AREVA analysis of San Onofre Unit 2 steam generators reveals new twist in restart debate

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For the last year, Southern California Edison has been working to resolve the serious problems and deficiencies found in the newly installed replacement steam generators at both Unit 2 and Unit 3.  As workers have removed the fuel from Unit 3, it seems unlikely that the unit will return to service.  The utility has been strongly advocating the restart of the Unit 2 reactor at reduced power to test their theory that the steam generators will not fail completely like they did in Unit 3.

As previously documented in our ongoing coverage of the San Onofre problem, independent analysis by contractors hired by Edison have shown that there is no resolution for the problems in the steam generators and that the wear will continue at an accelerated rate regardless during operations regardless of the power rate.  Their analysis and test models showed that it would be nearly impossible for the steam generators to meet leak requirements if forced to endure a full operational cycle at 100% power.  The utility has since adjusted their restart plans accordingly and has alluded to the fact that if allowed to restart for the proposed test, they would want to conduct another test as long as the steam generators don’t fail.

This week, the utility released another response to the NRC’s Confirmatory Action Letter, which addressed “patterns of dents and associated high contact forces” inside of the Unit 2 steam generators.  This latest revelation from analysis performed by AREVA showed that there are more dents and dings in SG 2E-089 (Unit 2) compared to SG 3E-089 (Unit 3) by a factor of about 13.  Overall, analysis found that nearly 12,000 contact indications were found in both Unit 2 steam generators as opposed to just under 4,100 contact indications in both Unit 3 steam generators. Even more alarming is that fact that these indications in Unit 2 were primarily found distributed very distinctly across entire rows of steam generator tubes, much more so than Unit 3.

San Onofre Unit 2 Steam Generator Contact Indications

This testing is performed by measuring signals between supports and tubes inside of the steam generators.  When they are in contact together a signal will be registered and based on the strength of the contact one can correlate the size and impact of the indications on the tubes.  What these results infer is that there is a large discrepancy between the amount of tubes out of place and touching the supports in the Unit 2 and Unit 3 steam generators.  Considering the fact that Southern California Edison has repeatedly stated that steam generators are of like design and that no evidence or data has been provided which showed any design deviation in this regard between the two units, it is likely that this accelerated wear seen in Unit 2 occurred within the last cycle of operation.

Simply this means that for every one indication found in Unit 3 steam generators, three indications were found in Unit 2 steam generators.  Though the Unit 3 steam generators failed more catastrophically, it appears from this analysis that there is a much larger pool of tubes out of alignment and in direct contact with support plates in Unit 2.  During any operation, it is presumed that there will be some vibration and movement of all of the tubes in steam generators, but this is offset by supports and spacing between tubes.  However in this case, nearly 12,000 tubes in Unit 2 are already in contact with supports, meaning that with any vibration or movement more contact and ergo contact indications will occur in the tubes regardless of operational power rates.

The utility still has not answered all of the additional follow-up questions to the Nuclear Regulatory Commission’s Confirmatory Action Letter which was issued on March 27th, 2012, and no restart date has been proposed as of yet.  The NRC announced a public meeting today on February 27th in Rockville, Maryland, which will focus on the utility’s reply from early October 2012.

San Onofre Nuclear Generating Station Unit 2 Response to Request for Additional Information (RAI 25) Regard… by Enformable

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