Using sample welds conducted on plates of aluminum, Mr. Cox shows viewers how heat from the welds can deform the surface of the vessel and may cause the vessel walls to contract, potentially applying too much force to the lower seal of the NRU. This fact, combined with the complexity of applying the welds from a remote location, further explains the need for AECL to conduct more in-depth research and numerous weld practices prior to completing the final two weld repairs.