Project Ouroboros was the mysterious tank Dr. Pryce kept hidden at The Godfrey Institute. The contents of the tank were never revealed to the viewers, but it was implied that the Ouroboros was relevant to the story line and played a significant role in many of the strange occurrences in Hemlock Grove.
Although it is never shown what exactly Dr. Pryce was keeping in the Ouroboros tank, the historical/mythological meaning of "ouroboros" provides several hints. The definition of the word Ouroboros means: "The Ouroboros or Uroboros, is an ancient symbol depicting a serpent or dragon eating its own tail. The Ouroboros often symbolize self-reflexivity or cyclicality, especially in the sense of something constantly re-creating itself, the eternal return, and other things such as the phoenix which operate in cycles that begin anew as soon as they end." So for short Ouroboros is a symbol of a never ending cycle (the serpent eating its tail is a complete circle), meaning that life is created from death.
This should all sound familiar to those who have watched Hemlock Grove, especially in the context of Shelley (Roman's sister). When Olivia killed her as an infant, her husband took her to Dr. Pryce so he could bring her back to life, completing a full circle (though there were a few complications, like her deformities). The Ouroboros tank is where Dr. Pryce brings the dead back to life. It was revealed that a humanoid body encased in some kind of crystal who managed to open it's eyes.
In Season 2 the humanoid body has manifested into a real living human body which has emotions and feeling like a normal human being which Dr. Pryce has named Prycilla. Dr. Pryce considered Prycilla to his life's greatest work and was going to show her off. However Dr. Pryce reconsidered and killed Prycilla and transfer half of Shelley's mind into her so Shelley could have a normal life and the other half would be transferred later. When half of Shelley's mind was transferred into Prycilla it was like Shelley was two people they knew each other's every thought, emotions and dreams like they were sisters. But when Olivia was diagnosed with cancer she learned from Dr. Galina Zhelezhnova-Burdukovskaya that Pryscilla could cure her of her illness.
On the day of Shelley's mind being transferred into Pryscilla, the operation was a success. However, Shelley's old body would die if her mind was transferred. When Dr. Pryce and Norman learned of Olivia's plan to kill Pryscilla to cure her cancer, Prycilla was nowhere to be found. When Prycilla was alone Olivia attacked her and killed her, eating her flesh which cured her. Norman and Dr. Pryce were able to save Shelley's old body, but when Shelley saw that she was still in her old body and Prycilla was dead, she went on a rampage and was carried away by officers.