The word from insiders at the [San Onofre nuclear] plant is that the problem stems from [steam generator] pipes being configured in such a way as to have unintentionally created a situation where water passes through the tubes at such a high velocity that it causes the kind of wear they would expect to see after 20 to 30 years of service. If true, ratepayers will be on the hook for huge repair and replacement costs in order to extend the life of the plant beyond its intended lifespan, and even then, reliability will be in question.

It was also stated that ruptured tubes under high pressure can result in a chain reaction causing adjacent tubes to rupture if not stopped in time, with potentially catastrophic results.

Another point stressed was that standard procedures were violated if they discovered the problem in Unit 2’s tubes when it was being serviced before the leak occurred in Unit 3. When a failure of any critical system is discovered it is the responsibility of the plant operator to make the conservative decision to shutdown and inspect any “like components”. In this case it appears that this was not done for the exact duplicate components in Unit 3…

Source: Gary Headrick’s comments on What’s Making Up For San Onofre’s Lost Power? – NBCLos Angeles.com  02/17/2012