A couple of days ago, one of the largest movable structures ever built was rolled into place to surround Chernobyl Unit 4, the infamous power plant in Ukraine. … [Read More...] about Giant new cover for Chernobyl is an engineering marvel – and a monumental waste of money
Researchers at the University of Bristol have excited geeks around the world by announcing they had successfully demonstrated artificial diamonds that produce an electrical current when exposed to radiation. Their research has been inspired by a fact that is almost unique to the UK. There is a large stockpile of radioactive carbon-14 available as a result of operating a number of graphite-moderated, gas cooled reactors starting in 1956 and continuing today.
When faced with a large inventory of potentially hazardous material that no one seems to want, people have two primary choices. They can fret about ways to store or dispose of the waste or they can find ways to extract value from the material.
The University of Bristol researchers have produced a short video to explain how they have chosen the second path and to describe the destinations to which it might lead.
The development has the potential to address an issue has been one of many obstacles to building Adams Engines. I’ve been wondering how to convince others to accept C-14 as a potentially useful byproduct that needs to be handled instead of thinking of it as an insurmountable barrier.
What is an Adams Engine?
Adams Engines have been under conceptual development since 1991. The fundamental idea is to use proven nuclear fuel capable of heating a flow of moderate pressure gas to ~ 800 ℃ or higher. That flow of gas would be piped directly to a simple cycle gas turbine to produce electricity. A variant would eliminate the power turbine and instead produce a hot stream of gas useful for process heat applications.
This path breaks from precedent but seems to be a path toward a radically simplified power system using atomic fission as a heat source.
High temperature reactors
High temperature gas cooled reactors have been under development since the late 1940s. Several, including Dragon, AVR, THTR, Peach Bottom 1, Ft. St. Vrain and HTR-10 have operated with varying degrees of success. Technolgists in the field have almost universally decided to use a tristructural isotropic (TRISO) coated particle fuel that contains fission products even when raised to temperatures in excess of 1600 C.
Almost everyone in the field of high temperature gas reactors selects high pressure helium as the heat transfer medium to move thermal power out of the reactor.
Using helium locks out the direct use of commercially available compressors and turbines. That doesn’t seem like a very big obstacle, but developing turbo machinery that is well suited for high pressure helium has proven to be challenging enough to kill several promising development projects.
A few designers have considered using a helium to air heat exchanger and a piping loop with a helium circulator to enable the use of conventional, air breathing turbomachinery, but that idea locks in a higher number of components. The heat exchanger, which is easy to insert in a drawing, has material and manufacturing challenges that will fundamentally change the system cost structure.
The Adams Engines concept avoids the challenges imposed by helium and instead uses nitrogen as the reactor coolant. The same hot nitrogen that transfers heat from the reactor serves as the working fluid in the turbo machinery that converts fission-originating heat into motion. Using nitrogen at appropriate temperatures, pressures and flow rates gives Adams Engine designers access to a wide range of proven machinery that has been designed and manufactured for the combustion turbine industry.
Why does everyone else use helium?
From a reactor engineer perspective, helium is an almost ideal coolant. Though its ability to move heat is limited by its low natural density, helium has a high specific heat transfer coefficient per unit mass. That gives it a reasonable volumetric heat remove capacity, especially if the system is operated at 50 – 100 times atmospheric pressure. It’s inert, eliminating corrosion inside pipes and tanks as a concern.
Its real beauty as a nuclear reactor coolant is that it doesn’t absorb neutrons. Helium doesn’t affect reactor core reactivity and it doesn’t become radioactive.
From a heat transfer engineer’s perspective, there are other gases that can move heat from a reactor just as well. Two of those available gases, atmospheric air and nitrogen, are useful in commercially available gas turbine machinery because they have the gas properties (density, specific heat transfer coefficient, etc) for which those machines are designed.
Atmospheric air has three drawbacks.
- Air contains oxygen that has the possibility of reacting with materials in the reactor and in the piping systems when at system operating temperature.
- Air contains a small amount of Ar-40, which gets activated to Ar-41 when exposed to a neutron flux. That isotope decays with a penetrating gamma emission that can cause exposure hazards. It is a short lived isotope with a 1.8 hour half life, so it is not a long term pollutant.
- Air contains nitrogen.
Using just the nitrogen component of atmospheric air eliminates the first two issues. Challenges associated with the third issue are increased a bit due to the marginally higher concentration of N2.
The main reason that almost all other high temperature gas reactor projects have chosen helium over nitrogen is that N-14, the most abundant natural isotope of nitrogen, has a moderate cross-section for neutron absorption. It undergoes a neutron absorption/proton emission reaction that produces C-14 and hydrogen. Hydrogen is stable and not a challenge to eliminate in the tiny quantities that it is produced.
Neutron absorption has a small effect on core reactivity, but that issue can be mitigated.
The issue that other designers have chosen to avoid is that C-14 is mildly radioactive. It decays with a 5,730 year half life by emitting a single low energy beta particle that turns it back into N-14. C-14 isn’t a general area radiation issue because its weak beta is readily shielded and will only travel a few centimeters even in dry air. There are concerns, however, that C-14 may cause health problems if enough of it is ingested to give the host a dose large enough to cause harm.
If the University of Bristol researchers successfully create battery products that use C-14 as a raw material, a former barrier could turn into a potential revenue opportunity. That’s an outcome that would stimulate a small celebration.
A couple of days ago, one of the largest movable structures ever built was rolled into place to surround Chernobyl Unit 4, the infamous power plant in Ukraine. That plant was destroyed more than 30 years ago when it suffered a steam explosion and fire after the operators violated a number of operating procedures with many engineered safety systems turned off.
Even though the accident happened in 1986 and the areas outside of the plant have radiation levels that are safe for general accessibility, bureaucrats in the European Union decided that the concrete sarcophagus hastily erected near the time of the accident needed to be encased in a shiny new structure. In order to reduce doses for construction workers to the internationally accepted “As Low As Reasonably Achievable” (with no dollar value assigned to “reasonable”) the new structure was built several hundred meters away from the damaged reactor.
The design included massive wheels and a rail system that would allow it to be slid into place when complete.
It was quite an engineering feat. It should be a source of pride for the workers that successfully completed their assigned tasks. Taxpayers, however, were asked to pay a large bill for something that wasn’t actually needed. In era when sports complexes are publicly funded and cost roughly the same kind of money, I suppose it wasn’t such a wild way to employ hard-working, skilled people in a productive fashion.
The endeavor, however, has resulted in headlines that indicate a need for a reasonable explanation for the real hazard and the actual need for the structure.
Here is one example of the reason this piece should be useful: New high-tech shelter reminds us that Chernobyl is still deadly, thirty years after the meltdown. Sadly, that headline appears on a site called ZME Science, a publication that claims to be “a trusted and provocative source of science news and features, covering research and developments from all scientific fields.”
Here is a letter about the new confinement that was shared on one of my mailing lists. I’m republishing it here with the author’s permission.
Dear friends of clean nuclear energy,
A giant sarcophagus has been built and is now inaugurated at Chernobyl. This technical engineering feet is described here :
It is described as shielding Ukraine from the deadly dangers of radiation.
Of course most readers of the Guardian and most world leaders that agreed to finance this huge box to “keep the devil in the box” don’t know the numbers and have no precise idea of what is a dangerous level of radiation.
In fact most of them have been wrongly led, by such articles which contribute to increasing radiophobia, into believing that any (even microscopic) level of radiation is dangerous and deadly.
This of course only results from fear and ignorance. In French we say “la peur est mauvaise conseillère” (fear is a bad counsellor).
Here are my comments on this new Chernobyl sarcophagus:
This sarcophagus is certainly an admirable engineering accomplishment : it is the largest movable object ever built by humanity, but it is useless health wise.
The world is spending €1.5bn (one and a half billion euros) to protect itself from harmless levels of radiation.
This sarcophagus is intended to keep the (said to be so) devil (radiation) prisoner in a big box (well bigger than that : the biggest box ever built!).
Some journalists, and non-scientists (which includes a large number of politicians) certainly might think and will believe that it is justified to build the biggest-ever prison box at any cost, even any number of billions of euros, to keep the biggest-ever devil as a prisoner encapsulated inside it. But it is not so : in this case the devil is no devil and it is not dangerous. The money is simply and sadly wasted.
In the days that followed April 26th 1986, when the reactor with no containment was in flames during two weeks, and indeed rejecting the largest-ever amount of radiation directly into the atmosphere, levels of radiation on site at Chernobyl and directly downwind, such as the city of Prypiat, were then extremely high of course, dangerous and even deadly for some of the firemen and workers courageously working on site at the moment of the accident.
This was mainly due to radioactive iodine 131, which has completely disappeared since the summer of 1986 (its half life is 8 days).
This is not the case any more. The danger has vanished. The evil radiation has disintegrated (as radioactivity always does, by definition) with time passing.
The radiation on the Chernobyl site now, outside the molten reactor building, even without the new sarcophagus, is hardly more than a few microsieverts per hour and has no detrimental health effects. It is millions of times less than the deadly radiation levels that occurred at the moment of the accident.
Such levels of radiation are lower than natural radiation in other locations of our planet where (and rightly so, as there is no danger) nobody is building a sarcophagus to contain an imaginary devil.
For example I have myself measured 50 microsieverts per hour on the beach of Guarapari in Brazil. Not only this popular beach is not considered as a potential health danger, but in fact it is famous for its BENEFICIAL health effects. Brazilians and South Americans come from far away to benefit from the thorium rich sands of this beach.
The new sarcophagus at Chernobyl is therefore useless health wise, a vast waste of international money and nothing but the financial and physical incarnation of the huge worldwide radiophobia that resulted from the Chernobyl accident and antinuclear propaganda amplified by the press.
This money would be better spent producing medical isotopes or developing small modular reactors to power energy-starving developing countries!
President of Environmentalists For Nuclear Energy (EFN) International
Support EFN by becoming a member or making a donation here :
Thank you for your support
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