Winter Trip to North Anna Nuclear Power PlantMay 13, 2010
Last December I had an opportunity to tour the North Anna Nuclear Power Plant with a few friends, thanks to the generosity of Michael Stuart, a nuclear training instructor at Dominion. He took the day off to show the four of us around. I brought along a sensitive BGO scintillation detector to check for gamma rays, but nothing above background is apparent at this spot. We’re standing in front of the once-through cooling water discharge channel, where billions of watts of waste heat—enough power for several million homes—are carried off from the plant’s condensers into Lake Anna. It’s hard to fathom from the appearance of that placid stream, but only about half as much energy leaves over the electrical transmission lines. In any power station that uses heat to do work, Carnot’s Theorem fundamentally limits the efficiency of the process.
This control room is the scene of high drama and nasty surprises on most days. And just look at those yahoos at the controls! No worries though—we’re actually in the simulator, where plant personnel come to take their NRC qualification exams and practice reacting to accident scenarios they’ll probably never confront on the job. The instruments may be fake, but for the operators being tested, the (employment-related) consequences of a single slip-up in here can be very real.
The first photo shows the main bench from the direction of the SRO’s desk. On the far side are the reactor controls, followed by reactor cooling system controls, feedwater and steam controls, and finally the turbogenerator controls at the near side.
Though it’s not possible to replicate the ground-shaking, pants-crapping thunder of a large-break LOCA a couple hundred feet distant in containment, for instance, surprising fidelity does seem to attend many simulated responses. Room lights go out when you remove the unit’s sources of electricity—disconnect offsite power and shut down the backup Diesel generators that fire up in response (controls for an emergency Diesel generator can be seen in the second photo). Meter needles surge upward on area radiation monitors as primary coolant blows down in a simulated accident. The turbine tachometer slows imperceptably during the first few minutes following a trip, mimicking the real machine’s enormous inertia.
We stopped by (actually, we went inside) this coolant chemistry sampling station beneath the turbine deck, where I foraged for radioactivity with the scintillation detector. In 1987, a steam generator tube rupture occurred at North Anna 1 that led to radioactive primary coolant entering the secondary side. We didn’t observe any noticeable radioactivity in the sample line leading to the affected secondary circuit, however. The highest readings (~100 times background) on my scintillator came from the Unit 1 refueling water storage tank (RWST), a large outdoor reservoir of borated water that covers the core during refueling and can also be used as an emergency coolant supply.
Here are a couple photos from the visitor center. Our tour guide, Michael Stuart, stands next to an exhibit illustrating the size and strength of a containment building’s walls. At right is a model of GE’s ESBWR power plant design. In 2007, Dominion received an Early Site Permit for siting a third nuclear unit at the North Anna, and applied for a Combined Construction and Operating License (COL) to build an ESBWR. More recent news indicates that Dominion now intends to build an APWR designed by Mitsubishi.
Thanks to Michael Stuart for all photos.