BWR CONTROL RODS ANTIREACTIVITY 1

[tony72]

Anyone please help me: how come antireactivity inserted by BWR cross shaped control rods varies from 17000 pcm to 25000 pcm with reactor at power??
Thank you.

 

[LinkNuc]

Although I am a PWR Reactor Engineer I would suspect that the reactivity difference you are speaking of is based on core location. It is all relative to the power of the surrounding assemblies. As you can imagine the power desity is higher towards the center of the core (not actually highest at center but about half way between the baffle and the center assembly...in our case) and lower at the periphery. For example our control bank 'A' is at the outer most locations of the core and has an integral worth of 282 pcm while control bank 'B' is closer to the middle located in high power assemblies and has an ontegral worth of 1389 pcm. Keep in mind we have 6 control banks made of 8 rods with identical percentages of Silver, Indium and Cadmium and the individual control rods change bank locations every cycle.

 

[tony72]

Thank you LINKNUC, you are great!!!!
If you work for a PWR reactor there is another question from me For YOU if you can please help me: what is the duty of tha baffle?!?
Does it distribue the flow rising up from the core to render it more omogeneous along the fuel assemblies?!?
P. S : It is funny and great at the same time taht in tha USA you specialize on different reactors!
Here in Italy we do not specialize so far!
Thank you!

 

[LinkNuc]

The main function of the baffle is to provide support for the fuel assemblies and do very moderate amount of shielding the reactor vessel from neutron fluence...Here's a brief synopsis of our 3-loop Westinghouse PWR's as far as flow goes:

Approximately 93% of the Rx. coolant flow passes in this manner:

a. Rx. Coolant enters through the Cold Legs
b. The water then flows down around thermal shield annulus between core baffle (barrel) and vessel walls.

c. when coolant enters the lower plenum, the coolant reverses direction and passes through the:
1. Core support forging
2. Diffuser plate
3. Lower Core plate
4. Reactor Core
5. Upper Core plate
6. Upeer plenum and out the Hot Leg nozzles

Approximately 6.5% of the Rx. coolant bypasses the core in the following manner:
1. Nozzle bypass, where the coolant enters the vessel through the cold leg and directly exits through the hot leg without ever going through the core.
2. Control rod and instrument thimble bypass, where coolant enters these channels and is not subject to contact with the fuel clad to remove heat
3. Baffle Wall bypass, where the coolant passes along the baffle and is not subject to fuel clad to remove heat
4. Head cooling bypass, where coolant passes directly into the uppper head region and is not available for rmoving heat from the fuel

Hope that helps!

 

[tony72]

Thank a lot linknuc, your help has been very good for me , thanx again!!!!!!!