General > General Technical Chat
something is leaking in europe
aqarwaen:
maybe it is that ship what sinked like 20 or 30 years ago..name was estonia..i readed that they burried and covered something near ship with cement..
jmelson:
--- Quote from: helius on July 01, 2020, 05:25:08 am ---
--- Quote from: jmelson on July 01, 2020, 02:53:42 am ---The only tricky part to get is the Silicon Photomultiplier, they are kind of a new part.
--- End quote ---
Would a mercury-cadmium-telluride detector not work here?
--- End quote ---
No, I think they are slow, and deep IR-sensitive. The BGO gives extremely fast flashes of blue light, and you
need either a Silicon photomultiplier or vacuum photomultiplier to respond to the fast flashes and very
low light level. When biased correctly, the SiPM gives about 1 million electrons per photon input.
Jon
jmelson:
--- Quote from: jogri on July 01, 2020, 07:33:30 am ---No, they use a zirconium alloy,
--- End quote ---
Yes, you are absolutely right, I typed the wrong element.
Jon
Siwastaja:
--- Quote from: jogri on June 30, 2020, 08:16:20 am ---You still need two separate failures before isotopes from nuclear fission get released into the atmosphere:
-one of the fuel cells has to rupture/get a tear in order to get those isotopes into the cooling loop
-the containment of the cooling loop has to fail to get them into the atmosphere
--- End quote ---
Small cracks and ruptures of the fuel rods (what you are calling "cells") happen time-to-time in fully operational plants, and are not considered accident-level events; not necessarily even incident-level. Then, if not earlier, at latest during the refueling, the containment is opened and the small amount of radionuclei are vented into atmosphere, possibly through some level of filtration.
This is considered normal operation and the amount of "leak" is regulated, and monitored.
Traditional boiling water reactors don't even have a full "containment" building, the steam enters the turbine building which is outside of containment. The idea is that you could close these steam valves during a serious loss-of-coolant accident, but it allows minor leak incidents whenever there is a rod clad leakage.
I find it extremely funny how people who try to give an impression of "nuclear safety" do not know such basics. Especially counting the fuel rod zircaloy cladding as an "independent safety layer" is beyond laughable, it does sometimes crack even during normal operation; and during loss-of-coolant accident conditions it takes some seconds max to break. This isn't any kind of safety layer against accidents, and isn't even supposed to be. I have seen "nuclear safety" posters by actual professors, and from the 4-5, maybe 6 claimed "layers" of safety, there actually is approx. 2. (Electronic equivalent: if you put a 1000W TVS and a 1W TVS in parallel, how many layers of safety against overvoltages do you have?)
Nuclear power is a low-probability-high-risk endeavor where the risk seems to realize every 30 years, every time followed by explanations "how this was a special case with special circumstances and it can't happen again", followed by explanations of "multiple safety layers", regardless the fact they all can fail, and there are no new levels introduced.
It's OK to be either pro-nuclear or anti-nuclear and actually I think both stances can be argumented quite well with real facts, so it's an interesting discussion, whenever the participants are truly knowledgeable.
jogri:
--- Quote from: Siwastaja on July 05, 2020, 09:03:54 am ---
--- Quote from: jogri on June 30, 2020, 08:16:20 am ---You still need two separate failures before isotopes from nuclear fission get released into the atmosphere:
-one of the fuel cells has to rupture/get a tear in order to get those isotopes into the cooling loop
-the containment of the cooling loop has to fail to get them into the atmosphere
--- End quote ---
Small cracks and ruptures of the fuel rods (what you are calling "cells") happen time-to-time in fully operational plants, and are not considered accident-level events; not necessarily even incident-level. Then, if not earlier, at latest during the refueling, the containment is opened and the small amount of radionuclei are vented into atmosphere, possibly through some level of filtration.
--- End quote ---
Like i described in other posts, the fuel rod has to crack and you need a leak in the primary cooling loop... And such a leak doesn't get any bigger than a partially disassembled pressure vessel for switching out fuel elements.
Did this happen here? Probably not, i still don't see how you would get such Cs emissions from a steam vent/fuel element change (source: i have worked with Caesium, one of the most unstable/reactive elements i ever handled). So let's make an educated guess about where those isotopes might have came from:
-They detected Ru-103 with a half life of 30d, so we can probably assume that the uranium was last radiated in the month/weeks before the incident (it wasn't an old fuel element that sat in a spent fuel pool for years)
-the fuel element could have been older as the Cs-134 predominantly gets created via neutron capture from Cs-133 (which is one of the main fission products). Take this with a grain of salt as i neither know the neutron flux, nor temperature of graphite reactors nor the cross section of Cs-133 at those conditions (wiki says 29 barns, but not at which energy)
-probably got released as dust (see Caesium+ water pools)
Edit: Forgot to add that the amount of material that was released was probably tiny as they only managed to detected the isotopes with the shortest half-life (except for the not reported, but expected Sr-90 peak, but it wouldn't surprise me at all if that was just due to "naturally" elevated Sr-90 levels [see russian lighthouse RTGs])
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