hands-on, extensively with actinide elements including Plutonium, and who would have experienced a relatively significantly elevated exposure to radioactivity over his early career working on actinide radiochemistry and the Manhattan Project, he lived to a relatively old age, and did not die from cancer. Many of the other famously brilliant physicists, chemists and mathematicians (I’m thinking of Feynman and von Neumann, just off the top of my head) of the 20th century who were involved with the project died prematurely, in some cases from unusual and aggressive cancers. Were some of these cases caused in part by radioactive exposure? I guess we’ll never know.

More from We Support Lee.

Written by Luke Weston

August 28, 2007 at 1:16 pm

Radiochemistry and Nuclear Chemistry

leave a comment »

This well-known and very useful textbook is freely downloadable on line.

http://book.nc.chalmers.se/KAPITEL/CONTENT.HTM

It’s a detailed textbook, covering a broad range of key aspects of radionuclides and their behaviour, nuclear reactions, nuclear physics, fission reactor, and so forth.

Just thought that this is a useful resource to point out to everyone out there who might be looking for a more detailed, scientific online reference on nuclear science.

Written by Luke Weston

August 6, 2007 at 2:50 am

Posted in nuclear chemistry