One of Tetra Tech Advent’s strongest areas of expertise lies in the area of safe shutdown assessments and evaluations. Such expertise is critical to successful operability evaluations, responses to NRC questions, new design, design modifications, and administration of most regulatory programs. This expertise has derived from diverse backgrounds, multi-discipline experience, cross-departmental research, and complex, logical assessments over the years responding to the question of can the plant achieve and maintain safe shutdown even though:

• A new postulated single failure must be considered;
• A new passive failure is being considered;
• Combination of failures from common causes (such as fire, pipe break environment, pipe break jet impingement, flooding, radiation, aging, etc) and a single active failure;
• A previously considered operator action is no longer allowed;
• A new or variation of a postulated accidence sequence of events with or without loss of off-site power must be considered;
• Cold rather than hot shutdown is the desired end state;
• A previously unforeseen loss of design margin has occurred; or
• Many other similar situations.

Tetra Tech Advent has also assisted in assessing safety significance through consideration of variations in realistic inputs to PRA models.

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