Engineering Question #3580

Chris Chase, a 33 year old male from Harrisburg asks on August 30, 2006,

Has anyone ever weighed nuclear reactions in reactors to see if the reactor weighs more while generating energy? Specifically, I am interested if fusion or fission reactors have been scientifically measured to see if they create a temporary gravity well by their reactions. I was wondering if there is any virtual mass produced and that temporarily increases during the reaction while energy is being produced through a nuclear reaction. I realize the standard science says this would not happen in a nuclear reaction, but has anyone ever tested it?

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The answer

Jeremy Whitlock answered on August 30, 2006

I doubt that anyone's weighed a nuclear reactor while operating (which would be quite a feat given their massive mechanical and civil structure); however, operators of nuclear-powered submarines might be able to tell you if any odd changes in buoyancy have been noticed when their nuke plant is switched on or ramped in power.

If we could weigh a reactor with sufficient accuracy, however, science tells us that it would probably weigh less while operating since mass is being converted to energy, and energy is leaving the reactor all the time through leakage.

On a much smaller scale, we have indeed "weighed" the individual components of a nuclear reaction, before and after, and have observed that the reaction products do have less mass than the reactants, as explained by Einstein's famous E=Mc^2 relationship.

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