Teachin g Notes

Operationa l Reacto r Safet y Course

Lecture : 2 1 – Davi s Bess e - Nea r Mis s 2002

Objective :

Despite the well known problem with Alloy 600 cracking for over 10 years, Davis Besse had a near m i ss that almost failed the reactor vessel in a non-isolable leak. The objective of this lecture is to appreciate th e circ um stances of that led to event and how m a nage m e nt ' s failure to have a questioning at titude alm ost created an event that co uld have created another meltdown. It also points out the failu res of NRC, INPO and the utility' s own oversight board.

Ke y Point s t o Brin g Out:

Slid e num be r Point s

3-7 Review history of Davis Besse pointing out good operations (which can lead to com p lacency ) and the his t ory of prim ary water stress corrosion cracking of vessel head penetrations (Inconel 600). The tim eline chart is im portant p art ic ularly since it se ts the stage for a discussion of why Davis Be sse m a nage m e nt did not respond to their ind i c ators.

8-18 Review design of Babcock and W ilcox design of the reactor vessel head and the control rod penetra tions pointing out weld locations. Photos graphically indicate extent of corrosion.

19-21 Point out th e m any indic ators the plant had and experiences with prim ary water leak s and specific DB indicators. Discuss why such obvious indicators were ignored or dism issed.

22 Discuss breakdowns in each of the ma jor players that shou ld have asked the qu estions and f o cused on th e problem . Utility m ade efforts to delay the inspection - why?

23-25 These slid es deserve a class discu ss of lessons learned to im press upon the students that what they do m a tters. The im portance of a questioning attitude and a proper sa fety culture are vital to safe operations. Not allowin g unacceptabl e conditio ns is vital to safety

even if the function is not perceived as critical at the tim e. Be aware of group think affecti ng good decision m a king. W hy did NRC and INPO not catch this?

26 Discuss the consequences to the util ity and possible to the industry should DB' s vessel fail? Point out the restart decision was not based on technical readiness but cult ure read ines s which is h ard to m easure.

MIT OpenCourseWare http://ocw.mit.edu

22.091 / 22.903 Nuclear Reactor Safety

Spring 200 8

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