This is an update on the situation at North Anna's two PWRs since the Cuckoo Earthquake of August 23, 2011. For those who aren't familiar with rural Virginia villages, the one that happened to be situated directly on top of the epicenter of that 5.8 earthquake is called "Cuckoo." What that has to do with the bulk of weird news coming out of North Anna - situated about 6 miles away from Cuckoo - is yours to weave as you like.
Follow below the Orange Squiggle Of Power for the full update…
I direct readers to the Reuters article, NRC rejects quick restart at Virginia nuclear plant, which looks at some of the issues that have come to light since the earthquake. Dominion claims that its detailed inspections inside the unit-1 containment have revealed exactly zero problems related to the quake, other than some cracked walls on the inside and a nice little, "easily patched" crack in the main containment dome wall. They also reported some fallen pipe insulation and 'cosmetic' damage to 115-ton spent fuel dry casks that did some dancing around in other areas of the facility. The NRC sent extra inspectors anyway, and is definitely double checking every little thing.
I cannot seem to find confirmation anywhere that unit-2 has yet reached a state of 'cold shutdown' that would allow containment depressurization and entry. It remained in 'hot standby' days after the emergency scrams triggered by the earthquake, which means there was still some fission going on after the shutdown and that is all by itself a definite eyebrow-raiser.
Remember when Dominion reported on the day of the earthquake that the scrams were initiated by the operators manually, then the NRC came back to insist the scrams were automatic upon loss of offsite power? Turns out both Dominion AND the NRC were wrong.
First off, the earthquake has been determined to have stressed the plants (unit-2 more than unit-1) to at least twice design criteria based not on the richter scale of the event, but on the actual g-forces applied both up and down and side to side.
Secondly, it was not the loss of grid power that caused the scrams. The grid never actually went down as first reported by Dominion, so they came back with transformer relays that opened during the earthquake as causal. Turns out that wasn't right either. Dominion now admits that "a problem inside the cores at both units" caused the shutdowns. The Reuters reporter misidentifies the rods at issue as fuel rods, but the only rods designed to "go into the core" during a scram are control rods…
Dominion officials said it now appears the reactors shut when the earthquake caused a problem inside the cores at both units rather than from the loss of outside power to the plant as initially reported.
"It looks like the (fuel) rods were going into the core prior to the transformer opening," possibly from a relay problem, a Dominion executive said.
Dominion is still working to understand the "root cause" of the plant shutdown as multiple automatic trip signals from various indicators were received within seconds of the quake.
Now, these are not boiling water reactors like those at Fukushima, they are pressurized water reactors like at Three Mile Island. A "problem inside the core" can't be waived away as water sloshing around or anything, since the systems are solid. The only open air is at the top of the pressurizer, and that's not in the core. They are talking rods 'going into the core', and this IS what they call a "scram." Those hafnium control rods all have to drop all the way to their bottom-stops in order to shut down the fission reaction. There will still be decay heat to be removed, of course, and previous reports maintained that cooling circulation was provided during the outage (when the reactor coolant pumps were not working) by "convection flow" via the Emergency Diesel Generators operating pumps in the secondary, heat transfer loop.
Any degree of scram failure - all rods not making it to their bottom-stops - allows fission to continue in the reactor, though in diminished energy level. Convection circulation isn't going to be all that effective in transferring heat from a still-fissioning reactor, which may help explain the far greater Emergency Steam Dump Valve [ESDV] discharge from North Anna's unit-2 reactor as opposed to the unit-1 reactor. In fact, the unit-2 ESDVs remained open for an entire day AFTER the transformer relays had been repaired and offsite power restored to restart the reactor coolant pumps.
Fortunately for Dominion (and the NRC, which doesn't much like for the public to know when things don't work as planned), unit-2 was scheduled for a refueling outage in October, so they're "taking this opportunity" to keep it shut down for that so they don't have to explain why it's not ready for "quick restart" like they say unit-1 is. It has been reported that unit-2 suffered bigger stresses than unit-1 during the quake, and there may well be significant damage inside the containment. Even if some of the rods didn't make it all the way in (a German reactor suffered a 100% scram failure a few years ago when its entire core got shifted during refueling, but that was during power-up so it wasn't a huge deal), the core section where fission is still occurring should burn itself out fairly quickly to allow containment entry.
At any rate, that's where things now stand at North Anna. Kudos to the NRC for not just taking Dominion's word for it this time, and going ahead with a full in-depth investigation before allowing restart for either unit. Those of us who aren't fond of nuclear electrical generation can hope that they will be so thorough the plants will never be returned to service, and that Dominion's planned third unit is never built. They lost their gamble on that fault they built these things directly on top of. That gamble was that the "once every hundred years" earthquake wouldn't happen during the 40 years - now 60 years, as both units got their licenses extended for another 20 - of their operation. 40 years was really pushing things, 60 is just plain old idiotic.
I will keep trying to track information as it is released and keep you all up to date. Meanwhile, I'll just say once again - because this situation lets me do that - not all scrams are entirely 'successful'. And a scram failure complicated by those ubiquitous "unforeseen events" can be positively catastrophic. Let's shut these suckers down for good.