Thursday, December 20, 2012

Radical Reactors Revisited

Although my main interest was in accelerators one sideline topic accompanying my professional life was nuclear reactors. Already in my early days experts kept telling that governments and industry had backed the wrong horse. They said that the light water reactor producing enormous amounts of highly radioactive waste had been as bad a choice as (remember) the VHS video tape system over Sony's Betamax. In those early days the Canadian CANDU reactor line using heavy water was considered as the better technical solution. One consequence of the "bad choice" is that we are now faced with a problem of safe storage of highly radioactive waste. To "incinerate" this waste my former director general and Nobel prize winner Carlo Rubbia even had proposed a new type of reactor, the accelerator driven Rubbiatron.

In view of the dramatic climatic changes due to the burning of fossil fuel the quest for cheap and safe energy is unbroken. In an article with the eye catching alliterated title Radical Reactors published in Nature Mitchell Waldrop sells old ideas for new. He mentions among others Kirk Sorensen promoting the Thorium molten-salt reactor while an American-Japanese collaboration is working on a fast reactor. Charles Forsberg of MIT said: Given the erratic output of both wind and solar generators, if you're going to get off fossil fuel, you have to have a serious nuclear programme. For such a revival of nuclear energy global security analyst Edwin Lyman states: Nuclear is hard, it's expensive, it's slow. Indeed, engineers and scientist must develop better radiation resistant materials, more efficient heat exchangers and improved safety systems.

Here you see Kirk Sorensen (First row, second from the right) with a banner advertising Thorium as reactor fuel

This is a sketch of the molten-salt reactor with its famous frozen plug.
In case cooling of the reactor is lost the plug melts and opens. The molten salt will flow out of
the reactor vessel and be caught safely in a container located below.
Let me predict that all these efforts for a comeback of nuclear energy are doomed to failure for all projects must work with higher pressures, temperatures, and radiation levels to increase their energy efficiency. Material science still does wonders in developing new materials for specific needs but with the metal and ceramic compounds tailored for the present nuclear industry we already approach limits. Any increase in pressure, temperature and radiation level will increase the failure rate of the materials used more than linearly, i.e., the planned new installations are accident bound. In addition all those efforts come to late. As a German proverb states: The train has left the station.

I prefer soft green to hard nuclear energy although develoments in the field of new energies are slow. In spite of an enormous funding of electric mobility the efficient electric car is still wishful thinking. The storage of energy essential due to the erratic output of both wind and solar generators is not solved. My favored storage medium is hydrogen produced in electrolysis during times when the industrial and household surge on solar and wind generators is low. Hydrogen is quite a "noble" energy although it may blow up your home when badly handled. Well, there are things you want and there are those you can do (Das eine was man will und das andere was man kann).

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