OPG beyond design basis accident and SAMG framework

In the days immediately after the Fukushima Accident on March 11, 2011, CNSC performed a comprehensive assessment of all the design features to reaffirm the readiness for a response to such an event at a Canadian NPP. As a result of this assessment, CNSC issued various actions known as the Fukushima Action Items (FAIs) catering Beyond Design Basis Accident (BDBA) response at Canadian NPPs. These actions led to various modifications to the existing plant Systems Structures and Components (SSCs) and the procurement of portable equipment to provide an additional line of defense. Canadian NPPs (including OPG) have adopted the term Emergency Mitigating Equipment (EME) to categorize such portable equipment which provide an additional line of defense during a Beyond Design Basis Accident (BDBA). Some existing SSCs in the plants such as Steam Generator Emergency Cooling System (SGECS) and Deaerator have also been credited to aid in BDBA mitigation. Additionally, there are a number of existing and new SSCs that have been modified or designed specifically for BDBA mitigation purposes. EME have a two phase deployment strategy. Phase I is dedicated to small portable generators and pumps which aid in repowering instrumentation and supplying water to the reactor in case of total loss of AC power resulting in a loss of heat sink accident. Phase II EME consists of a bigger generator which will be used to repower the existing design basis system (e.g. Filtered Air Discharge System (FADS), Emergency Coolant Injection (ECI) recovery, Emergency Water Supply (EWS) etc.) to maintain containment integrity. This portable equipment will be connected to existing station systems which have been modified with quick connects to pump in water from the intake channels to boilers, Heat Transport System, Moderator and the Shield Tank as required during an emergency. These portable equipment are stored at an offsite facility for both Darlington and Pickering. BDBA framework is specifically intended to provide response using Emergency Mitigating Equipment Guidelines (EMEGs) and Severe Accident Mitigation Guidelines (SAMGs) for events that are or have the potential to become Severe Accidents (SAs), and for supporting the implementation of these actions. Preparation for BDBA response (e.g. modifications, procedures) also ensures that the functionality of plant SSCs that aid in BDBA mitigation are not compromised under design basis conditions, and that the required functionality of BDBA mitigating actions is delivered with high confidence under the anticipated BDBA conditions. The current Pickering and Darlington NPP designs with new Fukushima Enhancements are capable of mitigating events ranging from Anticipated Operational Occurrence to Severe Accidents. (author)