Nebraska nuclear plant thread.

NUCENG

When the water level downstream of the dam is higher than normal it would be logical that the differential pressure that could fail the dam would be lower that during non-flood conditions. So why would the dam be likely to fail now?

Orcas George

There is a lot more water in the system than in normal times so the dam is near maximum capacity. That has more to do with anything than differential pressure which isn't usually a factor.

There are a lot of things involved in a flood; the change in force from a normal river to one at flood stage is something that has to be seen to be believed. There a lot of debries upstream that wants to come dow and it tends to collect into a large mass. Earth berms get soaked and the dirt looses its cohesion. Water going over the top of a dam quickly erodes even concrete. Temporary dams of junk form and suddenly release, which can increase the force in the system briefly and cause break throughs.


It is easy to underestimate what a couple of feet of water can do (ask the Japanese about that one.) Never drive through a flooded street, nor go kyaking on a flooded river. (I drove over a flooded bridge once which turned out not to be the smartest move of my life; if you can't be good be lucky...)

Orcas George

This is what drives me nuts about the circle the wagons mentality whenver there is a nuclear "oopsie".

OK, so this dam wasn't important or anything, they just put it in there as a backup. Redundancy, multiple lines of defence, defence in depth and all that good stuff.

Somehow that negates the idea that this was a non-critical backup just to be on the safe side...

NUCENG

Thank you,. I claim no expertise in civil engineering, and that is a little counter-intuitive. If the dam is near capacity are they releasing water?

NUCENG

Latest event report updates:

http://www.nrc.gov/reading-rm/doc-co.../event/en.html

zapperzero

Releasing water to where, exactly? I mean, what are you asking?

zapperzero

Slightly(?) offtopic. Minot is being flooded.
http://abcnews.go.com/US/minot-north...ry?id=13913535
Minuteman III nuclear missile silos are also in the flood's path. At least two silos are being protected by sandbags and pumps, but are reported to be safe.

Joe Neubarth

Nothing to worry about there. If the silos are flooded the missiles can not launch. I would expect that the warheads would have been removed days before any serious flooding scenario, but even if they weren't, they would cause no problem other than the fact that they would have to be retired from present service and ten tons of paperwork would have to be filed with all of the military agencies that would be involved. I was a Nuclear Weapons Officer at one time. Believe me, you do not want to do that paperwork.

Orcas George

Yes, which is why it is flooding downstream of the dam(s). The odd thing to realize is that these floods are "controlled"; the engineers have to make the heartbreaking decision to flood the towns downstream in order to prevent an uncontrolled dam collapse. Obviously the natural tendancy is to hold off doing it as long as possible in hopes that it stops raining but the longer you wait the worse it gets if you have to do it. This is one reason why NOAA (the national weather forecasting office) is such a critical resource to the country.

Joe Neubarth

In the overwhelming majority of dams I have seen close up, the spilling of water when they reach rated capacity is usually built right into the dam design, with the spillway designed to carry any water in excess of the rated maximum water height limit. I suppose you could sand bag the tops of the spillways to try to retain more water if you wanted to.

Off topic. It is a shame that we can not divert that flood water every spring to west of the Rockies. We sure could use it in the states further west. We could actually put people to work in agriculture in Arizona, Nevada, and California if only we could get it to the Colorado River.

robinson

The dams are supposed to used for flood control. There is much irony that they have led to the record flooding instead.

zapperzero

I don't think it's any sort of danger either. The thought of those missiles maybe drowning in mud made me giggle a bit, in fact, unlike that other little mishap at Minot a few years ago which still gives me the nuclear heebie-jeebies whenever I think about it.

Astronuc

The one specific to Ft. Calhoun is # 46988

http://www.nrc.gov/reading-rm/doc-co...n.html#en46988

See also -
http://www.world-nuclear-news.org/RS...d_2706112.html

NUCENG

In past years I have been in areas with flooding and was always told the worst thing for a dam is "over-topping" or water overflowing the dam itself. So most dams in this area have spillways to allow flow downstream to prevent that condition which could lead to dam failure. My understanding, may be wrong, so I'm asking if the dam upstream of Ft Calhoun is releasing water?

robinson

All the dams are releasing water. If an old earth fill/chalk damn is over topped it will fail. They have the spillways full open and are praying nothing more will happen.

NUCENG

I heard a report this morning on TV that they reconnected one line of offsite power to Ft Calhoun. Any confirmation?

Joe Neubarth

That incident was embarrassing to the Air Force but not THAT dangerous unless the plane carrying the weapon system crashed. Of course that can happen any time you transport a weapon via air in cargo planes. Weapons being returned are supposed to be separated from their delivery vehicle. In this case the young men involved did not understand that and just shipped the whole assembly on the wing of a plane back to the facility where they had the capacity to remove the weapon.