razzz said:
It opened flawless for me...
Adresses various cracks and degradations on RPV and especially PWR's RPV covers...
On this matter, and even if this is a lit bit OFF TOPIC because it's about a PWR MODEL, I wanted to mention this study with impressive cracks and holes (football sized! see the pictures and diagrams) discovered in Davis Besse PWR reactor cover head (Ohio).
http://www.nrc.gov/reading-rm/doc-collections/nuregs/brochures/br0353/br0353r1.pdf
Even if it may be PWR specific, it's interesting to note that it was caused by boric acid leakage (borated water) that has eaten the steel of the head to a point where only the stainless steel cladding inside the cover head was left for structural resistance (3/8 inch!). Any breakage of this (small) remaining thickness would have resulted in a Loss of Coolant (LOCA) accident...
Ok, now back to BWRs:
1) borated water is not normally use inside BWR, but it is used now since the beginning of the accident at Daichi. So a logical question question relates to the effect of this borated water injected in addition to seawater inside BWR reactors (this is "beyond design basis" operation!) for a time that could be long: what could be the impacts on non stainless steel materials for example (corrosion, etc.)?
2) this study shows clearly that as already mentionned before, the place of penetration of various holes, control rods and equipments inside the reactor, with welded parts, is always a weak point and a leakage source. In a BWR, most of these penetrations holes are at the bottom (control rods,etc.).
Something of general interest, because this is NOT PWR or BWR dependant, is also highlightened in this study concerning the reasons why this major damage wasn't discovered before during regular inspection:
Firstly, a lot of the regular inspection planned where... deferred -ending up discovering this much too late!
The staff made several changes to the process to enhance the NRC’s ability to detect declining plant performance, including the specific issues identified at the DBNPS. For example, the review of the event indicated the deteriorating condition had been underway for several years and that the planned inspection, maintenance, and modification activities that could have prevented, or enabled earlier discovery of the condition were frequently deferred.
Secondly the lack of culture of safety at this Davis Besse plant!
Safety culture weaknesses at Davis-Besse were determined to be one of the root causes of the reactor vessel head degradation event.
As we have in France mainly PWR's reactors, I'm wondering what is the situation on this subject of reactors vessels damages with time. I'm going to document on this after reading this NRC document!
