I. PURPOSE AND SCOPE

The containment atmospheric control - dilution (CAC/CAD) systems are in need of upgrade due to a combination of reasons. Outdoor equipment is corroded, instruments do not work properly, annunciators are often in continuous alarm in the control room, and maintenance costs are high. The root cause of the repetitive CAC tank annunciator alarms in the Control Room and invocation of LCOs has been traced to faulty level indicating transmitting switches and system monitoring and control instruments. These devices are obsolete and marginally serviceable, with parts unavailable and have been classified as repetitive failure items. Besides instrumentation problems, there have been problems with nitrogen inventory loss because of an inability to maintain the CAC liquid nitrogen tank jacket vacuum. These losses have been stemmed by a temporary installation of a jacket vacuum system. This project will make the installation permanent. Some CAC subsystems are no longer used but must be maintained.

After upgrade, the CAC and CAD systems will only consist of necessary components (i.e., obsolete subsystems/equipment will be eliminated, including unnecessary Control Room annunciators) and the remaining equipment will be more maintainable with approved availability of spare parts. Also, fewer LCOs will be entered because of faulty sensors and avoidable conditions.

II. EVALUATION

Schedule Index: 19 - The CAC/CAD systems are safety systems of low to moderate significance and will receive a minor to moderate increase in reliability as a result of this upgrade. The distraction of false alarms from systems of low to moderate safety significance could possibly impede actions of control room operators. However, this project does not improve the ability to vent containment during scenarios involving the loss of decay heat removal therefore, this initiative has no significant impact on nuclear safety (0 x 32). The personnel safety aspects of corroded components, degraded, low voltage electrical equipment and increased maintenance have industrial safety significance (0.5 x 29). Since false alarms from these systems have caused LCOs, failure to act on this modification has the potential to negatively impact availability (0.2 x 12). Maintaining subsystems which no longer have a use and obsolete components for which spare parts are unavailable has negative effects on worker productivity and morale; thus, this project represents a plant enhancement (0.2 x 8).

Economic Aspects: There should be a minor to moderate reduction in O&M costs when this project is completed. Cost benefit is hard to quantify because a large portion of potential avoided cost is unpredictable. Although the risk of LCOs caused by future system malfunctions actually resulting in reduction in net generation is low, the economic impact of such avoidable conditions are high and must be considered.

Related Standards: This project relates to the Work Management Policies on material condition and on management oversight and corrective action. A part of the enhancement would address corrosion problems with outdoor equipment in direct response to the applicable standard. The management oversight and corrective action policy states, in part, "… the result of the action taken shall address and resolve the root cause of significant adverse conditions."

Other Considerations: Project completion will reduce the number of disabled annunciators in the Control Room. The work for this modification can be performed with one or both units operating. Either CAD loop being inoperative places the plant in a 31 day LCO. Minor simulator changes will be required as a result of completing this project.

III. CONCLUSION - The material condition of these systems is in need of improvement. Corroded outdoor equipment is a significant problem. The condition of the system results in alarms in the Control Room that distract operators and necessitate entering into LCOs.