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G0ldfinger

Fukushima I: four reactors in trouble.

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The ensuing explosion would send massive amounts of radioactive material into the air. Massive amounts. (See Chernobyl)

 

The situation at present is more like pouring water on a car engine. Lots of steam (actually, at present, its the formation of hydrogen from extreme temperatures, but the analogy is close).

 

In an exposed core situation, it’s much more like pouring water on a petrol fire. A big no no.

 

 

I read that the reason the fuel rods are getting hotter despite the control rods having been dropped in is that during normal operation short-lived isotopes are produced, caesium and iodine etc that have a decay time of a few days. Even though the fuel rods are no longer self-sustaining in terms of neutrons, the isotopes simply decay at a predetermined rate which cannot be altered as it is a function of the material itself, there are no neutrons being communicated between rods necessary to keep these reactions going unlike with plutonium/uranium.

 

So, without cooling water the rods will get hotter and may melt, at which point they'll run down to the bottom of the reactor, hopefully the splitter will prevent enough molten uranium/plutonium accumulating there to achieve criticality and it'll solidify. When it's cool some muppet will have to go in and chip it out for reprocessing...

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The ensuing explosion would send massive amounts of radioactive material into the air. Massive amounts. (See Chernobyl)

 

The situation at present is more like pouring water on a car engine. Lots of steam (actually, at present, its the formation of hydrogen from extreme temperatures, but the analogy is close).

 

In an exposed core situation, it’s much more like pouring water on a petrol fire. A big no no.

 

Why a huge explosion? The government had already said they would release the 2.1 times over designed pressure from the coolant by atmospheric venting.

 

It would then be a boiling water reactor boiling the coolant away at atmospheric pressure where it was not designed as a pressurised water reactor, where in fact seawater and boric acid are being pumped in as absorber moderator

 

What actually do you mean by exposed core though? In a light water reactor one of the safety features is that if the water boils off the fuel cools because the water when present acts to slow the neutrons so they can be absorbed to drive the reactor rather than water acting as an absorber or remover of neutrons

 

So help me put all of these elements together so they make sense please.

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Obviously these things have blown to hell and the clean up is likely to need people prepared to die for their country, but Japan has such a culture that people will come forwards who are prepared to help save their country whatever the personal risk and once you get to a certain age it is not like you want to live for ever anyway.

 

Even so the nature of these reactor cores is that they will end up a horrible mass of hot stuff rather than something that is going to do anything that distant folk need to worry too much about. Once they start melting the surrounding material of the reactor the additional material will moderate the pure fuel by diluting it and making it further apart.

 

What is more the air is surprisingly heavy and can effectively dilute this stuff to harmless levels even if traces of it get everywhere.

 

Even so, I agree that a disaster of epic proportions is underway and who knows what consequences this will have for a country like Finland that has a fairly large base load created by nuclear power and is entirely dependant on outside fuel other than wood - just like Japan.

how is it obvious?

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Goldfinger

 

Imagine a very large empty container. Now insert a honeycomb of parts in that container while operating remotely at a distance so you can remove and add parts with a crane above to keep this operating for 30 years. Now expose this honeycomb to a violent shaking where some of the parts weigh a few tonnes and they all rock and roll together

 

Now imagine before the shaking some of the parts were control rods raised by automatic equipment so that the other inserted fuel rod parts got hot so that there were gaps between the honeycomb and the other heavy hot parts had freedom of movement in forces they were not designed to withstand. This whole honeycomb structure and rods weighs a few thousand tonnes

 

Now imagine a process lowers by force the rods sticking out of the honeycomb into the honeycomb so that once these parts are fully inside the honeycomb the fuel rods go cold

 

Now imagine that some of these rods get stuck and then have even more force applied to them to get them to enter the honeycomb. Then imagine this process damages a few things better not damaged and many of the rods cannot be forced down into the honeycomb.

 

Now imagine that most of the fuel cell rods cannot be raised out of the honeycomb and are stuck in a warped structure that is totally broken

 

Get the picture? So far it is all contained.

 

Now imagine a too hot reactor that cannot be shut down, with no power supply where hot fuel is super heating the water surrounding the hot fuel where if the water evaporates the hot fuel will be cooler but still too hot because the control rods are not fully in

 

If the control rods were in do you think you would have seen the reactor building blown to hell?

"not designed to withstand" doesn't mean what you think it means. My flat is not designed to burn, however, i'm sure it will burn just fine if faced with the right circumstances.

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True. The more I read the more I think panic is setting in, no news is not good news in this case. We'll see what tomorrow brings.

 

I don't think the people working on the reactors have full information either. How could they? Don't you think many important sensors have been blown away? A fact is, radiation as high as in Chernobyl could not been hidden. Furthermore, the more time goes by the IMHO more unlikely it is that we see a really "dirty" blowout as in Chernobyl.

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I think someone said they are PWR's, if so there is a separate cooling circuit with heat exchangers. If that's still intact, the water won't be in contact with radioactive material.

Hi John, we are told there has been some release of radioactive material in the steam and therefore the cooling circuits are NOT intact. We don't know how bad it is yet. My gut feel is they will have to manage this for 40 - 60 years before they can get in and have a clean/tidy up.

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I read that the reason the fuel rods are getting hotter despite the control rods having been dropped in is that during normal operation short-lived isotopes are produced, caesium and iodine etc that have a decay time of a few days. Even though the fuel rods are no longer self-sustaining in terms of neutrons, the isotopes simply decay at a predetermined rate which cannot be altered as it is a function of the material itself, there are no neutrons being communicated between rods necessary to keep these reactions going unlike with plutonium/uranium.

 

So, without cooling water the rods will get hotter and may melt, at which point they'll run down to the bottom of the reactor, hopefully the splitter will prevent enough molten uranium/plutonium accumulating there to achieve criticality and it'll solidify. When it's cool some muppet will have to go in and chip it out for reprocessing...

 

I dont buy this explanation. My oil boiler heats dirty water to 60C which passes via large diameter 6cm pipes to a heat exchanger to heat clean water and only relies on the natural convection of hot water where hot water strongly layers above cold water. It does not require a pump and the hotter the boiler flame the faster it pumps the water.

 

The whole point about safe reactor design is you have multiple redundancy so if all the systems fail water still flows thru the heated core into the heat exchanger and whatever over pressure is created just vents to the atmosphere

 

The other thing about a nuclear reactor is that a relatively small amount of fuel creates a large amount of heat and lasts a long time. How can it be that when shut down the waste products are present in such large quantities that it creates a heat hazard for days on end when we are told they are very short life elements??

 

This after all is supposed to be one of the safest designs every made?

 

But now it turns out if the generator fails you are totally furked? Come on!!

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I dont buy this explanation. My oil boiler heats dirty water to 60C which passes via large diameter 6cm pipes to a heat exchanger to heat clean water and only relies on the natural convection of hot water where hot water strongly layers above cold water. It does not require a pump and the hotter the boiler flame the faster it pumps the water.

 

The whole point about safe reactor design is you have multiple redundancy so if all the systems fail water still flows thru the heated core into the heat exchanger and whatever over pressure is created just vents to the atmosphere

 

The other thing about a nuclear reactor is that a relatively small amount of fuel creates a large amount of heat and lasts a long time. How can it be that when shut down the waste products are present in such large quantities that it creates a heat hazard for days on end when we are told they are very short life elements??

 

This after all is supposed to be one of the safest designs every made?

 

But now it turns out if the generator fails you are totally furked? Come on!!

 

I believe this is a very old version of a BWR and there are more naturally failsafe designs in use nowadays. Here is the thing, even if natural boiling and convection removes heat from the core, where does that heat go? You must find a sink for that heat. Normally it would go to a turbine and then a condenser. There would be a cooling water flow which presumably was seawater on the exterior of the condensers, no doubt pumped into the reactor building then out again, warmer from the waste heat. Now imagine the earthquake takes the turbine and condenser out - clearly they must have a back-up system to remove the heat from the core somehow, but I believe (a) they lost all mains power when the earthquake came and (B) though they switched to diesel generators the tsunami took them all out. No power, no pumps, = no water = no cooling...so the water inside the BWR just gets hotter and hotter. It starts to dissociate into hydrogen and oxygen. The operators see this and vent it to keep the pressure down. Maybe they vent it inside the reactor building to keep the chance of any secondary radiation reaching the outside to a minimum...but the oxy-hydrogen mixture is ignited by whatever and the roof and sides of the reactor building blow off.

 

Don't know what happened with the large explosion earlier today, it didn't look like oxy-hydrogen, I have heard speculation it was a steam explosion mixed with pulverised concrete.

 

I don't know what the problem is with believing that decay isotopes can keep a reactor hot for several days after it is switched off, the way to deal with it normally would have been to just remove the waste heat for whatever, a week or two until most of the caesium/iodine had decayed...decay isotopes keep supernova shining for weeks after the main explosion, usually nickel-56 I believe...

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Why a huge explosion? The government had already said they would release the 2.1 times over designed pressure from the coolant by atmospheric venting.

 

It would then be a boiling water reactor boiling the coolant away at atmospheric pressure where it was not designed as a pressurised water reactor, where in fact seawater and boric acid are being pumped in as absorber moderator

 

What actually do you mean by exposed core though? In a light water reactor one of the safety features is that if the water boils off the fuel cools because the water when present acts to slow the neutrons so they can be absorbed to drive the reactor rather than water acting as an absorber or remover of neutrons

 

So help me put all of these elements together so they make sense please.

I actually meant a reactor that had a graphite moderator, which “could” technically remain critical and when exposed to air would ignite. Then you can have an exposed critical core. Anything landing on it, concrete or water etc would result in a massive ejection of material. Even with nothing added, the fire would spew loads of crap into the atmosphere.

 

Also, if, and it is a big if, the core then melted and the mixture of moderator and U235 was in the right quantity, then you would have the "theoretical" China Syndrome. Nasty.

 

That’s what I meant by saying the Japanese reactors were sub critical.

 

Normally, the water "cools" the neutrons enabling the U235 to absorb them and leading to fission as you said. So, no water and the fission stops. But even after the control rods are put in (also stops fission, ie sub critical) everything is very hot and must still be cooled with water. If that water isn't supplied in the correct quantities, the temp will rise to reach is natural point (in the absence of cooling). So, with no water, the stored heat could melt the fuel rod coatings.

 

From what I have just read re the cesium and iodine detection, this might be happening now. On the bright side, the Uranium needs much higher temps to burn.

 

Also lots of secondary short lived reactions as pointed out. These add temp to the system.

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Hi John, we are told there has been some release of radioactive material in the steam and therefore the cooling circuits are NOT intact. We don't know how bad it is yet. My gut feel is they will have to manage this for 40 - 60 years before they can get in and have a clean/tidy up.

If the reports are correct, I guess it would depend on just how big a breach there has been between the two "closed" circuits.

 

You might well be right, but hopefully they will just be the short lived radioactive species. (ie I think radioactive Nitrogen lasts a few seconds).

 

One thing about radiation is, the more active it is, the quicker it decays.

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I believe this is a very old version of a BWR and there are more naturally failsafe designs in use nowadays. Here is the thing, even if natural boiling and convection removes heat from the core, where does that heat go? You must find a sink for that heat. Normally it would go to a turbine and then a condenser. There would be a cooling water flow which presumably was seawater on the exterior of the condensers, no doubt pumped into the reactor building then out again, warmer from the waste heat. Now imagine the earthquake takes the turbine and condenser out - clearly they must have a back-up system to remove the heat from the core somehow, but I believe (a) they lost all mains power when the earthquake came and (B) though they switched to diesel generators the tsunami took them all out. No power, no pumps, = no water = no cooling...so the water inside the BWR just gets hotter and hotter. It starts to dissociate into hydrogen and oxygen. The operators see this and vent it to keep the pressure down. Maybe they vent it inside the reactor building to keep the chance of any secondary radiation reaching the outside to a minimum...but the oxy-hydrogen mixture is ignited by whatever and the roof and sides of the reactor building blow off.

 

Don't know what happened with the large explosion earlier today, it didn't look like oxy-hydrogen, I have heard speculation it was a steam explosion mixed with pulverised concrete.

 

I don't know what the problem is with believing that decay isotopes can keep a reactor hot for several days after it is switched off, the way to deal with it normally would have been to just remove the waste heat for whatever, a week or two until most of the caesium/iodine had decayed...decay isotopes keep supernova shining for weeks after the main explosion, usually nickel-56 I believe...

 

And the 4 day decay time quoted is the half life, ie half the amount of radiation emitted after 4 days, then half again after another 4 days then.... (ie doesn't all just stop after 4 days).

 

As the reactors automatically shut down, power was shut off and I guess it's possible the circulating pumps lost power due to external power supplies also down due to quake/wave.

 

Some reactors use liquid sodium as a coolant and this can continue circulating by convection when the pumps stop. Water cannot (doesn't have the density or heat conductivity of liquid Na). They do have other not so nice qualities though.

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I believe this is a very old version of a BWR and there are more naturally failsafe designs in use nowadays. Here is the thing, even if natural boiling and convection removes heat from the core, where does that heat go? You must find a sink for that heat. Normally it would go to a turbine and then a condenser. There would be a cooling water flow which presumably was seawater on the exterior of the condensers, no doubt pumped into the reactor building then out again, warmer from the waste heat. Now imagine the earthquake takes the turbine and condenser out - clearly they must have a back-up system to remove the heat from the core somehow, but I believe (a) they lost all mains power when the earthquake came and (B) though they switched to diesel generators the tsunami took them all out. No power, no pumps, = no water = no cooling...so the water inside the BWR just gets hotter and hotter. It starts to dissociate into hydrogen and oxygen. The operators see this and vent it to keep the pressure down. Maybe they vent it inside the reactor building to keep the chance of any secondary radiation reaching the outside to a minimum...but the oxy-hydrogen mixture is ignited by whatever and the roof and sides of the reactor building blow off.

 

Don't know what happened with the large explosion earlier today, it didn't look like oxy-hydrogen, I have heard speculation it was a steam explosion mixed with pulverised concrete.

 

I don't know what the problem is with believing that decay isotopes can keep a reactor hot for several days after it is switched off, the way to deal with it normally would have been to just remove the waste heat for whatever, a week or two until most of the caesium/iodine had decayed...decay isotopes keep supernova shining for weeks after the main explosion, usually nickel-56 I believe...

 

OK thanks for that. You have covered most of the bases to my satisfaction.

 

But how is it that accidental removal of the cooling water is a safety feature because the water in fact increases the fission, if on shutdown circulating cooled water is required via substantial electrical power for a safe shutdown?

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OK thanks for that. You have covered most of the bases to my satisfaction.

 

But how is it that accidental removal of the cooling water is a safety feature because the water in fact increases the fission, if on shutdown circulating cooled water is required via substantial electrical power for a safe shutdown?

 

I am not an expert on reactors though have some connection with Radioisotope ThermoGenerators, so BWR operation is not my field but there are two distinct nuclear processes we are talking about here. The main nuclear process is criticality for the uranium fuel rods when the release of a neutron from a uranium atom can release at least one ( and hopefully on average EXACTLY one other neutron ) from another uranium atom and so on. Thus a stable nuclear reaction carries on with a constant number of uranium atom disintegrations (and hence neutrons being released) per second. This process is controlled by the moderator rods and maybe too by the water.

 

Now remove the water and maybe the absence of it does reduce the number of neutrons produced, by not slowing what neutrons there are down to the right speed to knock out other neutrons from the uranium. So if that's the way it works, that would be a safety feature. That doesn't account for the secondary radioactive process though whereby the decay of uranium atoms, as well as producing neutrons, produces new, unstable atoms of smaller atomic number. These atoms have a half life of whatever, let's say 4 days as JD suggests. The decay of these isotopes is not dependent on the presence of neutron moderators. They are going to decay in the next few days come hell or high water, they don't need to be dosed with neutrons to encourage them to decay. So the control rods and presence of water have no effect at all on the decay of these isotopes, they just do their stuff and decay when they feel like it.

 

Absence of water is perhaps then a safety feature for the uranium reaction, but is irrelevant to the short-lived decay isotopes...

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The holy Bhagvad Gita tells us that you can kill people, but you can never kill a soul. No weapon can cleave it, no fire can burn it, because the soul is immortal. The Gita also says: "For death is certain to one who is born...thou shalt not grieve for what is unavoidable."

 

These wise words from the Gita will console the grieving heart in our saddest moments.

na jaayate' mriyate' vaa kadaachin naayam bhuthva bhavithaa na bhooyah: |

ajo nithyah saasvato'yam puraano na hanyate' hanyamaane' sareere' ||

 

 

Bhagwad Gita is a book which answers all the questions you have. It will produce more questions the answers you have to find on your own accord.

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This is the big explosion....the one they didn't want as reactor 3 has the mox (mixed oxide). News out indicates

(not surprisingly) that the reactor rods may have been exposed for a few hours now. In other words it is too

late to run for most people. The world should be bracing itself NOT listening to the tired line that another

Chernobyl is "unlikely".

 

They are saying its reactor 2 that has blown........does that also have mox as in the case of reactor 3

 

I am in agreement with you with regards to the official announcements. Yesterday when R3 blew, they had announced within 30 minutes that the explosion was hydrogen and the core was intact!!...30 MINUTES!! Are they trying to tell me that they can do a full inspection of the reactor and make such a judgement in such a short space of time???....I dont think so. It all sounds a bit desperate to me and they are saying anything to prevent mass panic

 

Personally, I dont believe a bloody word of it

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They are saying its reactor 2 that has blown........does that also have mox as in the case of reactor 3

 

I am in agreement with you with regards to the official announcements. Yesterday when R3 blew, they had announced within 30 minutes that the explosion was hydrogen and the core was intact!!...30 MINUTES!! Are they trying to tell me that they can do a full inspection of the reactor and make such a judgement in such a short space of time???....I dont think so. It all sounds a bit desperate to me and they are saying anything to prevent mass panic

 

Personally, I dont believe a bloody word of it

 

Sorry I went back to edit that out since I thought reactor 3 had gone. However given the level of desperation (using seawater which will leave salt deposits that will eventually block venting, not to mention long term consequences) this strongly suggests they are buying time more than anything else. Also I hear they are evacuating some staff members from the plant...

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BBC reporting 3rd explosion possibly reactor 2

 

Apparently if you remove a spent fuel array from a nuclear reactor it can take up to a year or more to cool down due to the decay of the fission products. So i am not sure where people are getting the information about the few days for this to happen. At least some of the fuel pins will have significant amounts of spent fuel and will require significant cooling - compared to the newer fuel arrays which have fewer fission products. There is a lot of talk at the moment about the fuel arrays not being fully under water for the cooling to happen

 

Additionally if you shut these reactors down and you have inadequate cooling of the core you then get burst fuel containers because the fission gases expand and the containers get shocked and brittle and since you have inadequate cooling and you are releasing the highly radioactive boiling water to avoid an over pressure event then you need large exclusion zones. It sort of adds up that this is happening now and nothing can be added to the reactor to stop the fission products from decaying so somehow the gases coming out of the reactor will have to be stored and compressed and processed for months or years to come.

 

Sad. Very sad.

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I read the inner high pressure container of the reactor core has been damaged this time, and radiation is higher than in previous explosions. But apparently (?!?) there is still no human life in danger.

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I am not an expert on reactors though have some connection with Radioisotope ThermoGenerators, so BWR operation is not my field but there are two distinct nuclear processes we are talking about here. The main nuclear process is criticality for the uranium fuel rods when the release of a neutron from a uranium atom can release at least one ( and hopefully on average EXACTLY one other neutron ) from another uranium atom and so on. Thus a stable nuclear reaction carries on with a constant number of uranium atom disintegrations (and hence neutrons being released) per second. This process is controlled by the moderator rods and maybe too by the water.

 

A few neutrons are usually emitted when the U235 (that absorbs a neutron then) splits. For the critical (or self sustaining)condition (opposed to sub or super critical) then only one of these neutrons is absorbed by another U235 atom. The others strike the surrounding material giving up their energy as heat (also the moderator takes heat from the neutrons as they slow down).

 

Now remove the water and maybe the absence of it does reduce the number of neutrons produced, by not slowing what neutrons there are down to the right speed to knock out other neutrons from the uranium.

 

Yes, the absence of water (in this case) stops the critical condition.

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Third explosion at nuclear plant

 

SOMA, Japan — A third explosion in four days rocked the earthquake-damaged Fukushima Dai-ichi nuclear plant in northeast Japan early Tuesday, the country's nuclear safety agency said.

 

The blast at Dai-ichi Unit 2 followed two hydrogen explosions at the plant — the latest on Monday — as authorities struggle to prevent the catastrophic release of radiation in the area devastated by a tsunami.

 

The troubles at the Dai-ichi complex began when Friday's massive quake and tsunami in Japan's northeast knocked out power, crippling cooling systems needed to keep nuclear fuel from melting down.

 

The latest explosion was heard at 6:10 a.m. Tuesday (2110 GMT Monday), a spokesman for the Nuclear Safety Agency said at a news conference. The plant's owner, Tokyo Electric Power Co., said the explosion occurred near the suppression pool in the reactor's containment vessel. The pool was later found to have a defect.

 

International scientists have said there are serious dangers but not at the level of the 1986 blast in Chernobyl. Japanese authorities were injecting seawater as a coolant of last resort, and advising nearby residents to stay inside to avoid contamination.

 

Tokyo Electric Power said some employees of the power plant were temporarily evacuated following Tuesday morning's blast.

 

The accidents — injuring 15 workers and military personnel and exposing up to 190 people to elevated radiation — have compounded the immense challenges faced by the Tokyo government as it struggles to help hundreds of thousands of people affected by twin disasters that flattened entire communities and may have left more than 10,000 dead.

 

The crisis also has raised global concerns about the safety of such reactors at a time when they have enjoyed a resurgence as an alternative to fossil fuels.

 

Japanese authorities said there have been no large-scale radiation releases, but have detected temporary elevations in levels, and have evacuated tens of thousands of people from around affected reactors. Prevailing winds were pointing out to sea, and U.S. ships assisting tsunami recovery moved further way to avoid potential danger.

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Sorry I went back to edit that out since I thought reactor 3 had gone. However given the level of desperation (using seawater which will leave salt deposits that will eventually block venting, not to mention long term consequences) this strongly suggests they are buying time more than anything else. Also I hear they are evacuating some staff members from the plant...

The use of seawater suggests they have written the reactors off. A sign how desperate they are.

 

Just heard about the third explosion.

 

Very sad indeed.

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Sorry I went back to edit that out since I thought reactor 3 had gone. However given the level of desperation (using seawater which will leave salt deposits that will eventually block venting, not to mention long term consequences) this strongly suggests they are buying time more than anything else. Also I hear they are evacuating some staff members from the plant...

 

No problem..think we got our wires crossed there :D

 

Strange that there is no footage being shown on TV of the latest developments. I hope its because there is nothing to see but the cynic in me is wondering if this time its serious!

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