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In other words an Overmoderated Core.

When I was at Fermi we did only one Startup with a positive alpha T. The coefficient was real small and we took a few special precautions.

So far as Voids, this coefficient is really only prevalent during real steaming Ops. During Heat Up Voids aren't a major affect. I used to love watching the SRM/IRM Strip charts during heatup and thinking of the theory behind why they did what they did.

So far as Startup, I''ll give the ROs here a good thumbrule Take your initial countrate with all Rods in. Multiply it by 50 and 60. You'll go critical somewhere between those numbers, it works for all reactors regardless of vintage or type.

Another thing, a very good period to establish after criticality is 100-120 Seconds, in most cases that should take you to around a 60 to 70 degree/hr heatup when you hit the POAH. Anything higher and if you happen to be on those BWR that still manually switch IRM ranges you'll be in for quite the party after you hit critical and you'll have one remarkably pissed off SRO to deal with. I used to tell my guys I wanted about 120 Seconds.


Yep, I used to time an onscale IRM between 25 and 68 using a stopwatch.
That's a demonstration of reactor period in seconds.
68 = ~ 25 x e

Reactivity- The fractional change in neutron population per generation.


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