Nuclear industry uses fuel. It needs fuel which is capable of nuclear fission. Nuclear fission is ” In nuclear fission the nucleus of an atom breaks up into two lighter nuclei.” The fuel commonly used by nuclear industry is uranium. Fission is not the same decay.
Radioactive decay is described here: https://www.nde-ed.org/EducationResources/HighSchool/Radiography/radioactivedecay.htm
“As an unstable atom tries to reach a stable form, energy and matter are released from the nucleus. This spontaneous change in the nucleus is called radioactive decay.
“When there is a change in the nucleus and one element changes into another, it is called transmutation. source: RADIOACTIVE DECAY, NDT Centre, link as given above.
Uranium is used as a nuclear fuel not because it is radioactive. It is used as a fuel because it is “meta stable”.
“Meta Stable”: (of a state of equilibrium) stable provided it is subjected to no more than small disturbances.
“the amount of supercooling a liquid can accept while remaining in metastable equilibrium is limited” Which is a dictionary definition. Meta Stable substances decay slowly and have long half lives. A mass of uranium naturally decays over many many years and through about a dozen steps into stable lead (Pb). However, in addition to this slow rate of radioactive decay, uranium has a spontaneous fission rate.
“In uranium-238, alpha decay is about 2 million times more probable than is spontaneous fission.” Spontaneous fission | physics | Britannica.com
https://www.britannica.com/science/spontaneous-fission Spontaneous fission in uranium is so rare that it took many years of working with uranium to discover the fact. It’s an interesting story, which centres around the discovery of the neutron by Chadwick in 1932. Which led Szilard to thinking and lodging his fission patents in London in 1934. Which was about 4 years before Hahn et. al. confirmed artificial fission by neutron bombardment in December 1938, published 1939.
So yes, fission is natural. It’s rare, but it exists alongside the natural alpha decay of uranium.
Why is uranium “meta stable”? How come only a few elements and specific isotopes of those few elements capable of undergoing fission? Let’s stay with uranium.
Its a big, densely population atom, with 92 protons in the nucleus and ordinarily it has 92 electrons outside the nucleus. The electrons are negatively charged. The protons are positively charged. The electrons, being free to move about and space themselves out, within the tight constraints of various energy related laws, such as Coulomb’s law.
The protons are heavy and positively charged and not free to move. They are packed in tightly, compared to say the protons in the helium nucleus. Helium has only 2 protons. Uranium has 92. So, ok, they are like little electromagnets all repelling each other. So how come the protons of all the uranium in the world didn’t fly off from electromagnetic repulsion the moment the uranium was originally formed? Why does uranium exist ? or What glues the 92 protons together in the uranium nucleus despite the fact that the laws of electromagnetism causes a very large mutual repulsion in the uranium nucleus?
What ever holds the 92 protons together can’t be gravity – electromagnetism is a far stronger force within each proton that the gravitational attraction between each proton. It can’t be the electromagnetism of the electrons – that merely might add, but for Coulomb’s law etc to the forces which try to fling the 92 protons apart.
There must be another force. A force no one had thought of or knew about. It was a big mystery to science until Chadwick discovered the neutron in 1932.
The neutron is the means by which the multiple protons of any atom – from helium up – are kept together in the nucleus. How does the neutron do this glue job? When neutrons are in the nucleus of an atom, in the presence of protons they exert – not gravity, not electromagnetism – the nuclear force.
The discovery of the nuclear force via the neutron was made like this:
“British physicist James Chadwick discovered that the nucleus of each atom contains neutrons in 1932. Shortly after this, Hungarian-American physicist Eugene Wigner suggested that the electromagnetic force is not involved in holding the nucleus together, and that there are two different nuclear forces.”
Carl Sagan suggested that we can imagine the nuclear force the neutron exerts on protons as being like little hooks (say like velcro) that works only at short distances – short distances at the atomic scale.
As the uranium nucleus is very crowded, the number of neutrons which “fit” is only just enough to generated the nuclear force needed to keep the 92 protons together for a period of time. As we know, uranium tries to become stable by emitting two protons and two protons (a helium atom) at very high levels of energy or speed if you like. Travelling at the speed of light renders the emitted helium atom “alpha radiation” because the energy level is such that the package acts exactly as if it were an electromagentic wave. Except, it has mass and momentum and, unlike gamma and X rays, it has size and electromagnetic charge. Alpha radiation has a very good chance of crashing into any atoms that happen to be nearby. At the end of its run, after numerous collisions, the alpha radiation runs out of energy and becomes a plain old helium ion in search of 2 electrons in order to become an atom again.
All of this is a natural process.
Uranium fission occurs in nature spontaneously. It is different to alpha decay or any other kind of decay. Spontaneous uranium decay is rare. How does fission occur. Remembering that uranium meta stable, a musician might understand that word “meta stable” as meaning, for him or her, that uranium’s nucleus is like a high frequency guitar string. Wound up so tight with opposing electromagnetic repulsive forces one side and only just adequate nuclear forces generated by the neutrons on the other side. Much Like the Australian government Under Gillard and Abbott. Left vs right until a stray neutron (Rudd) came along bouncing off the walls. And twanging the the 92 protons until they resonated and the whole show broke into two bits.
What Szilard realised in 1934 was this: if one could take a neutron and shoot it at a meta stable nucleus, the neutron with the right energy level could cause the nucleus to break into 2 bits. And there would be a huge amount of energy released. Far more than possessed by even alpha decay.
You see, when a neutron is working in a nucleus, exerting the nuclear force to keep protons together, it weighs more than it does when it is not in a nucleus and not exerting the nuclear force. Not that it lasts long outside of a nucleus. It has a very short half life.
When fission occurs, mass is converted directly into energy as a result of the loss of mass of neutrons. This energy can be calculated according to Einstein’s formula. E = MC squared, and conversely, M = E/C squared. Or Mass and energy are the same stuff, modified from state to state by the constant C squared (the speed of light squared.) in the beginning there was nothing much, then it became energy and some of it then it became mass. Stuff has two states. Mass and Energy. If you can trick mass into becoming energy, it takes very little Mass to become huge amounts of energy.
But that’s no excuse for nuclear waste. And fission is a very wasteful process. Fission is very rare in nature for a reason. There are no fission stars. Only fusion stars. The cosmos generally is a builder, not a destroyer.
Some people will ask at this point or earlier – how did the 92 protons which define uranium (it is the number of neutrons which determine the isotope of uranium, and it is the number of electrons (normally 92) which determine the chemical properties of uranium.) come together in the first place given the large total repulsive force between them all. Forces great enough to cause such events are found in the hearts of stars where huge amounts of gravity and violent motion caused by vast temperatures are common. Carl Sagan explains it much better than I can. This takes about 10 minutes and shows the actual motion of uranium atoms:
Now I can get into the natural radioisotopes and fission radioisotopes. There is a difference where it matters : rates of radioactivity per unit mass of the radioactive chemical in question. It is only after an attempt is made to describe decay and fission that the origin of a radionuclide can be seen to make a difference.
Uranium is the heaviest non esoteric element on the earth. Apart from a vanishing small amount of naturally occurring plutonium, nothing else on earth can match uranium’s density. The natural decay of uranium is relatively simple. All stable lead on earth signifies the end of the uranium decay chain.
Here is the natural decay chain for Uranium 238:
Compared to the uranium fission product creation and decay chains, the natural uranium decay chain is simple. However many of the natural decay products are far more radioactive and far more chemically toxic than uranium itself. There are 18 decay steps including the last one (stable lead). 18 different radioactive chemicals.
The fission of uranium in a nuclear reactor creates over 200 fission products – all of which are radio active, and many of which are far more radio active than any natural decay product of any natural radioactive chemical.
Among the natural decay products of uranium it radium and radon which are the most common and the most hazardous in the normal course of events.
As we can see from the decay chart above for U238, Radium, a solid at room temperature, decays to Radon 222 which is a gas at room temperature. In turn Radon 222 decays to Polonium 218. Polonium 218 is a solid at room temperature.
Let’s compare the three decay products.
Radium 226: “The Curie, a unit used to describe the activity of a radioactive substance, is based on radium-226. It is equal to the number of atoms in a one gram sample of radium-226 that will decay in one second, or 37,000,000,000 decays per second.” source:
It’s Elemental – The Element Radium
So every second radium 226 decays into a lot of atoms of radon gas.
The half life of radium 226 is “Radium’s most stable isotope, radium-226, has a half-life of about 1600 years. It decays into radon-222 through alpha decay or into lead-212 by ejecting a carbon-14 nucleus. The Curie, a unit used to describe the activity of a radioactive substance, is based on radium-226.” source:
It’s Elemental – The Element Radium
How energetic is the radiation produced by the decay of radium 226? 4.7 MeV (millions of electron volts per decay) (Source: TOXICOLOGICAL PROFILE FOR RADIUM
Agency for Toxic Substances and Disease Registry
U.S. Public Health Service
In collaboration with:
U.S. Environmental Protection Agency 1990. at https://www.atsdr.cdc.gov/toxprofiles/tp144.pdf
It is interesting to note that radium 226 is about a million times more radioactive than uranium 238 . 1 Gram of radium 226 produces 1 Curie of radioactivity. 1 gram of uranium 238 produces about 1millionth of a Curie.
Radium is a bone seeker and tends to concentrate in the same tissues as calcium. Bone. I don’t know if it can cross the placenta like strontium does, and I think it is found in the milk of mammals contaminated with it, in the same fashion that strontium is. Calcium ions are important components of both reptile and mammalian nervous systems, and correct nerve functioning is dependent upon calcium ions. How the presence of radium and strontium in nerve tissue and structure affects correct nervous system signalling I do not know. (Pecher, Belgium, 1932.)
Radon: the following is taken from TOXICOLOGICAL PROFILE FO RADON
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service
Agency for Toxic Substances and Disease Registry
2012. at https://www.atsdr.cdc.gov/toxprofiles/tp145.pdf
We can see the hazards of Radon 222 are very much greater than that of radium 226 gram for gram. As a gas Radon is capable transport away from an ore body or store of radium or uranium by diffusion and air movement. Most soils release low amounts of radon. Where the gas becomes trapped in basements and well sealed modern buildings, a health hazard may be created. We can also see that as an inhalation hazard radon is not subject to any biological demand at the gut wall but rather moves in and out of the lung due to the process of breathing. We see that radon 222 has a shot half life of just under 4 days. The chances of radon decay in the lung is very great. As radon decays to a Polonium which is a solid, there is the prospect of very finely sized particles of Polonium becoming entrapped in lung tissue and perhaps being picked up by the lymph system. The Lymph system is very radio sensitive.
It is important to live and work in well ventilated buildings. It is a mistake to think that buildings which may be good shelters against airborne pollutants of all kinds are safe in all matters, for where such buildings allow the ingress of radon, their very nature presents the possibility of radon build up and hazard inside the structure. In my opinion this is an aspect of staying indoors with closed doors and windows due to outside pollution and fallout of all kinds. It is relevant to living anywhere and must be considered by those with duties toward the populations of places known to be subject external environmental hazards. Such as towns in which lead smelting occurs, petrochemicals are produced and areas around mass ranks of nuclear reactors which all exploded at around the same time due to what the industry told us from 1946 until March 2011 was an impossible combination of events which only a person not fit to live in a nuclear world would worry about. Health Physics meets sociology yet again.
Polonium 218: see Radon table above for the radiological characteristics of Polonium 218. The higher the energy of the radiation, the greater the ability to damage DNA and cause ionisation within the living cell. Ionisation of cell contents creates increased reactivity in the cell contents and resultant abnormal cell chemistry. The products of such abnormal chemistry include increased production of carcinogens and increased production of inflammatory cytokines.
Class Small Molecule
Description Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie and Pierre Curie. A rare and highly radioactive metalloid, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. When it is mixed or alloyed with beryllium, polonium can be a neutron source and has been used in this capacity as a neutron trigger or initiator for nuclear weapons. Polonium has also been studied for possible use in heating spacecraft. It is unstable and all isotopes of polonium are radioactive. It is one ingredient of cigarette. (2)
Radioactive Isotope” Source: Polonium-210 (T3D0122) http://www.t3db.ca/toxins/T3D0122#reference-L1837
The Fission products Compared with the Radium – Radon – Polonium sequence
The following table is taken from “Toxicological Profile of Strontium” at https://www.atsdr.cdc.gov/toxprofiles/tp159-c4.pdf
There are four naturally isotopes of Strontium, none of which are radioactive.
The above table gives five fission isotopes of strontium all of which are radioactive. It can be seen that the shortest lived isotopes of strontium have the highest rates of radioactivity while the longest lived isotopes have the lowest rates of radioactivity. Non the less some of the beta emissions of some of the strontium radioisotopes approach levels of energies associated with alpha emitters. Strontium is a bone seeker and in cases of calcium deficient diets the body uses strontium in the structure of bone. The crystal lattice of strontium consists of larger crystals than those of calcium. Further, strontium tends to occupy the outer surface of bone. During pregnancy strontium is easily displaced from bone and travels to the foetus and nursing infant via the mother’s soft tissue (Pecher, 1939 – 1941 Journal of Experimental Biology and Medicine, SA Universities Joint Research Repository, Bedford Park, SA) (Sr89 created by Pecher using a cyclotron method of production first used by Stewart, Lawson and Cork in 1928).
It can be seen from the chart above that Strontium 89 is 27,800 times more radioactive than Radium 226, per gram, which itself is about 1 million times more radioactive than uranium. Meaning that compared to uranium 238 strontium 89 is about 28,000 million times more radioactive than unrefined natural uranium. And so on. Though being alpha emitters both radium and uranium have higher energy levels and thus higher ionising effectiveness than strontium radionuclides per decay.
Generally one can pick the fission product on the basis of its curie number. It is generally, but not always, higher than the natural radionuclides of most concern in the uranium decay series.
In conclusion, in terms of the radioactive chemicals, absorbed dose is dependent upon and proportional to the weight of the chemical one is exposed to. When the fission product Strontium 89 is compared to uranium 238, there is a very big difference in the absorbed doses delivered by the two substances. While neither Sr89 nor U238 pose much of an external hazard, the material safety data sheet for the Sr89 (marketed as Metastron by GE Health) defines the chemical as a carcinogen. It is far more potent in this role than uranium 238 as an internal emitter.
Tomorrow: Cesium fission products compared to the radium- radon – polonium series and to the banana effective dose. Or, how many banana farmers wear rad suites during harvest season in Brazil. Are they at the same risk as the Fukushima 50 were? What was in spent fuel pool number 4 ? Fruit ? Overheated spent fuel rods? Is there a difference? What is the difference between propaganda, training, education and inculcation?