Nuclear Symposium Insights on Containment Integrity

Guest post by Kara Schmitt, Doctoral Student, Florida Institute of Technology

Dilip Rao, Supervisor/Advisory Engineer, AREVA Inc., presenting at the 8th Nuclear Plants Current Issues Symposium.

I spent a few days at the recent 8th Nuclear Plants Current Issues Symposium in Orlando, Florida. I’m ABD (all but dissertation) on the way to a PhD looking at function allocation in the control rooms of nuclear power plants, so I had hoped that the conference would update my perspectives on the current trends and interests of the industry. My background is in spaceflight airframes, so learning about the nuclear industry has been equally rewarding and challenging. The conference overall, did not disappoint.

Eager as I was, I attended every talk trying to get the most of the experience, and one in particular stood out. Dilip Rao of AREVA presented a compelling talk on Ensuring Containment Integrity for Mark I and Mark II BWRs during Extended Design Basis Events based on a paper written by himself and Robert Sanders. I’d come across AREVA a number of times in my research, and much like the rest of the industry, was personally impressed with the company’s goals and culture.

Mr. Rao described a holistic look at the events that could challenge the containment integrity in order to determine mitigating actions for improving safety. Much like other safety studies, they considered the outcomes of varying severity for several events. The primary safety goals are preventing fuel failure, vessel failure, containment failure, and the uncontrolled release of fission products.

One of the interesting discussions was the evolution of the severe accident mitigation techniques over the past 35 years. Obviously significant changes were made post Three Mile Island through Kemeny Report, but even more recently the NRC put into effect the “B.5.b” reactions to the events of 9/11/01. The industry is again learning from experience by implementing the FLEX program in response to Fukushima, which alters perceptions from planning for single events to planning strategies for the unknown.

He walked us through two scenarios outlining the sequence of events and responses for loss of all AC power – the first with DC power available, and the second without. The recommendations that came out of those scenarios are that:

  1. Containment Integrity must be the priority in a severe accident situation
  2. If DC power or core cooling is lost, filtered controlled containment venting is essential
  3. Decay heat needs to be removed, and reliable monitoring must be maintained using FLEX strategies

He introduced some modeling software I was unfamiliar with, where they were able to verify some major components of that model against real data from Fukushima. He also made some really interesting points about passive systems, proposing that the ability to intervene and control is required. I hadn’t considered that, but I can think of a few scenarios where that could not only be applicable, but required for safety. One of the things we’ve been looking at in my research is how much automation is too much, and what levels of control should be required for safety systems, and the ability to control a passive system has some interesting implications.

All in all, Mr. Rao’s talk provided good solutions for mitigating action for issues, and how to move forward in incorporating some of the lessons learned, and I’ll be incorporating some of those ideas into my research.