Catalyzes the ring-opening cleavage of the alicyclic alcohol cyclohexane-1,2-dione. cyclohexan-1,2-dione + H2O = 6-oxohexanoate + H(+) Binds 1 Mg(2+) ion per subunit. Binds 1 thiamine pyrophosphate per subunit. Binds 1 FAD per subunit. Optimum pH is 8. Homodimer. Belongs to the TPP enzyme family.