WE Colloquium: Jon Tatman, Development of Advanced Welding Processes for Repair of Highly Irradiated Nuclear Reactor Internals

Abstract

Austenitic materials in light water reactor (LWR) nuclear power plants are exposed to harsh environments combining stress, temperature, and radiation fields coupled with transmutation effects, the latter producing helium in the materials used for core internals.  Recent inspections performed in the aging nuclear power plant fleet have revealed numerous flaws in various reactor internal support systems, specifically the core support lugs, jet pump riser brace, core shroud and core barrel components.  Replacement of these highly irradiated components is not a viable option and it is anticipated that they will eventually require welding repair to ensure the continued safe-operation of nuclear power plants with expected service life up to 80 years. 

While repair of reactor components may seem to be a trivial task to perform with current welding technologies, the presence of helium in these irradiated reactor internals poses a major issue.  This helium is formed by nuclear transmutation reactions of boron and nickel and increases as neutron fluence accumulates.  The high heat input transferred to highly irradiated materials from typical nuclear arc welding repair processes causes the formation of helium bubbles in the grain boundaries of the heat-affected zone (HAZ) upon cooling.  Extensive HAZ intergranular cracking (termed “helium-induced cracking”) can then result from high localized tensile stresses generated during the formation of these helium bubbles.  One method for preventing this cracking mechanism is the use low heat input welding processes, such as laser beam welding.

This presentation provides an overview of a collaborative research effort between the Electric Power Research Institute, U.S. Department of Energy, Oak Ridge National Laboratory and Westinghouse Electric Company to develop advanced repair solutions for highly irradiated, reactor internal components.

Bio

Jon Tatman is a Senior Technical Leader in the Welding and Repair Technology Center at the Electric Power Research Institute (EPRI).  He obtained his M.S. degree from the Ohio State University Welding Engineering program in 2008. His first engineering position was with Bettis Atomic Power Laboratory in Pittsburgh, PA; where he performed various R&D and emergent repair efforts for the Naval Nuclear Propulsion Program. He then joined the Electric Power Research Institute in 2011, where he now performs engineering R&D for the nuclear power industry and leads the research focus areas on optimization of repair processes and development of advanced welding techniques for reactor internal repairs.