Sunday, May 1, 2011

Post # 42: Early BWR Station Blackout Severe Accident Analyses

I've noted back in Post # 31 that unmitigated BWR severe accident sequences similar to the recent Fukushima Dai-Ichi event were analyzed as early as 1981 at Oak Ridge National Laboratory.  Several folks have asked me if the original NUREG/CR reports for the two original Oak Ridge analyses were available.  I've located them and uploaded them here.

The first report is the original 1981 report in which the unmitigated long-term station blackout sequence for Browns Ferry nuclear plant (a BWR-4 / Mark-I) was analyzed:


Recall the "long-term" qualifier implies that, while the accident sequence assumptions assumed both off-site power and on-site station diesel generators were unavailable from the on-set of the event, the station batteries were assumed available until they were exhausted four hours or longer after accident initiation.

In 1982, ORNL released a second companion report in which the fission product transport phenomenology for the Browns Ferry long-term station blackout sequence was evaluated:


I caution everyone that these were the original analyses, performed with a suite of computer codes and models (accident progression and fission product transport) that were primitive by today's standards.  Additionally, Browns Ferry is a larger plant than Fukushima, and had a shorter station battery life.  

In subsequent years, ORNL analyzed other station blackout and loss-of-decay heat removal sequences in BWRs, developed more advanced tools for invessel accident sequence analysis (the BWRSAR code, developed by  Larry Ott is particularly notable), and worked closely with Sandia National Laboratory to develop BWR modeling approaches for the MELCOR code.

In 1994, one of our colleagues, I. K. Madni, then at Brookhaven National Laboratory, performed a similar long-term station blackout analysis with MELCOR for the Peach Bottom plant (another BWR-4/Mk-I plant):


While I cannot go into all of the details here, a close read of these reports will aptly demonstrate the significant influence station battery lifetime, automatic safety system operating logic protocols, and manual operator actions can have on key accident event timings.

Just thinking...

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