DOE is trying to develop accident tolerant fuel and structural materials for future light water reactor (LWR). TREAT irradiation vehicle will be testing new accident-tolerant fuel for nuclear reactors. TREAT irradiation vehicle needs 718 alloy pressure vessel. Fabrication of pressure vessel by additive manufacturing 718 alloy is needed. But 100% dense component by AM fabrication process is difficult. Low cost rapid fabrication process of 718 alloy pressure vessel/expansion tank is needed for TREAT irradiation vehicle to replace current conventional fabrication process with equal or improved high temperature strength and neutron embrittlement resistance. Low cost, rapid fabrication of this porosity free pressure vessel can be done by Additive Manufacturing (AM) process using APS engineered 718 alloy powder. By AM each layer is melted to the exact geometry defined by a 3D CAD model and the same part could be fabricated within hours. This DOE SBIR Phase I program will fabricate 718 alloy pressure vessel by Additive Manufacturing and subsequent heat treatment using APS developed AM machines compatible engineered 718 alloy powders with high temperature strength, neutron embrittlement resistant properties. This program will reduce the time required to get part for DOE. Phase II will continue to fabricate more specific TREAT irradiation vehicle components for DOE.If successful, the rapid fabrication of robust component developed by AM in this SBIR program will reduce the cost and enhance the life and performance of current TREAT irradiation vehicle components such as primary/secondary heat exchanger, reactor vessel.