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PostPosted: Jan 26, 2010 12:12 pm 
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STG wrote:
Cyril R wrote:
USPWR, doesn't that kind of thing damage the turbine and generator, in the event of a total grid failure? Seems like suddenly bypassing a big chunk of the steam input from the turbine directly to the condenser is going to be hell on the equipment?


That is only limited damage if such an event would occur. In all circumstances fuel damage and possible releases should be avoided!


I guess what I'm trying to say is, in that event, if the load can be immediately dumped in a resistance heater onsite, both the reactor and power block can be shut down orderly and slowly, while the resistance heater dumps the declining output...

Another way to look at it, is adding another layer of safety, one that is highly reliable and comes at a very low cost and complexity.


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PostPosted: Jan 26, 2010 2:38 pm 
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Cyril R wrote:
USPWR, doesn't that kind of thing damage the turbine and generator, in the event of a total grid failure? Seems like suddenly bypassing a big chunk of the steam input from the turbine directly to the condenser is going to be hell on the equipment?


It is definitely a transient you have to account for in plant design. You typically will "design in" the assumption of so many plants trips over it's lifetime. It's actually hardest on the plant condenser with all that high velocity high temperature steam hitting the tubes all at once.


Last edited by USPWR_SRO on Jan 26, 2010 2:59 pm, edited 1 time in total.

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PostPosted: Jan 26, 2010 2:38 pm 
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STG wrote:
Cyril R wrote:
USPWR, doesn't that kind of thing damage the turbine and generator, in the event of a total grid failure? Seems like suddenly bypassing a big chunk of the steam input from the turbine directly to the condenser is going to be hell on the equipment?


That is only limited damage if such an event would occur. In all circumstances fuel damage and possible releases should be avoided!


You are not even in the realm of possible fuel damage with these kinds of transients.


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PostPosted: Jan 26, 2010 2:58 pm 
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Cyril R wrote:
STG wrote:
Cyril R wrote:
USPWR, doesn't that kind of thing damage the turbine and generator, in the event of a total grid failure? Seems like suddenly bypassing a big chunk of the steam input from the turbine directly to the condenser is going to be hell on the equipment?


That is only limited damage if such an event would occur. In all circumstances fuel damage and possible releases should be avoided!


I guess what I'm trying to say is, in that event, if the load can be immediately dumped in a resistance heater onsite, both the reactor and power block can be shut down orderly and slowly, while the resistance heater dumps the declining output...

Another way to look at it, is adding another layer of safety, one that is highly reliable and comes at a very low cost and complexity.


I suppose. But reactor and turbine trips are analyzed to happen many times (~10 times a year is usually the assumed number) but actually only happen once every 3 years or so on average. It's just not a huge problem really.


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PostPosted: Jan 26, 2010 5:37 pm 
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Luke wrote:
USPWR_SRO, thanks for the clarification, it's clearly more complicated than I thought (unsurprisingly). One point I'm still not clear on, though, is whether it is permitted to run a reactor, at some power level, with no grid link. I only became aware of this issue from news reports of the Katrina aftermath, which said that there was a reactor within the damaged area that had to shut down, even though there was no damage to the plant itself. Power to run pumps, (and hospitals, and air con...) would have been very welcome, but the reactor could not supply it, even with the link from it to New Orleans fixed, until they had also fixed the links from other parts of the grid to the reactor. I thought this was because grid power availability was part of the safety case, so that a generator trip couldn't leave you with nothing but the diesel backups.


There are definite technical specification requirements on grid diversity. If you have lost large parts of your grid and you have not in fact tripped, you would probably enter shutdown action requirements. However there is a mechanism in place to request enforcement discretion from the NRC if it is in the best interest of the public to maintain generation. There is nothing technically preventing you from operating at low power with very little grid you are supplying. It just would not meet legal requirements for offsite power source diversity.


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PostPosted: Sep 07, 2010 9:17 pm 
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Interesting stuff about power trips, etc.

I also was concerned about heating the salt to start things. I think the logical way is to heat the air or gas in the hot cell with an electric heater. If it's already hot, no problem.

One of the weaknesses of the MSRE was that almost every pipe with salt had a small electric heater. I have the impression that if one of those failed, something could go wrong.


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PostPosted: Sep 07, 2010 9:31 pm 
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Which it did several times. Nothing major (since the salt doesn't expand dramatically when it freezes like water does) but they did damage some pipes once when there were multiple spots in the pipe that froze. They melted most of them thinking they had them all and then started up - that did some modest damage.

In their second generation design (MSBR) they decided to simply keep the entire space hot rather than endure the reliability issues of multiple heaters.


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PostPosted: Sep 08, 2010 1:14 am 
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That is the sort of problem which can be prevented during the R & D phase before a LFTR or other liquid salt reactor is put into production. Good design should eliminate the problem.


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