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Japanese nuclear accident FAQ 7

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Thanks again Trottiey. I had that diagram but without the containments identified. I thought that green wavey stuff looked suspiciously like seawater. So if the blue primary cooling water gets quite radioactive, I suppose the green secondary cooling water would get slightly radioactive. So it should be no surprise to find radioactivity in the neighbourhood ocean?

HAZOP at
 
owg said:
So if the blue primary cooling water gets quite radioactive, I suppose the green secondary cooling water would get slightly radioactive. So it should be no surprise to find radioactivity in the neighbourhood ocean?
Click to expand...
That doesn't sound right to me. The loop through the condenser is all to do with normal plant operation. At the moment, I don't think there's any circulation through it (especially on the seawater side), so the fission products they're finding in the sea (fission products implies a release of water that's been in direct contact with broken-down fuel rods inside the reactor pressure vessel) probably escaped some other way.

A.
 
The alpha/beta/gamma ionizing radiation that we're talking about here is not contagious. (Neutron radiation is contagious in some situations, but it's not relevant here.) During normal operation, the green secondary cooling water does not get radioactive. (Except from fugitive emissions such as leaks, spills, maintenance activities, etc.) The high levels of radioactivity that they're measuring now can only be due to fission products (contaminants) that originated in the core or in the spent fuel bays.

There are many ways in which the radioactive contaminants could have reached the sea. They might have been carried by steam that was vented to primary containment, condensed in the torus, and then released to sea (with as much filtration as they can do) per Fermi2's analysis. Or the contaminated torus water might have leaked out through a primary containment breach and bypassed the filters. Or the steam vented straight to atmosphere might have carried particulates and low-volatility liquids with it, and these would have fallen out in the neighboring area. But I suspect that the most likely possibility is simply that water leaked or overflowed out of the spent fuel bays.

But regardless of how the water is getting out, this is the essential reason why blindly dumping sand and concrete would accomplish little: contamination would still leak out into the groundwater. The stress of an unpredictable and poorly controlled event tends to push people to rash physical exertions. That stress mechanism was useful in the wild, but please keep in mind that this is a technological problem that can only be solved by clear level-headed thinking. In the end, the stress and depression may have a greater public health impact than the radiation. (At least no one here has suggested sending in an air strike to bomb the place. I've seen that in the comments section of some news websites.)
 
What Trottiey says is generally true, but again we have to remind ourselves that we are dealing with the aftermath of a 9.0+ earthquake that literally moved Japan 8" closer to the USA plus some very unusual and unpredicted after effects so there is nothing to guarantee that the integrity of anything hasn't been compromised in this plant, including the normal and usual isolation of the seawater cooling system from the "hot" side.

I can't really see that being the reason for radioactivity in the sea, but I remind that we can't think this through with rational thought.

rmw
 

Just to clarify a couple of points:

- zuesfaber is right. In the diagram above, the condenser shown in only used when they are making electricity. The turbines, condenser, and the circulating water system is not used if offsite power is lost. They would likely have another seawater cooling system used to reject core decay heat and spent fuel decay heat to the ocean. There are no cooling towers because the plant is right on the ocean and uses once-through cooling. All heat will ultimately be rejected to the ocean.

- I am not a BWR expert, but I am pretty sure that they have a recirculation cooling system with heat exchangers that are cooled by another cooling system (not shown in the figure). I believe that the wetwell also has a cooling system.

- Most of the fuel in the SFP has been sitting long enough that it will not melt. Only the more recently used fuel assemblies are at risk of melting.
 
rcchap - Thanks for the additional information. But I was wondering, if they have power to run a backup cooling circuit, would they not have power to run the regular cooling circuit? Maybe they have some power now but not not enough for the big stuff.

HAZOP at
 
Here is a clip from a March 28 newspaper report. "The water must be removed and safely stored before work can continue to power up the plant's regular cooling system, nuclear safety officials said." So this may be the reason that the main cooling circuit is not yet back on in one or more of the units.




HAZOP at
 
The diagram shows only the power producing si side of the plant.
The two pumps and piping shown inside the containment are the reactor recirc pumps. They were used to vary power output but not for ememgency cooling.
There are four RHR and two core spay pumps not shown. There would also be 2-4 emergency service water pumps to provice RHR cooling via heat exchangers and cooling for the emergency generators.
The diagram does not show the HPCI and RCIC systems.

I can't tell from the pictures but I would suspect the refueling cranes are gone and the reactor building bridge crane as well.

trottiey - What can the reactor water clean up system do?


 

owg:

The "normal" cooling circuit with the circ water system would not be used without offsite power available. The circ water pumps are very large and require a large amount of power. These pumps would not be able to be supplied from the emergency diesel generators. The EDGs would only feed the safety related busses, and the circ water pumps are non safety related and designed to reject the 60-65% of the full power heat production for the steam turbine (Rankine) cycle.

The safety related cooling system used for shutdown cooling would be relied upon in a loss of offsite power scenario such as this. These pumps are smaller, would be safety related, and would be powered by the EDGs and would be designed to only reject decay heat, which would be just a few percent of the full power. When they talk about restoring power to the "regular" cooling system, this is what they are talking about.

BJC:

The reactor water cleanup system would be used during normal power operation to keep contaminants out of the water and control pH (and numerous other parameters) within spec. To keep normal operating dose down and to ensure proper operation of the plant, it is very important to keep the water extremely clean. This system will have a series of demineralizers to do this. At this point, this system would have very little use, and may not be powered from safety related busses.
 
Don't be fooled by advertising. "Shielding test results indicate that two layers of Demron, with [...] a thickness of 0.4 mm each, [...] would have equivalent shielding power as lead with [...] a thickness of 0.2 mm."

So what does 0.2 mm of lead buy you? Well the half-thickness value for lead shielding on typical radioactive waste is about 13 mm, so I = Io / 2^(0.2/13) = 0.989 Io. Wearing two demron suits one on top of the other will cut down your external gamma exposure by about 1.1%.

Personal protective gear does not provide much protection from external radiation exposure. The plastic suits are worn primarily to stop radioactive vapours from being absorbed through your skin. They also prevent radioactive dust from clinging to your clothes or skin and being dragged back to clean areas with you.
 
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