Mar. 15th, 2011

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.
 


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