Once again, Entergy is cited for violations. Dr. David Lochbaum of the Union of Concerned Scientists responds:
It was not that two emergency diesel generators (EDGs) were out of service at the same time. It's that workers failed to do the checks necessary to prevent that situation after finding one EDG to be inoperable.
In the old days, when one EDG was discovered to be inoperable, workers had to start the other EDG and test again every day until the broken EDG was repaired and returned to service.
Pilgrim received NRC's permission to change this testing requirement.
Now, when one EDG is discovered to be inoperable, workers have a choice: (a) they can start the other EDG to verify that it is not also inoperable, or (b) they can perform an assessment to determine whether the cause of the first EDG's failure might also disable the second EDG.
On two recent occasions, workers discovered EDG A to be inoperable. Each time, workers did a quick check that concluded EDG B was not also inoperable. They verified its last test had been completed satisfactory and that there were no industry reports received since that test which would explain the failure of EDG A and imply that EDG B may also be affected.
The NRC, quite properly, found these casual checks to be deficient. For example, that check would also have concluded that EDG A was okay, a minute prior to the test that proved it to be broken.
The proper way to perform this check is to identify the cause or potential causes of the broken EDG and then assess whether EDG B might also be affected.
Essentially, workers at Pilgrim did some of the necessary homework on EDG B after finding EDB A broken, but not enough of the required homework to truly verify that answer.
Even the proper way is not foolproof. There are times when workers applying the proper method turn out to be wrong. For example, they identify potential causes of the first failure and conclude the second unit is not likely to be affected, only to having the ensuing diagnostic testing reveal an unexpected failure cause that could also have affected the second unit. In that case, they must submit two notifications to the NRC: one for the first unit's failure, and the second for the failure to accurately determine it could affect another unit.
But NRC requires a good-faith verification. In this case, workers did not do enough homework to accurately conclude that EDG B had not been affected.
It turns out that EDG B had not been affected, but that was more luck than skill and NRC properly sanctioned them for substituting luck.