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The President and numerous experts tell us that the radioactivity coming from Japan will have no health risks associated with it.



How much will the radioactivity coming from Japan affect you?

I'd say less than...

...that luminous LCD wristwatch you’re wearing, which offers 0.006 mrem of exposure per year.

...cosmic radiation from space, which varies from 26 to 96 mrem/year.

...the radiation from the naturally occurring elements in the very ground you live on, which varies from 23 to 90 mrem/year.

...than the exposure from the concrete, stone, or brick building you live or work in (7 mrem/yr).

...than the naturally occurring radiation in your body, including the potassium-40 and carbon-14 that’s been in your tissues since birth or the naturally occurring radon you take in with every breath (240 mrem/yr).

...the radiation from traveling by airplane, which comes to 1 mrem/year for every 1,000 miles traveled.

...the exposure from those porcelain crowns and/or false teeth (0.07 mrem/year).

...the activity from your gas camping lantern (0.003 mrem/year).

...the x-ray machines at the airport (0.002 mrem/year).

...the radiation from your television or video screen (1 mrem/year).

...the activity from your smoke detector (0.008 mrem/year).

...the radiation from your plutonium-powered cardiac pacemaker (100 mrem/year).

...those diagnostic x-rays (40 mrem/year).

...that provided by nuclear medicine, such as thyroid scans (14 mrem/year).

...the exposure from living within 50 miles of a nuclear power plant (0.0009 mrem/year).

...the exposure from living within 50 miles of a coal-fired electric plant (0.03 mrem/year).

 

All told, naturally occurring sources provide you with roughly 300-350 mrem/year. When they tell you there’s no health risk, they’re telling the truth.



So, don’t panic.

 

 

Sources:

Personal Annual Radiation Dose Calculator

Sources of Radiation

Man-Made Radiation Sources

Natural Radiation Sources

Doses in Our Daily Lives


womprat99: (Default)

Yesterday I posted about the situation in Japan. That post can be found here at Creative Criticality and cross-posted to Fringe Scientist. As with most crises, things change rapidly, so I am taking the time to revisit the topic with updates and more level-headed discussion.

 

What Happened Overnight

Last night, an explosion occurred in the vicinity of the suppression pool at Unit 2. The suppression pool is part of the Reactor Pressure Vessel’s (RPV) cooling system, and the explosion may have damaged a portion of the reactor’s primary containment structure.   Pressure in the suppression pool rapidly decreased and radiation levels rose, which indicates a potential release of fission products (fuel material) outside the RPV. Officials have called this release a “small” one.

Of the 800 staff members that remained at the power plant, all but 50 who are directly involved in pumping water into the reactor have been evacuated due to the radiation.

On top of that, a fire was reported near the Unit 4 reactor building. It was believed to have been from a lube oil leak in a system that drives recirculation water pumps. The fire was extinguished, but the roof of the reactor building was damaged. Units 4, 5, and 6 were shut down at the time of the earthquake, and the fuel was removed from Unit 4 for inspection. The concern was a spent fuel pool, where the used fuel rods are kept before disposal. The fire was assumed to be releasing contamination to the atmosphere, which I will address later on.

Units 1 and 3 are stable and cooling is being maintained through seawater injection. Primary containment integrity has been maintained on both reactors. Unit 2 cooling efforts continue.

 

Background and Perspective on Contamination and Radiation

Before we go any further, it’s important to discuss the basics and differences between contamination and radiation. The best way to consider it is in terms of perfume.

Consider the bottle of perfume as your RPV. If you have a leak, you get perfume all over the place. That substance is contamination. The smell that comes off the perfume is radiation. A radiac (think Geiger counter) measures the amount of “smell” coming from the contamination. You can wash off the perfume, and that will remove the smell, but depending on the surface the perfume was spilled on, clean-up methods will vary.

Radiation is a transfer of energy through a space. The problem is that the energy can penetrate body tissues and cause damage which can potentially cause cancer or other problems. The effects of radiation can be minimized by spending less time around it, getting further away from it, or blocking the energy with shielding. Any material can act as a shield – some are more effective than others – so even being inside a house will block some amounts of radiation.

Per procedures, residents within a 20-kilometer (12.5 mile) zone around the plant were ordered to evacuate last Saturday. This was due to the hydrogen explosion at Unit 1. That radius has been extended to 30 kilometers (18.6 miles).

Radiation is measured in many units, but you may see “Rem” or “millirem” most often. At its most basic, a Rem – abbreviated as R – is a measure of radiation received. One thousandth of that amount is a millirem (mR). 

A single dose of under 50 R is will typically produce nothing other than blood changes. 50 to 200 R may cause illness but will rarely be fatal. Doses of 200 to 1000 R will likely cause serious illness with poor outlook at the upper end of the range. Doses of more than 1000 R are almost invariably fatal.

The typical value for a normal exposure is 300 mR/year. That includes sunlight, air travel, particulates in the soil, smoking, ingestion in water and food, medical procedures, cosmic radiation, and so on. That value breaks down to 25 mR/month. For comparison, while underway on a nuclear submarine, living within 300 feet of an operating reactor 24 hours a day, I got between 5 and 10 mR/month. Yes, the reactor provided less dosage than living outside in the sun.

The Nuclear Regulatory Commission (NRC) has a limit for public exposure due to reactor operations of 100 mR/year. The NRC’s whole body limit for radiation workers is 5000 mR/year. According to the NRC’s guide on health effects from radiation, a 3 mR exposure generally poses the same chance of death as (1) spending 2 days in New York City, (2) riding one mile on a motorcycle or 300 miles in a car, (3) eating 40 tablespoons of peanut butter or 10 charbroiled steaks, or (4) smoking a single cigarette.

You can see various effects of annual radiation at this interactive calculator.

The news talked about the aircraft carrier USS Ronald Reagan (CVN-76) which is currently operating in the area. The decks and planes had to be decontaminated after some radiation was detected. The commanding officer, a nuclear trained officer, moved the ship as a precaution and an exercise of legal responsibility, and the report stated that the affected crewmembers received a “month’s dose”. I interpret that as 25 mR in one shot, which is not a big deal. Yes, they were exposed, but it won’t kill them.

Also, reports of a large RADIOACTIVE CLOUD OF DEATH AND DESTRUCTION (TM) are exaggerations. While the contamination likely came to the carrier’s decks by way of gas release, this isn’t science fiction.  The gas that moved that little of contamination to the carrier will dissipate long before it hits our soil.

To put this all in perspective with relation to the Japan reactors, the radiation levels at the site have been reported as high as 40 R/hr (ouch!) to a low of 60 mR/hr. After the explosion on Unit 2’s suppression pool, reported radiation readings at the site increased to 96 mR/hr, peaked at a reported 1,190 mR/hr, and are decreasing. As of this writing, they are around 60 mR/hr and lowering.

A measurement in Kitaibaraki, 200 km south of site, was reported at 0.4 mR/hr.

The 40 R/hr dose rate was recorded in a localized area on the site. The evacuation radius should be sufficient to prevent exposure to the populace, so the populace shouldn’t see anywhere near those levels.

Since the contamination is restrained to the containments, there should be no major ecological concerns at this time.

 

Fire? Fire!

Let’s go back to the perfume analogy. Fire can be looked at as the atomizer on the bottle. If you’ve ever enjoyed a campfire, you’ll understand how bad a radiological fire can be. As you can see from the smoke from the fire, a great deal of matter is propelled skyward. The estimates are usually around 10% of the total contamination being made airborne when exposed to a fire.

That’s a problem when it comes to a fire over a spent fuel pool, but the spread will depend on fire size and duration. Radiation workers will need to investigate and clean the area to know how far the contamination was spread, however I don't believe a fire of this size will put contamination on the U.S. West Coast, so don’t panic.

 

Why This Is Not Chernobyl – Revisited

Comparisons still continue between Fukushima and Chernobyl. Experts have compared Chernobyl to 1,000,000 Three Mile Island incidents in terms of radiation release. The Three Mile Island (TMI) incident resulted in no detectable health problems, but Chernobyl’s explosion killed dozens and increased the cancer risk for thousands. Fukushima is much closer to TMI than to Chernobyl.

Remember that Chernobyl was sparked by an out of control reactor, and the explosion added to the reaction spewed a huge plume of radiation into the air above the site. All Fukushima reactors shut down at the time of the earthquake. 

Considering meltdowns, even if Fukushima melted all of its fuel and somehow burned through the bottom of the RPV, the resulting slag would be contained within the secondary containment. To compare, TMI only melted half of its fuel, and Chernobyl didn’t have a similar containment system for its explosive meltdown.

There’s also a big difference between a nuclear bomb and a nuclear power plant. The two cases are mutually exclusive. The explosions at the plants are not nuclear explosions.

 

What Next?

Operators continue to work on cooling Unit 2 while Units 1 and 3 are stable. Once radiation levels are low enough, workers can go in and determine if something got out of the Unit 2 containment. If something did, they’ll follow a plan for cleanup.

I’ve talked to a lot of people who are concerned because they don’t quite understand what going on and can’t make heads or tails of the press reports. My goal is to make these types of posts to clear up confusion and alleviate fear.

From what I read, the operators in Japan are doing the best that they can with what they have. I trust that they will get this under control and we will be able to learn from their actions and continue to perfect our own nuclear operations.

I don’t anticipate the United States seeing any rise in radiation or contamination from this event. Seriously, don’t stock up on Geiger counters or potassium-iodide tablets. Also, ignore the acid rain rumors, the false text messages, and the chain e-mails. They’re all fear-mongering crap.

Please feel free to leave questions or comments below.  Please send this to anyone who has questions or fears about this emergency event.
 


womprat99: (Default)

I’ve come across quite a few people who are understandably afraid of what’s happening with the situation at the Fukushima Nuclear Power Plant after the earthquake in Japan. The situation is not helped by the media reporting without context to a public that does not understand how nuclear power works. This post is an attempt to break down what’s going on and mitigate some of those fears.

 

Part I: How it Works

First, we need to understand how the Fukushima reactors work. They are Boiling Water Reactors (BWR), which use pure water to move heat from the core to electrical generating turbines.

The core is built around multiple fuel bundles.
 

 

 

At its most basic, the fuel bundle is constructed of multiple fuel rods. A fuel rod is a metal tube filled with the nuclear fuel which is usually uranium. The fuel bundles are loaded with an assortment of other components into the Reactor Pressure Vessel (RPV), which is essentially a metal can filled with water. The RPV is enclosed in a concrete pit and a concrete and metal containment building, commonly referred to as the Reactor Building. The components inside the RPV can be considered “the core”.

 


Power generation gets a little more technical and depends on the physics of nuclear fission. Basically, a neutron passes into the fuel and causes a fuel atom to split. When it splits, heat is generated along with more neutrons. The water in the RPV serves two purposes: 1) It removes the heat from the fuel and, 2) slows down some of the neutrons to limit the reaction rate.

In a BWR, the water is allowed to boil, and the steam is collected at the top of the RPV. The steam goes through a drying process, and then goes to an adjacent building with a turbine. The steam spins the turbine to generate electricity, and then is collected and cooled. The cooling process turns the steam back into water, which is then injected back into the core. The whole thing is considered to be a “plant”. In this diagram, the reactor is on the left side.

 


In a BWR, it is imperative to keep the core covered. Without water to cool it, the reactions will continue and heat will build until the metal covering the fuel rod begins to melt and/or break. This fuel element failure is the beginnings of what is known as a “meltdown”.

 

Part II: Why it "Stopped" Working

When the earthquake occurred, the reactors all attempted an emergency shutdown by rapidly inserting control rods to stop all neutron reactions. This procedure is known as a “scram”. This procedure worked as advertised. Without reactor power, the plant will shift to using offsite electrical power from the grid to keep certain pumps running to cool down the core. When power generation stops, the core doesn’t just become cool. Think of it like boiling water for tea: After you remove the pot from heat, it still is hot for some time and continues to steam. That continued steaming removes water from the core.

Unfortunately, the resulting tsunami swept away all of the power lines, so the plants shifted over to on-site diesel-powered generator units, just as expected. What wasn’t expected was diesel fuel damage from the tsunami, which resulted in diesel generator shutdown after about an hour. Other methods were used to cool the core and pumps from the Reactor Core Isolation Cooling (RCIC) system were used. The valves were able to operate until the batteries expired after eight hours.

At this point, the plant was in complete blackout with no electrical power at all.

As the core continued to cool, the water inventory continued to shrink and fuel elements were exposed. Portable diesel generators were delivered to the site and power was restored, allowing the operators to start putting cooling water into the RPV.

Pressure was also rising in the containment, so gasses were vented to lower the pressure. The gasses come from the reactor, so they are contaminated with radioactive material, however the radiation was reported to be within safe limits. One other problem was the interaction between heated water and the metal around the fuel rods. As natural oxidation (very, very simply, think rusting or corrosion) occurs, one by-product is hydrogen gas. Normally, it is managed, but during the accident, it had to be vented into the containment building. This hydrogen accumulated and eventually exploded, causing damage to the containment building, however the RPV was reported to be intact.

To continue the cooling process, operators decided to inject seawater into the RPV, which is a backup system designed into the plant but essentially ruins the core.

This situation is the same for the #1 and #3 plants. The #2 plant is similar up to the hydrogen explosion as of this post. Plants #4, #5, and #6 were offline for inspection at the time of the incident.

 

Part III: Where We Go From Here

The emergency still continues, but even if a complete meltdown occurs, will the world suffer? Possibly, but I don’t think so. Let’s not detract from the seriousness: Any meltdown is a bad event. It requires replacement of the core, RPV, and/or associated reactor components, and is one of the worst things that can happen to a nuclear reactor.

The term meltdown, which is not officially defined by either the International Atomic Energy Agency (IAEA) or the U.S. Nuclear Regulatory Commission (NRC), tends to elicit a great degree of fear because of Chernobyl, Three Mile Island, and pop culture events like The China Syndrome.

A “China Syndrome” event, where the core gets so hot that it melts through the RPV, containment, and into the earth is highly unlikely. Also unlikely, I believe, is a major release of fuel/fission products to the environment. Let’s remember that the RPVs are all currently intact, and unless they are damaged by an aftershock or a large explosion, any released fission products will remain in the vessel. That also means that there will be no fallout to spread on the trade winds around the world.

Fission product release at Three Mile Island was a result of operator error. The Chernobyl disaster occurred during the scram to shut down the core, and it resulted in destruction of the RPV and the Reactor Building in an explosion that spread contamination around the world and left the area in Ukraine uninhabitable. Neither is applicable here.  Japanese officials are distributing potassium iodine to the local populace in order to prevent thyroid poisoning by radioactive iodine from the fuel elements.

There’s also a claim that the released hydrogen will cause acid rain. No, it won’t. I’ll leave that one to the chemists and meteorologists.

The worst case scenario without a breach of the RPV is that the fuel completely melts down and they have to replace the three RPVs as a result.  There may be some limited gaseous release -- hence, the potassium iodine -- but likely nothing more. 



Part IV: Wrap-Up

There are already rumblings that we should put nuclear advances in the United States on hold as a result of this emergency event. I disagree wholeheartedly. Nuclear power plants have been operating safely for decades with the exception of two major accidents, and the operators in Japan are following procedures to the letter and doing their best to maintain safety of the cores. The accident wasn’t a result of breakage from the earthquake, and had the tsunami not affected the diesel generators or offsite power so significantly, we wouldn’t be having this discussion. Nuclear power is very safe and much less polluting than other power generation methods. It’s also more efficient than other green methods like solar, wind, or hydroelectric, and doesn’t directly rely on the season.

These reactors aren't just slapped together and brought online.  There's a significant amount of engineering and planning for nearly every contingency and emergency, and people need to remember that.

There’s another simple explanation by Kathy Gill at The Moderate Voice. There’s also a more-detailed explanation at Barry Brook’s blog.

One of the best sources for non-spun up-to-date information on the emergency is the Nuclear Energy Institute.

Please feel free to leave questions or comments below.   Please send this to anyone who has questions or fears about this emergency event.



Part V: References

Nuclear fuel bundle image sourced from Wikipedia via the United States Government and is used under public domain.

Containment building image sourced from Wikipedia via the United States Government and is used under public domain.

Boiling Water Reactor power generation schematic sourced from Wikipedia via Nicolas Lardot. The image is used under a Creative Commons Attribution-Share Alike 3.0 Unported license.


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