Update on Fukushima Leaks: Unrepresentative Sampling Supports Fear Mongering
- August 31, 2013
- 120 views
After posting Fear mongering over WATER leaks at Fukushima Dai-ichi a number of people challenged the concentration numbers I used in the supporting calculations. This August 23, 2013 Tepco press release contains numbers that roughly correspond to those I used, so I pressed the challengers for a source.
They pointed me to a Tepco handout dated August 19, 2013 which contains a table of measurements that are vastly different from the ones that were reported in the press release that I cited. The line labeled as “leakage water” includes numbers that are also vastly different from the huge number of similar measurement tables that Tepco has published on their web site.
This handout gave me pause and made me wonder if I had made a serious error in trying to calm people down. If the numbers from that handout are correct and representative, they show there is something to worry about, at least in the local area.
I turned to my friends to try to help sort out the problem. Some advised sticking with the highest measured numbers in order to bound the problem and prove to people frighted about nuclear energy and radioactivity that nuclear professionals are not taking their concerns lightly. That course of action does not appeal to me.
It is not constructive. It just reinforces fear; it does not reflect reality. Radioactive material is finite; it cannot be spread or diluted without becoming less and less concentrated. It is wrong to take the highest reading you can find and then mathematically assume that it is a representative sample. I kept digging and eventually figured out that the numbers that people were using to frighten others were from an isolated sample that was not representative of anything.
Here is an extract from the comment thread on the original post that deserves to be read by more people.
Here is a link to the original press release from Tepco.
From the link;
“In addition, it is as follows: nuclide analysis results of water analyzed so far.
4.6 × 10^1 Bq/cm3: 134 cesium
cesium 137: 1.0 × 10^2 Bq/cm3
131: less than detection limit (detection limit : 3.1 × 10^0 Bq/cm3)
Cobalt 60: 1.2 × 10^0 Bq/cm3
manganese 54: 1.9 × 10^0 Bq/cm3
antimony 125:7.1 × 10^1 Bq/cm3
all beta: 8.0 × 10^4 Bq/cm3
chlorine Concentration: 5200 ppm”
Doesn’t appear from these numbers that there is a unit conversion issue, and this is the Tepco press release, so I would agree that the level of scrutiny and fact checking is much higher than numbers buried in a table on page 5.
When converted to Bq/l, the all beta count is equal to 80 million Bq/l. This is the same number reported by the media.
The cesium 137 number seen here when converted to Bq/l is equal to 100,000 Bq/l. This is ten thousand times the legal drinking water limit for Cesium 137 in drinking water. I confirmed this from the Health Canada website on the Guidelines for safe drinking water and the level for artificial radionuclides was listed at 10Bq/l.
80 million Bq/l means there are 80 million clicks per second on a geiger counter.
Converted to counts per minute this water is registering;
80 million counts per second x 60 seconds = 4.8 billion counts per minute.
4.8 billion counts per minute.
This is a staggering amount of radiation.
(Note the use of nonstandard units like “counts per minute” and the purposeful selection of numbers that sound as scary as possible to go along with the selection of “staggering” as an adjective.)
A reader who posts as CW responded:
This measurement was taken from a pool of water .1 cubic meters in volume on the ground, and appears to be anomalous compared to all other water readings at the site. Until confirmed with other readings from the tank it’s very possible these readings come from cross-contamination from another area of the site, possibly tracked in on a worker’ s boot.
Here is my response:
Based on the voluminous number of readings from all other locations, I believe that the particular sample described in that single press release is highly unrepresentative of the average content of the tanks. Tepco is a company that has experienced more than two years worth of focused demonization from both enemies and “friends” about its “lack of transparency.” It has decided to take a “worst case scenario” approach and treat the sample as if it actually says something about the potential magnitude of the radioactive material that might be released.
I believe that the particular small puddle probably was contaminated. I do not have full details needed to make a complete diagnosis from 12,000 miles away, but my experience with holding tanks is that they often develop a sludge at the bottom as particulate material settles out of the water column.
Similar scary reports have happened as a result of fish sampling. A small fish (29 cm long) that is a known bottom feeder showed up with what looked like a very high concentration of radioactive material that, when scaled to a tuna weighing a couple hundred kilograms, showed a very frightening possible release.
No other fish have been found with that kind of concentration. I suspect that the small fish ate material that happened to contain a physically tiny, but quite radioactive, bit of cesium. After all, a single milligram of cesium-137 contains about 3E9 (3 billion) Bq of radioactivity. The quantity of cesium required to produce a concentration of 254,000 Bq per kg in a 2 kg fish is just 0.0002 milligrams. It would most likely be undetectable without magnification on a physical basis, but it sure is easy to find with a radiation detector.
Hot particles exist; the material released from Fukushima Dai-ichi is not uniformly spread over all of the places that it could have reached. There are a finite number of particles, however, an a finite probability (very small) of encountering enough of them to cause any harm.
It is quite unproductive, unless your goal is to frighten people about nuclear energy, to pretend that the single measurement means there is a risk worth worrying about.
That small accumulation of water, described as 0.1 cubic meter in volume, was also the place where a radiation meter located about 50 cm above the water read 100 mSv/hour (beta + gamma) but just 1.5 mSv/hour gamma. A sheet of paper or a meter or two of distance would be sufficient shielding to protect a person from nearly all of the radiation from that pool. Since most human beings are not likely to drink from a puddle of water on the ground, no one would be likely to ingest the material that was causing the high radiation readings.
It is the height of absurdity to make believe that a 0.1 cubic meter puddle on an industrial clean up site is something people who live in the United States should worry about. Heck, no one anywhere should worry that the material is going to harm them.
As someone who has handled a spill or two in my career, many containing far more dangerous materials than reported to have been in this puddle, I would guess that the cleanup was pretty simple.
Of course, since it was done by nuclear professionals, it is possible that it took many hours and cost tens of thousands of dollars. As Galen Winsor told the world many years ago, certain types of people in the nuclear business have turned revenue-increasing “feather bedding” practices into an extreme art form. (Feather bedding is also known as paycheck protection, but the practice is onerous when conducted by contracting companies that collect billions in revenue for doing tasks using 2-100 times as many hours as needed.)
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