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Isn’t one major problem with nuclear is that it’s hard to shut down when you don’t need it? Hopefully they understand that

cmeacham98 5y ago
My understanding is that it's relatively easy to shut down, but costly/time consuming to start back up.
redwall_hp 5y ago
Usually they have fail safes that will more or less immediately shut them down. On any reactor designed in the last 50 years, they pretty much default to a safe state, as they require power to keep the failsafes open. Starting back up after is the slow part.
- necheffa 5y ago
  The one snag is that even with the reactor shut down (just drop all the control rods in) you still have to deal with the decay heat. Which, in the case of a controlled manual shut down shouldn't be a problem.
  - PeterisP 5y ago
    It's not a problem if you can continue to run the cooling system for quite some time. If you bomb the plant or its connections to the outside, that might be a problem - just as in Fukushima, where a key cause of the disaster was that the cooling system could not be properly powered when required.
- eru 5y ago
  No clue how old the Ukrainian reactor (and its design) is. Perhaps more than 50 years?
Merad 5y ago
They're easy to shut down, but when the reactor is first turned off the core is full of unstable isotopes that are byproducts of the fission reaction. Those isotopes continue decaying even with the reactor "off" until the become stable, and they put out enough heat to cause a meltdown on their own. This means the reactor needs active cooling for a couple of weeks until it reaches a safe state. That's what happened at Fukashima; the reactors were shut down when the earthquake hit, but then the tsunami disabled the backup generators that were powering the cooling pumps, and they weren't able to restore cooling before the core melted.
- newby 5y ago
  I did not know about that aspect of nuclear plants and in my non-expert view it would be a major point against nuclear plants in the discussion how to solve climate change (at least until we learn how to secure them in case of a war). Am I wrong? EDIT: I would also like to ask if you can recommend some source where curious layman with no knowledge of physics could learn a bit more about this.
  - yazaddaruvala 5y ago
    You’re right about old nuclear design. The new designs are built with the expectation that power can be cut off. The new design shut themselves off passively without any damage (that we know of) when the power is gone.
    - jliptzin 5y ago
      Seems to me like it should have been this way from this start. Catastrophic meltdown caused by power loss, no matter how many power backup systems there are should have been a non-starter. Basically requiring a 100% SLA, 6 nines not enough, with catastrophic consequences for failing to adhere to 100% uptime. That is scary as hell.
  - tarsinge 5y ago
    You are not wrong that it's a major point in the discussion, but even with that it can still be better than the alternatives for baseline production (the part that intermittent sources like solar and wind can't cover). Remember that coal power add insult to injury by continuously releasing radioactive pollution.
qbasic_forever 5y ago
Russia most likely designed and built that reactor and the others in the country, back when it was part of the Soviet Union. I think it's safe to say they fully understand and are capable of operating nuclear reactors like it. edit: Construction started on it in 1980. This is a Soviet designed and built reactor. Russia should have no problem maintaining it.
- ethbr0 5y ago
  Per Wikipedia, all 6 units are VVER-1000 [0]. So, unlike RBMK, water-moderated / negative void coefficient. [0] https://en.m.wikipedia.org/wiki/VVER#Design https://en.m.wikipedia.org/wiki/VVER#Design
- altacc 5y ago
  It is highly unlikely there are be nuclear scientists with that knowledge amongst the armed forces currently invading Ukraine. The type of reactor may be known but each reactor and its instruments, controls and protocols will be unique in some way. The only people who are qualified to run this reactor safely are the staff who work there every day.
  - mcv 5y ago
    It's not impossible, though. Russia seems to have pressed a lot of civilians into service. Ukraine recently captured an entire squad of school teachers.
- deleted 5y ago
  [deleted]

cmeacham98 5y ago

My understanding is that it's relatively easy to shut down, but costly/time consuming to start back up.

redwall_hp 5y ago

Usually they have fail safes that will more or less immediately shut them down. On any reactor designed in the last 50 years, they pretty much default to a safe state, as they require power to keep the failsafes open. Starting back up after is the slow part.

necheffa 5y ago
The one snag is that even with the reactor shut down (just drop all the control rods in) you still have to deal with the decay heat. Which, in the case of a controlled manual shut down shouldn't be a problem.
- PeterisP 5y ago
  It's not a problem if you can continue to run the cooling system for quite some time. If you bomb the plant or its connections to the outside, that might be a problem - just as in Fukushima, where a key cause of the disaster was that the cooling system could not be properly powered when required.
eru 5y ago
No clue how old the Ukrainian reactor (and its design) is. Perhaps more than 50 years?

Merad 5y ago

They're easy to shut down, but when the reactor is first turned off the core is full of unstable isotopes that are byproducts of the fission reaction. Those isotopes continue decaying even with the reactor "off" until the become stable, and they put out enough heat to cause a meltdown on their own. This means the reactor needs active cooling for a couple of weeks until it reaches a safe state. That's what happened at Fukashima; the reactors were shut down when the earthquake hit, but then the tsunami disabled the backup generators that were powering the cooling pumps, and they weren't able to restore cooling before the core melted.

newby 5y ago
I did not know about that aspect of nuclear plants and in my non-expert view it would be a major point against nuclear plants in the discussion how to solve climate change (at least until we learn how to secure them in case of a war). Am I wrong? EDIT: I would also like to ask if you can recommend some source where curious layman with no knowledge of physics could learn a bit more about this.
- yazaddaruvala 5y ago
  You’re right about old nuclear design. The new designs are built with the expectation that power can be cut off. The new design shut themselves off passively without any damage (that we know of) when the power is gone.
  - jliptzin 5y ago
    Seems to me like it should have been this way from this start. Catastrophic meltdown caused by power loss, no matter how many power backup systems there are should have been a non-starter. Basically requiring a 100% SLA, 6 nines not enough, with catastrophic consequences for failing to adhere to 100% uptime. That is scary as hell.
- tarsinge 5y ago
  You are not wrong that it's a major point in the discussion, but even with that it can still be better than the alternatives for baseline production (the part that intermittent sources like solar and wind can't cover). Remember that coal power add insult to injury by continuously releasing radioactive pollution.

qbasic_forever 5y ago

Russia most likely designed and built that reactor and the others in the country, back when it was part of the Soviet Union. I think it's safe to say they fully understand and are capable of operating nuclear reactors like it. edit: Construction started on it in 1980. This is a Soviet designed and built reactor. Russia should have no problem maintaining it.

ethbr0 5y ago
Per Wikipedia, all 6 units are VVER-1000 [0]. So, unlike RBMK, water-moderated / negative void coefficient. [0] https://en.m.wikipedia.org/wiki/VVER#Design https://en.m.wikipedia.org/wiki/VVER#Design
altacc 5y ago
It is highly unlikely there are be nuclear scientists with that knowledge amongst the armed forces currently invading Ukraine. The type of reactor may be known but each reactor and its instruments, controls and protocols will be unique in some way. The only people who are qualified to run this reactor safely are the staff who work there every day.
- mcv 5y ago
  It's not impossible, though. Russia seems to have pressed a lot of civilians into service. Ukraine recently captured an entire squad of school teachers.
deleted 5y ago
[deleted]