Question for nukeman

[Jimbo]

Don't know if you have been following the saga at San Onofre NGS. Both reactors have been shut down for a year. They replaced the steam generator tube assemblies, in the process re-designing them to increase power output capacity by 10% to 15%. Within a year of retubing, they started to have leaks in the tubes, including at least one case resulting in minor release of radiation to the atmosphere! Turns out the redesign compromised the separation of tubes, and vibration caused tubes to rub against each other. My laymens take on this from the get-go: SOMEONE pulled the wool over SOMEONE'S eyes in this whole process. Today, the NRC stated that the problem was caused by "faulty computer modeling of steam velocities, in the design process" . Sounds just like what I said, and you would think some engineer-types would be sporting new pink slips today, but no such luck!

Unit 3 is so badly damaged it may never restart, but Souther Cal. Edison has requested permission to restart unit 2 with a whole lot of tubes plugged, and operating power limited to 70%.

Better late than never...the NRC has been holding public hearings, seems disinclined to grant this request until the proper engineering studies are completed.

As a submariner, I do not "fear" nuclear power, and support continued use of the plant, but ONLY if and when safety rises to its proper priority in the grand scheme of things. We survived the hottest summer on record in S. Calif. with San Onofre off-line. If they never restart, it will not be the end of the world.
Naturally, all parties are fighting over who pays for the delays, the restart, or the decomissioning. Ratepayers? Shareholders? Looks like I am screwed either way!!!!!

This was really just a rant. Wonder if you have any comments!

 

[Nukeman]

Yep, it certainly looks to be a design issue. From what I understand, the tubes were rubbing together and also against those retainer bars. This provides some info:

http://www.nrc.gov/info-finder/reactor/songs/tube-degradation.html

It sounds like there is too much space between the tube support plates. As the steam is generated and flowing, the tubes were rubbing agaist each other and created the wear (not enough pipe hangers ). Like everything, there is a trade-off. More plates means more pressure drop and more cost, but steam generators are very expensive and safety is very important, so it isn't like they tried to save a couple bucks by using fewer plates. I don't know if they will replace the generators, do something to repair them, etc.

The average steam velocities should be well known. It is a function of core power and water properties. There may have been some local velocities that they didn't get modelled correctly. It seems that there was some aspect of this design that was overlooked. It takes a lot of people to design something like a steam generator, but I guess this issue snuck by. It is a whole other thing if someone did it on purpose (signed off on a design they knew was bad, etc.). In the nuclear industry, this would be not only losing your job, but you may end up doing time in federal prision. Nuclear power is governed by federal regulations, so you really get in trouble if you try to cheat.

It would be nice if they can bring them back online. Right now, nat. gas is cheap and probably has been used to fill the void. However, if gas goes up, I bet your rates will go up with it.

 

[Sponsor]

 

[Jimbo]

It seems the basic problem was they increased the number of tubes, to squeeeze 10 to 15 % more power from the reactor, and in so doing, compromised the bracing. Mitsubishi built the new generators, so what did they know?

Both units have been shut down for a year, and we got through the hot summer with no brownouts. One unit is so badly damaged, it sounds like it is a write-off.

The other one...they want to plug the bad tubes in the generator as it is, and operate the reactor at 70% max power. The NRC is evaluating. Public reaction has been less than favorable, and the biggest issue right now is the fight over who pays for the idle time, who pays for the decomissioning. Since I am both a ratepayer and a shareholder of Sempra, I am screwed either way!!!!!

And of course , as is the case with I guess all plants, there is the issue of the spent fuel still being stored on-site. No one seems willing to tackle that issue!!!!!!!!!!