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Hiddencamper•

Ho-Ly-Shit.

I'm just mind blown that the ESBWR might actually get it's design certification. They had huge issues with their chimney design and some of their neutronics models, and when they finally got through that, this steam dryer thing held them up and allowed Westinghouse (AP1000) to get ahead of them significantly.

Sincerely hope we will start to see some boilers to up.

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rynvndrp•

Could you explain the chimney design in an ESBWR? I know the BWR2/6 designs well and have seen the schematics for the ESBWR and am just not sure what the chimney is there for.

Also, if you know, how is spectral shifting going to work in the 'pancake core'? Its a huge thing for the older boilers to save fuel but it seems like it would be near impossible for the ESBWR.

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Hiddencamper•

So..............

I had this power point about the ESBWR sitting on my thumb drive that talks a little bit about the chimney.

Big picture the chimney does a few things. It gives you a higher water column to work with. This is important, because in a BWR, when you scram, your voids collapse and your indicated water height decreases drastically. In my reactor, with no makeup at all, a scram will drop my water level almost 80 inches. So by having the chimney, you have this large amount of extra inventory and it slows down the rate of transients. The higher volume and chimney effect also allows for a larger natural circulation driving head. Seeing as the ESBWR is a natural circulation core, natural circulation is going to need to be efficient to support higher power levels. The chimney also has significant benefits with regards to pressure transients. BWRs have pretty severe pressure/load reject transients. A BWR5 plant will reach around 600% peak flux on a delayed load reject without bypass. The chimney provides a hydraulic 'cushion' to help limit those transients, which in turn limits the MCPR penalty which must be applied for those events. This is more important in the ESBWR because you don't have the ability to trip recirculation pumps to void the core and limit the peak flux (many BWR plants have trips or runbacks on their recirculation pumps during load rejects to help soften the transient).

As for spectral shifting.........I'm not really sure. My brain might be scramming right now, but that's not a term I've really heard in BWRs, what exactly are you referring to?

Anyways, it looks like they are going to use the improved control cell design with a low leakage outer ring. The control blade and lattice design give them a lot of capability for flux control.

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rynvndrp•

Spectral shifting is common axial power shape design used in a lot of BWR's. At the start of the cycle you design it so the power is at the bottom of the core. This increases the amount of void that exists in the top which in turn decreases moderation and increases plutonium production. As a long cycle continues, the bottom starts to deplete out and the power shape moves up in the core. By all rods out, you are running mostly on the plutonium in the top half of the core.

Fuel is designed with part length rods to increase this effect, driven flow is designed higher to increase this effect. Gad is axially changed to increase this effect. So long as the thermal limits can handle it, pushing power down early and power up late is the most important thing to get as much GWd per MT of uranium as possible. You can hit breeder ratios of 0.68 with modern fuel and non uprated cores.

Take 20" of fuel away and you decrease this ability. Breeder ratio drops and you use more enriched uranium and cost to provide the same heat.

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Hiddencamper•

Ok I know exactly what you are talking about. For some reason I never mentally associated the term "spectral shift" with BWR cycle burnup response.

I get the impression that GE wants to sell as many fuel bundles as possible :X

I'm not really sure what they are going to do about that. They had to pancake the core to make it more amenable to natural circulation. I do know that they are going to have a power-to-feedheating map, similar to the power to flow map, with increased and reduce feedheating regions. So there may be some ability to control the boiling boundary with that.

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Triffgits•

Oh wow, this is big.

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