Undergraduate Reasearch

Development of a surveillance program for the argentinian reactor CAREM 25.

Integration Project in Nuclear Engineering, Universidad Nacional de Cuyo, Instituto Balseiro. June, 2014.

Abstract

To comply with standards and regulations and ensure safe plant operation, the critical components of nuclear plants must be monitored. The reactor pressure vessel is constructed with a very high safety factor because its failure would cause a severe accident. Nowadays, ferritic steels are used in the reactor pressure vessel's structural component. These materials are of body-centered cubic (bcc) structure and exhibit a ductile-brittle transition when the temperature decreases. Although the vessel is designed so that the operating temperature is always greater than the ductile-brittle transition temperature, neutron irradiation increases the temperature below which the reactor pressure vessel fails by brittle fracture. Because of this, it is mandatory during the plant operation life to avoid this temperature increases to operating levels due to neutron irradiation. This work assesses the need to implement a surveillance program for the CAREM 25 reactor pressure vessel. CAREM 25 reactor is an Argentinian project whose integrated design allows the reactivity control mechanisms, hydraulic mechanisms of control rods, and steam generators to be contained within the reactor pressure vessel. A surveillance program is developed based on the ASTM E185-10 standard using MCNP probabilistic transport code for neutron calculations. The possibility of implementing SPT and microhardness tests is also discussed. Damage caused by low-energy neutrons, which are not considered by current standards, is analyzed. The need to include the steam generators in the surveillance program is discarded. Finally, we assessed the phenomenon of Irradiation Assisted Stress Corrosion Cracking (IASCC), concluding that there are mild probabilities of occurrence of this phenomenon in some internal components near the core.