Nuclear Reactors in Japan - An interesting review...

Good Morning, below is a very good read on the Fukushima nuclear reactors in Japan. This comes from a professor of Nuclear Science and Engineering at MIT - Dennis Whyte.

"Given the extraordinary events in Japan over the last week, and the associated issues with the Fukushima nuclear reactors, I wanted to provide a set of data and perspective on this event. The mainstreammedia has been ridiculously irresponsible in its coverage of the events in Japan. If you were to take your cues from them, you would think we approaching nuclear armageddon.
The reality is that while this was a serious nuclear accident, it is insignificant to the magnitude
of destruction caused by the quake and tsunami.

I will note that fission reactors and accident scenarios are not in my area of research
expertise; but I do teach, and deal with, nuclear/radiation safety.

First I will provide two streams of "de-sensationalized" information.

A. A web-site blog which was set up by MIT nuclear engineering students: This provides very good background materials, explanation of terms, etc. http://mitnse.com/

B. A technical review of the incident is inserted below from Lake Barrett, who is an expert in fission accident scenarios.

My own comments:

1. The nuclear accident must be kept in perspective of the astonishing natural catastrophe that has occurred in Japan. A 9.0 earthquake is almost unimaginable. Remember this is on the Richter scale so each increment of 1 is a factor of ten increase. Most of us recall the devastation from the Northridge earthquake in Southern California in the mid 90's (I was living in San Diego then) which was a 6.7 earthquake. The Japanese earthquake was about 200 times more powerful! Then you throw on top of that a 30 foot high tsunami wave! You saw the pictures: this wipes out a civilization. Over 10,000 dead.

While the nuclear accident is of course a concern, the media completely lost perspective on this, which to date has killed one person (not killed by radiation, but by a chemical/H explosion in the plant).

2. While technical assessment will need to continue, if anything this accident will prove how incredibly good the engineering of a nuclear reactor really is. The size of the quake + tsunami were outside the limits of any scenario envisioned. Yet the reactors safely shut down as designed. The accident in the end, which came about because they just could not pump water around, was the result of the utter devastation to the entire infrastructure of northeastern Japan. Certainly all present and future reactors will use the lessons learned to make them even safer.

I am not trying to downplay the seriousness of the accident: this was a serious situation, particularly for the plant workers. But let's gain some proper perspective.

Nuclear fission is by far the safest form of generating large amounts of centralized electrical power. There has been exactly zero deaths due to radiation exposure from fission power plants producing 20% of US electricity for over 40 years. ZERO. About 30 people die every year in US coal mines. In China coal mining: 5000 deaths per year. Yet somehow the (probably horrible) deaths of these coal miners has never triggered a headline like "Deadly coal: Crisis for the world's coal reactors...all coal mining plants shut down"Perspective.

3. The biggest misperception comes from the dangers of the radiation release. This is so exaggerated by mainstream reporting that it borders on criminal intent to instill unnecessary fear into people. The perceived risk from radiation implied by the media is completely at odds with the physical reality. Here's the reality: a) What is radiation? Radiation arises from nuclear processes (like fission) because you are re-arranging the nuclear components. The characteristic energy of the "radiation", which is actually just light, is about a million times larger than radiation/light you get from chemical processes (like burning gas). This is why nuclear energy gives you millions times more energy per amount of fuel. We cannot directly see this light, and it penetrates deeply into solid materials including human bodies which is why you use it look inside the human body, i.e. an X-ray. The health hazard arises from this penetration: basically the energy of the light can get absorbed in human tissue and possibly cause local damage.....But at the same time, it is extremely easy to measure. in comparison with other toxins for human health (chemical, biological).

b) But isn't any exposure to radiation dangerous? NO, NO, NO - This is where the media is particularly egregious. You must be quantitative about radiation exposure. Again it is very easy to measure radiation. We use a specific unit called a "micro-sievert" to measure radiation exposure in humans; this is called a radiation "dose", i.e. the cumulative amount of radiation energy the human body has absorbed.

We also use a 'dose rate' which is just the dose divided by the time in which the dose was received. The easiest unit here is "micro-sieverts per hour" . Why? Because right now as you read this email you are receiving a radiation dose rate which is about one micro-sievert per hour. Wow, because of Japan? NO, because there is a continuous source of "background" radiation for any human living on the surface of the earth. In fact, this is why radiation is so benign to people: all organisms evolved in a radiation filled environment.

Our bodies have repair mechanisms for radiation damage through natural evolution. This "background" varies from location to location. For example Saskatchewan has a higher rate than Boston because of its higher elevation. It is this natural variation in natural radiation rates that obviously tell us that radiation exposure at levels like micro-sieverts per hour have no measurable impact on human health. In fact there are locations which have background radiation at approximately 100 micro-Sieverts per hour. The local populations there have on average better overall health and less cancer! And we willingly expose ourselves to radiation for health reasons: if you have ever received a CT scan, you got about 10,000 micro-sieverts, or about how much you receive naturally in one year. This has no measurable effect on human health.

So when is it dangerous? Radiation at very high dose rates will be dangerous to human health, basically because the body cannot heal the damage fast enough. This is called "acute" dose, which means when you get the dose in about a day. The first measurable signs of effect on human health are at about 500,000 micro-sieverts per day. In order for the dose to be lethal you need about 3,000,000 micro-sieverts. You can see these numbers are enormous compared to background radiation. So yes you can die from radiation exposure, but it must be at a radiation dose rate which is staggeringly large.

It is trivial to avoid harmful amounts of radiation. First, you can measure the radiation very easily so you readily know when the levels are too high. Second, just walk away from the radiation source: the dose rate decreases like the square of distance between you and the radiation source. So if you move 10 times further away from source, the dose rates goes down by 10x10=100 times. Third, put some combo of water, concrete and lead between yourself and the source and your dose rate goes down very rapidly to zero. This is the basis of how radiation is "contained" in a nuclear power plant...there are many meters of these materials between the radioactive source and people outside....this is why you can stand beside a nuclear reactor when it is operating. I do it everyday at work.

You can also get exposure by ingesting radioactive materials...again easily avoided... don't eat it.
Ah, ha you say, but isn't the real problem long term health effects. Aren't these people going to get cancer and die later on. Simple answer: NO Survivors from the atomic weapon attacks on Hiroshima and Nagasaki give us the best clue of this. It is a misconception that people died from
radiation in those cases: it was primarily the explosion itself and subsequent fires that killed people. The health of survivors was very carefully monitored because they received very large acute doses. In reality, their radiation exposure barely passed the threshold for causing increase in long-term chances of getting cancer compared with the general population. Unless you get nearly fatal radiation exposure, it is not possible to measure the effects of low-level radiation on long term human health. Again, this is almost certainly because we evolved in this radiation environment.

4) Let's quantify the problems at the nuclear plants. Because of the lack of cooling water, fuel rods have been exposed both in the cores and (probably) in the outside cooling pools. The radiation levels right up beside these radioactive fuel rods would pass the threshold for danger, which makes repair difficult. The biggest danger for workers has not been nuclear radiation: the fuel rods get hot and start to "burn" chemically with air. This releases explosive hydrogen. The explosion shown on TV at the plants were NOT nuclear explosions, but more like the Hindenburg. One of the explosions killed a worker. Workers are simply kept away from being in close vicinity to the exposed rods to limit their radiation exposure. Finite amounts of radioactive materials have been "mobilized" by all of this.. this means that it gets into the air and is carried by wind to other locations. Luckily the wind has mostly pushed this out to sea. This is the source of radiation exposure to the general public. What are the levels? We'll go through a few example headlines (paraphrased) and look at the reality:

"Plant workers sacrificing their lives in nuclear catastrophe"

The largest radiation dose for any worker inside the power plant was under 200,000 micro-sieverts. This means that all workers remain below the health and regulatory threshold for adverse health risks.

"Nuclear disaster increases radiation by 100!! We're all going to die!!!"

The present data shows some increase in close vicinity to the plant. Most of the readings are actually near 1 micro-sievert per hour...that is at the background level! The largest jump has been to about 100 micro-sieverts per hour right at the boundary to the site. So while it seems alarming (a factor of 100!), in fact it is well known that this has no measurable negative effect on human health at all.

"Radiation found in food!"

This invokes long-term poisoning of all the area, with sick kids, etc....WRONG The excess in radiation was easily detected in some spinach from nearby fields. You would have to eat kg's of this spinach every day for an entire year to get the same dose as from one CT scan...which itself has no measurable effect on human health.

"Radiation cloud reaches US West Coast"

This apparently cause a panic buying of iodine pills....ABSOLUTELY RIDICULOUS Because radiation is so easy to detect, you can find very minute changes in radiation type. What was measured is about 1/billionth the level of even the most conservative protection against radiation. You will get more radiation by taking an elevator to the top of a tall building.

Again, I in no way trivializing the accident. The situation is looking better there and will continue to evolve. There will be much work in safely containing the exposed fuel.

I hope this helps put these recent events in the proper perspective.

cheers

Dennis

Glossary:
TMI: Three Mile Island
PWR: Pressurized Water Reactor (the type of fission reactors at Fukushima)
fuel rods: the assembly of fissile materials and cladding which is inserted into a fission reactor
spent fuel: the same assembly which is removed after about 1-2 years in the reactor and
left to cool. This is often called "nuclear waste" but in fact is mostly unspent Uranium fuel.
spent fuel pools: basically a swimming pool of water in which the spent fuel is kept
decay heat: fission produces a complex chain of nuclear isotopes, some of these decay
by radioactivity into more stable isotopes, which releases heat.