This work plan proposes to build a systematic knowledge base for the thermal aging behavior of cast stainless steels (CASSs) within a limited time of five years. The final output of execution of the plan is expected to provide conclusive predictions for the integrity of the CASS components of LWR power plants during the extended service life up to and beyond 60 years. Mechanical and microstructural data obtained through accelerated aging experiment and computational simulation will be the key input for the prediction of CASS behaviors and for the integrity analyses for various CASS components. While the accelerated aging experiment and computational simulation results will comprise the main components of the knowledge base for CASS aging, the data obtained in-situ at power plants or from plant-served components are needed to validate the accelerated aging methodology as well as to provide realistic guidelines for plant life extension. In addition to using existing database, therefore, a systematic campaign to obtain mechanical data from used materials or components is pursued and a semi- nondestructive testing technology is developed or acquired if needed. Further, the detailed studies on aging and embrittlement mechanisms as well as on deformation and fracture mechanisms are performed to understand and predict the aging behavior over extended lifetime. The following sections include an introduction to CASS thermal aging, microstructural backgrounds, and a five year plan.