Issue 10
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The most dangerous substance known to man

24th February 2023
11 Mins

We have learned to fear plutonium – one of the world’s most useful materials. But as long as you don’t eat it, you’re probably safe.

Plutonium is an element. It’s essentially nonexistent in nature, and had to be artificially produced to get any useful quantities. It was used in the first nuclear bombs, and it contributes about one third of the power in nuclear power plants. Therefore, worries about plutonium matter. Unjustified extreme caution around plutonium risks the practicality and viability of nuclear power, something which might otherwise solve both global warming, and energy supply.

Plutonium is the most dangerous substance known to man. We know this because Walter Cronkite told us so. Cronkite was the dean of network broadcasters and at the time (1977) one of the most trusted voices in America. Ralph Nader, a few years earlier, told us just how dangerous. Nader said in a speech at Lafayette College in 1975 that a pound of plutonium could kill eight billion people. He repeated that claim many times, as have many others, over and over, sometimes mixing apples and oranges, as Chester R. Richmond notes in the US Department of Energy’s 1980 report The Plutonium Controversy, citing claims like:

a piece of plutonium the size of an orange is sufficient to kill the population of the British Isles . . .

The byproduct of breeder reactors, Plutonium-239, has a half-life of 25,000 years, yet experts suggest that a lethal dose for the whole human race need not be larger than an apple.

As a whole the public accepts these claims which are reinforced by TV shows such as Edge of Darkness (1985), which has the principal character Jedburgh dying of radiation sickness following contact with plutonium. 

But in 1956 at the opening of the Calder Hall plutonium production facility in the UK, a young Queen Elizabeth was invited to handle a lump of plutonium and feel the warmth of the extraordinary material, which she did.i The shielding was a plastic bag and I presume the royal gloves. The Queen outlived almost all her contemporaries. 

I need to preface this next story with a little bit of background. If enough highly enriched plutonium, called the critical mass, is brought together into a single piece, it will produce a short-lived chain reaction, a blue flash of neutrons and photons, which can be fatal if you are close enough to it. This happened twice during the Manhattan Project when mistakes were made during the bomb core assembly process. In both cases, the assembler, Harry Daghlian and Louis Slotin, died of acute radiation sickness within a few weeks.

A radiation dose is measured in units called millisieverts (mSv). Daghlian received 5,900 mSv in a few seconds. He died 25 days later. Slotin was hit with 21,000 mSv in about the same time, and died in nine days.ii In both cases, everybody else in the room survived with little or no aftereffects. 

Galen Winsor worked at the US plutonium production plant at Hanford, Washington, for 15 years. The staff there regularly carried around lumps of highly enriched plutonium in their lab coat pockets. Winsor described the process in 1985:

Well, through the years we got pretty good at telling what a critical mass was, and I have worked in a plant where I had half a critical mass in this hand, barehanded and dressed in street clothes, and half in this hand, wearing a lab coat, and I’d put this half in a pocket on this side and this half in a pocket on this side and walk down the hall. If those two ever got together, there’d be a blue flash. They never got together because I was between them. And we’d do that every day. And each half had definite dimension characteristics, and so we’d take them down and pass them on half at a time and they’d measure it and say, ‘Yeah, that one passed’. And then we’d pass the other half, and that one will pass too, but they were carefully put in separate birdcages, so they would not get together accidentally.

Winsor died in his eighties.

Delivery of Trinity Test core pieces to assembly room, 12 July 1945.

The image above shows Sergeant Herbert Lehr delivering the plutonium core pieces for the Trinity test into the assembly room at the test site. The plutonium he is carrying in his right hand is in shock-mounted birdcages. Philip Morrison, one of the smartest physicists of all time, a man who understood radiation well, carried the core pieces 210 miles from Los Alamos to Alamogordo in a standard Army sedan. Morrison lived to be 89.

So how can we reconcile Cronkite and Nader with Winsor and Morrison? The answer is simple. What Nader and the other claimants almost always forget to mention is that plutonium is an alpha-particle emitter. Alpha is a form of radiation that has almost no penetrating power. Alpha particles will be stopped by a piece of paper or a few centimeters of air or a royal glove.

Lesson 1: For plutonium to be hazardous it must be ingested or inhaled.

Decades earlier, the Manhattan Project managers understood that plutonium was safe in most conditions. They undertook a number of experiments to find out how dangerous it was. Their problem was that the human body is terribly inefficient at absorbing plutonium. Plutonium will quickly react with air to form insoluble oxides. The body has no use for these ceramics. The plutonium oxide molecule is so large that it has trouble penetrating cell membranes. Of ingested plutonium, 99.99 percent will be excreted in a day or two.iii The experimenters had to figure out a way around this. Their solution was reprehensible.

In 1950, Manhattan Project doctors injected 18 people, ages 4–69, with plutonium without their knowledge. The researchers made every effort to maximize the damage. The subjects were injected directly into their bloodstream with highly soluble plutonium nitrate. All these people had been diagnosed with terminal disease. Eight of the 18 died within two years of the injection, all from their preexisting illness or cardiac failure. None died from the plutonium. 

One of the involuntary subjects was Albert Stevens, a 58-year-old house painter. Stevens had been misdiagnosed. His terminal stomach cancer turned out to be an operable ulcer. Stevens died at the age of 79 of heart failure, never knowing he had been injected. The other problem the Manhattan experimenters faced is that Plutonium 239 (239Pu), the principal bomb isotope, has a half-life of 24,000 years. It decays far too slowly for their purposes. To inflict the dose they wanted, they had to spike the injection with 238Pu. This isotope has a half-life of 88 years. It emits alpha particles 300 times as rapidly as 239Pu. Almost all the dose that Stevens received was from 238Pu, an isotope that forms an extremely tiny fraction of nuclear waste. The 238Pu had to be produced separately from the bomb-making process in a research reactor.

Over the 21-year period between his injection and his death, Stevens’s body received a cumulative dose of 64,000 mSv, three times the dose that killed Louis Slotin. The central hypothesis that guides our nuclear regulatory policy is called the linear no-threshold model (LNT). LNT claims that radiation harm depends only on the total dose – that it does not matter whether you get that dose in 20 seconds or 20 years. According to LNT, Stevens should have been dead ten times over. We know he would have died in a week or two if he had received one tenth of that dose in a few hours or less. As it was, his body absorbed and repaired eight mSv per day for 21 years. 

Most opponents of nuclear power believe that it is the long-lived material, stuff that remains radioactive for millennia, that is the real problem. In fact, it is the very short-lived substances that kill because they release highly penetrating energy fast enough to overwhelm the body’s repair mechanisms. These are the particles that killed Harry Daghlian and Louis Slotin. It’s dose rate, not dose, that kills. Plutonium is not only an alpha emitter; it releases its particles slowly, far more slowly than the radon that is found in just about every basement in the USA.

Lesson 2: If plutonium somehow did get into our bloodstream, for which there is no efficient natural pathway, the radiation is released gradually, so gradually that the body’s repair processes are usually able to cope with the damage.

That leaves the inhalation route. It turns out that if you:

  1. Create very fine plutonium dust,
  2. somehow deliver just the right amount of this mist to the right place in everybody’s lungs, and
  3. assume that the rate at which the dose is delivered is irrelevant despite the fact that the gradual plutonium dose rate will be within the capabilities of our repair processes,

then you can come up with a number that is only 4,000 times lower than Nader’s claim.iv In a debate with Nader, Ralph Lapp, a radiation expert, pointed out that you could make the same claim for air. Take a tiny bubble of air, inject it in just the right way into the bloodstream, and a fatal embolism will occur. That’s why nurses carefully squirt out a little bit of liquid before giving you a shot.

Nader’s argument depends on an unrealizable delivery scenario. God knows we tried. During atmospheric bomb testing in the 1950s through 1963 (when almost all such testing stopped), about 4,000 kilograms of plutonium was released into the atmosphere, 10,000 times the amount that Nader said would kill us all. Fortunately the transfer of plutonium to people’s innards is horribly inefficient. Our best guess, using International Commission on Radiological Protection (ICRP) models, is that about 0.25 grams of the atmospheric plutonium ended up in human bodies.v The cumulative dose per person up to 1974 was estimated to be 0.16 mSv to the lungs, 0.09 mSv to the bones, and 0.05 mSv to the These figures are 100–200 times smaller than the lifetime alpha dose to these organs from natural sources. 

There are all sorts of substances that will kill people much more surely than plutonium (or air) if you concoct a Nader-like delivery scenario. They include relatively common industrial chemicals such as chlorine, phosgene, and ammonia.vii

And let’s not forget assumption 3, that the rate of delivery is irrelevant. The Manhattan Project did do a number of much less deplorable plutonium experiments. The most important was the UPPU (U P Pu – you pee Plutonium) Club. This was a group of 26 workers who had the highest level of plutonium in their urine of all the people on the Manhattan Project. They had worked with plutonium in a number of chemical forms, often with no protection at all. These men were periodically examined over the 50-year period between 1944 and 1994. Their cumulative doses ranged from 100 to 7,200 mSv with a median value of 1,250 mSv.

As of the end of 1994, seven of the group had died compared with an expected 16 deaths based on mortality rates of U.S. white males.8 The UPPU group mortality rate was also less than that of 876 unexposed Los Alamos workers of the same period. The 19 living persons had diseases and physical changes characteristic of a male population with a median age of 72 years (range: 69–86 years). Eight of the 26 workers had been diagnosed as having one or more cancers, which is within the expected range. The cause of death in three of the seven dead was from cancer, namely cancer of prostate, lung, and bone. If LNT were correct, the UPPU Club would have a cancer rate 30 percent higher than their unexposed peers.

Lesson 3. Avoid breathing a lot of plutonium dust.

For just about all of us, this is a commandment that is impossible to break.

Plutonium needs to be handled with care. You must avoid a critical mass. If you are machining or grinding plutonium as is required in reprocessing used nuclear fuel for solid-fuel reactors, you should avoid breathing the dust. But because it is a slowly decaying alpha emitter with very inefficient body uptake, it is one of the more easily handled toxic substances known to man. Our fear of plutonium is totally overblown.

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