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[cdn-nucl-l] Davis-Besse Part 2
As you are no doubt aware, Davis-Besse has recently experienced cracking of its CDRM nozzles.
These are not trivial, as coolant has escaped and boric acid plated out on the outside of the reactor vessel head... i.e. some of these cracks are through wall.
This comes only 6 years after the vessel head was replaced (due to the massive hole that had developed in the original).
This leads to a question I have been trying to answer all morning... what are the design details of the replacement head? I know the head itself is of the same vintage as the original and comes from an uncompleted plant... but what about the nozzle attachment welds... did they use the same type of dissimilar metal welds as in the original design? Is that what is resulting in cracking now?
Once again, I am reminded of the old adage: "the dedefinition of insanity is doing the same thing over and over again and expecting different results.".
PWSCC, which leads to borated water leaking out of a PWR reactor vessel was first detected in the early 90's. The "fix" was enhanced inspection and repair when cracks were detected. The NRC agreed that when an inspection program was initiated, there was no safety issue.
Then Davis-Besse part 1 happened.
From the reports I am reading, the "root cause" of Davis-Besse 1 was "human performance". One of the engineers covered up inspection results which lead to the degradation.
I am sorry but I do not think this is the root cause. It was the contributing cause that lead to the EXTENT of the condition but the actual root cause is the design itself.
It is the design that leads to PWSCC, that leads to through wall cracks, that leads to boric acid leaking onto your vessel head, which leads to holes in your reactor.
If the replacement head used the same type of welds that the original did (which is what i am trying to confirm) then I am not surprised these nozzles cracked AGAIN.
One of the so-called "ten commandments of reactor safety" is "Don't live with problems".
In the case of PWSCC of CDRM's... well it appears to me that this is exactly what they have decided to do.
*Please note: The views expressed in this e-mail are solely those of the author. The contents are personal opinion only. No further meaning can be attributed in any circumstance.*