At 02:15 the following morning, the hydraulic lock of the cleaning vessel lid was released, and immediately the dose rate increased significantly (6-12 millisieverts/hour) around the spent fuel pond and the pool containing the cleaning machine, and the water level dropped for a short time, by about . Water samples from the pond showed contamination due to damaged fuel rods. The lid on the cleaning machine was winched up at 04:20, but one of the three lifting cables attached to it broke; and it was not finally removed until 16 April.