Anyone watching the Chernobyl miniseries on HBO?

[OVERKILL]

Originally Posted by Wolf359
I think they will cover it in the final episode, but in the wiki, it mentions that the tips of the control rods were covered with graphite which instead of slowing down the reaction, actually increased it. So that's why the plant blew up when they hit AZ-5 instead of shutting it down. That was a design quirk that they weren't really familiar with because the Soviets kept so many things secret. It shouldn't really have mattered that much if it had been operating inside parameters, but it was too far outside the parameters they had originally envisioned.


Yes, the control rods were graphite tipped, but it was the fact that they were almost all completely retracted out of the unit and their holes were filled with nearly boiling water that aided in the power level shooting up dramatically (100-fold) to the point where the steam tubes ruptured and then things went sideways. If you haven't read the document I linked earlier in the thread, I suggest giving it a going through. It is far more thorough than the Wiki and it will give you a very concise account of the events leading up to the failure, and the failure itself.

Originally Posted by Wolf359
And yes, it was a strange test. There were 3 other reactors near the site. I think it would have been very unlikely for all of them to be shut down and the place to have no power but I suppose anything is possible, maybe an issue with the connection to the grid would have prevented it from getting power from the other reactors. At least with the gas plant I was at, it was the only plant in the area and if it was off the grid and both generators were offline, it would need backup power to continue to run the pumps etc for an orderly shutdown.


It wouldn't have mattered. The time gap between a full trip, including grid disconnect and back-up ramp up wasn't enough time for anything to go "horribly wrong". They were just looking for ways to minimize the time the circulation pumps were down, or prevent them from going down entirely, during an event like that, by harnessing the power produced while the turbine slowed.

IIRC, it's policy or protocol in most places/for most units for a shut down when a grid disconnect takes place. I believe the exception is some of our reactors in Canada, where they are allowed to idle, because they can, at massively reduced power output, reliably. So if Chernobyl were to experience a grid disconnect, the odds are that it would transition to backup power and all the units would have commenced shutdown protocol, with all the support systems running on backup (generator) power. There are usually batteries to run the control systems so that they don't experience an interruption. Things like pumps, which can tolerate a break in operation as a transition from one power source to another takes place, are not run on batteries. I don't know why they thought it was necessary to try and limp them along on the output from spin-down, since it was noted that it wasn't necessary, but for whatever reason, it was deemed to potentially be beneficial, so it was tested for. It wasn't of course the test that was the issue, it was the state of the unit, which falls entirely at the hands of the operator, that led to the disaster. Had the unit not been accidentally almost shut off, we wouldn't be talking about it.

Originally Posted by Wolf359
What's somewhat crazy is that even though the whole area was evacuated, they kept running the other 3 reactors for years afterwards, I think they finally shut down the last reactor there in the 2000's.


It was a 4,000MW site, it provided a significant amount of power, necessary power, to the area. It was 3,000MW (with the one unit gone) that couldn't be readily replaced, so yes, the decision was made to continue to operate the other three units, even after the disaster, with crews that rotated in and out. I'm not as surprised as to the fact that they kept operating them as I am to the fact that the three remaining units, which weren't any more inherently safe than the one that failed, as they all lacked containment, were allowed to remain that way. I would have expected that full containment for the remaining units would have been mandated, but as far as I know, that never happened

 

[OVERKILL]

Originally Posted by Quattro Pete
Originally Posted by OVERKILL
Wow! That would have been intense!
It really wasn't intense because we didn't learn about it until a few days after the explosion. By that time, the cloud already passed over us. Living in a communist country at that time meant lack of facilities to properly and proactively measure radioactivity as well as overall unwillingness of the government to share such information (even if it were available) in order to keep people in the dark and avoid wide spread panic and revolt. Still, even if information about an approaching radioactive cloud was disseminated quickly, I'm not sure it would have changed much. It's not like people could have just gotten up and left (where would they go?) on such a short notice or could have stopped eating. Food supply in those days wasn't all that great to begin with. Farmers had to go ahead and plant their crops as usual, or else, come Fall, the country would have starved.

Still, being 400 miles away meant a lot smaller dose of radiation relative to some other areas.

Quote
Were you in the path of the smoke and contamination due to the winds or did that miss you?

Not only did the radioactive cloud fly over us, it also rained during those days, which means the rain pushed it down and contaminated the soil and farm lands for many years to come. See maps on slides 5, 6, and 11 in this slide deck. (Warsaw area)


Thanks for that, it was a good read-through.

I see they mention the contamination in mushrooms that pre-dates Chernobyl due to atomic weapons testing. That's another facet of this topic that I don't think gets anywhere near enough attention and ties into the obscene amounts of pollution we've either carelessly, or intentionally, exposed ourselves to over the decades. Be it an industrial accident, a chemical spill, a weapons programme....etc. We are quite literally still discovering the impacts of the fallout (no pun intended) from this abuse, and yet we continue it every day.

 

[Bottom_Feeder]

The finale was excellent. The anxiety brought on by the slow pacing of the 'flashback' was amazing. What a brilliant series! Shame that, overall, the story it tells is a total downer.

 

[Quattro Pete]

Well summed up, Bottom_Feeder.

 

[bbhero]

Originally Posted by OVERKILL
Originally Posted by dailydriver
Addicted to this series!

There was so much cover-up (by the Soviets/KGB) shrouding what actually happened when it was a current event that it is enlightening (but VERY dark despairing) to finally get some truth on the whole disaster.

"Black eye" to the whole industry, or not, the warnings the facts of this incident bring to light, had BETTER BE heeded going forward (YES even with our 'superior' and now much updated technology, and much more conscientious and fastidious plant workers.)!

If you read the report I linked (and I highly suggest doing so for a more analytical account of the events that haven't been sensationalized for your "viewing pleasure"), the design itself was not failure-tolerant. Basically, the safety of the plant hinged on operation and avoiding failure, there was very little in terms of provisions or protection if things DID go wrong. And of course they did. Plants in the rest of the world had containment and other disaster mitigation measures for the unlikely event of things going wrong. The events that transpired at Chernobyl were essentially impossible at the units operated elsewhere, because they were not of that style. The Soviets were aware of the risks of the design, and its lack of containment, which is why it was being phased out.

Now obviously lack of cooling incidents can still cause a meltdown in other reactor types like the LWR (Fukushima, Three-Mile Island) but the resulting incident is not on the same scale. Other reactor types like the CANDU are essentially immune, which is also covered in that paper.



Exactly right ^^^^^^^^

The terrible and inherently bad design of Chernobyl is what was the real problem. Add in a cascade of human errors piled on top one another equals the really severe results.
The lead engineer in that incident was a big contributor has well. Amazingly he survived that whole disaster while other engineers right there with him died shortly thereafter.

 

[ls1mike]

Soviet are reactors suck, period.
I can believe it was one a loop system.

 

[WhizkidTN]

Originally Posted by dave1251
I've been forced to learn more about Chernobyl then I thought I would learn for professional reasons. What the Soviet government did to cover up and clean up was criminal.


Well, they are "The Evil Empire" as Reagan said!

 

[mk378]

Originally Posted by ls1mike

I can believe it was one a loop system.

All boiling water reactors such as the GE design widely used in the US use steam directly from the reactor into the turbines. That wasn't the problem at Chernobyl.

A really crazy design would be the open cycle, like a steam locomotive.

 

[Cujet]

It turns out the most deadly radiation does not come from uranium, it comes from communism.

 

[ls1mike]

Originally Posted by mk378
Originally Posted by ls1mike

I can believe it was one a loop system.

All boiling water reactors such as the GE design widely used in the US use steam directly from the reactor into the turbines. That wasn't the problem at Chernobyl.

A really crazy design would be the open cycle, like a steam locomotive.

The largest precentage of reactors on the planet are Pressurzsed Water Reactors. They have a primary and sedondary loop. The US has about a 50/50 mix of both.
There are something to the tune of 280 PWR and 75 BWR plants on the planet.

I know that was not the problem at Chernobly, just not a fan of the single loop design always seemed odd to me. I wasn't aware, until I watched this, it was a BWR.

 

[ls1mike]

Just finished episode 5. Pretty good stuff, powerful show.

 

[RDY4WAR]

The wife and I watched Episode 1 tonight. We like it so far.

 

[OVERKILL]

Originally Posted by ls1mike
Originally Posted by mk378
Originally Posted by ls1mike

I can believe it was one a loop system.

All boiling water reactors such as the GE design widely used in the US use steam directly from the reactor into the turbines. That wasn't the problem at Chernobyl.

A really crazy design would be the open cycle, like a steam locomotive.

The largest precentage of reactors on the planet are Pressurzsed Water Reactors. They have a primary and sedondary loop. The US has about a 50/50 mix of both.
There are something to the tune of 280 PWR and 75 BWR plants on the planet.

I know that was not the problem at Chernobly, just not a fan of the single loop design always seemed odd to me. I wasn't aware, until I watched this, it was a BWR.


CANDU's are technically 2-loop, as the non-moderator heavy water loop heats a fresh water one attached to the boiler. However, because it's a pressure tube rather than pressure vessel design, the moderator, which is also heavy water, is separate from the primary cooling loop. So there are three layers of water in a CANDU, however the moderate does not participate in the cooling process to any real degree, but is viewed as a thermal sink and safety feature.

 

[ls1mike]

Originally Posted by OVERKILL

CANDU's are technically 2-loop, as the non-moderator heavy water loop heats a fresh water one attached to the boiler. However, because it's a pressure tube rather than pressure vessel design, the moderator, which is also heavy water, is separate from the primary cooling loop. So there are three layers of water in a CANDU, however the moderate does not participate in the cooling process to any real degree, but is viewed as a thermal sink and safety feature.

That is interesting. Wonder why they did it that way. I would think it would make it pricier to build and maintain.

 

[Wolf359]

Originally Posted by ls1mike
Originally Posted by OVERKILL

CANDU's are technically 2-loop, as the non-moderator heavy water loop heats a fresh water one attached to the boiler. However, because it's a pressure tube rather than pressure vessel design, the moderator, which is also heavy water, is separate from the primary cooling loop. So there are three layers of water in a CANDU, however the moderate does not participate in the cooling process to any real degree, but is viewed as a thermal sink and safety feature.

That is interesting. Wonder why they did it that way. I would think it would make it pricier to build and maintain.


Well yeah, that was the whole point of the RBMK reactor. It was cheaper to build without a containment building and put out a lot of power for the price of the reactor. It's too bad there were design defects and operational mistakes which led to the incident. No one else outside of Russia used that design.

It's interesting that in a US centric world, we tend to think of the fall of the Soviet Union was partly due to the US defense build up, but Chernobyl was also a factor in bankrupting them. Over 700,000 liquidators took part in the clean up.

 

[ls1mike]

Originally Posted by Wolf359

Well yeah, that was the whole point of the RBMK reactor. It was cheaper to build without a containment building and put out a lot of power for the price of the reactor. It's too bad there were design defects and operational mistakes which led to the incident. No one else outside of Russia used that design.

It's interesting that in a US centric world, we tend to think of the fall of the Soviet Union was partly due to the US defense build up, but Chernobyl was also a factor in bankrupting them. Over 700,000 liquidators took part in the clean up.


Ole' Mikhail Gorbachev said that himself in 2006. I read somewhere, or heard in a video they still pay 7,000,000 people some sort of money due to the incident.

 

[OVERKILL]

Originally Posted by ls1mike
Originally Posted by OVERKILL

CANDU's are technically 2-loop, as the non-moderator heavy water loop heats a fresh water one attached to the boiler. However, because it's a pressure tube rather than pressure vessel design, the moderator, which is also heavy water, is separate from the primary cooling loop. So there are three layers of water in a CANDU, however the moderate does not participate in the cooling process to any real degree, but is viewed as a thermal sink and safety feature.

That is interesting. Wonder why they did it that way. I would think it would make it pricier to build and maintain.


Because of the use of natural uranium.

An NU reactor requires a larger volume of fuel to produce the same amount of power. We wanted to use NU because we had absolutely zero enrichment capability at the time and so using NU made it easier, and cheaper.

So, in using NU, and subsequently requiring a bigger pressure vessel, the issue then became how in the heck do you fabricate a pressure vessel of that size? We concluded that you don't. So, instead of a pressure vessel, we used pressure tubes, fitted to a massive grid, called the calandria, which, not under pressure, housed the moderator. These tubes pass through the calandria and the fuel channels sit inside these pressure tubes, insulated from the moderator via carbon monoxide, which fills the void between the pressure tubes and the fuel channels, hence the moderator not really taking part in the cooling process, despite technically being a 3rd layer of water.

Now, the fuel turnover on an NU reactor is far more frequent than on a unit that utilizes EU, so the calandria setup was built with the intention to refuel on-line. A set of fuelling machines, one working from the back, the other from the front, can depressurize, unload and load a fuel channel with no interruption to operation. This is why for the longest time, CANDU units held the world record for unit uptime.

The original thought process here was that, despite there being more components, and the units being physically larger than a traditional PWR or especially a BWR, that the economies of online refuelling and the use of natural uranium would result in the units being cheaper overall. I'm not sure that ended up actually being the case, as EU prices continued to decline and refuelling windows at LWR plants were able to be shortened.

What did help was the vision of massive multi-unit plants, which drove down operating costs. Pickering, at 8 units, had a nameplate of 4,124MW with its ~500MW units. Things got bigger from there. Bruce has an installed capacity of 6,384MW. Darlington, had the B-site been built, would have dwarfed all that had come before it with a 7,024MW installed capacity. Only it's A-site has been built however, so it sits at 3,512MW.

What was never compromised on was safety (unlike the Soviets) due to a small incident we had early on at one of our tiny test reactors at Chalk River. All CANDU units are housed within massive containment buildings with 2 meter thick concrete walls, lined with steel. The pressure tubes are horizontal, and the fuel channels have to be perfectly straight for the units to function. So even if the two shutdown systems were to fail and an LOC event took place (which would be incredibly difficult given that the units can be passively cooled) if things ever got hot enough, the fuel channels would bend, killing the unit. And of course the moderator presents another massive sink. Light water also kills a CANDU, so a leak from the primary to secondary cooling loops would also kill the unit.

All that said, because of the pressure tube design, a CANDU requires a mid-life refurbishment, which is a complete replacement of all the pressure tubes and support devices. Typically, other things are rolled into this process to make it more cost-effective. Bruce A has been uprated twice for example, and two units have been refurbished. Bruce B has been uprated once and I suspect we'll see a 2nd up-rate when its refurbishment commences. Refurbishments are expensive: the cost to refurbish Darlington's 4x units is pegged at $12 billion dollars, the cost to do the 6x remaining units at Bruce is slated to be $13 billion thanks to momentum from the Darlington refurbishment and experienced gleaned from the previous 2-unit refurb that took place at the Bruce site.

While a CANDU "mid life" is supposed to be ~30 years, we will have units well into their 40's before they start that process. This pushes out overall operating life to 80+ years. In theory, they could be refurbished again, since you are replacing all the "cause for concern" components during the refurb process including the steam generators, tubing....etc.

The HWR fuel cycle also brings with it flexibility that isn't possible with other conventional designs. A CANDU can be setup to operate on thorium, MOX and nuclear weapon waste. They can also run on spent LWR fuel, with a reprocessing step, which is how the Chinese are intending to use the two units at Qinshan.

IIRC, the largest an HWR ever got was the ~900MW units at Darlington. Unlike an LWR, the ability to grow them to well beyond 1,200MW simply wasn't there due to the calandria requirement. Our "next generation" CANDU, the ACR1000, which was a 1,200MW design, utilized slightly enriched uranium for that reason. It was never built.

 

[dailydriver]

Originally Posted by ls1mike
I read somewhere, or heard in a video they still pay 7,000,000 people some sort of money due to the incident.



Hard to believe that ol 'Uncle Putie', and his merry band of faschy oligarchs, did not find a way to steal ALL of those funds as well.

 

[ls1mike]

Originally Posted by OVERKILL
Originally Posted by ls1mike
Originally Posted by OVERKILL

CANDU's are technically 2-loop, as the non-moderator heavy water loop heats a fresh water one attached to the boiler. However, because it's a pressure tube rather than pressure vessel design, the moderator, which is also heavy water, is separate from the primary cooling loop. So there are three layers of water in a CANDU, however the moderate does not participate in the cooling process to any real degree, but is viewed as a thermal sink and safety feature.

That is interesting. Wonder why they did it that way. I would think it would make it pricier to build and maintain.


Because of the use of natural uranium.

An NU reactor requires a larger volume of fuel to produce the same amount of power. We wanted to use NU because we had absolutely zero enrichment capability at the time and so using NU made it easier, and cheaper.

So, in using NU, and subsequently requiring a bigger pressure vessel, the issue then became how in the heck do you fabricate a pressure vessel of that size? We concluded that you don't. So, instead of a pressure vessel, we used pressure tubes, fitted to a massive grid, called the calandria, which, not under pressure, housed the moderator. These tubes pass through the calandria and the fuel channels sit inside these pressure tubes, insulated from the moderator via carbon monoxide, which fills the void between the pressure tubes and the fuel channels, hence the moderator not really taking part in the cooling process, despite technically being a 3rd layer of water.

Now, the fuel turnover on an NU reactor is far more frequent than on a unit that utilizes EU, so the calandria setup was built with the intention to refuel on-line. A set of fuelling machines, one working from the back, the other from the front, can depressurize, unload and load a fuel channel with no interruption to operation. This is why for the longest time, CANDU units held the world record for unit uptime.

The original thought process here was that, despite there being more components, and the units being physically larger than a traditional PWR or especially a BWR, that the economies of online refuelling and the use of natural uranium would result in the units being cheaper overall. I'm not sure that ended up actually being the case, as EU prices continued to decline and refuelling windows at LWR plants were able to be shortened.

What did help was the vision of massive multi-unit plants, which drove down operating costs. Pickering, at 8 units, had a nameplate of 4,124MW with its ~500MW units. Things got bigger from there. Bruce has an installed capacity of 6,384MW. Darlington, had the B-site been built, would have dwarfed all that had come before it with a 7,024MW installed capacity. Only it's A-site has been built however, so it sits at 3,512MW.

What was never compromised on was safety (unlike the Soviets) due to a small incident we had early on at one of our tiny test reactors at Chalk River. All CANDU units are housed within massive containment buildings with 2 meter thick concrete walls, lined with steel. The pressure tubes are horizontal, and the fuel channels have to be perfectly straight for the units to function. So even if the two shutdown systems were to fail and an LOC event took place (which would be incredibly difficult given that the units can be passively cooled) if things ever got hot enough, the fuel channels would bend, killing the unit. And of course the moderator presents another massive sink. Light water also kills a CANDU, so a leak from the primary to secondary cooling loops would also kill the unit.

All that said, because of the pressure tube design, a CANDU requires a mid-life refurbishment, which is a complete replacement of all the pressure tubes and support devices. Typically, other things are rolled into this process to make it more cost-effective. Bruce A has been uprated twice for example, and two units have been refurbished. Bruce B has been uprated once and I suspect we'll see a 2nd up-rate when its refurbishment commences. Refurbishments are expensive: the cost to refurbish Darlington's 4x units is pegged at $12 billion dollars, the cost to do the 6x remaining units at Bruce is slated to be $13 billion thanks to momentum from the Darlington refurbishment and experienced gleaned from the previous 2-unit refurb that took place at the Bruce site.

While a CANDU "mid life" is supposed to be ~30 years, we will have units well into their 40's before they start that process. This pushes out overall operating life to 80+ years. In theory, they could be refurbished again, since you are replacing all the "cause for concern" components during the refurb process including the steam generators, tubing....etc.

The HWR fuel cycle also brings with it flexibility that isn't possible with other conventional designs. A CANDU can be setup to operate on thorium, MOX and nuclear weapon waste. They can also run on spent LWR fuel, with a reprocessing step, which is how the Chinese are intending to use the two units at Qinshan.

IIRC, the largest an HWR ever got was the ~900MW units at Darlington. Unlike an LWR, the ability to grow them to well beyond 1,200MW simply wasn't there due to the calandria requirement. Our "next generation" CANDU, the ACR1000, which was a 1,200MW design, utilized slightly enriched uranium for that reason. It was never built.


Thanks for sharing OVERKILL. I found this to be very interesting. We had a Navy Nuke on the boat when I was qualifying who would like to talk about civilian plants too. It was just his thing. I have always been interested in it since serving on the boat with him. Plus when you sleep a few feet from an operational one you like to know about it.

 

[OVERKILL]

You are quite welcome!