Monday, April 11, 2011

Post # 40: Mitigating BWR Station Blackout Accidents – Foundation Documents

During the past month there's been a great deal of discussion in the media, here on the internet, and elsewhere, regarding possible approaches to halting the accident progression at Fuskushimi Dai-Ichi and stabilizing Units 1-3.  As I've previously mentioned, there was a significant amount of work done in this area in the 1980s through the late 1990s.  Steve Hodge and his colleagues at ORNL performed a detailed analysis of various approaches to terminating the station blackout severe accident progression, in conjunction with the BWR Owners Group Emergency Operating Procedures then in effect.  Steve and company looked at both "early-phase" (pre-core-damage), and "late-phase" (post-core-damage) strategies.  Based in large part on their work, the Emergency Operating Procedures and Severe Accident Management strategies then in effect were modified.

The first document is "Assessment of Two BWR Accident Management Strategies,"CONF-911079-2, by Hodge and Petek.  You can find it here:  Conf 911079--2

Quoting from the abstract of the document, ,  "Candidate mitigative strategies for management of in-vessel events during the late phase (after core degradation has occurred) of postulated BWR severe accidents were considered at Oak Ridge National Laboratory (ORNL) during 1990. The identification of new strategies was subject to the constraint that they should, to the maximum extent possible, make use of the existing equipment and water resources of the BWR facilities and not require major equipment modifications or additions. As a result of this effort, two of these candidate strategies were recommended for additional assessment. The first is a strategy for containment flooding to maintain the core and structural debris within the reactor vessel in the event that vessel injection cannot be restored to terminate a severe accident sequence. The second strategy pertains to the opposite case, for which vessel injection would be restored after control blade melting had begun; its purpose is to provide an injection source of borated water at the concentration necessary to preclude criticality upon recovering a damaged BWR core. Assessments of these two strategies have been performed during 1991 under the auspices of the Detailed Assessment of BWR In-Vessel Strategies Program. This paper provides a discussion of the motivation for and purpose of these strategies and the potential for their success."

The second document is the definitive analysis, "Identification and Assessment of BWR In-Vessel Severe Accident Mitigation Strategies", NUREG/CR-5869, by Hodge, Cleveland, Kress, and Petek.  I've uploaded the entire report here: Cr 5869

Quoting from the abstract of NUREG/CR-5986:  "This report provides the results of work carried out in support of the U.S. Nuclear Regulatory Commission Accident Management Research Program to develop a technical basis for evaluating the effectiveness and feasibility of current and proposed strategies for boiling water reactor (BWR) severe accident management.  First, the findings of an assessment of the current status of accident management strategies for the mitigation of in-vessel events for BWR severe accident sequences are described. This includes a review of the BWR Owners' Group Emergency Procedure Guidelines (EPGs) to detennine the extent to which they currently address the characteristic events of an unmitigated severe accident and to provide the basis for recommendations for enhancement of accident management procedures. Second, where considered necessary, new candidate accident management strategies are proposed for mitigation of the late-phase (after core damage has occurred) events. Finally,  recommendations are made for consideration of additional strategies where warranted. and two of the four candidate strategies identified by this effort are assessed in detail: (1) preparation of a boron solution for reactor vessel refill should control blade damage occur  during a period of temporary core dryout and (2) containment flooding to maintain the core debris within the reactor vessel if the injection systems cannot be restored."

These are both very technical documents (especially the NUREG), but give the amount of interest and dialog about the topic, I felt it would be appropriate to make these two public documents a bit more accessible...

For those of you who are wondering... I do plan to return to my central theme - sustainable energy – very soon.  However, given recent events in Japan, and their relevance to the anchor of a sustainable energy future (nuclear power), I feel it important to focus on the BWR severe accident safety topic for a bit.

Just thinking...

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