[ARC5] OD3 VR Tube - Not At All Like A Nuclear Reactor

[J. Forster]

My point was that a reactor is balanced between a growing and dying
exponential. Not the details of how that is implemented.

-John

===============



> John wrote:
>
>> The math is very similar to a nuclear chain reaction, where a reactor is
>> balanced on a knife edge between running away and shutting down. Control
>> rods adjust the 'loop gain' of the reactor to exactly 1. Reactors do not
>> work w/o active control.
>
> Well, er...nuclear reactors do in fact *often* operate without active
> controls
> of the type you imply.  Especially naval propulsion pressurized water
> reactors.
> For those, the operator's opening of throttles to a steam turbine
> increases
> the heat demand on the steam generator, which lowers the temperature of
> the water coming out of the primary side of the steam generator that
> then goes into the reactor core.  This lower temperature water is denser,
> which moderates or slows down neutrons to the point that more nuclear
> reactions occur as a result, which increases reactor fission thermal power
> generation, which raises the temperature of the water coming out of the
> reactor that is going back to the steam generator, to the point where
> in a matter of about a minute or so the thermal power generated by the
> nuclear core has matched the increased thermal power demand that was
> caused when the operator opened the throttles to the turbine.  Everything
> then stabilizes.  Had the throttles to the turbine been closed, the
> response would be identical, but in the opposite direction of parameter
> change.  This response is automatic and controlled by the physics of
> the process, not by **any** external automatic human-designed control
> loop.  It's rather beautiful to watch, especially when one understands
> what is taking place!
>
> Plus...it's all rather slow and easily controlled, once again, by the
> physics
> of the process, not by a man-made external control system.  About 94
> percent
> of the neutrons that initiate one fission process cycle were generated
> "prompt" one-hundredth of one-trillionth of a second earlier.  But the
> other
> 6 percent of neutrons taking part in one fission process cycle come from
> neutrons generated by the decay of radioactive products of fission cycles
> that occurred as long as several **minutes** earlier.  It's the effects of
> these "delayed" neutrons that control the rate at which the fission cycles
> take place, to the point that slow-moving control rods or thermal changes
> as described above or any other man- or physics-made effect will very
> easily control the fission and thermal power generation process.  There's
> no "knife edge" anywhere in the process!
>
> Commercial pressurized water reactors and boiling water reactors are
> not quite as simple in practice as the naval reactors, but are still
> fundamentally similar.  I spent thousands of hours at the controls
> of naval propulsion reactors and commercial boiling water reactors in
> the past 38 years, before retiring.
>
> Returning to the subject of gas ionization avalanche, that is somewhat
> analogous in nuclear fission terminology to a reactor operating from
> one fission cycle to the next on prompt neutrons only.  That's called
> a nuclear weapon...not a nuclear reactor!!
>
> 73,
> Mike / KK5F
> Former Senior Reactor Operator
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