MEAG Power, Participant & Public Power News

 Spring 2023

Vogtle News


Plant Vogtle Unit 3 Passes Final Two Milestones Before Commercial Operation

In March, Unit 3 reached initial criticality — a sustaining nuclear reaction in the core — and on April 1 generated electricity for the first time, successfully synchronizing and connecting to the electric grid. Both milestones are part of ongoing startup testing, and operators will continue to raise reactor power for electricity generation while performing tests at various power levels.


Plant Vogtle Unit 3, left, and Unit 4. Unit 3 has now synchronized to the grid and is producing power.

On March 6, Vogtle Unit 3 safely reached initial criticality, a key step during the startup testing sequence in which operators have safely started the nuclear reaction inside the reactor.

A reactor achieves criticality when the nuclear fission reaction becomes self-sustaining. Achieving initial criticality is necessary to continue the startup of the unit in order to generate sufficient heat to produce the steam needed for the production of electricity.

Operators then continued to raise power to support synchronizing the generator to the electric grid and begin producing electricity. This step was achieved on April 1.

Next, operators will continue increasing power through multiple steps, over several weeks, ultimately raising power to 100 percent. Vogtle Unit 3 is projected to be placed in service in the May or June.

After syncing to the grid, Unit 3 will be ramped up and down to several power plateaus before reaching 100% power. Then the unit will be taken back down to 0% again for routine maintenance for commercial operation before it enters commercial operation.

Testing has progressed through a series of “modes,” from Mode 6 to Mode 1. Unit 3 has now reached Mode 1. Unit 4 will go through the same testing modes later this year or early in 2024.

Unit 4 Progress Update

Hot functional testing started in late March and marks the last series of major tests for the new nuclear unit ahead of fuel load. Hot functional testing is conducted to verify the successful operation of reactor components and systems together and confirm the reactor is ready for fuel load. As part of the testing, the site team runs Unit 4 plant systems at normal operating pressure and temperature without nuclear fuel.

Nuclear operators are using the heat generated by the unit’s four reactor coolant pumps to sustain the temperature and pressure of plant systems at normal operating levels, and the unit’s main turbine will be raised to normal operating speed using steam from the plant. Operators are also able to exercise and validate procedures as required ahead of fuel load.

Unit 4 is focused on the remaining construction work — primarily electrical — and completions of Inspection, Test, Analyses, Acceptance Criteria (ITAAC) to support the 103g filing – the request to the Nuclear Regulatory Commission (NRC) for permission to load fuel, fuel load and commercial operation.


Plant Vogtle Unit 4

Another recent milestone for Vogtle Unit 4:

  • Cold hydro testing – In early December, Unit 4 completed cold hydro testing, which is required to support the last major test remaining for Unit 4, hot functional testing. Hot functional testing is projected to commence by the end of the first quarter of 2023. Unit 4 is slated to enter commercial operation in the 1st quarter of 2024.Cold hydro testing on Unit 4 confirmed the reactor’s coolant system functions as designed and verified the welds, joints, pipes and other components of the coolant system and associated high-pressure systems do not leak when under pressure. As part of the testing, the reactor coolant system was filled with water and pressurized above-normal operating conditions, then lowered to normal design pressure while comprehensive inspections were conducted to verify the systems meet design standards.


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