Reference, Questions and Help > Definitions

Doppler coefficient

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xobxdoc:
This reminds me of the battle of wits in " The Princess Bride"

cincinnatinuke:

--- Quote from: Broadzilla on Jan 08, 2008, 11:08 ---Due to the Enrichment of the Fuel and it's design Doppler wasn't very prevalent in Naval reactors. In truth the Doppler coefficient in civilian reactors isn't hugely high compared with other coefficients however it's always there and as soon as fuel starts heating up it starts feedback. This is important as in most cases there is a significant time constant before the moderator sees any heatup and reacts. That's why on a BWR there's a time delay on the power to flow trips. A commercial PWR doesn't need the time constants because it's Power to Flow trips are based on number of Pumps Running as a flat out comparison with Power.

If you have any questions about Doppler just ask. Self Shielding and Energy Boxes are quite the concept. Doppler gets more negative as the core ages due to the buildup of Pu and it gets less negative as the core heats up because the doppler bands lower however there are more of them due to self shielding going away. It always remains negative.

It effects the resonance escape probability.

Mike

--- End quote ---

There you go Jason.  BZ's first sentence confirms that and along with that link which discusses the effect being observed in low enrichment RX's.  So we would have/should have never seen that concept. 

Look up resonance absorption and grasp that concept.  Then apply what happens when you heat things up.  Hope things are well.

Rad Sponge:
Thanks Broad. I have a clearer understanding of the material now.

Now how about a brilliant description of the Doppler Defect?

tr:
Note that while the Doppler coefficient is small, it is very important in several limiting UFSAR accident analyses.  This is due to its rapid response as compared to the other coefficients (such as moderator temperature).  In the commerical PWR world, events like CEA ejection are mitigated almost completely by Doppler (in a CEA ejection initiated from critical at zero power, power goes from zero to about 2000% to zero in around a second).  The moderator temperature barely has a chance to change before the event is over.

ddklbl:

--- Quote from: Jason-YP on Jan 08, 2008, 08:50 ---So was this ever part of the Navy Reactor Principles discussion or did it just get "N/A"d? Did I miss something?

--- End quote ---

Chapter 3 of a certain T Manual.  That is a subject, among many, that the Navy is deeming Need-to-Know.  Whether or not RO's and EOOW's need to know is debatable, according to NR.  That is a subject worthy of its own thread.

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