Archive for the ‘nuclear power’ Category

Nuclear reactors and meltdowns 101

May 10, 2011

Posted on May 10, 2011 – When the Fukishima accident had just occurred.

I am not an expert at nuclear power, but I feel there needs to be a layman’s article about nuclear power reactors, meltdowns, and their consequences to the health of the public from someone who can explain it to the public in understandable language.

I am a physician and my father’s best friend was Leo Szilard, who with Enrico Fermi produced the first nuclear chain reaction under the stands at the University of Chicago football stadium a 1/2 century ago. My father was a college student & worked in the U. of C physics department during college and during the Manhattan project. Both were ethnic Hungarians. After Szilard quit physics due to the use of the bomb on a large civilian population, despite his and Einstein’s letter to President Truman, Szilard became a world renowned biologist and kept in touch with Dad, Allan Lorincz, MD, a world renowned medical researcher.

I studied physics at the University of Chicago and had long discussions with many who were involved in the Manhattan project or went into the science and medical fields as sons, daughters, students and friends of those that were involved in producing the first A-Bomb. I particularly miss my conversations with Dr. Leon Jacobson, who was the medical doctor for the Manhattan project at the U. of C. during the war and perhaps the “father of radiation therapy.”

I feel this post will contribute to the public’s understanding of the tragic events in Japan today, along with the difficulties inherent in producing electricity from nuclear power reactors.

Nuclear Reactors 101 – I have simplified the physics, chemistry and biology!

1) What are nuclear reactors?
2) How do they work?
3) What are the dangers to health and the environment of a meltdown?

Nuclear reactors produce energy using the principle of “fission”.

Uranium atoms are split into smaller other atoms and in the process this reaction releases heat energy, which is used to boil water, that produces steam, which turns turbines, and thus the turning turbines make electricity. The reaction involves turning mass into energy.

Mass is everything you can touch or feel (think of weight – the greater the mass, the heavier the object). Even air has mass as it is made of nitrogen (80%) and oxygen (20%) plus a few other things. You can feel the weight or “mass” of air because you can feel it push you when the wind blows. [I am not strictly using the term “weight” correctly, as weight is really just a reflection of gravity, but the average person misuses the term “weight” so I’m trying to use this misinterpreted definition of weight to aid understanding.]

The “mass” of the larger atom is greater than the sum (combination) of the “mass” of the smaller atoms. Therefore, some “mass” is “lost”. Whenever a heavy atom splits into two smaller atoms, some “mass” is lost and energy is produced.

Famous physicist, Albert Einstein, discovered that E=mc2 [note the 2 should be a superscript] or Energy (E) equals Mass (m) times the Speed of Light (c) squared (multiplied by itself). He explained how mass is turned into energy.

Energy has great power. Think of electricity, light, and heat. You can’t hold it, but we know it exists and we use it as heat and electricity. Some energy you can feel or see (heat or light). Some energy you cannot detect (microwaves, radio waves, gamma waves).

Fission is when a large atom such as uranium is split into two smaller atoms which are no longer uranium, but are other elements or their isotopes. In a nuclear reactor about 3 % of the uranium undergoes fission and is converted to smaller atoms many of which are radioactive. Over time the smaller radioactive atoms may split or decay into stable elements and isotopes. Eventually a steady state is achieved. Most of the short-lived radioactive isotopes or substances decay within a few days to months. There are some radioactive isotopes that have medium or very long half-lives (the time it takes for ½ of the isotope to decay – or no longer be radioactive). Long half-lives may be thousands of years.

When neutrons are released in a nuclear reactor containing uranium, the neutrons, which are highly energetic may hit uranium and cause the fission or splitting of the uranium into two other atoms, thus again releasing energy (heat).

The mass is not actually lost when a large atom splits into two smaller atoms. The “lost” “mass” is converted (changed) into energy.

Nuclear fission (splitting of atoms) is used to release energy. Energy is used as heat to boil water in water based nuclear reactors. Boiling water makes steam. Steam pressure is used to turn turbines, which make electricity. That is how nuclear power plants make electricity.

The by-products or end-products of a nuclear reactor producing electricity are radioactive isotopes (remember that during the operation of a nuclear power plant, 3 % of the uranium is converted into other atoms or isotopes, many of which are radioactive – which means they are prone to decay and release of gamma waves, alpha waves, beta waves, and infrared waves [AKA heat]). Alpha, beta, and gamma waves are types of ionizing radiation that can damage cells.
What is radiation and how is it dangerous?

Radiation is the ionizing energy (alpha, beta, or gamma waves) that can damage DNA or other chemicals in the body. This energy is released when unstable atoms or isotopes decay (release this energy or ionizing particles – smaller pieces of atoms such as neutrons). Alpha radiation is low energy and is stopped by paper. Beta radiation is medium energy and is stopped by aluminum. Gamma radiation is high energy and takes many layers of lead to stop it. Washing after exposure can get rid of radioactive isotopes or substances on clothes and skin.

Mass of an element or substance is made up of atoms of different sizes depending upon the substance, element, or combination of elements (silicon – think of glass and sand; steel – think of iron mixed with other elements like nickel; coal – think of carbon). Each element has a symbol on the periodic table of the elements (C=carbon, Si=silicon, I=iodine, U=uranium, Pu=plutonium, Cs=cesium, Sr=strontium). Elements have all the same type of atoms such as pure carbon or pure gold. Alloys are mixtures of elements such as bronze (tin and copper mix). Compounds are separate substances like water, made up of several elements (water is made of hydrogen and oxygen).

Atoms are made of protons, neutrons, and electrons. An element has a constant number of protons – all isotopes of Iodine have 53 protons.

Isotopes have the same number of protons but a different number of neutrons. Iodine-127 is a staple normal isotope of Iodine. Iodine-131 is a radioactive isotope of Iodine that has a half-life of 8 days. Every 8 days ½ of it breaks down releasing energy or ionizing particles such as a neutron. This means that most of the radioactive iodine will be gone within 40 days and only a miniscule amount will be present in 80 days. Staying indoors and using filters for the air can therefore reduce exposure to radioactive isotopes or substances. If an area is exposed, staying indoor for months will greatly reduce exposure to ionizing radiation as much of the isotopes will have decayed. That is why it is safe to walk at ground zero at Hiroshima today.

Distance from the radioactive source is also a critical factor in amount of exposure. The exposure is exponentially related to distance and NOT linearly related. Think of it like this.

The numbers that follow and distance are illustrative and not exact in order to explain what I mean by exponential.  If the amount of radiation is 1000 rads at the source, 1 foot away it is 1/2 the amount (500 rads). 2 feet away the amount is 1/4 (250 rads). 3 feet away the amount is 1/16 (6.25 rads). 4 feet away the amount is 1/256 (4 rads), 5 feet away the amount is 1/65,536 (.02 rads). So standing 5 feet away reduces a lethal dose to a non lethal dose and standing  10 feet away makes the exposure essentially non-existent. Each time in an exponential relationship the denominator is multiplied by itself.

In a linear relationship at 1 foot the exposure would be 500 rads, 2 ft 250 rads, 3 feet 125 rads, 4 feet 62 rads, 5 feet 31 rads, 10 feet about 2 rads.

So a linear relationship versus exponential relationship for exposure means a lot of difference. Radiation does not fly through the air unimpeded. It doesn’t just keep going.

Elements are usually stable – their atoms don’t split spontaneously or release energy or particles spontaneously. If they are unstable, then their atoms split spontaneously or release particles or energy spontaneously – they are “radioactive” because they split easily or spontaneously and release neutrons, or other forms of energy. All isotopes of Iodine have 53 protons. But Iodine – 127 has 74 neutrons, while Iodine – 131 has 76 neutrons. Iodine-131 is “unstable” because it “decays” by spontaneously releasing its extra neutrons.

Radioactive by-products of nuclear reactors such as Iodine-131 and Cesium-135 or Strontium-90 can be dangerous to humans because they are water soluble and can be absorbed into the body. This is what scientists call being “biologically active.” Iodine is a particular problem because the body can concentrate it in the thyroid gland. Stontium can be concentrated into bone. Growing children, who make a lot of new bone, are therefore at a greater risk of cancer from strontium-90 exposure. Many radioactive isotopes are not biologically active, but still can emit radiation energy that can damage cells.

Radioactive iodine (Iodine-131) quickly decays. Every 8 days ½ of it decays so that after a few months there is almost none left. Therefore, if a person takes potassium iodide, in the right dose, into their body and saturates the thyroid gland so that they cannot absorb any more Iodine, if they are exposed to the radioactive Iodine isotope Iodine-131, it will pass through the body quickly, be excreted and do no damage. If iodine tablets are NOT taken immediately after exposure, then the radioactive Iodine will be stored in the thyroid, where it will sit for months and produce damage to tissue and tissue chemicals such as DNA, which can lead to cancers or thyroid dysfunction. Some damage to tissues is normally repaired by the body, but too much damage leads to radiation sickness or even cancer within years (thyroid) or later in life.

Only a doctor can tell you how much Iodine to take in (the dose), the timing of the dose (since you excrete Iodine, taking it months before exposure may not help), and whether or not you need to repeat the dose. You don’t want to take too much iodine on a regular basis or you can get iodine poisoning. Pregnant woman taking too much iodine may end up with babies with birth defects. Iodine can be concentrated into milk by cows that feed on contaminated grass, but within 80 days the fields, cows, and milk should be free of the contamination due to normal decay of Iodine-131.

Radioactive Cesium (Cs-137) has a ½ life of 30 years. It is absorbed into grain crops and ingested by eating grains grown in fields contaminated with this isotope. If the top few inches of soil are scrapped off or if the top layers are plowed deep under or into deep trenches, then the plants will not absorb the Cs. Certain fertilizer chemicals can also bind the Cs and prevent plants absorbing the Cs. Certain chemicals can be given to cows so that they don’t absorb the Cs from the grass they eat. This is all rather complicated.

Some radioactive isotopes won’t hurt you if you are a few inches away. Some can only hurt you if you breathe them in or ingest them. Some can be absorbed into the thyroid gland or bone. Others have ½ lives of centuries, but can be bound up to chemicals in the ground so that they are not absorbed and their energy release may be non-harmful unless they are exactly next to a cell. So you see, it is very complicated issue when one considers the hundreds of radioactive isotopes produced by a nuclear chain reaction, the many different 1/2 lives and the biochemistry and physiology, as well as the ecology related to each of the water soluble isotopes that may be absorbed into the body by ingestion or breathing.

Japan is giving Iodine to persons who may have been or are about to be exposed to radioactive Iodine due to the Fukishima nuclear power plant disaster in early 2011. This will protect them from the radioactive isotope Iodine-131. Iodine tablets cost about 1 penny each in mass quantities and is a standard “antidote” to I-131 exposure. Do NOT take overdoses of iodine on a regular basis or you will get iodine poisoning. Also the dose needed to saturate the thyroid gland with stable iodine may cause nausea and some people are allergic to iodine and could die of the allergic reaction. This is an issue where the public should listen to public health experts in their area of the world for guidance.

Hundreds of isotopes of all sorts of elements are produced in nuclear chain reactions but most decay in milliseconds. There are very few isotopes that cause great danger to human populations except if you are closely exposed to them at the time of the nuclear reaction or shortly thereafter. If we can keep people away long enough for the majority of radioactive isotopes to decay and protect persons from radioactive isotopes that are concentrated in the body like Iodine, Cesium and Strontium isotopes, public health can be preserved.

What is a nuclear reactor meltdown and how is it dangerous?

A nuclear reactor has 12-foot long fuel rods made of zirconium which are hollow and contained powdered uranium. When the reactor is working and producing heat, the uranium is hit with neutrons which eventually split 3 % of the uranium causing heat production. The rods are surrounded with water that is boiled by the heat, producing steam that is used to turn turbines and make electricity.

When the fuel rods have used 3% of their uranium in a fission reaction they are removed as “spent” fuel and disposed of. However the disposal takes decades.

The nuclear chain reaction is controlled by control rods which are lowered between the fuel rods. Control rods contain boron which absorbs neutrons. Neutrons released during the fission reaction cause uranium atoms to be split into smaller atoms, producing heat, releasing more neutrons, splitting more uranium, releasing more heat and neutrons, et cetera. The reaction is shut down when the control rods absorb the neutrons.

However, everything remains hot for a long time, as the by-product (smaller radioactive isotopes) continues to decay for years. That is why old or “spent” fuel rods must be stored under circulating cooling water for years before they are put in dry “cold” storage – usually about 5 years. Eventually, after years or decades, most of the radiation is gone and the fuel rods can be stored in dry storage in a more safe condition where heat is not generated (“cold storage”)..

If a fuel rod in the middle of a chain reaction (actively being hit by neutrons, undergoing fission, and producing heat) or a shut off fuel rod during the first years after they stop using it (surrounded by control rods but still causing heat from the byproducts decaying) is not cooled by water, it will get hotter and hotter and melt. The zirconium will react with water and produce zirconium oxide and hydrogen. Hydrogen gas will build up pressure and can react with oxygen causing an explosion.

Zirconium oxide is more brittle than zirconium. So the fuel rod casing will become more fragile. This is like super fast rusting and we all know rust makes metal (zirconium is a type of metal) more fragile. An oxide is like rust.

As the fuel rods become more brittle because of the heat, oxidation, and lack of cooling water, they can also melt as the temperatures may get to thousands of degrees. A full meltdown transforms the entire system of fuel rods consisting of zirconium tubes filled with uranium and the surrounding control rods containing boron into a blob of oxidized zirconium, uranium, and radioactive by-products of fission or a molten and very hot blob like lava, but radioactive. It can melt through anything and contaminate the ground and groundwater. If there are explosions or release of steam and radioactive gases, then the radioactive by-products such as Iodine-131 and Caesium-137 can be released into the atmosphere and the jet stream may distribute some of this radioactive “fallout” through the entire hemisphere.

Please NOTE: The Three Mile Island accident several decades ago was a class 5 accident with core meltdown into the containment vessel. However, it did NOT melt through the 8 inch steel containment vessel. The amount of radiation released was small. It may have been the boric acid and water that helped to prevent this turning into a class 7 Chernobyl type disaster where there was a gigantic explosion spewing particles and gases high into the atmosphere in concentrated amounts. I’m way oversimplifying here. It is NOT inevitable that the core will melt down through the containment vessel. Also understand that the purity of the uranium and plutonium (in reactor 3’s MOX fuel – a mixture of uranium with plutonium) is nowhere near the purity in a nuclear bomb. That is also why nuclear reactors don’t turn into bombs when they meltdown.

Heroic firemen and nuclear reactor workers and helicopter pilots are trying to keep the fuel rods in wet storage containment pools (not in the reactors – where seawater is cooling the cores, which are all shut down with control rods) covered with water and cooling down, as well as pouring boron on the melting rods to absorb the neutrons and keep the nuclear chain reaction shut off as well as prevent further fire, explosions releasing steam, or full meltdown due to the increasing heat if not cooled.

If the fuel rods can be kept cooling over the next few years, then a full meltdown will not occur. Right now only hydrogen explosions have occurred and there has NOT been a massive release of the many radioactive by-products of the nuclear chain reaction which occurred in the fuel rods before the control rods were lowered to shut off the nuclear chain reaction. There have been some releases (spikes) where small amounts of radioactive gases and particles were released with steam (at the time of each hydrogen explosion and when water boiled off of the spent fuel pools), but they did not go high into the atmosphere.

The release of radioactive isotopes has only been to low altitudes, which do not get into the jet stream and therefore, very little would be expected to migrate to the American continent. Only if there was a huge explosion spewing radioactive isotopes into the jet stream (>> 2000 feet into the air) would we expect radioactive isotopes to reach the U.S. or Canada (depending upon the weather). Even then, traveling thousands of miles would greatly dilute the plume and make exposure small, unless the explosion was really massive and threw a lot of the radioactive isotopes high into the atmosphere. As it takes 1-2 weeks for the jet stream to bring a plume of radioactive isotopes from Japan to the U.S., the Iodine-131 would be decreased to 1/4 of the amount by the time it reached the U.S. due to decay.

A chain reaction is when the uranium atom is split releasing neutrons and making two smaller atoms of different elements, then the neutrons split more uranium, releasing more neutrons, resulting in splitting of uranium atoms in a chain reaction or continuing reaction ultimately changing about 3 % of the uranium powdered fuel into smaller atoms of other elements by the reaction called “fission”, which produces heat energy.

All atmospheric nuclear blasts from the past ½ century including Hiroshima, along with all atmospheric bomb tests, as well as nuclear power plant accidents where radioactive compounds are spewed into the atmosphere like in Chernobyl have contaminated the soil of the entire northern hemisphere. Most of the radioactive substances have already decayed, but there remains a very small amount of radioactive chemicals with ½ lives in the hundreds to thousands or millions of years. Fortunately, other than producing a very slight increase in the cancer rate, there is very little harm going on. However, we don’t want to increase the contamination of the planet with radioactive long- ½ life isotopes!

Note that nuclear bombs explode over an area causing widespread instant destruction and death from a massive sudden nuclear chain reaction with the by-products of the reaction (radioactive isotopes) spread by wind; while nuclear power plant explosions are NOT nuclear bombs, but may spread radioactive isotopes that are by-products of fission into the atmosphere and surrounding countryside due to explosions of hydrogen (produced during a meltdown when the zirconium is oxydized) combining with oxygen, or due to build up of pressure by steam that explodes into the atmosphere – both essentially spreading the same type of isotopes around the atmosphere by wind and then the fallout onto the soil. The farther you are from the incident in both space and time, the more dilute and less radioactive will be the by-products of the reaction.

Most of the danger is in the first few weeks to months in areas where a high concentration of radioactive substances are in the air or deposited as fallout on the ground or in the soil as the fallout is blown by the wind.

This is why there is very little danger of radioactive substances spreading to the U.S. or Canada from the Japanese nuclear power plant disaster presently in progress.

The heroic Japanese nuclear power plant workers and firemen fighting to contain the meltdown of the nuclear reactors in Japan today, March 16, 2011, are allegedly being exposed to high levels of radiation that may cause their death. They are fully aware of the danger and have chosen to sacrifice themselves for the greater good. Bone marrow transplant centers around the world are on stand-by to try to treat them and save their lives. The first cells to be damaged by acute radiation sickness are the bone marrow (the body no longer will make blood) and rapidly multiplying cells like the membranes in the mouth, on the skin, and the gut. They will die from massive bleeding due to burns-like destruction of skin, loss of fluids, poor absorption of nutrients and infection as their mucus membranes and skin will be compromised. If they survive, they will have increased risk of cancer over their lifetime. [Update: 3/19/11 – reports are that there are very few of the workers exposed to high levels of radiation and there are hundreds of workers being rotated in and out of the area to minimize individual exposure. The previous reports of many exposed to deadly levels may have been rumor and exaggeration. I haven’t been able to confirm initial reports from various news agencies, although there are apparently a few who were heavily exposed.]

A meltdown is NOT a nuclear explosion like an A-bomb. This is because there are control rods, boron, and water mixed in that prevent a full rapid nuclear explosion. A nuclear bomb is a very rapid, uncontrolled chain reaction of highly purified and concentrated uranium and plutonium that is exploded in the air over a spot on the earth.

I hope this was clear and that any physicists who notice errors will inform me so I can correct them. I also have been informed that one of the reactors may have been using plutonium instead of uranium as a fuel. Anyone who knows about this please leave a comment and explanation.

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