Nuke plant and super heat

[frankiee]

Why do nuclear plants run with so little superheat??

 

[stephenw22]

My guess would be for safety margin.

 

[TheBlacksmith]

In order to superheat steam, it must be separated from the water and then re-exposed to the heat source. Relatively easy in a fossil fueled plant, although the cooling properties of the steam is limited, so the superheater tubes are typically shielded from direct radiant heat by screen wall tubes. Most reactor design make separate superheater pass impractical.

 

[GrimesFrank]

Temperatures reached in a LWR are lower than in a fossil boiler and therefore to achieve the same temperatures and maintain phase/coolant flow/etc alot of other components change. As has been stated the practicality of rerouting water HTS coolant to superheat your steam is impractical when the point is to compact your reactor design as much as possible. The additional coolant inventory required alone makes it a headache.

This becomes less of an issue when dealing with HTGR (High Temperature Gas Reactors) however compact design is still key.

Frank "Grimey" Grimes
You can only trust statistics 90% of the time.

 

[rmw]

Actually, some superheating does happen in the nuclear cycle, but not in the reactor. At lower turbine stages (I am not going to dig out heat balances to say at what stage this occurs) steam that has already expanded through the turbine to a point of having lots of moisture in it is taken out of the turbine and passed to the MSR's (Moisture Separator Reheater) where it is dried mechanically via chevron vanes and then it is reheated with main steam. Since at this point in the cycle, main steam temperature is well above the saturation temperature of the steam, some superheating does occur. A lot of how much has to do with the approach temperatures of the MSR.

rmw

 

[sailoday28]

In a pwr, compare the reactor coolant outlet temperature with steam generator pressure. I believe from this you will see why superheat is relatively low.

regards

 

[frankiee]

Are there any trial nuke plant simulators out there or any reasonably prices home versions.
I think it is a great learning tool.
Thanks you

 

[frankiee]

Whoops
The above post was going to be a new post
Sorry about that

 

[hydrae]

The maximum temperature in a PWR or BWR nuke plant is about 500 to 600 degrees and this is at the reactor
The maximum temperature in a coal fired boiler is 3500 to 4000 in the center of the flame
It then becomes how to best use this heat to generate the power, other limits in material strength at temperature then dictate what you can do.
Both steam cycles try to mimic the carnot cycle where they can to get the best efficiency

Hydrae

 

[davefitz]

The safety margin for upsets in heat generation, cooling fluid unbalance, and operarig transients is greatly increased by ensuring zero superheat in the outlet fluid, and to avoid dryour overheat in the outlet section, wet steam would be the design objective.

There was an externally fired superheat on one of the Con Ed reactors , which was an oil fired superheater.

The current research effort at the Gen IV supercritical reactor SCWR is attempting to show that superheat can be provided within the reactor, but my own opinion is that unbalances in flow to the "worst" channel would cause an unacceptable overheat in the outlet of that worst channel . Standard unbalances of channel effective diameter, heat flux patterns ( at worst unabalanced mdoerator condition), flow unbalance due to inlet distribution plate issues combined with the swift deteriioration in fluid heat capacity above the "pseudo critical point" has been shown ( in the 1950's) to lead to unacceptable outlet temperature unbalances when all heat is absorbed in a single pass device.