Low Cost/Risk Approach for Verifying Modifications to Dynamic Plant Operation and Instrumentation & Control System Resulting from Steam Generator Replacement

Abstract

Steam generator replacement projects have become quite common among nuclear utilities having pressurized water reactors. The projects characteristically include only safety analysis for licensing the new steam generators. However, there are operating and control issues not addressed by licensing analysis that can impact startup schedule and cost. For example, the operation and control may be significantly different even for one-for-one replacement, since the plant operating parameters and steam generator heat transfer parameters are different after the changeout. Examples of changed parameters include hot-leg temperature, steam header pressure, steam generator tube thermal conductivity, heat transfer surface area, and recirculation ratio. The paper points out that it is extremely prudent and cost effective to address operating and control issues in parallel with licensing analysis. This can be done by extending the scope of the steam generator replacement projects to include startup support in the form of operating analysis and familiarization of dynamic response of the modified plant, and verification of the plant control system changes in a hardware-in-the-loop fashion before startup. The safety analysis is typically performed with codes like RELAP5 and RETRAN that require extensive computing resources. Complementary to safety analysis codes, plant models based on the Modular Modeling System (MMS) are ideally suited for verifying changes in dynamic plant operation and the instrumentation and control system. The MMS models can be used even after the steam generator replacement for checkout of future plant upgrades or modifications, training, and transient analyses.