Here is the full list of all 121 Atlas Reactor achievements.
Reach Reactor Level 350
Play 50 games in which you use Aegis 3 or more times as Brynn
Heal or Shield 150,000 Damage
Shield 5000 total damage with Resonance Burst as Khita
Deal 200 damage with Oblivion Shell in one game as Elle
Do 5000 total damage with Rebounding Charge as Asana
Do 10000 total damage with Combat Reflexes as Elle
Do 1875 total healing with Astral Fusion as Orion
Reach Reactor Level 300
Do 1000 total damage with Vaulting Shot as Khita
Play 25 games in which you use Quantum Collision 2 or more times as Quark
Dodge 100,000 Damage
Do 3750 total damage with Ion Cloud as Aurora
Reach Reactor Level 250
Shield 1000 total damage with Paralazer as Aurora
Play 50 games in which you use Stalker Suit 3 or more times as Nix
Heal or Shield 100,000 Damage
Do 2500 total damage with Flight of the Valkyrie as Brynn
Do 3750 total damage with Putrid Spray bug detonations as Phaedra
Reach Reactor Level 200
Dodge 75,000 Damage
Shield 5000 total damage with Blast Shield as Helio
Do 2500 total damage with Vortex Round as Nix
Deal 250,000 Damage
Heal or Shield 75,000 Damage
Reach Reactor Level 150
Do 1875 total damage with Juggernaut as Phaedra
Deal 200 damage with Scorched Earth in one game as Blackburn
Do 750 total damage with Lurker Drone as Elle
Deal 200,000 Damage
Deal 200 damage in one game with Cataclysm as NEV:3
Dodge 50,000 Damage
Do 1125 total damage with Retribution as Asana
Heal or Shield 50,000 Damage
Heal at least 200 damage with Take Aim! in one game as Khita
Reach Reactor Level 100
Deal at least 200 damage and dodge at least 100 damage in one game as Brynn.
Deal 200 damage with Fusion Pulse in one game as Nix
Deal 150,000 Damage
Deal more than 200 damage with Missile Storm in a game as Zuki.
Heal for 100 with Mending Swarm and deal at least 200 damage in one game as Phaedra
Heal 200 damage with Positronic Surge in one game as Quark
Heal or Shield 25,000 Damage
Shield 200 damage with Blast Shield and Battleforged in one game as Helio
Dodge 25,000 Damage
Deal 25,000 Damage
Deal 50,000 Damage
Deal 75,000 Damage
Deal 100,000 Damage
Do 10000 total damage with Razor Tempest as Kaigin
Deal 200 damage with Subwoof in one game as PuP
Reach Reactor Level 50
Deal 100 damage with Voltaic Cage in one game as Grey
Deal 200 damage with Lay Down the Law in one game as Juno
Deal 150 combined damage and healing with Heart of the Storm in one game as Aurora
Heal or Shield 10,000 Damage
Heal 200 damage with Refreshing Spray in one game as Dr. Finn
Dodge 10,000 Damage
Deal 150 damage with Deathblow in one game as Titus
Deal 80 damage with Mark of the Void in one game as Kaigin
Dodge 150 damage and deal 500 damage in one game as Oz
Deal 10,000 Damage
Deal 200 damage with Run and Gun in one game as Lockwood
Deal 200 damage with Maniacal Mayhem in one game as Gremolitions Inc
Deal 200 damage with Safecracker in one game as Celeste
Deal 300 damage and shielding with Guardian Angel in one game as Asana
Deal 150 damage with Shock Pod in one game as Garrison
Heal for 75 health with Augmented Regeneration and deal 100 damage with Uncontrollable Fury in a single game as Rask.
Deal 150 damage with Aegis Protocol in one game as Rampart
Deal more than 250 combined damage and healing with Cosmic Flare in one game as Orion
Shield more than 150 damage with Karmic Justice in one game as Su-Ren
Deal 200 damage with Rushing Steel and Showdown in one game as Tol-Ren
Reach Reactor Level 400
Reach Reactor Level 450
Reach Reactor Level 500
Heal and shield more than 400 combined damage in one game as Meridian
Dodge 150,000 Damage
Dodge 200,000 Damage
Dodge 250,000 Damage
Heal or Shield 200,000 Damage
Heal or Shield 250,000 Damage
Do 10000 total damage with Sticky Bombs as Zuki
Do 5000 total damage with Proteus Grenade as Blackburn
Do 10000 total damage with Photon Spray as Oz
Do 10000 total damage with Light 'Em Up as Lockwood
Do 3210 total damage with Splort as Gremolitions Inc.
Do 10000 total damage with Hawk Drone as Grey
Do 7500 total damage with Pounce as PuP
Do 5000 total damage with Proximo Charge as Celeste
Do 5000 total damage with Lockdown as Juno
Shield 3000 damage with Ren's Fury as Tol-Ren
Play 50 games in which you use Embiggify 3 or more times as NEV:3
Do 5000 total damage with Hand Cannon as Garrison
Do 5000 total damage with Berserker Charge as Titus
Do 3750 total damage with Upheaval as Rask
Do 3750 total damage with Bulwark as Rampart
Do 10000 total healing with Atomic Bond as Quark
Do 10000 total healing with Refreshing Spray as Dr. Finn
Shield 3750 total damage with Fate Transfer as Orion
Do 10000 total healing with Serenity as Su-Ren
Do 7500 total healing with Reforge as Meridian
Play 25 games in which you use Shadowstalker 3 or more times as Kaigin
Do 750 total damage with Rocket Jump as Zuki
Do 2250 total damage with Blitz as Blackburn
Play 25 games in which you use Made You Look 3 or more times as Oz
Do 500 total damage with Bombing Run as Gremolitions Inc.
Play 25 games in which you use Backup Plan 2 or more times as Lockwood
Play 25 games in which you use Slip Away 2 or more times as Grey
Play 25 games in which you use Prowl Protocol 3 or more times as PuP
Do 1000 total damage with On The Run as Celeste
Shield 2000 total damage with Riot Shield as Juno
Do 2500 total damage with Rushing Steel as Tol-Ren
Do 2500 total damage with Acrocat as NEV:3
Do 1250 total damage with Heavy Metal as Garrison
Do 1250 total damage with Dirty Fighting as Titus
Do 1250 total healing with Augmented Regeneration as Rask
Play 25 games in which you use Unstoppable Force 3 or more times as Rampart
Do 2500 total damage with Disruption Matrix as Helio
Shield 2500 total damage with Bubble Trouble as Dr. Finn
Play 25 games in which you use Spirit Bend 3 or more times as Su-Ren
Do 1250 total damage with Solar Strike as Meridian