Drilling a hole in rock is about the least delicate job on a construction site. You line the bit up, pour on the torque and let the machine chew. Nobody shows up afterward with measuring gear to check whether the hole leaned a little to the left on its way down.<\/p>\n
Finland’s nuclear waste company shows up afterward with measuring gear. On August 26, roughly 1,300 feet (400 meters) under the island of Olkiluoto, a boring machine started cutting the first hole at the Onkalo repository that will actually hold spent nuclear fuel. That hole is allowed to drift just under an inch (25 millimeters) off its vertical centerline over the entire depth, according to World Nuclear News<\/a>. Go past that and the hole gets rejected, and the crew drills another one.<\/p>\n I had to read that tolerance twice.<\/p>\n Posiva, the company owned by Finland’s two nuclear operators, has drilled at Onkalo before. Four practice holes went in during late 2022, cut by a crew from the machine’s manufacturer, and Posiva’s own people later drilled four more with the supplier looking over their shoulder. Those were rehearsals. This one is meant to take a canister.<\/p>\n The finished hole is 27.6 feet deep and 5 feet 9 inches wide (8.4 by 1.75 meters). The canister going into it is 3 feet 5 inches across (1.05 meters), according to Posiva<\/a>. Subtract one from the other and you have roughly 14 inches of empty space wrapped around the canister. That gap is where the bentonite clay goes, and the clay is doing more work in this design than the hole is.<\/p>\n Bentonite swells when it gets wet. Groundwater that works its way toward the canister runs into a clay collar that has already expanded to fill everything around it. Copper is the first barrier, clay is the second, and 1,300 feet of granite is the third. Posiva has spent 40 years arguing that those three together hold up for far longer than anyone can meaningfully plan for, and the whole case depends on each layer sitting where the drawings say it sits.<\/p>\n Posiva hasn’t spelled out the failure mode for a crooked hole, so I won’t invent one. But the geometry is easy enough to picture. A shaft that wanders leaves the canister off center, with a thicker clay ring on one side than the other, and that is an expensive thing to find out after you have lowered 27 short tons (24.5 metric tons) of copper and cast iron into a tunnel floor. You get one attempt at placing it. That is a frankly unforgiving spec for a hole cut into granite by a machine the size of a shipping container.<\/p>\n Posiva calls the machine a Deposition Hole Boring Machine, which is about as literal as equipment names get. It arrived at Olkiluoto in June 2022 from Herrenknecht, the German manufacturer whose borers turn up on a good share of the world’s large underground projects. We wrote about one of the same company’s 197-foot shaft borers working under an English national park<\/a> earlier this year.<\/p>\n This one is squatter and stranger. It runs more than 29 feet long, about 10 feet wide and just under 13 feet tall, and it weighs 86 short tons (78 metric tons), with a separate energy unit and a drill processing plant parked alongside. All of that hardware cuts one vertical hole at a time.<\/p>\n Kimmo Lehtola, Posiva’s construction manager for operations, said the crew finished adjusting the equipment through the morning and had the drill into the rock by early afternoon. That rock formed about 1.9 billion years ago.<\/p>\n Lehtola put the drilling time for an eight-meter hole at around ten hours of effective work. “Ten hours is a pretty good rule of thumb in our conditions,” he told World Nuclear News, adding that harder rock slows the process down.<\/p>\n Once the operation settles into production, Posiva wants about two finished holes per working week. The first disposal tunnel runs roughly 1,080 feet (330 meters) and will take about 30 holes. Across the repository’s planned 100-year operating life, the company estimates around 100 tunnels totaling 22 miles (35 kilometers).<\/p>\n Each of the first three holes gets measured again as soon as it is finished, before drilling moves on to the next one. Posiva said on August 27 that it expected to know within days whether the first hole passed, and I can’t find a published result yet, which is a slightly odd thing to leave hanging after announcing the milestone.<\/p>\n Finland’s Radiation and Nuclear Safety Authority, STUK, published its safety assessment in early August and concluded that the requirements for granting an operating license have been met. Director General Petteri Tiippana described it as a significant step in a project prepared over more than 40 years. STUK also proposed conditions for the license, including an earlier periodic safety review and an updated long-term safety case.<\/p>\n The government makes the actual call. Posiva applied on December 30, 2021, for a license running to the end of 2070, and the Ministry of Economic Affairs and Employment has said a proposal could reach the government in the fall. Even with a positive decision, Posiva cannot start operating until STUK carries out an inspection under the Nuclear Energy Act.<\/p>\n So the paperwork is close, but it is not done. We covered the state of play in June, when Onkalo was still waiting on the regulator’s verdict<\/a>.<\/p>\nSo why does an inch matter down there?<\/h2>\n
The rig came out of a German shaft-boring shop<\/h2>\n
Ten hours a hole, and two holes a week is the goal<\/h2>\n
Posiva still needs the government to sign off<\/h2>\n