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PostPosted: Mar 14, 2011 3:38 pm 
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Cyril R wrote:
That's true. Advanced BWRs are naturally evolving to be simpler. The simplest is the ESBWR:

http://www.youtube.com/watch?v=vmHmSOf7oCA


Presumably the advanced BWR tanks, pipes, etc., would be designed to withstand a 9.9 Richter quake. However, I have reservations about BWRs. The steam for the turbines is slightly radioactive, and would be more radioactive than normal if a fuel rod were defective. I understand why BWRs exist; they are simpler and cheaper because they eliminate the need for a heat exchanger / steam generator.

With the work being done on the Brayton cycle, it may be that the first commercial LFTRs will be able to use it. The combination has the potential of being safer than any system currently in use, at least if the drain tank system is designed not to crack from thermal shock and has adequate passive cooling.


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PostPosted: Mar 14, 2011 4:20 pm 
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In my first days as a member of this site I lobbied hard for the use of heat pipes as a fail safe delayed heat removal mechanism for the Lftr.

Heat pipes allow for delayed reactor heat to be removed to the ambient environment no matter what that environment might be; air water or a combination of the two.

Using heat pipes when properly engineered, the Lftr could be submerged under a 1000 foot tsunami wave caused by an offshore impact of an large asteroid and not release radiation.

Air cooling using chimneys are not fail sale (never fails no matter what happens) because they can be flooded, filled with debris or can collapse in an earth quake or plane crash.

Heat pipes could well be ruggedly integrated into the very walls of the reactor vessel. Heat pipes are stand along and need no circulating coolant pipes or values to function.

The heat pipe idea is not a radical concept; on the contrary, they are central to the passive heat removal strategies throughout Indian reactor design.

Indian reactor designs use heat pipes to passively remove decay heat from their various reactors. More specifically, the removal of heat from upper plenum, under both normal and postulated accidental conditions is accomplished by heat pipes.

The emphasis on safety in Indian reactor design is passive heat removal. C/C composite heat pipes are utilized under postulated accidental conditions including LOCA to remove of heat from the core.

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PostPosted: Mar 14, 2011 4:35 pm 
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Heat pipes are great but still have to reject their heat to something else which is more complicated and can fail. A radiator or chimney will still be required for final heat rejection during emergencies. However it is not hard to design chimneys that can easily take 9+ Richter earthquakes. They must be designed to resist moisture so flooding them will increase cooling not hamper it. Chimneys can also be designed with vertical 360 degree armored top vents which makes debris from aircraft crashes a nonproblem.

Passive BWRs such as ESBWR are very safe due to fully passive operation and the presence of 72 hours of decay heat cooling water that is inherent to the reactor. All the valves are highly redundant and have their own simple and diverse energy supply.


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PostPosted: Mar 14, 2011 6:50 pm 
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Cyril, I have a questiona about the steam venting in the ESBWR and all the BWR designs.

In LFTR's the fission products are vented and removed from the core continuously. In conventional reactors they are supposed to remain inside the fuel rods, but sometimes the products do get released along with the steam, as happened in Japan. Conventional reactor designs treat this as an extreme event and try to cope with it in a way that won't allow a major release to the environment, whereas LFTR's handle it as a part of normal operation.

Would it make sense to release the steam and decay products in a BWR through a dedicated line, passing through cooled condensation pipes and perhaps hydrogen burners, before being diverted to a shielded remote containment vessel, perhaps already half filled with water. Basically, treat a conventional design as if the decay products were released from the fuel rods an inevitable part of operation and add systems to contain and process them, just like a LFTR.


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PostPosted: Mar 14, 2011 7:36 pm 
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Does anyone understand why the hydrogen builds up inside the building? Is there a good reason not to ventilate the buildings to prevent such a buildup? Those photos of buildings blowing up and reports of explosions at the nuclear power plant are making for devasting PR even if no one is killed in the process and no significant radiation is released.


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PostPosted: Mar 14, 2011 8:13 pm 
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Quote:
Heat pipes are great but still have to reject their heat to something else which is more complicated and can fail.


A heat rejection system for a heat pipe can be as simple in design and concept as the heat pipe itself. Through simplicity in design, the probability for failure of this component of the heat pipe system can be reduced to a very low level.

Such simplicity and robustness of design is the enabler of high reliability.

That being said, there is always a finite through small probability for a failure of any component of a system.
But a heat pipe itself should be engineered as an independent system to eliminate any single points of failure.

When this is done, the principle of redundancy can be applied such that an overcapacity in the number of heat pipes would eliminate total system failure and provide a strategy of graceful system degradation to preclude the possibility of total system failure under any possible contingency.

The design of a chimney system is not amenable to a high level of redundancy.

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PostPosted: Mar 14, 2011 8:23 pm 
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Lars wrote:
Does anyone understand why the hydrogen builds up inside the building? Is there a good reason not to ventilate the buildings to prevent such a buildup? Those photos of buildings blowing up and reports of explosions at the nuclear power plant are making for devasting PR even if no one is killed in the process and no significant radiation is released.



Vented hydrogen contain fragments of melted fuel pellets; the function of the containment building is to confine this stuff, not explode.

I though containment buildings have two meter thick reinforced concrete walls that could withstand the impact of a plane chash. Such a building should be capable of confining a hydrogen release.

Who designed that containment building, and who allowed it to be built?

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PostPosted: Mar 14, 2011 8:54 pm 
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alexterrell wrote:
gturner6ppc wrote:


They run on steam (obviously), they always work, they're almost bullet-proof, and even 19th-century farmers could maintain and operate them.


But where would you get the steam from?

Now there's a thought - steam was vented at hight pressure from a containment building.

Or could you use some Spent Nuclear Fuel, housed in a small Richter-9.5 proof building, as a steam generator?

I've always been suggesting spent fuel as a source of emergency power. It is always there at the plant after the first few years. I've only stated conservation of diesel but it gets new meaning after the tsunami damage to the generator has been highlighted. I think a thermo-voltaic blackbox using spent fuel as a source of emergency power should be provided. Perhaps the Japanese will be the first to develop it.


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PostPosted: Mar 15, 2011 12:41 am 
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Guys,

I just updated my blog with a more extensive bibliography of primer documents relevant to the Fukushima accident...

You can find it at:

http://www.sustainableenergytoday.blogspot.com/

Sherrell


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PostPosted: Mar 15, 2011 1:00 pm 
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Bringing in new diesel generator sets does not do much good when your electrical switchgear is in a basement flooded with sea water as was Fukushima.

It would take you several months to pump out the water, disassemble the electrical gear, flush extensively with fresh water and dry out, then replace components destroyed by arcing, reassemble.

In the marine industry, electronics submerged in salt water are not allowed to dry out but are transferred to multiple baths of fresh water to remove the salt and then dried out for testing and repair


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PostPosted: Mar 15, 2011 3:49 pm 
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In the marine industry you keep the electronics dry.

Perhaps one has to assume that a coastal nuclear plant will be covered in water at some point and everything needs IP67 rating?


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PostPosted: Mar 15, 2011 10:44 pm 
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Thanks for the links, Sherrell. I was up most of the night reading one.

The Fukushima reactors will provide quite much more data, not that anybody wanted the data except to help with accidents like this.

They've now pulled all the crews out. The radiation got too high, about 1 Sv/hr.


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PostPosted: Mar 15, 2011 10:58 pm 
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Where was the 100 rem/hour taken?


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PostPosted: Mar 16, 2011 12:30 am 
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Ida-Russkie wrote:
Where was the 100 rem/hour taken?


From what I read, in unit #1, forcing the crews pumping water to abandon the effort. I also read that it was 800+ in one of the other units.

The levels aren't mentioned in this news story, but it says that all workers were evacuated and that they've essentially thrown in the towel.
http://news.yahoo.com/s/ap/as_japan_earthquake

ETA: But those are press stories, so all figures are only reliably accurate to within 3 orders of magnitude.


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PostPosted: Mar 16, 2011 8:02 am 
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gturner6ppc wrote:
Ida-Russkie wrote:
Where was the 100 rem/hour taken?


From what I read, in unit #1, forcing the crews pumping water to abandon the effort. I also read that it was 800+ in one of the other units.

The levels aren't mentioned in this news story, but it says that all workers were evacuated and that they've essentially thrown in the towel.
http://news.yahoo.com/s/ap/as_japan_earthquake

ETA: But those are press stories, so all figures are only reliably accurate to within 3 orders of magnitude.


The official March 16 figure is 0.3 mSv/h at NPP border:

http://bravenewclimate.files.wordpress. ... atus_6.jpg


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