Chernobyl loses power, spent fuel storage question #Ukraine

[artis]

So the news are in that for whatever reason the electricity to the plant has been shut down. Now given the reactor have been long stopped there is no danger I would assume to the plant as such but the question is about the spent fuel assemblies that are still on site.

https://www.wsj.com/livecoverage/ru...ower-outage-at-chernobyl-ve8HvLoh7Lipvfc2lgz5

https://www.france24.com/en/live-ne...s-contact-with-chernobyl-nuclear-data-systems

Media doesn't really explain this, from what I know decay heat in used spent fuel decreases exponentially after reactor shutdown.
Also from what I know the heat given off by given fuel assembly after a fixed time has passed is proportional also to the burnup in the fuel, aka how much fission elements have accumulated and are decaying ?

Now given the last reactor in Chernobyl was stopped in the year 2000, means 22 years have passed. Is cooling of the fuel still an issue after this much time ? I wonder do we know the current heat average given off by the fuel from Chernobyl and whether that needs water cooling with circulation? I recall reading that they built a facility called "Interim storage facility - 1" which was a wet storage with water circulation to store some of the fuel from reactor spent fuel pools, then they built the "ISF - 2" which is a dry storage to which they planned to deliver the spent fuel.
I read some already has been loaded into the dry ISF -2 but not sure how much.

https://world-nuclear-news.org/Articles/First-assemblies-loaded-into-new-Chernobyl-used-fu

https://www.osti.gov/servlets/purl/1145261

Would our experts care to comment? Like @Astronuc for example, on the situation.

 

[Rive]

 

[PeterDonis]

from what I know decay heat in used spent fuel decreases exponentially after reactor shutdown.

I think "spent fuel" normally means "fuel assemblies that were removed from the reactor and stored in pools of water on site". Decay heat from those is the same whether the reactor is running or not.

I think what you mean is fuel assemblies that are still in the reactor. Decay heat from those is what needs to be dealt with after reactor shutdown. The optimal way to deal with that is to have a sufficient volume of water in the cooling system to absorb all the expected decay heat without being pumped (i.e., without electrical power available) and still stay below boiling point.

 

[artis]

I think what you mean is fuel assemblies that are still in the reactor. Decay heat from those is what needs to be dealt with after reactor shutdown. The optimal way to deal with that is to have a sufficient volume of water in the cooling system to absorb all the expected decay heat without being pumped (i.e., without electrical power available) and still stay below boiling point.

Well I meant fuel assemblies in the pools and those that are out of them , because I know that the last RBMK at Chernobyl was stopped in 2000. So I would assume there are no more fuel assemblies in the channels of any of the reactors. And even if they were there they would have been cooled by now.
Anyway that is why I asked this question because I was under the impression that given so much time has passed cooling of those spent fuel in the fuel assemblies should not be a problem anymore. And that they can be taken to dry storage or kept in the pools if they are still there but that circulation was not important anymore.
But I cannot comment any further I have limited information.

 

[PeterDonis]

I was under the impression that given so much time has passed cooling of those spent fuel in the fuel assemblies should not be a problem anymore.

IIRC some fission products have half lives in the century range so they would still be significant sources of decay now, but I don't know what the expected heat load from those would be.

 

[gmax137]

After 22 years shutdown, the decay heat is something like 0.00005 of the power when operating. I am not sure how much spent fuel is stored from the operation of the four units. Guessing, maybe 11 or 12 cores? At 3200 MW core power, the total decay heat load now would be about 2 MW.

 

[artis]

I am not sure how much spent fuel is stored from the operation of the four units

I think that would be 3 units to be more precise as the 4th unit exploded and the blast pretty much threw most of the core including fuel up in the air.

Hmm but that still seems like a lot of heat, why was I under the impression that for typical PWR you can cool the fuel for 5 years or so and then it can be moved to dry storage whether off site or on site?

Shouldn't it be the case that for more compact reactors with higher fuel enrichment the need for cooling is higher and longer since the same amount of decay products are concentrated in a smaller volume fuel while for lower fuel enrichment and higher fuel volume the cooling requirement would be less?
RBMK IIRC has a rather low enrichment, I think after 1986 no more than 2.4% and it has I think the largest volume of core and fuel from the known commercial reactors?

 

[anorlunda]

https://en.wikipedia.org/wiki/Dry_cask_storage#Ukraine
In Ukraine, a dry storage facility has been accepting spent fuel from the six-unit Zaporizhzhia Nuclear Power Plant (VVER-1000 reactors) since 2001, making it the longest-serving such facility in the former Soviet Union. The system was designed by the now-defunct Duke Engineering of the United States, with the storage casks being manufactured locally.

Another project is underway with Holtec International (again of the USA) to build a dry spent fuel storage facility at the 1986-accident-infamous Chernobyl Nuclear Power Plant (RBMK-1000 reactors). The project was initially started with Framatome (currently AREVA) of France, later suspended and terminated due to technical difficulties. Holtec was originally brought on board as a subcontractor to dehydrate the spent fuel, eventually taking over the entire project.

Dry storage is used only when passive, natural circulation, air cooling is sufficient to keep the temperatures in a safe range. Dry storage is used in the USA, Canada, Germany, Bulgaria, Lithuania, Russia, and Ukraine.

 

[Astronuc]

Chernobyl’s Unit 2 was shut down in 1991 [31 years ago] after a serious turbine building fire; Unit 1 was closed in November 1996 [26 years ago]; and Unit 3 was closed in December 1999 [22.3 years ago], as promised by Ukrainian President Leonid Kuchma.

https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/chernobyl-bg.html

 

[gmax137]

I think that would be 3 units to be more precise as the 4th unit exploded and the blast pretty much threw most of the core including fuel up in the air.

Hmm but that still seems like a lot of heat, why was I under the impression that for typical PWR you can cool the fuel for 5 years or so and then it can be moved to dry storage whether off site or on site?

Shouldn't it be the case that for more compact reactors with higher fuel enrichment the need for cooling is higher and longer since the same amount of decay products are concentrated in a smaller volume fuel while for lower fuel enrichment and higher fuel volume the cooling requirement would be less?
RBMK IIRC has a rather low enrichment, I think after 1986 no more than 2.4% and it has I think the largest volume of core and fuel from the known commercial reactors?

I found dates: (these are approximate)
Unit 1 1978 to 1991 = 13 years
Unit 2 1978 to 1991 = 13 years
Unit 3 1981 to 2000 = 9 years
Unit 4 1983
assuming none of the unit 4 fuel made it into the pools, that's 13 + 13 + 9 = 35 reactor years; assuming the fuel resides for 3 years we get 35/3 = 11 or 12 cores.

I have since read that they have ~21,000 assemblies on site and at 1661 assy in the core that would be 21,000/1661 = 12.6 cores.

say 13 * 3200 * 0.00005 = 2.1 MW.

The enrichment doesn't have a first order effect on the decay heat, it is the number of fissions that occurred to make the power that really matter. Because the decay heat is just that, the energy released by the fission products as they decay to lead. The enrichment probably affects how much of the core power is from U235 fission vs Pu239 fission, and that would affect the decay heat. The operating scheme also would come into it, short runs between refueling and putting more fresh fuel in vs 2nd and 3rd burns.

Getting back to the need for cooling, that 2.1 MW over 21,000 assemblies works out to 100 watts per assy so as long as they are not packed together, air cooling is not far-fetched.

 

[artis]

I found dates: (these are approximate)
Unit 1 1978 to 1991 = 13 years
Unit 2 1978 to 1991 = 13 years
Unit 3 1981 to 2000 = 9 years

For Unit 3 I believe you meant 19 years instead of 9?
And unit 1 I think was to 1996 as @Astronuc pointed out earlier

 

[Rive]

More than 10,000 hectares of forest are burning in the Chernobyl Exclusion Zone

link

Although some radiation inevitably will be released, it's unlikely to have any health impact anywhere in Europe.
Even in that forest, likely the most dangerous is the smoke and the fire itself.

What's concerning:
- not good attitude to have an affected area around a nuclear accident site on fire.
- the fires might affect the plant itself.
- that area is now practically a wildlife reserve. It was, at least.

 

[Oldman too]

There are studies to use modeling the impact. Radiation aside, fires are a healthy process for forests or grasslands,

https://www.nature.com/articles/s41598-020-67620-3
https://www.nature.com/articles/srep26062

 

[Rive]

There are unclear claims about Russian soldiers digging trenches in the 'Red forest' and getting radiation sickness.
Without knowing the details not much can be said about this. Feels unlikely (I mean, the radiation sickness part), but from this far I don't think anybody can say for sure.
Digging trenches there is definitely not a good idea.
Maybe there were even some bonfires there too, from local wood. At this point nobody knows.

Anyway, regarding the expected health impact around the exclusion zone: no change. Still negligible.

 

[Rive]

Feels unlikely

Well, not anymore. It's hard to dig up real data, but according to Wiki:

In 2005, radiation levels in the Red Forest were in some places as high as one roentgen per hour (~9 mSv/h), but levels of ten milliroentgens per hour were more common. More than 90% of the radioactivity of the Red Forest was concentrated in the soil.

With 9mSv as maximal value on the surface it's entirely possible that some unlucky soldiers got radiation sickness (required level is ~ 1Sv: 100 hours - only 4-5 days, worst case...) during a prolonged stay.

And there are unclear factors too, like trenches, ingestion of radioactive material (soil) due insufficient hygiene, bonfires from local wood against the cold weather...

This kind of neglect of human life is just plain criminal, albeit not uncommon these days, in that war.

 

[artis]

Given there has been little rain in this part of the world, also the reason for the exclusion zone fires lately, it might be that digging contaminated soil with shovels and then staying there might resulted in some breathing in of contaminated particles.

 

[Rive]

I would like to see more sources for this claim.

Russian soldier dies from radiation poisoning in Chernobyl

Serviceman was part of a unit camped in the toxic nearby Red Forest, clueless about what they were being exposed to

 

[anorlunda]

I would like to see more sources for this claim.

IMO, IAEA is one of the few sources anywhere that can be trusted to provide unvarnished news.

https://www.iaea.org/newscenter/pre...tor-general-statement-on-situation-in-ukraine
The IAEA has still not been able to confirm reports of Russian forces receiving high doses of radiation while being in the Chornobyl Exclusion Zone.

 

[Rive]

IMO IAEA will be a bit too slow with following up on the story (and that's just right, since their purpose is completely different).

The story so far: according to news they were indeed there: they were indeed diggin'.
No radiation readings so far.
Assumed site

 

[artis]

 

[Rive]

Russian Blunders in Chernobyl
(New York Times: multiple reloads might help)

In a particularly ill-advised action, a Russian soldier from a chemical, biological and nuclear protection unit picked up a source of cobalt-60 at one waste storage site with his bare hands, exposing himself to so much radiation in a few seconds that it went off the scales of a Geiger counter, Mr. Simyonov said. It was not clear what happened to the man, he said.

Without measurements and confirmation it's still just speculation, but (based on previous maps of radiation) the site of the checkpoint does not seems so polluted to cause ARS, even when dug up: at the same time it's bad enough that any sane commander would send the men for medical checkup.

On the other hand, mishandled C60 sources are well known about their notoriety.