Cesium 137 Half-Life vs. Chernobyl Contamination

[Mackenzie Cobb]

Let me start out by saying that I have no idea what I'm talking about. I graduated from Indiana University with a Bachelor's in Spanish, and I work as a Loan Review Specialist at a bank, which has NOTHING to do with my degree, and still yet nothing to do with this topic.

But lately, I've become fascinated with Man-Made Disasters and their subsequent abandonment and exclusion. I've been doing a lot of research on Chernobyl and other Nuclear disasters, and now I have questions that none of the articles I have access to seem to be able to answer.

I've read that Cesium 137, the radioactive compound with the longest half-life of all radiation released, has a half life of some 30 years. Meaning that now, some 30 years after the Chernobyl Disaster, it should theoretically be a lot safer, per my limited understanding of the half-life of chemicals. However, all of the articles I read and research say that Chernobyl won't be safe for some 20,000 years.

Even if the site itself is still drastically contaminated and unsafe, shouldn't the majority of the exclusion zone be much less hazardous? Why is the site itself taking so much longer to degrade in radioactivity?

Pardon my ignorance here, but my curiosity is driving me up a wall, and this seemed like a good place to get some answers.

 

[.Scott]

The first issue is the used of the term "Chernobyl". In one case you are talking about the town as a whole. In the second case, you are talking about the reactor - or perhaps the control room.

When you start out with a situation where your life expectancy is only a few minutes, it takes a lot of 30 year half-lives to get to something "safe", like a few centuries. Still, a thousand years from now, the Cesium 137 will not be a problem there.
But then there's Plutonium-241 (14.4 years) which decays into Americium-241 (430 years).

 

[Mackenzie Cobb]

The first issue is the used of the term "Chernobyl". In one case you are talking about the town as a whole. In the second case, you are talking about the reactor - or perhaps the control room.

When you start out with a situation where your life expectancy is only a few minutes, it takes a lot of 30 year half-lives to get to something "safe", like a few centuries. Still, a thousand years from now, the Cesium 137 will not be a problem there.
But then there's Plutonium-241 (14.4 years) which decays into Americium-241 (430 years).

So it's not the half life of the Plutonium that's the problem, but the fact that it decays into the Americium with a much longer half life. That makes more sense. I guess I didn't understand that upon decay, the radioactive components would break down into different radioactive components.

Thank you for the answer!

 

[Rive]

I've read that Cesium 137, the radioactive compound with the longest half-life of all radiation released, has a half life of some 30 years.

I don't know where that comes from, but one serious problem with the Chernobyl accident was that it does not released 'only' the classic Iodine/Cesium/Strontium isotopes, but due the graphite fire inside the core (wreck) it released every possible fissile and decay product you can find in a core: with the half-life from a few minutes to few 10000 years.
Due the fire it includes particles too.

Why is the site itself taking so much longer to degrade in radioactivity?

With higher starting point it takes more time to fall below a set limit. 'Safety' in this regard means something like 'above legal radiation limits'.

shouldn't the majority of the exclusion zone be much less hazardous?

It is. Right now most of the exclusion zone is fairly safe: and due the lack of the main disaster (human presence) it is like a national park in regards of animal life.

 

[snorkack]

The stuff with half-life over the 30 years of Cs-137 includes:
44 years: Sn-121
69 years: U-232
88 years: Pu-238
89 years: Sm-151
141 years: Am-242
432 years: Am-241
6600 years: Pu-240
7400 years: Am-243
24 000 years: Pu-239
160 000 years: U-233
210 000 years: Tc-99
etc. etc..

 

[Marc Rindermann]

what I learned only recently and find very interesting is the fact that even after the accident in unit 4 they continued construction on units 5 & 6 for two years until 1988 and operation of units 2, 1, 3 until 1991, 1996, 2000

 

[nikkkom]

The main contaminants are indeed Cs-137, Sr-90 and Pu-239, in that order. Here's a combination of contamination maps for each. Check out legends to understand contamination levels for each color.

 

[russ_watters]

Oops... forum has it downscaled, let's try tumbnail:
View attachment 230810
No, still no way to see it in full resolution (the file I uploaded is 9Mb in size). Help?

I don't think you can upload a 9mb file to the forum. A dropbox or finding it online would be the better options.

 

[nikkkom]

Here it is
https://imgur.com/a/YYD9Ak3

 

[snorkack]

Still too fine print to read the legends.

 

[nikkkom]

Still too fine print to read the legends.

How about this?

https://www.dropbox.com/s/zv9rhp2y1q92j7r/Chernobylmap_Cs_Sr_Pu_f.png

 

[snorkack]

How about this?

https://www.dropbox.com/s/zv9rhp2y1q92j7r/Chernobylmap_Cs_Sr_Pu_f.png

Thanks - that finally makes it clear!

 

[snorkack]

And now to actual features:

Note the striking patch of Cs activity to the northeast of Gomel, southeast of Mogilev - separated from the station by very much lower activity near Gomel itself.

What is the reason?

 

[nikkkom]

No particular reason for that patch. Cs-137 deposition correlates with rain.

OTOH, the arc-shaped easternmost patch has that shape for a reason. See where the arc's circle center is? Near Moscow.
Russians seeded clouds with silver iodide to induce rains and prevent them from reaching Moscow.
Not a single power reactor is closer than 200 km from Moscow, despite it being a large industrial center (consumer of electrical power).

 

[snorkack]

No particular reason for that patch. Cs-137 deposition correlates with rain.

Ah. So separated patches generally are rain showers, and the less radioactive intervals between them are places where clouds passed over without raining.

That map is from 1989.
This is 29 years ago. Close to 1 half-life for Sr-90 (28,8 years) and Cs-137 (30,2 years).
About 50 % of these isotopes are decayed and no longer present on Earth.
What has become of the remaining 50 %?
It is present somewhere on Earth, but where?
Just because Cs-137 was in Gomel 30 years ago and 50 % has not decayed since does not require that that 50 % is still in Gomel.
It might have been washed down the tributaries of Dnieper and be now dispersed around the water mass of world ocean or precipitated in bottom sediments of Black Sea at concentrations too low to be harmful.
Are any numbers known? Of the 50 % of Cs-137 that was around Chernobyl 30 years ago and has not yet decayed, how much is still there and how much has gone down Dnieper?

 

[nikkkom]

Ah. So separated patches generally are rain showers, and the less radioactive intervals between them are places where clouds passed over without raining.

That map is from 1989.
This is 29 years ago. Close to 1 half-life for Sr-90 (28,8 years) and Cs-137 (30,2 years).
About 50 % of these isotopes are decayed and no longer present on Earth.
What has become of the remaining 50 %?
It is present somewhere on Earth, but where?
Just because Cs-137 was in Gomel 30 years ago and 50 % has not decayed since does not require that that 50 % is still in Gomel.

Research shows that radionuclide migration rate is on the order of 10 meters per year. So, they are still largely there.

 

[nikkkom]

This allows to accurately predict how contamination maps will look even 30+ years in the future. The last map on this web page:

http://homel.greenbelarus.info/articles/06-05-2016/karty-zagryazneniya-gomelskoy-oblasti-ceziem-137-s-1986-do-2056-goda

is for year 2056. (This is a part of Belarus just to the north of the station, the lowest border is ~10 km away from the station).

 

[HowlerMonkey]

If original poster is curious about chernobyl, here is a link that has a lot of information.

http://www.dtic.mil/dtic/tr/fulltext/u2/a335076.pdf

 

[oksuz_]

My hometown in Turkey was affected by Chernobyl back in 1986. I am not sure about the exact date but it was around 1998, my advisor measured the environmental radiation in the soil along the coast of the Black sea in my hometown and found considerably high Cs-137 activity. I did a similar measurement in 2014, however, the region from Which I collected the samples was different, it was around 1000 km west of my hometown. And samples were containing Cs-137 isotopes. But there were factories in that region, and they were obtaining raw materials from my hometown. And also they were dumping their wastes into the sea from which I collected the samples. Regions which are near the dumping sites had relatively higher Cs-137 activity.

 

[CWatters]

Just curious... Are they still monitoring beef/lamb in turkey? They had to do that in Wales until 2012.

 

[oksuz_]

I did not come across when I was doing my research related to environmental radiation. But they did monitoring cows' and lamb' milk as well as various types of fishes in the late 80s and in the early 90s. Was there a fallout in Wales or in its vicinity?

 

[CWatters]

Was there a fallout in Wales or in its vicinity?

Yes.

I understand the first indication that radiation had arrived in the UK was about a week after the event when workers arriving for work at a nuclear power station in Anglesey (North West Wales) set off alarms. When they were checked it was found the radiation had come from outside the plant.

Soon after there were concerns that Caesium was being rained out onto grasslands and eaten by sheep and Cows...

https://www.bbc.co.uk/news/uk-wales-36112372

In total, 344 Welsh farms were put under restrictions, with animals' radiation levels monitored before they were allowed to be sold at market. The number of failing animals peaked in 1992, but some still recorded higher levels of caesium as recently as 2011.

 

[nikkkom]

My hometown in Turkey was affected by Chernobyl back in 1986. I am not sure about the exact date but it was around 1998, my advisor measured the environmental radiation in the soil along the coast of the Black sea in my hometown and found considerably high Cs-137 activity.

"Considerably high" is not a number.

 

[oksuz_]

Yes, you are right. It is my fault. 'Considerably high' does not give information related to the activity level caused by Cs-137. I do not remember the exact figure but one thing I remember that the Cs-137 activity was lower than the natural background radiation. I hope that this clarifies somethings.