Did Southern California Edison Operate Unit 3 At San Onofre With Knowledge Of Tube Failure?

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Source: Power-Engineering.com

One of the questions I have had about Southern California Edison's handling of the tube leak situation at San Onofre is this: Since Reactor 2 was offline for maintenance January 31st this year when the tube burst in Reactor 3, were they checking the tubes on Reactor 2 during this outage, and did they know there were problems with the tubes before the tube burst on Reactor 3?

Because if they were working on Reactor 2 and finding problems with the tubes, yet still operating Reactor 3, I have a real problem with that.

And there's nothing telling me that this didn't happen.

As far as we know, and as far as we're being told, Edison had no idea there was a problem with tube wear until the tube blew on Reactor 3 on January 31st.

That's as far as we know.

Below is an outline of Edison's investigation of the tubes in Reactor 2, without a timeline for comparison so we can see when they began checking the tubes.

I wouldn't hold my breath waiting for a clarification that, either. But what we can clearly see from this article just published, Edison was checking Reactor 2 and did find tube wear.

Before or after Reactor 3 blew?

Wonder if we'll ever know?




Unit 2 experience

Unit 2 started an outage on 10 January, 2012 for scheduled refuelling, plus reactor vessel head replacement. This was the first outage after the steam generator replacement. In accordance with the plant's technical specifications, a 100% inspection of all steam generator tubes was conducted.


Mechanical wear was observed at various locations along the tube lengths, similar to what has been observed in comparable steam generators at other plants.

The wear observed at the retainer bars (which, as already noted, are unique to steam generators fabricated by Mitsubishi) was not expected.

The severity of one of the wear indications at a retainer bar was significant enough (90% through-wall) to warrant in-situ pressure testing (although this pressure test confirmed the structural integrity of the tube and there was no leakage).


Based on the severity of tube-to-tube wear found in the unit 3 steam generators, the operator completed additional rotating coil eddy current testing in an area of concern consisting of 1375 tubes in each of the unit 2 steam generators.

Tube-to-tube wear of 14% was identified in two adjacent tubes in each of the unit 2 steam generators.



Based on the initial 100% tube inspections, the operator carried out plugging and staking on 192 tubes in total: 98 in one steam generator and 94 in the other. A total of six tubes required plugging because they exceeded the plugging criterion of 35% tube wear, while all tubes adjacent to the "retainer bars" were plugged as a precautionary measure due to unusual wear at that location.

As a result of information coming from the unit 3 investigations, a total of 318 additional tubes, located in areas similar to those where tube-to-tube wear had been found in the unit 3 steam generators, were plugged in the unit 2 steam generators. The total plugging for unit 2 was 205 tubes in one steam generator, and 305 in the other.



And:


With the exception of the wear found at the tube retainer bar locations, the wear related to support structures is said to be similar to wear found at other replacement steam generators after one cycle of operation.

Most of the tube wall thinning is less than 20%, which is well below the 35% wall-thinning limit that requires a tube to be plugged.

According to SCE "the nature of the support structure wear is not unusual in new steam generators and is part of the equipment settling in" and it says it continues to work on its response to the commission's Confirmatory Action Letter, the formal step in the process of restarting units 2 and 3.




And:


The press release announced SCE's intention "to downsize the SONGS' organization to 1500 - a reduction of approximately 730 employees, beginning fourth quarter of 2012" - although it was emphasised that this was as a result of a benchmarking exercise initiated more than two years ago "to align SCE's processes and staffing levels with the top performing nuclear operating plants in the industry."


(This last means that even before all this started, Edison planned to lay off over 700 employees from San Onofre anyway---operating the plant with that many hundred fewer staffers.)