Boron in a PWR

[TheEngineer]

Short and simple: rods control reactor power, and boron adds positive reactivity (due to its burnup) to compensate for fuel use at end of life.

hmm ok so where are you going to put a neutron in a reactor where it will last long enough to decay on it's own?  I have never heard of a "magic cup" that can do that.  Like I said before the neutron will leak or get absored, they will exist in the reactor only small fractions of a second.

The neutron can go several mean free paths before absorption... or it can be absorbed right away. Let's consider leakage and absorption to be essentially the same beast as far as neutron economy goes. The point is that a neutron can probably exist for any amount of time in the core (within reason). Reactor control has a lot to do with delayed neutron precursors.

And... I'm not sure who brought up multi-group diffusion, but I'll bite. 6 groups is a statistical model... but as far as MCNP goes, isn't everything just a statistical model? I'm not sure if deterministic models work the same way... I've only dealt with MCNP at this point. Any deterministic folks in here?

[Already Gone]

Short and simple: rods control reactor power, and boron adds positive reactivity (due to its burnup) to compensate for fuel use at end of life.

ROFLMAO!!!
This is a typical answer from a NucE major.  It is like saying that the brakes control the speed of your car, and the gas pedal provides for slowing down the car because you can take your foot off of it.
I see from your other posts that you are a Navy nuke.  So, you are about to learn that Boron plays a much larger role in reactivity management in civilian power reactors.  While you are referring to Boron Carbide embedded in fuel, we are talking about Boric Acid which is added to coolant by the truckload out here.  Rather than burnup, it is reduced by dilution to maintain balance with the negative reactivity from Xenon and other FP poisons.  I suggest you read back a page or two.

[Fermi2]

Short and simple: rods control reactor power, and boron adds positive reactivity (due to its burnup) to compensate for fuel use at end of life.

The neutron can go several mean free paths before absorption... or it can be absorbed right away. Let's consider leakage and absorption to be essentially the same beast as far as neutron economy goes. The point is that a neutron can probably exist for any amount of time in the core (within reason). Reactor control has a lot to do with delayed neutron precursors.

And... I'm not sure who brought up multi-group diffusion, but I'll bite. 6 groups is a statistical model... but as far as MCNP goes, isn't everything just a statistical model? I'm not sure if deterministic models work the same way... I've only dealt with MCNP at this point. Any deterministic folks in here?

LOL!!!!!!!! Got any experience at a commercial plant?

Mike