Electrical Consultants, Inc. provided Marathon with a proposal to prepare the Engineering Services & Design drawings and other documents for their TGU D-265 Reactor High Temperature Trip Project.

Marathon implemented a new control narrative to trip the TGU C-205A/B heaters and put the unit in cool down circulation mode when there is a high D-265 reactor temperature. The scope of this work involved removing thermocouples from the TGU I/O, installing temperature transmitters, and bringing the analog temperature signals into the SIS located in the SRU I/O room. The previous flow control valve was converted to an Air Fail Open (AFO) valve and installed with a new 3-way solenoid valve in line with the instrument air supply. If the solenoid valve is de-energized or power is lost, the instrument air line of the flow control valve was vented to atmosphere, causing the valve to open.

Marathon had already modified or redlined several of the required drawings for the project. ECI reviewed and modified these drawings as required and generated new drawings and documents necessary to implement the work.