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Reply #46: Well, Aliens are also beyond design basis, but [View All]

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Throckmorton Donating Member (1000+ posts) Send PM | Profile | Ignore Wed Aug-31-11 02:19 PM
Response to Reply #45
46. Well, Aliens are also beyond design basis, but
Edited on Wed Aug-31-11 03:03 PM by Throckmorton
The Station Blackout (SBO) diesel isn't CAT-1, nor is it as large as the Primary Diesels. It doesn't autoload and requires entry into Emergency Operation Procedure space to use. This is an operator burden, and can distract from other duties.

Beyond design basis events also present the possibility that a single point of vulnerability will compromise multiple systems. The EDG's are redundant, but they are not diverse. A single beyond design basis event has the potential to fail both from a common cause. The SBO diesel, while diverse from the main diesels, is not a 1 for 1 replacement for them, nor has it been analyzed or tested for all design basis events as it is not Cat-1.

The SBO events are not seismically induced, but are postulated to run along the lines of complete loss of offsite, with an attendant loss of all onsite prime mover based AC power due to a maintenance issue or fuel supply failure with both diesels. This is similar to the ATWS rule, in that it does not cover all scenarios, only those demonstrated to be the most likely. In the ATWS Rules case, Reactor Trip Breakers (TCB's)that fail to open on demand due to a common cause issue (At Salem, this was improper maintenance on all TCB's, rendering them unable to respond to a valid trip signal from the reactor protection system).

Those of us that do this kind of thing don't bother looking at what went right, we look at what could have happened and what went wrong. We tend to leave the flowery prose and the feel good press releases to the Liberal Arts Majors.

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