Fuel Reactors is a Mass Effect 3 N7 mission which becomes available after Priority: Perseus Veil.
When to start
After Priority: Perseus Veil
“A vital depot has gone silent, leaving allied fleets short on desperately needed fuel. Investigate the depot and get it operational again.”
Advanced Starship Fuel War Asset
N7 Fuel Reactors is added to your journal if you talk to Specialist Traynor after Priority: Perseus Veil, also known as Priority: Geth Dreadnought.
To start the mission open the Galaxy Map and in the Milky Way, locate Silean Nebula. Enter the system and land on Planet Cyone. Select your crew and weapons, and dont forget to use the weapon mods you have acquired so far, to improve your equipment.
The mission starts with a dialogue between Admiral Hackett and Shepard.
As soon as you assume control over Shepard, head left and on a crate you will find Rosenkov Materials Chestplate. Maintain your current position and head forward, until you reach a platform, at the end of the area.
To the right you should see another crate, and on it, a Medical Treatment Plan.
This important item allows you to complete the Chemical Treatment Citadel mission.
Reach the right side of the area and talk to Captain Riley. During the conversation you will find out that the lower level of the facility is contaminated by a toxic gas.
NOTE: The gas is deadly, and will instantly kill you.
Behind Captain Riley is a crane, and the control panel to activate it, is near it, to the right. Inside, you will also find some Spare Parts (right side) you can salvage for 4,000 Credits.
Approach the Crane Display and activate it to move both containers from left to right. Exit the control room and go right, then move forward and active the Vent Sector A1 console to remove the gas.
Now, you can go down and activate the fuel rod. Next to it, on the ground, to the right is a PDA. Examine it for 3,000 Credits.
After you activate the fuel rod, take cover, because a wave of Husks and Marauders will attack your position. After you kill them, go back up, and follow the ramp to the left which allows you to reach the first tank.
Seal it and advance toward the second tank. Repeat the step, then turn around and you should see a console which allows you to restart the reactor.
On the left side of the console, on the ground is another PDA (3,000 Credits). Get it then activate the reactor and take cover. Destroy the barrier engines, and then focus on the Reapers.
When Riley calls you seeking help you have to make a tough decision. You can send one of your crew-members to save her (Paragon) or you can seal her fate and let her die (Renegade). After you decide, a door will open and a Brute will attack you.
Make sure the monster keeps a fair distance from the barrier engines, and then take it out along with the Marauders that spawn near it. Next, go through the door opened by the Brute and use the console to start the reactor.
Sprint to the extraction point to complete the mission. New achievement/trophy unlocked: Explorer. After you complete the mission, in Silean Nebula, scan planet Hanalei to find War Asset: Dr. Jelize.
Next N7 mission: Communication Hub.