The Importance of a System Perspective in the Classification, Modification, and Maintenance of Safety-Class and Safety-Significant Structures, Systems, and Components (SSCs)
At a manufacturing facility, upgrades to safety documentation lead to changes in the classification of various SSCs supporting safety in the operation. The facility addressed control of these safety-class and safety-significant systems at a component level. As a result, the operability or the confirmation of operability of several safety systems were challenged with an unsatisfactory response. The operational requirements for the building ventilation systems did not ensure that flows assumed in the BIO for certain fire scenarios were met. While many system level safety functions were confirmed by the operational requirements, the lack of a systems approach to safety may have contributed to the lack of appropriate operational controls of ventilation flow checks in the facility. Another example of the danger of component as opposed to systems level control was found in the cooling water used in casting furnaces. A check valve in this system was identified as a component important to safety, and surveillances prescribed to verify the components function. It was later discovered however, that in two of the casting furnaces, a return line was in place upstream of the check valve in question, negating the ability of that valve to perform it's safety function.
Lesson Learned: Built in assurances like configuration control and preservation of safety functions at the system level are essential to managing the safety basis. A systems approach to safety should be considered in the operation of DOE nuclear facilities.
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