Atomic Insights

Atomic energy technology, politics, and perceptions from a nuclear energy insider who served as a US nuclear submarine engineer officer

isotopes

“The Martian’s” RTG science includes jarring errors

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During the holiday weekend, I finally got around to watching “The Martian.” Though it was a terrific, suspenseful drama, its treatment of the radioisotope thermal generator (RTG) was wrong on a number of levels. That was disappointing in the context of a high budget movie that has received numerous kudos for the significant effort its creators invested in getting the science right.

The issue that leaped out and almost spoiled my viewing experience was the scene where the protagonist — Mark Watney — is depicted removing a flag marking the location of the RTG with a skull and cross-bones and then shown digging the RTG out of the Martian soil. As his portable crane lifts the device the fine red soil is shown falling away from the device’s fins.

I remain perplexed that no one in the technical review chain of the movie wondered aloud why RTGs have fins.

Even space geeks should recognize heat sinks when they see them. RTGs produce electricity using the semiconductor thermoelectric effect discovered by Seebeck nearly 200 years ago. One junction is heated by the decay of Pu-238, but if the other junction has no way to reject heat by either radiation, convection or both, temperatures across the two junctions equalize. At that point, no current will flow. No one who knows how the devices work would bury them.

After watching the movie, I searched to find a discussion about that particular flaw; the only mention I could find came on Quora from a science fiction writer named C. Stuart Hardwick. I sent him a congratulatory Tweet on Twitter.

Though the Oak Ridge National Laboratory took the opportunity of having an RTG in a major movie to promote its involvement in the RTG manufacturing supply chain, its nicely produced 2.5 minute video doesn’t point out that burying the device would negate its utility.

Neither does the DOE blog post titled The Science Behind “The Martian” — Staying Warm on Mars.

Another problem is that the movie provides inaccurately scary information about RTG safety.

Andy Weir, the author of the book on which the movie is based, conducted three years worth of research in support of his creative effort. Unfortunately, he failed to spend 10-30 minutes learning about RTGs, which are reliable, robust, compact, well-proven and rigorously-tested power-producing devices. Here is what Weir told Popular Science about RTGs during an interview after the movie was released.

PM: Wait, so how many problems did you think of that would have just killed him?

Weir: A few!

PM: Can you tell me what they were?

Sure. One thing was, he has the RTG (radioisotope thermoelectric generator). It’s basically the lump of highly radioactive material that gives off heat. The reason he has that is that I was trying to work out how to do a long-range trip with the rovers. I did all the math and there was just no way for him to get any decent distance out of it. I’ve got to find a way for him to suddenly become a lot more power-efficient with the rovers.

Well, if there’s a 100-watt heater in the rover, and he’s able to turn that off, then all of the sudden he’s able to get much more range. But then I did some math on heat loss and realized, oh no, he would absolutely freeze to death. You would freeze. to. death. It would get down to -100 C inside that rover eventually, and that’s no good. So I need him to have a heat source.

Then I work it backwards: If they had an RTG, why wouldn’t they use them in the start? Well, they’re kind of dangerous, and they don’t like to have big piles of radiation near the astronauts, and so on. So I worked it into the story.

One plot idea I had was that once he’s driving along, there’d be a breach in the containment of the RTG. Now, suddenly, it’s emitting radiation. It cracks. But I kept running all the numbers and there’s just no way he survives. Even a small radiation leak would be almost immediately fatal. Now, I could say he gets lucky and he happens to be wearing his EVA suit at the time, which has radiation shielding. So then he could just physically hurl the RTG away in time. But then he’s without the RTG and he freezes.

I just got rid of that concept. Which is good! Because I later learned that with RTGs—it’s not just a lump of radioactive material, it’s a bunch of little pellets encased in lead. It would be very, very hard to get irradiated. You’d have to break it open, get the pellets, and cut them in half.

There are a number of things wrong with that passage.

  • RTG’s cannot kill anyone with radiation. They might be able to be used as a battering ram.
  • RTG’s generate electricity as well as heat. They’re only about 6-8% efficient, but plutonium-238-heated devices the size of the one Watney uses in the movie produce ~ 100 Watts of continuous electrical power for at least 14 years.
  • A manned Mars mission would use several RTGs on its rovers as well as rechargeable batteries, just like Curiosity, the unmanned rover, did.
  • The containers used to encapsulate RTG’s are made of iridium, not lead. Lead shielding is completely unnecessary for a pure alpha particle emitter like Pu-238 and it would be a terrible heat shield in the case of a reentry event.
  • The only way that the Pu-238 could be a danger to human health is if after cutting the iridium container in half and extracting the pellets of PuO2, those pellets were ground up into fine dust and inhaled. Even that would not be immediately fatal.

Admittedly, an obstacle for a creative writer to getting RTG science and engineering right is that the devices can spoil some of the suspense associated with approaching and overcoming obstacles.

Used to their full capacity, RTGs can make life on a desolate planet substantially less daunting. Their use increases comfort and mission accomplishment potential for real astronauts but they make stories about imaginary astronauts a bit less interesting.

I don’t want to spoil the movie creation and viewing experience, but when a creative work takes credit for realism, it is incumbent on audience members to point out significant flaws associated with their areas of expertise.

Bill Sacks – Radon abatement contractor giving poor advice in syndicated column

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By Bill Sacks

This is in response to Rosie Romero’s article in the January 27 issue of the GV News (p. B8), What you need to know about radon.

It is wrong, just plain wrong. In the low concentrations encountered in homes, radon is not a cause of lung cancer, let alone “the second leading cause,” as claimed by the EPA. On the contrary, in this setting radon acts like a vaccination and is actually protective against lung cancer, even though in a few uranium mines, where the concentration of radon in the air can be hundreds and thousands of times higher than that found in homes, it can indeed contribute to causing lung cancer.

Any attempt to mitigate the concentration in homes lowers that protective feature, and leads to a greater, not lesser, probability of developing lung cancer.

Sounds absurd? Perhaps an analogy will help. To claim that the low concentration of radon found in homes causes lung cancer, based on the fact that it has been found to contribute to lung cancer at very much higher concentrations, is like claiming that taking one aspirin a day (for cardiovascular protection) is deadly, based on the fact that swallowing an entire bottle will kill you. Or worse, that one aspirin a day is possibly “the second leading cause” of heart attacks. The fact is that small doses of radon and aspirin are beneficial to most people, while large doses can kill. This is true of most agents, from oxygen to water, from vitamins to sunshine.

In the early 1990s, University of Pittsburgh physics professor Bernard Cohen did a study of radon, examining homes in over 1,700 counties containing over 90% of the US population. He had hoped to measure how quickly lung cancer rates increase with higher home radon levels.

Much to his surprise and consternation, he found that the higher the average county radon levels the lower the lung cancer rates and, reciprocally, the lower the radon the higher the lung cancer rates. He enlisted the aid of a statistician to find possible confounding influences, such as smoking or other carcinogens, that might explain this unexpected and very strong inverse relationship. Together they examined hundreds of possible combinations of confounders but were unable to explain the result in that fashion.

At first Cohen was reluctant to conclude that it was the radon that was tending to protect, even smokers, from lung cancer, since it was so counterintuitive at the time. But eventually he grew to accept that explanation, since there was none other that arose. A number of scientists have repeatedly tried to refute Cohen’s conclusion, but the best that their arguments could do was explain half the discrepancy between the expected positive correlation and the observed negative one, and even that required them to invoke an implausible and highly improbable coincidence of high smoking rates with low radon levels, and vice versa.

Furthermore, Cohen’s discovery of radon’s protective effect at low levels of exposure has been corroborated by dozens of studies since then. Still regulatory agencies like the EPA and the Arizona Radiation Regulation Agency, whose administrators have a stake in maintaining the status quo – as well as companies who profit from home foundation repairs – refuse to credit the science.

Indeed exemplifying the pragmatic, rather than scientific, basis of radiation regulations, one of my colleagues at the Center for Devices and Radiological Health at the FDA told me that he is well aware that low levels of radiation are beneficial but that it would be a nightmare to change the regulations. Furthermore, many scientists continue to seek, and obtain, funding to attempt to refute the science.

Two other researchers and I have just submitted to a scientific journal a paper– one of hundreds of ongoing attempts to inject reality into the field of radiation science – showing that all studies concluding that low doses of radiation are harmful either ignore biological reality (experimentally and observationally confirmed in countless studies) or distort and/or dismiss it.

Furthermore, we show that all such studies contain hidden circular reasoning, in which the authors start by assuming that which is to be proven. The “all radiation is harmful” paradigm, along with its extra-scientific reward system, is a powerful hindrance to scientific objectivity. It has justifiably been called “the greatest scientific scandal of the 20th century” by the former director of the Swedish Radiobiology Society, Gunnar Walinder.

As we said in our September 30 opinion piece (p. 7), Why low-dose radiation exposure is not to be feared – published also as a letter in the January 2016 issue of Physics Today – Low dose radiation exposure should not be feared.

In conclusion, contrary to Rosie’s advice, spending money to test for, much less lower, the radon concentration in your home will not lower your probability of developing lung cancer, but rather will increase it. If you want to lessen your chances of developing lung cancer, quit smoking, which will also save you money.

I hasten to add that I do not attribute Rosie’s assertions to any dishonesty on his part, but rather to the official paradigm that has us all trapped in its clutches – until we find an escape route. Escape ultimately requires our own investigation, for which there is no substitute.

About the author:

Bill Sacks is a physicist turned radiologist who is now retired. He has spent the past few years studying global warming, nuclear energy, and the beneficial biological responses to low level ionizing radiation. He has coauthored a number of articles including Nuclear Energy: The Only Solution to the Energy Problem and Global Warming. His following pieces have appeared on Atomic Insights: Why does conventional wisdom ignore hormesis? , The Left Needs to Reconsider its Automatic Position Against Nuclear Energy and Physics Today Reader’s Forum: Low-dose radiation exposure should not be feared

Atomic Show #246 – Carmen Bigles, Coqui Pharmaceuticals Update

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In November 2014, I spoke with Carmen Bigles, the founder of Coqui Pharmaceuticals, a company that is preparing to build a $330 million medical isotope production facility near Gainesville, FL. Since that discussion 11 months ago, Coqui has made steady progress in completing their construction and operating license application to the NRC for a class […]

Atomic Show #227 – Carmen Bigles, Coqui Radiopharmaceuticals

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Coqui Radiopharmaceuticals is a start-up company founded in 2009 with a laser focus on solving a problem affecting the health of tens of thousands of people. The founder, Carmen Bigles, noticed that many of the patients arriving at her clinic had not been properly diagnosed and discovered that the reason for that condition was an […]

Radiation, Pollution and Radiophobia

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While researching answers to comments made on the Atomic Insights post titled Healthy doses of radiation, I found a book titled Nuclear Shadowboxing: Legacies and Challenges. It includes a fascinating appendix titled Radiation, Pollution and Radiophobia that should be required reading for people who are interested in understanding more about the health effects of low […]

Gold standard nuclear regulator – CNSC

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If you want to know something about radiation and have a five minute time window, invest your available time by watching What is Radiation: Understanding Radiation With the Canadian Nuclear Safety Commission. In my opinion, the Canadian Nuclear Safety Commission has lapped the competition. They are in a commanding lead as the true “gold standard” […]

Airborne radiation at WIPP

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Update: A reader pointed out that the headline is inaccurate. The issue at WIPP is airborne contamination (by radioactive material), not airborne radiation. In order to be gentle with search engines and existing links, the headline will remain as is. End Update. On Friday, February 14 at 11:30 pm, a continuous air monitoring alarm went […]

How much I-131 and Cs-137 was released into atmosphere at Fukushima?

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Total mass of main isotopes of concern from Fukushima: I-131 – 43 grams Cs-137 – 4 kilograms The Journal of Nuclear Science and Technology Volume 50, Issue 3, 2013 contains a paper titled Source term estimation of atmospheric release due to the Fukushima Dai-ichi Nuclear Power Plant accident by atmospheric and oceanic dispersion simulations. Using […]