Radiation from Fukushima Powerplant, Putting the leaks into perspective

There is a lot of talk about the leaks at the Fukishima nuclear power-plant in Japan. Most of the things I have read sound pretty scary. But then again when you start to break down the reporting on these leaks and their effects on the United States there isn't a lot of real clear information on the subject. Typical reports state that "radiation levels have increased by a bazillion percent!" or radiation levels in California measured at 500 mRem. While those kind of headlines sound horrible and terrifying it helps to understand the overall picture of what the numbers mean. After all, an increase of 500% of something sounds worse than an increase of 2% doesn't it? But if one is measured in micro-Rems and the other in Rems then there is a vast difference. So I shall attempt to give a little perspective on this whole mess by giving you a whole boatload of numbers to dwell upon. The bottom line is I don't really know what levels of radiation can cause what and neither do the folks at MIT. Sure, we know what is fatal and all, but what causes damage? But when dealing with radiation in the oceans we can at least get a little perspective on the amount leaked versus the amount it is diluted.

So first we will start with the Pacific Ocean. The radiation from Fukushima that is of primary concern is that which is leaking via water. The airborne radiation has long since dissipated and is no longer a real concern.
Here are the volumes of the Pacific and specifically the North Pacific Ocean. The volume numbers are in millions of cubic kilometers. Source: NOAA Volumes of the Worlds Oceans

Ocean Statistics	Area+ (km2)	% Ocean Area	Volume (km3)	% Ocean Volume	Avg. Depth (m)	Max Depth (m)
Pacific Ocean	161,760,000	44.7	660,000,000	49.4	4080	10,803
North Pacific	77,010,000	21.3	331,000,000	24.8	4298	10,803#

For the purpose of this article we will just use the North Pacific statistics. So we are looking at 331 million cubic kilometers of water. To put that in perspective that works out to 87,440,949,330,000,000,000,000,000,000 gallons of water (or simply put: 8.744094933e+19 gallons). Conversion courtesy of Unitconversion.org.

So when we hear about 225 tons of water being leaked we are looking at roughly 53923.86 gals (at 8.3451 lbs/gal source: engineeringtoolbox.com). That is definitely a problem when considering the ground water supply in the local area. However, when compared with the total volume of the North Pacific Ocean it is close to a drop in the bucket.  So if that amount were to leak into the Pacific every hour for 365 days it would account for 0.0000000000000000000142048940141 of the Ocean's total volume in gallons. We can probably hazard a guess that nowhere near that much has leaked out in total. Of course we don't have the figures, but it is unlikely that they are using almost 54,000 gals/hr to keep the reactor cool and losing every drop of it. So my worst case scenario is probably far above the actual amount of radioactive water that has been released.

Now moving on to all those radiation numbers. They can be very confusing and misleading to say the least. We will start with some of the basic measurements that people are familiar with.

 

1 Rem=1000 mRem (milliRem) 0.001Rem

1 millirem = 1000 uRem (microRem)0.000001Rem

1 sievert = 100 rem

1 becquerel (Bq) = 1 count per second (cps) 

1 curie = 37,000,000,000 becquerel = 37 Gigabecquerels (GBq)

There are some good sites for getting perspective on what is a normal dosage of radiation. These are located at the American Nuclear Society and the EPA site on Radiation Doses in Perspective. According to the American Nuclear Society: "The average dose per person from all sources is about 620 mrems per year. It is not, however, uncommon for any of us to receive less or more than that in a given year (largely due to medical procedures we may undergo). International Standards allow exposure to as much as 5,000 mrems a year for those who work with and around radioactive material."

I checked my annual dose at the American Nuclear Society page and it would appear to be around 332 mRem/year. That is just from background and normal radiation sources. There are dozens of other ways to get radiation.

The Nuclear Regulatory Commission states that there are 4 different but interrelated measurements of radiation. These can be remembered by the acronym R-E-A-D which stands for Radiactivity Exposure Absorbed dose and Dose equivalent.

• Radioactivity refers to the amount of ionizing radiation released by a material. Whether it emits alpha or beta particles, gamma rays, x-rays, or neutrons, a quantity of radioactive material is expressed in terms of itsradioactivity (or simply its activity), which represents how many atoms in the material decay in a given time period. The units of measure for radioactivity are the curie (Ci) and becquerel (Bq).
  
• Exposure describes the amount of radiation traveling through the air. Many radiation monitors measure exposure. The units for exposure are the roentgen (R) and coulomb/kilogram (C/kg).
  
• Absorbed dose describes the amount of radiation absorbed by an object or person (that is, the amount of energy that radioactive sources deposit in materials through which they pass). The units for absorbed dose are the radiation absorbed dose (rad) and gray (Gy).
  
• Dose equivalent (or effective dose) combines the amount of radiation absorbed and the medical effects of that type of radiation. For beta and gamma radiation, the dose equivalent is the same as the absorbed dose. By contrast, the dose equivalent is larger than the absorbed dose for alpha and neutron radiation, because these types of radiation are more damaging to the human body. Units for dose equivalent are the roentgen equivalent man (rem) and sievert (Sv), and biological dose equivalents are commonly measured in 1/1000th of a rem (known as a millirem or mrem).

For practical purposes, 1 R (exposure) = 1 rad (absorbed dose) = 1 rem or 1000 mrem (dose equivalent).

Last but not least are the types of radiation. There are numerous types. Below is a short list:

Alpha particles are charged particles, which are emitted from naturally occurring materials (such as uranium, thorium, and radium) and man-made elements (such as plutonium and americium). These alpha emitters are primarily used (in very small amounts) in items such as smoke detectors.

In general, alpha particles have a very limited ability to penetrate other materials. In other words, these particles of ionizing radiation can be blocked by a sheet of paper, skin, or even a few inches of air. Nonetheless, materials that emit alpha particles are potentially dangerous if they are inhaled or swallowed, but external exposure generally does not pose a danger.

Beta particles, which are similiar to electrons, are emitted from naturally occurring materials (such as strontium-90). Such beta emitters are used in medical applications, such as treating eye disease.

In general, beta particles are lighter than alpha particles, and they generally have a greater ability to penetrate other materials. As a result, these particles can travel a few feet in the air, and can penetrate skin. Nonetheless, a thin sheet of metal or plastic or a block of wood can stop beta particles.

-Gamma rays and x-rays consist of high-energy waves that can travel great distances at the speed of light and generally have a great ability to penetrate other materials. For that reason, gamma rays (such as from cobalt-60) are often used in medical applications to treat cancer and sterilize medical instruments. Similarly, x-rays are typically used to provide static images of body parts (such as teeth and bones), and are also used in industry to find defects in welds.

Despite their ability to penetrate other materials, in general, neither gamma rays nor x-rays have the ability to make anything radioactive. Several feet of concrete or a few inches of dense material (such as lead) are able to block these types of radiation.

That is about all I could dig up in one morning of Googling and playing with my calculator. I am neither saying that all those articles folks read about Fukushima are crap or that we should all be moving to the middle of the country. That is up to you folks to figure out by reading those articles and then breaking down the information that they are actually giving you.

You may now return to your regularly scheduled surfing.

Tim

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