Potential problems may be building up at Chinese nuclear plant... 8

[dik]

Additional...

https://hackaday.com/2021/05/14/increased-neutron-levels-at-chernobyl-4-how-dangerous-is-corium/

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Spartan5]

Also (and closer to home)…

https://www.nrc.gov/docs/ML2107/ML21077A094.pdf

February 3, 2021

09:10:00
During a reactor startup following a refueling outage, facility operators started to raise reactor power from 10 MW(t) to 20 MW(t).

09:10:45
After reactor power reached approximately 87 percent (17 MW(t)) an immediate decrease was observed in reactor power (no automatic actions, no manual operator action to reduce power) to approximately 50 percent power.

09:11:15
Fission Product Monitor (Radiation Monitor (RM) 3-2) (which samples helium from a layer of gas above the coolant in the reactor vessel) started to show an exponential increase in radioactivity.

09:12:00
Stack Monitor (RM 4-1) (which samples air at a point located two-thirds of the way up the confinement exhaust stack) started to show an exponential increase in radioactivity.

09:12:15
Stack Monitor Alarm at 50,000 counts per minute (cpm) initiated a Major Reactor Scram signal (reactor automatically shuts down, confinement doors close, ventilation system realigns).

09:12:30
Irradiated Air Monitor (RM 3-4) and Normal Air Monitor (RM 3-5) (which samples air from ventilation systems serving different areas of the confinement building) started to show an exponential increase in radioactivity following realignment of the ventilation system to emergency mode, which recirculated air inside of the confinement building.

09:13:00
Facility operators started evacuating the confinement building and sounded the building evacuation alarm. Prior to evacuating, facility operators ensured the reactor was in a safe condition (i.e., reactor shut down, primary coolant pumps running to maintain cooling). The reactor was then monitored by operators from the remote Emergency Control Station located outside of the confinement building.

The inspectors observed one fuel element in a position that indicated it was not fully seated in its normal position within the grid plates. Specifically, this fuel element was slightly raised and angled and sitting outside of the nozzle opening on the lower grid plate. The inspectors also observed the presence of a small amount of material that was once molten deposited on the lower grid plate surfaces near the displaced fuel element nozzle. While actual conditions inside the fuel element during the event are still under investigation, the inspectors note that the aluminum alloy used for fuel cladding would melt if temperatures reached a range of 1076°F - 1202°F (580°C - 650°C). Although the inspectors have observed the licensee’s remote visual inspection activities, additional information is needed to draw definitive conclusions about the condition of the fuel element and deposited material. Based on primary coolant and confinement exhaust stack air sample results, inspectors’ observations, and interviews with NIST staff, the inspectors preliminarily determined the fuel temperature safety limit was exceeded for at least a single fuel element (likely the displaced fuel element), resulting in fuel plate damage (i.e., blistering, cracking, and melting) in that element. At the time of this report, the inspectors note that the licensee is still investigating the positioning and condition of the fuel element.

 

[dik]

Thanks... you're sparter than I...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Alistair_Heaton]

That corium is interesting stuff.

I presume there is something similar under the reactors in Japan.

 

[electricpete]

I'm not sure how we got from this Chinese reactor problem which is fairly innocuous safety-wise over to Chernobyl and Fukushima.

I doubt the increasing neutron counts at Chernobyl represent a serious danger. Increasing counts can mean subcritical multiplication rather than criticality. If there were a concern about criticality, why not just flood the place with borated fluid?

Chernobyl and Fukushima both had severe fuel damage but I'm under the impression Chernobyl was far worse. (Whatever small corium criticality danger exists at Chernobyl, it is probably far less at Fukushima)
[ul]
[li]Chernobyl had a severe overpower event, possibly prompt critical (which is the same thing that happens in a bomb).[/li]
[li]Fukushima had an undercooling event, i.e. reactors shut down and stopped producing power when the wave hit, but cooling was not established to remove decay heat resulting in fuel damage, which led to hydrogen explosion that helped spread the radioactivity (not necessarily damage the fuel further). I heard the combined radioactivity release of the Fukushima plants is < 10% of Chernobyl[/li]
[/ul]



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(2B)+(2B)' ?

 

[Spartan5]

I heard the combined radioactivity release of the Fukushima plants is < 10% of Chernobyl

Upwards of 42% if we’re keeping score:

https://web.archive.org/web/2014010...ident-Fukushima--New-international-study.aspx

Regarding Cesium-137, which is of high relevance for human health due to its physical properties and the long half-life time of 30 years, the new estimate shows that emissions started earlier and ended later than assumed in most studies so far. The total release amounts to 36 PBq, which equals 42% of the Chernobyl emissions. 19% of the caesium was deposited on Japanese territory, while about 80% was deposited in the water.

(Whatever small corium criticality danger exists at Chernobyl, it is probably far less at Fukushima)

“probably”

They’re still trying to figure out how much of the fuel wandered off and where exactly it went. But yeah. Probably.

 

[electricpete]

I heard the combined radioactivity release of the Fukushima plants is < 10% of Chernobyl

Upwards of 42% if we’re keeping score...Cesium-137

The numbers are not exact and it depends on what isotope you're looking at. Here is a statistic related to estimated total (all isotopes) radioactivity release
Comparison of the Chernobyl and Fukushima nuclear accidents: A review of the environmental impacts
"For Chernobyl, a total release of 5300 PBq (excluding noble gases) has been established as the most cited source term. For Fukushima, we estimated a total source term of 520 (340–800) PBq."
520 / 5300 is slightly less than 10%.
(and the 520 includes contributions from 3 different Fukushima reactors whose corium / etc ended up in different places)

“probably”

They’re still trying to figure out how much of the fuel wandered off and where exactly it went. But yeah. Probably.

Wandering off aka dispersion means critical reaction is less likely. The fissile material has to be assembled closely together for criticality. Even moreso for prompt criticality.
I haven't heard of any neutron count or criticality concern at Fukushima. But again if there is such concern it can be addressed by injecting borated water for neutron absorption.


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(2B)+(2B)' ?