Wednesday, August 04, 2010

RBMK Control Room

Control room of Chernobyl NPP Unit 1

These gauges indicate position of control rods in the active zone. Black boxes are neutron flux indicators.

These are the controls for some of the many control rods in the RBMK. You hold down the appropriate button and use the joystick on the left to move them in or out of the active zone.

Six emergency shutdown switches. "АЗ5" switch (top row, center) initiated rapid emergency shutdown.

Tuesday, August 03, 2010

Can You Spot the Math Error?

Trawling around the interwebs, I encountered the following critique of vertical farm concepts at TreeHugger:
This led us to wonder, "What would be the consequences of a vertical-farming effort large enough to allow us to remove from the landscape, say, the United States' 53 million acres of wheat?"...Our calculations, based on the efficiency of converting sunlight to plant matter, show that just to meet a year's U.S. wheat production with vertical farming would, for lighting alone, require eight times as much electricity as all U.S. utilities generate in an entire year [see calculations here].
This evoked a raised eyebrow from me, given the widespread claim that American agriculture uses vastly more fossil fuel energy than it delivers in terms of total food calories. Something doesn't add up here--clearly, someone is very, very wrong about the amount of energy embodied in our foodstuffs.

Fortunately, the included "calculations" reveal the source of the problem:
The following is a very rough estimate of the amount of power needed just for lighting vertical farms to grow the U.S. wheat crop. Note this is under ideal conditions for nutrients, temperature, and other productivity factors. Under excellent conditions, wheat has radiation use efficiency of 2.8 grams of biomass produced per 106 joule of photosynthetically active radiation (PAR). So to produce one metric ton (106 g) of wheat biomass requires [106 g / (2.8 g/106 J)] = 3.6 × 1011 joules of PAR over a season under ideal conditions.
Oops. >BANGS HEAD ON DESK< (3.6 x 1011 joules is the amount of energy in 10,526 liters of gasoline. That's a lot of energy for just one metric ton of wheat... )

To be fair I've seen equivalent mathematical goofs from the proponents of these fanciful vertical farm concepts. A lot of people aren't dotting their Is and crossing their Ts, so to speak. I actually like the concept, but it needs ample cheap energy to work--basically, it would have to be coupled with nuclear reactors. I have no problem with that myself. But I don't think it will be a near-term development in any case.