Understanding the Role of Fuel Rods in a BWR - Explained Simply

[biferi]

I need just one thing I need help to understand?

The Core in a BWR just a BWR has Fuel Rods that Heat water to make Steam.

But one thing when the watter Heats up is the Steam in the same place as the Fuel Rods?

What I meen is this.
Every photo I look at shows Fuel Rods in the Watter and the Steam builds up in the same place the Fuel Rods are in. And then gets Pumpt out to the Turbines or what have you.
Is this right?

 

[rmattila]

Only about 1/7 of the water pumped past the fuel rods turns to steam and goes to the turbine, the rest of the water is circulated inside the reactor vessel. This 1/7 takes about 70 % of the volume at the top of the assembly, but there's still enough liquid water to take care of cooling the fuel rods.

 

[biferi]

Thank you for postting back to me.

So if I undersatand you right

The Fuel Rods are Submarged in a Tank of watter and 70% of the watter ontop turns to Steam and the other watter that's left gets used to Cool the Rods?

 

[Astronuc]

Thank you for postting back to me.

So if I undersatand you right

The Fuel Rods are Submarged in a Tank of watter and 70% of the watter ontop turns to Steam and the other watter that's left gets used to Cool the Rods?

The core of the BWR is surrounded by a stainless steel shroud or core barrel, and around the core barrel is the pressure vessel. The water in the core, that is, in the assemblies boils. Low power assemblies have about 40 to 50% void or steam volume near the top. High power assemblies have 70 to 80% volume which is steam at the top. The wet (saturated) steam actually does cool the fuel rods. The fuel rods of a BWR are surrounded by a channel which forces the steam-water mix to flow vertically. The coolant outside of the assembly, and between the channels is mostly water, since it is not heated directly from the fuel rods. Water in and between the assemblies provides moderation.

The wet steam leaving the core passes through moisture separators and steam driers such that the steam passing to the turbine is very close to dry, which is desirable for the turbines. Nuclear plants use wet (saturated) steam.

The separated water flows back to the annulus between the core shroud and pressure vessel where it is mixed with the cooler feedwater. That mixture is pumped back into the core.

 

[biferi]

I know what gets me mixed up.

The Fuel Rods are in the Core and you say the Core is in Steel.

But around the Steel is the pressure vessel

So when the Core Heats the watter the steam goes up I get this.

Then it gets Pumpt ot of the Steel and into the pressure vessel?

You see I am making a little Drawing of how it all works and this part is where I get lost?

 

[Hiddencamper]

I know what gets me mixed up.

The Fuel Rods are in the Core and you say the Core is in Steel.

But around the Steel is the pressure vessel

So when the Core Heats the watter the steam goes up I get this.

Then it gets Pumpt ot of the Steel and into the pressure vessel?

You see I am making a little Drawing of how it all works and this part is where I get lost?

The water and the fuel are in the same place. It's not like in a CANDU reactor where the Calandria has fuel tubes and coolant tubes which never touch. In a BWR, the water is literally surrounding the fuel at all times.

The core is the part in the center of the reactor pressure vessel. The core is where the fuel assemblies, control rods, dry tubes and incore detectors are. Surrounding the core is the Core Shroud. The shroud separates the outer part of the core from the core itself. This prevents a pipe rupture from draining all the water out of the core. In between the shroud and the reactor pressure vessel wall is where the jet pumps are. Then all the way at the outside is the pressure vessel wall itself.

http://www4.ncsu.edu/~doster/NE405/Manuals/BWR6GeneralDescription.pdf

At the above link, there are a LOT of great illustrations on the BWR-6 design.