Japan Earthquake: nuclear plants

Astronuc

There would be attenutation with distance and shielding. The problem is mostly gamma radiation which is highly penetrating. Beta particles go a relatively short distance in air, and much less in metal.

A dosimeter measures at the location of the dosimeter.

With respect to any dose rate, I'd want to know the portion that is beta and the portion that is gamma.

tsutsuji

http://www3.nhk.or.jp/news/html/2011...703941000.html : alongside the poor decontamination factor at the Kurion facility, an unexplained phenomenon took place. Although the radioactive substances were expected to accumulate more in the first absorption tower upstream, it is in the last absorption tower downstream that a 3 mSv/h radiation was observed on June 21st or even 15 mSv/h on June 22nd.

Bandit127

The sievert is (as far as i understand it) is a dose equivalent based on gamma. If the radiation were reported in grays, then you would indeed want to know the proportion of beta and gamma. But I am hoping we can ignore this for the sake of this question since the proportion should be accounted for.

Let us assume that the dosimeter was placed at my average height of (just under) 1m, then we can ignore height.

My question remains, if I stand in an area of ~30 mSv does this mean my dose is ~30 mSv?

I ask this beacuse 3 workers who stood in water containing 2-6 Sv were reported to have a recived a dose of many times less that that.

In fact, thinking it through as I am typing - perhaps I should ask a different question.

If I were a worker on Floor 1 of Unit 2 where the radiation appears to average ~30 mSv/hr, would I accumulate 30 mSv/hr of dose in 1 hour and therefore reach my annual limit after (250 / 30 = 8.333 hrs] 8 hours and 20 minutes?

Jorge Stolfi

Presumably workers wear their dosimeters inside their protective suits, whereas the ambient contamination measurements are taken with unshielded meters; is this correct?

etudiant

Seems that there is considerable incremental performance potential once they get this system properly balanced.
TEPCO should be happy to have the performance starting at 99+% removal, simply to free up some space in the plant. Additional improvements will require tweaking the process.

MadderDoc

Chromatography?

SteveElbows

How long did they stand in the water for? You have already acknowledged that length of exposure time is an important factor, so should not miss it out of that example as it will be a huge difference maker.

The dose a worker receives will be based on what the dosimeter records, and this will reflect the changing levels of radiation depending on exactly where they are standing in relation to radioactive hotspots, not some average figure like the one you speak of. We have seen from various surveys of different reactors that the detected radiation levels have varied considerably in different areas, and a key to minimising workers exposure is to locate these hotspots and either avoid them or find ways to shield workers from them.

I doubt that dosimeters are perfect, and it is possible to imagine scenarios where they fail to capture a decent picture of the radiation a person is actually exposed to. Especially early on TEPCO struggled badly in this regard, since they were not even able to give each individual human their own device.

Despite protective clothing & breathing apparatus designed to guard against internal exposure, to evaluate workers exposure as best as possible they also need to do forms of scanning on people, and add any results to the ones from dosimeter history to get a persons total.

Finally, if the workers are involved in some sort of incident where solid data personal to them is not available, or is suspected of being inaccurate, it may be necessary to estimate doses based on whatever incident factors that are known and measured. Im not sure entirely how the dose was calculated for the workers who got their feet wet, but I tend not to lose too much sleep over it because at the end of the day these Sievert figures are not a perfect guide to the health consequences in any given person anyway, they just give us some sense of the magnitude of risk that people are being exposed to.

MadderDoc

I am not sure about that. I've seen them using meters packed in all kind of plastic and stuff, that ought to be protective against radiation in a fashion quite similar to the personal Tyvek suits.

WhoWee

Another quake with tsunami warnings
http://www.usatoday.com/news/world/2...-tsunami_n.htm

MadderDoc

Yes, that would seem to be the case, as a first approximation of the potential exposure it ought to do.

Most Curious

Also depends on the part of the body exposed. Say the feet vs whole body.

joewein

I can see that the Kurion filtration rates are lower than expected, but the final outcome is "ND" (below detection level), which is presumably what you would want.

Lest anybody misread the above, the result for the Areva stage did not achieve a 1:400 instead of a 1:1000 reduction, it's input was 400 times as radioactive as the detection limit for the output (which came out ND), so it must have achieved at least a 1:400 reduction.

The overall cesium decontamination factor came out as at least 1:20,000 on Cs-134 and 1:22,000 on Cs-137.

If they were expecting a higher decontamination factor, presumably they would have used a more sensitive test on the final output? Their cutoff was at 100 Bq/cm3, which still is 500 times the limit for drinking water, but then they're not hoping to be able to drink this, only use it for reactor cooling or perhaps send it by boat to a nuclear reprocessing plant.

Astronuc

They shouldn't get much of a tsunami from that.

http://earthquake.usgs.gov/earthquak...usc0004e5w.php

A mag 6.7, close to the coast, 39.980°N, 142.247°E at a depth of 32 km (19.9 miles).

Edit: I looked up the location of Fukushima Daiichi:
Then applied: Distance = sqrt(x² + y²)

where x = 69.1 * (lat2 - lat1)
and y = 69.1 * (lon2 - lon1) * cos(lat1/57.3)

x = 176.8, y = 66.65
distance (earthquake to Fukushima Daiichi) ~ 189 mi, 304 km.

The quake is a challenge to nearby structures, but not a tsunami threat.

http://ptwc.weather.gov/ptwc/text.ph...1.06.22.215933

It's the vertical displacement of the sea floor or solid/liquid (crust/ocean) interface, particularly abrupt vertical displacement, that matters.

It's all about the physics (and the math)!

Joe Neubarth

But the individual is also picking up exposure to ionizing radiation while on the Grounds of the plant and on the way to the plant.

jim hardy

""Presumably workers wear their dosimeters inside their protective suits, whereas the ambient contamination measurements are taken with unshielded meters; is this correct?""

common sense applies it's just a little hard when you are unfamiliar to know what makes sense.

where i worked we wore dosimetry outside protective clothing. Not for shielding value of the clothing ( basically zero) but so it'll be obvious if you lose it and your buddies will holler at you.. It goes at chest level so as to be not far from most of your organs.
If you're going someplace that's contaminated you put it in a teeny ziplock bag and affix that with masking tape and a twistie-tie, still on outside of clothes. The ziploc bag keeps the dosimeter from picking up radioactive dirt. It needs to be kept clean so you can take it to the clean area of plant at shift's end.


and to bandit's question regarding dose vs rate...

yes, in a 30 mr(or mSv) per hour field you will accrue that amount every hour and reach your limit in the time you proposed.

Standing water in a radiation area is a red flag - stay away because it may be chock full of Beta contamination.
Beta rays go only inches in air so at chest level your dosimiter may read safe while your feet are getting a pretty good dose. Survey meter wont see it either unless you put it right down at surface.
That's what happened to those poor guys laying cables - they just didnt know to stay away from water. Their feet took a big dose but fortunately Betas mostly go only skin deep. And there's not many important organs in our extremities, maybe a little bone marrow.

if i can help others with practical basics that's my contribution here.

old jim

tsutsuji

http://www.tokyo-np.co.jp/article/na...302000200.html : There was a mistake on a command panel. One or more bypass valves marked "closed" on the command panel were actually open, so one or more absorption towers were being bypassed.

http://www.asahi.com/national/jiji/JJT201106230039.html : As a result of the mistake, only 1 out of 4 cesium absorption towers was actually being used. After checking the valves and correcting the mistake, the test has been started again with a 50 ton/hour flow.

If my understanding is correct, what this Asahi/Jiji article is saying is that in a normal operation, one cesium tower is bypassed for maintenance, while the other 3 are active. As a result of the mistake, they were doing just the opposite. Yet only one valve was wrong.

Tepco provides a diagram explaining the mistake : http://www.tepco.co.jp/en/nu/fukushi...10623_01-e.pdf

SteveElbows

The following document from IAEA meeting does not contain new information, but I found it to be a handy compendium of stuff we have seen in a variety of other documents. It includes the graphs which show estimated release from each reactor, and total estimated release rates from site over the first couple of weeks of the disaster.

http://www-pub.iaea.org/MTCD/Meeting...1_K.Hirose.pdf