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Design flaw in Canadian Maple Reactor 
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#1
Nov808, 08:35 PM

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I am trying to figure out why the design problem with the Maple1 and Maple 2 reactors cannot be fixed. This Globe and Mail article explains the decision to end the projects.
These reactors have been built. During commissioning, they became aware of the problem with a positive power coefficient of reactivity, which means that reactor power output increases with temperature. Obviously that has to be corrected. But why would it present such an insoluble problem that the reactors must be scrapped? AM 


#2
Nov908, 12:44 AM

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I don't understand this. How come that was not noticed upon design simulation ??



#3
Nov908, 01:14 AM

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It was designed to have a negative power coefficient of reactivity of –0.12 mk/MW. But in operation it was measured at +0.28 mk/MW. The units are some kind of measure of the increase in ratio of neutrons produced to neutrons used per MW increase in power output. AM 


#4
Nov908, 09:18 AM

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Design flaw in Canadian Maple Reactor
I wonder what neutronics/core simulator was used in the design process, and what crosssection library, and how it was collapsed. Perhaps the methods lead to faulty predictions in moderation or resonance absorption (Doppler coefficient), which ostensibly could be fixed with an appropriate burnable absorber or fuel composition. 28062006  INVAP to perform nuclear calculations for Canadian company http://www.invap.net/news/novedades...20060628192056 An article on the design of Maple and the fuel. Ostensibly, they could redesign the fuel. http://anes.fiu.edu/Pro/s4ma1.pdf 


#5
Nov908, 05:46 PM

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I heard somewhere that to save on design effort they essentially just scaled up a previous smaller fully engineered design. I'm not too sure how true that is.



#6
Nov908, 06:48 PM

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Of course that's what the Soviets did when they built the RBMK reactors like those at Chernobyl. The Soviet RBMK reactor is a smaller Soviet nuclear weapons material production reactor scaled up by a factor of 2. The mistake the Soviets made was not redesigning the fuel to go along with the reduced neutron leakage afforded by the larger RBMK. The Soviet RBMK thus had the wrong feedback characteristics; which led to the infamous accident. If they have a reactor that has the wrong feedback characteristics; it's best not to pursue startup unless the problems are corrected. Perhaps the mistakes in the design are too integral to the design that they can't be fixed without essentially scrapping the original design. This means that they really don't have a good model for their design simuation. Somebody made a BIG MISTAKE somewhere  be it in processing the nuclear data, the transport simulation software; the design calculations....who knows where the error is  but evidently the error is large. I hope someone follows up on this; I'd be curious as to what part of the design process was faulty. Dr. Gregory Greenman Physicist 


#7
Nov1008, 07:58 AM

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Or, they could improve the Doppler coefficent by changing out the Usilicide fuel with UO_{2}, which has lower thermal conductivity, so the fuel runs hotter and that would produce more negative reactivity at a given power level. 


#8
Nov1008, 09:34 AM

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One would hope that they have a "coupled physics" simulation code; neutron transport coupled with a thermalhydraulics response solver. That way they don't have to "assume" anything about the density or temperature of the heavy water moderator. The thermalhydraulics code will calculate that for them. Dr. Gregory Greenman Physicist 


#9
Nov1008, 10:27 AM

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#10
Nov1008, 10:35 AM

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You mean remeniscient of the miscommunication between NASA and Lockheed on the Mars Orbiter mission due to a confusion over whether the units were metric or English: http://www.cnn.com/TECH/space/9909/30/mars.metric/ Dr. Gregory Greenman Physicist 


#11
Nov1008, 11:50 AM

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It would seem pretty easy to figure out what's wrong with the initial design and develop a remedy. Afterall, TRIGA fuel was redesigned from HEU to LEU, but still had to meet all the same tech specs. It should be a simple proposition to modify the driver fuel. 


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