[Fukushima, power stations, nuclear scare]

[Gigabyte]

Just for clarity, that's a video on the Three Mile Island cleanup.

Yes, and it shows how the same material was found after the accident, far removed from containment.

New video and preliminary analysis from TEPCO reveals an interesting substance found adhered to fuel assemblies in the Unit 3 fuel pool. It's the same stuff previously seen inside primary containment and under the reactor vessel which appears to be the result of interaction of melted fuel (called corium) and concrete. For it to be found in the fuel pool suggests there was a whole lot of corium-concrete interacting going on after the accident, further suggesting that a significant amount of fuel escaped containment after the explosion.

Lots of photos in this link.

The following video shows how material escaped containment, even with out a massive explosion that destroyed the building.

This video is educational and relevant

https://www.youtube.com/watch?v=wY3qCKZOF30

Of great interest is the removal of melted fuel from the cooling system and steam generation areas. This was a minor disaster compared to Fukushima, yet corium was spread all over by travelling through the pipes. There was no explosion, but melted fuel still escaped primary containment.

There is zero doubt melted fuel escaped from primary containment at Fukushima reactor 3. And secondary containment. Since secondary containment pretty much was blown to little pieces.

The real question is how did melted fuel get into the cooling pond? Was it through water pipes? Or did it fly through the air and land? I doubt we will know for a very long time. But the knowledge that a disaster in this type of reactor can lead to melted fuel escaping, outside containment, is valuable data to have.

The obvious hypothesis is that the steam explosion blew melted fuel that had already escaped the reactor core (primary containment) out of the secondary containment. Which seems quite disturbing.

[geonuc]

Yes, and it shows how the same material was found after the accident, far removed from containment.
The following video shows how material escaped containment, even with out a massive explosion that destroyed the building.


The real question is how did melted fuel get into the cooling pond? Was it through water pipes? Or did it fly through the air and land? I doubt we will know for a very long time. But the knowledge that a disaster in this type of reactor can lead to melted fuel escaping, outside containment, is valuable data to have.

The obvious hypothesis is that the steam explosion blew melted fuel that had already escaped the reactor core (primary containment) out of the secondary containment. Which seems quite disturbing.

I suggest as a start that we get our terms correct.

BWRs (Fukushima) and PWRs (TMI) have different physical layouts and containment structures. The reactor core is not the 'primary containment' in either type of reactor. The reactor core is an assemblage of fuel bundles designed to allow free flow of water around the fuel rods, the opposite of containment. In both reactor types, there are three 'barriers' to prevent fission products* from escaping to the environment:

1. the fuel cladding. This is the metal tubing that holds the fuel pellets. The cladding together with the fuel pellets make up the fuel rods. There are many of them and they are not particularly robust as their main purpose (beyond holding the fuel pellets in the proper configuration) is to transfer heat to the surrounding water. The cladding serves to prevent fission products from entering the primary coolant. Except for small instances, cladding cannot contain melting fuel.
2. The primary system. In a PWR, this is the heavy gauge steel reactor vessel and piping system designed to transfer heat to the steam generators via pressurized water. In a BWR, it is the same vessel and piping but the water in the reactor boils, sending steam directly to the turbines. The primary system is capable of preventing fission products from escaping and dealing with limited fuel melting.
3. Containment. In a PWR, it is the big steel and concrete building. Inside the building are all the main primary systems; outside is the environment. It is capable of preventing fission products and melted fuel from escaping to the environment in the event of a massive meltdown, such as at TMI. One of the lessons from TMI was the demonstration that the containment structure worked. In a BWR, it is a bit more complicated. There are two structures termed ‘containment’ but only one is important in this discussion. Primary containment is a robust steel and concrete structure housing the reactor vessel and primary piping and is often referred to the ‘drywell’. Attached to the drywell is the wetwell, a system designed to act as a heat sink in the event of an accident (PWRs have no analog to a BWR wetwell). The wetwell sits outside primary containment. Surrounding the primary containment and wetwell is the secondary containment. In the lower portion, this is an unreinforced concrete building. The upper portion is a building structure designed mainly to enclose the turbine and other components. It is this upper portion of secondary containment that blew apart due to hydrogen explosion (not steam explosion) at three of the units at Fukushima. In a BWR, the spent fuel pool is in secondary containment. In a PWR, the spent fuel pool is in a separate building attached to the containment building.

* Fission products are what we want to contain - they are the highly radioactive isotopes that constitute the hazard to human life and the environment. Un-fissioned fuel (Uranium dioxide) is of no great concern.

[Jens]

There's an issue going on right now about releasing radioactive water into the ocean. I don't really know how serious it is, but suspect it will be fairly seriously locally not not on a global scale. I just saw an article in The Guardian, that caught my attention.

https://www.theguardian.com/world/20...x-tUgFypEIXuJA

Of course, it's true that carbon-14 can damage DNA... But two things that the article didn't really note, is that:
(1) we already have carbon-14 in our bodies, obviously.
(2) A million tonnes sounds like a lot, but how many tonnes of water are there in the ocean? Forgive me for the bad pun, but it's really a drop in the ocean...

[Van Rijn]

I was already rolling my eyes looking at the title - Greenpeace is the last organization I would consider for an objective discussion regarding radiation. Of course the article has no experts giving any kind of analysis of what actual risk would be posed, what the practical options are with associated cost, and so forth, so I don’t see anything useful there to help a reader evaluate the issue. Typically with things like this it works out to: We could take option A which presents such and so minimal risk and spend the money saved on these other things that could save many lives, or we could take the far more expensive option B to reduce the minimal risk to a very slightly lower risk at the expense of substantially increasing risk elsewhere.

[geonuc]

Releasing the water to the ocean is the only reasonable solution.

[Swift]

This seems to be the article that triggered this discussion, a "Perspective" from the 7 August 2020 issue of Science.

According to that article, the ¹⁴C level is between 10 and 100 Bq/liter.

I couldn't find a reference for ocean water in the same units, but I did find this paper about concentrations in various substances and Figure 2 shows the concentrations in various food products from about 10 to 100 Bq/kg. So, the Fukushima waste water has as much Carbon 14 as most grains.

This post from Reddit indicates the Pacific Ocean has 6.8 x 10²⁰ kg of water, or 6.8 x 10¹⁷ tons. A million tons of Fukushima water would be less than 1 x 10^-9% of that weight.

[Swift]

According to that article, the ¹⁴C level is between 10 and 100 Bq/liter.

I found this in the wikipedia article about becquerel (Bq).

For practical applications, 1 Bq is a small unit. For example, the roughly 0.0169 g of potassium-40 present in a typical human body produces approximately 4,400 disintegrations per second or 4.4 kBq of activity.[11]

The global inventory of carbon-14 is estimated to be 8.5×10¹⁸ Bq (8.5 EBq, 8.5 exabecquerel).[12] The nuclear explosion in Hiroshima (an explosion of 16 kt or 67 TJ) is estimated to have produced 8×10²⁴ Bq (8 YBq, 8 yottabecquerel).[13]