Debunking myths on nuclear power

December 31, 2013 by Martin Boland, The Conversation
Nuclear power and nuclear weapons: what’s the difference? Credit: Patrik Hermansson

It is the received wisdom that nuclear weapons and nuclear power are inseparable. Consequently, any country that builds a civilian nuclear power station is able to build an atomic bomb within a couple of years.

Clearly there are overlaps in knowledge and technology between the civil and military nuclear industries. How closely is power generation connected with weapons production?

Experiments in the 1960s, and a student project in the 1970s, showed that a well-informed scientist could get close to recreating the design of Fat Man, the used at Nagasaki.

Information about the physics of a nuclear weapon's core is probably not the limiting factor in . The critical part of a , which sets it apart from any other weapon, is the presence of an amount of a material (known as fissile material) that is capable of maintaining a nuclear chain reaction (called the critical mass). This usually means either uranium or plutonium.

While uranium is naturally occurring, plutonium is for all practical purposes a synthetic element – only produced by man.

However, it's not as simple as digging up sufficient uranium ore and extracting the uranium metal. Only one isotope of uranium (235U) and one of plutonium (239Pu) can conveniently be used to manufacture a weapon (I'll explain what the numbers mean below).

235U only occurs as around 1% of natural uranium. The other 99% is 238U.

To make a practical uranium bomb, about 60kg of 80% pure 235U is needed. There are several methods for separating 235U from 238U. All methods are complex and the details of some remain classified.

Heavier isotope, smaller bomb

You probably noticed that the superscript 238 (as in 238U) is one less than 239 (from 239Pu) – this is important.

Inside a nuclear reactor there is a large number of free particles called neutrons. It is the neutrons that mediate the nuclear reactions.

Trinity, the site of the world’s first nuclear explosion. Credit: CHUCKage

When a neutron hits the nucleus of a 235U atom, the nucleus usually splits into two large pieces and releases several new neutrons. This is the process known as fission.

A neutron hitting a nucleus does not always cause fission. 238U can absorb a neutron and after a couple of other reactions become 239Pu. This process is known as breeding.

Again this is significant – compared with 235U's bare critical mass of ~50kg, the bare critical mass of 239Pu is around 11kg. In other words, the amount of material needed to make a bomb with 239Pu is a fifth that of 235U.

These figures can be lowered to around 4kg 239Pu for very advanced designs. Fat Man used around 6.2kg and some advanced methods, such as using a tamper and polonium based neutron boosting. The potentially much lower of plutonium makes it the preferred material for weapons production.

Another advantage of plutonium is that it has different chemical properties and reactivities to uranium. So, rather than needing sophisticated isotope separation technology, the two metals can be separated by well-known metal processing chemistry (such as the PUREX method which involves dissolving them in acid, reacting both metals with an organic compound, extracting the organic compounds into kerosene and selectively reducing the plutonium so that it can be re-extracted back into water).

Side effects of breeding plutonium

239Pu is fissile, if a neutron hits it; about 75% of the time it splits. The other 25% of the time, the nucleus captures another neutron to become 240Pu.

240Pu is much less likely to capture another neutron. Therefore, over time the amount of 240Pu compared with 239Pu in a reactor core will go up. This isn't a problem as such for the reactor (although it can create waste issues), but is a huge problem for nuclear weapons manufacture.

Induced vs spontaneous

Above I described induced fission. The question left hanging is – where does the first neutron in the chain come from?

Part of an ION Accelerator. Credit: Shutterstock

Some atoms, when they undergo radioactive decay, do not follow their usual pathway (alpha decay for 239Pu and 240Pu). One in five million 240Pu atoms and one in five trillion 239Pu atoms undergo spontaneous fission, meaning they break up without warning and release some neutrons. These events are where those "first neutrons" can come from.

The high spontaneous fission rate of 240Pu acts as a kind of poison in the core of nuclear bombs. More than about 7% 240Pu and the likelihood that the warhead won't work increases, and the dangers of handling the more radioactive 240Pu become too great.

The 7% limit is reached in a typical nuclear reactor after about 90 days (depends on the reactor design and the 235U enrichment). Typical commercial power reactor fuel cycles are around two years. If the fuel cycle is shorter the electricity becomes uneconomic.

All this means that the plutonium than can be extracted from the fuel rods of a commercial nuclear power reactor is not suitable for making nuclear weapons.

Historical perspective

There are five declared and four other nuclear-armed countries (assuming Israel's warheads detonate). There are 31 nations with nuclear power stations (and 58 with research reactors). Only seven of the nine nuclear-armed countries have civilian power programs.

All of the technical factors can be circumvented with sufficient time and money. Uneconomic fuel cycles can be run and warheads built with high levels of radioactivity. However, no country has developed indigenous after deploying civilian stations.

Historically, if a country wants to produce a nuclear bomb, they build reactors especially for the job of making plutonium, and ignore civilian power stations.

Explore further: Plutonium in troubled reactors, spent fuel pools

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3.3 / 5 (3) Dec 31, 2013
The attitude of most nuclear powers:

'Atomic weapons don't kill people--people kill people'

'You can have my launch key when you pry it out of my old fried hand'
3 / 5 (4) Dec 31, 2013
What good is a warhead built with high levels of radioactivity? At what point is it then assembled into a usable device? Nuclear warheads have roughly zero radioactivity, same as unfluxed nuclear fuel.

μολὼν λαβέ MOLON LABE
5 / 5 (1) Dec 31, 2013
The main threat includes the ease with which a mass of radioactive material can be concentrated for missile warheads which use conventional explosives to disperse the 'dirty bomb' contents the radioactive material cloud becomes over a population center. Remember the health effects and deaths caused by 'depleted uranium' shells used in the gulf war? That would be magnified many times by the purposely concentrated (not 'depleted') radioactive uranium being exploded by conventional means over concentrations of population and critical agricultural lands. Better to be safe than naive about ANY unstable country/regime concentrating ANY radioactive material, regardless of its 'unsuitability for nuclear detonation'. Good luck to us all. :)
4.7 / 5 (3) Dec 31, 2013
Nuclear warheads do not have "roughly zero" radioactivity prior to being detonated. An unshielded nuclear core is clearly detectable as radioactive. A warhead built with material that has a higher level of radioactivity has a higher chance of failure or semi-failure, but so long as it still goes "boom" when triggered, it's still a bomb.

As for what GOOD it is... well, you have me there.
5 / 5 (4) Dec 31, 2013
"However, no country has developed indigenous nuclear weapons after deploying civilian nuclear power stations."

I think this assertion is incorrect.

India's first nuclear test used plutonium produced in the Canadian-supplied CIRUS reactor,
and uranium used for the weapons program has been separated from the power program, using uranium from indigenous reserves.

Here in the United States, the West Valley Reprocessing plant extracted plutonium from spent fuel from commercial LWR reactors (although 67 % of its SNF was from defense reactors). 80% of the plutonium went to Hanford, presumably to feed our weapons program.

I think there is a conversation to be had about the development of civilian nuclear power in oil-rich nations (nudge-nudge, wink-wink), but I don't thing arguing an alleged disconnect between reactors and weapons is a productive approach.
1 / 5 (6) Dec 31, 2013
Imagine the difference it would have made if the research money had gone int Cold Fusion, then everyone could have his own.
we could just let the planet burn carbon and go the way of Venus.
Descisions, descisions.
we could do a bit of readical genetic and Morphic engineering and become a bit more suited to survival.
4.2 / 5 (6) Dec 31, 2013
Or we could just let the planet burn carbon and go the way of Venus.

We could never go the way of Venus, no matter how much carbon we burned and no matter how much we would want to do it. That is a myth. It is physically impossible, Al Gore notwithstanding.

Venus's atmosphere is somewhere between 965,000 ppm and 967,000 ppm CO2 at over 90 times the density of the atmosphere of earth.We are barely on the cusp of reaching 400 ppm with all the carbon-based fuels we have burned. Because of the mass and density of the atmosphere of Venus, there actually is four times the amount of N2 in that atmosphere than exists in our own, even though our atmosphere is more than three-fourths N2.

This isn't something that people like to hear but it still needs to be said.
2 / 5 (8) Dec 31, 2013
The same people that created those old myths are the same people pushing the AGW agenda.

Damn watermelons.
3.3 / 5 (3) Jan 01, 2014
happy new year
not rated yet Jan 03, 2014
Imagine the difference it would have made if the research money had gone int Cold Fusion, then everyone could have his own.

Cold fusion? What do you want to do with Java apps?
2.3 / 5 (3) Jan 03, 2014
"The same people that created those old myths are the same people pushing the AGW agenda."
I vote this the most clear headed statement here in 2013.
1 / 5 (2) Jan 05, 2014
Another myth of nuclear power is it's safety...
not rated yet Jan 07, 2014
5 / 5 (1) Jan 10, 2014
Another myth of nuclear power is it's safety...

Scare tactics and not much more. For example, the Bald Eagles in Utah are dying because they ate birds infected with West Nile. They are not dying because of Fukushima radiation. The reader isn't told about that, though. Much is made about the government soliciting suppliers of KI tablets. The truth is that it is no big deal. The government procures stuff like that all the time for emergencies. Old and dated stockpiles have to be replaced somehow. As to the now 71 soldiers on the Naval vessel, many of their symptoms actually are caused by KI sensitivity. Some people are supersensitive to it and it can cause lifelong side effects in such people. Cooper's swinging thyroid and six-month menstruation are among such side effects for female sensitives. That is why you never take KI tablets unless you absolutely must. GIGO...

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