"Around two-thirds" is right. Many online sources quote 32% and I recall 33% from a class I took eons ago.
Two other things: 1. Controlling the reactivity of an operating reactor is extremely complex. See for example Section 3, "Core Cell Improved Design", here: http://www4.ncsu.edu/~doster/NE405/Manuals/BWR6GeneralDescription.pdf 2. For any large generator, the load has got to roughly match the generating capacity unless you want to damage or destroy the equipment. This why generating plants (of all types) trip offline so aggressively when something goes seriously wrong with the electrical grid. The idea of the operators trying to modulate the plant reactivity and also switch in massive dummy loads to match the plant output, all in the midst of an accident scenario that may have left the plant in an unknown condition, seems wildly unrealistic to me. Jeff On Fri, Nov 23, 2012 at 10:41 PM, <mix...@bigpond.com> wrote: > In reply to David Roberson's message of Fri, 23 Nov 2012 23:07:53 -0500 > (EST): > Hi, > [snip] > >That is the same question I asked myself when the problem first came up. > I concluded that a scram most likely was necessary since the output of the > reactor is normally many times the requirement to supply the backup > equipment load. I suspect that it would be extremely difficult to back the > power output downward enough without loosing system stability. In fact, > the power resulting just from the nuclear decay elements might exceed the > load required with no ability to dissipate the excess energy safely. One > might wonder if the left over heat could be deposited within the inlet > water as long as the pumps were operating. I suppose that it might have > been possible had the personnel at the reactors been trained to handle the > problem in that manner. > > I think the thermal efficiency of most nuclear plants is around 25-30%. > That > means that they usually dispose of around two thirds of their full power > output > as waste heat. IOW if the auxiliary equipment is operating, then they can > easily > dispose of even the total power output at a reduced operating level. > > Regards, > > Robin van Spaandonk > > http://rvanspaa.freehostia.com/project.html > >
