Federal laws/regulations; Background;

OLR Research Report

April 4, 2011




By: Kevin McCarthy, Principal Analyst

You asked how spent nuclear fuel is stored in Connecticut.


At one time Connecticut had four operating nuclear power plants, Connecticut Yankee and Millstone Units 1, 2, and 3. Spent nuclear fuel from Connecticut Yankee, which has been decommissioned, is stored in dry casks built of concrete and steel on a site located near the site of the former plant. Spent fuel from Millstone Unit 1, which is being decommissioned, and Unit 3 is stored in pools located at the plants. Spent fuel from Unit 2 is initially stored in its spent fuel pool and then in dry casks.

The Nuclear Regulatory Commission's (NRC) General Design Criteria for Nuclear Power Plants (10 CFR Part 50, Appendix A), requires that nuclear plant structures, systems, and components that are important to safety be designed to withstand the effects of the most extreme natural phenomena, such as hurricanes and earthquakes, that could reasonably be predicted to occur at the site, without loss of capability to perform their safety functions. These regulations apply to dry cask storage facilities as well as the plants themselves.


Connecticut Yankee

Connecticut Yankee began commercial operation in 1968. Its decommissioning began in 1998 and was completed in 2007. Its owner chose the dry cask option to store its spent fuel assemblies after decommissioning. The fuel storage facility site is located about three-quarters of a mile from the former plant site at Haddam Neck. Construction of the reinforced concrete storage pad and vertical concrete and steel storage casks that hold the fuel was completed in 2002.

The casks are licensed by the NRC for storage and transportation. There are 43 casks on a 100 by 200-foot, three-foot-thick concrete pad at the site. Forty of the casks contain spent fuel assemblies and three store sections of the reactor vessel components that NRC classified as high level radioactive waste (greater than class-C waste). Each concrete cask has a three and a half-inch steel liner surrounded by 21 inches of reinforced concrete. Each storage cask, when loaded with the canister containing the spent fuel, weighs 126 tons. Connecticut Yankee began transferring the fuel from the spent fuel pool to the site in 2004 and the transfer was completed in March 2005. Further information about spent fuel storage at the site is available at http://www.connyankee.com/. NRC periodically inspects the design, fabrication, and use of dry casks, to ensure licensees and vendors are performing activities in accordance with radiation safety and security requirements, and licensing and quality assurance program commitments.


Millstone Unit 1 began commercial operation in December 1970. It ceased operating in July 1998 and is being decommissioned. Currently all of the spent fuel from the unit is being stored on-site in a spent fuel pool located in the plant's containment structure. The steel-lined pool is filled with water, and the fuel assemblies are lowered into storage racks in the pools. The racks, along with neutron-absorbing materials in the water, serve to prevent the fission process from restarting. The water also cools the fuel.

Unit 2 began commercial operation in December 1975 and is operating. When the plant was built, its then owner (Northeast Utilities) anticipated that the Department of Energy facility at Yucca Mountain in Nevada would be available for the disposal of the spent fuel, as was required by federal law and designed the spent fuel pool accordingly. (Federal law required the Department of Energy to begin moving spent fuel from nuclear plants in 1998, but it has not yet begun to do so.) In 1986, Unit 2's spent fuel pool capacity was increased from 667 spent fuel assemblies to 1,346 spent fuel assemblies. Initially, the spent fuel from the unit is placed in spent fuel pools. Over time, the spent fuel becomes less radioactive. Dominion (Millstone's current owner) has moved spent fuel from The Millstone 2 plant into dry cask storage after its radioactivity has decreased.

The fuel is placed in a welded, leak-tight, dry-shielded steel canister that is capable of holding 32 fuel assemblies. Once filled, the lid on the canister is seal-welded in placed to ensure the radioactive material is permanently isolated from the environment. The canisters, which weigh more than 40 tons fully loaded, are then inserted into a hollow cylindrical sleeve in the center of a Horizontal Storage Module (HSM). These modules are steel-reinforced concrete bunkers that are approximately 20 feet high, 10 feet wide and 20 feet deep, with walls and roof up to 5 feet thick. The modules are located within the protected area at the Millstone plant.

Unit 3 began operating in April 1986 and is currently operating. Spent fuel from the plant is stored in a spent fuel pool on site. The pool at Unit 3 is larger than that at Unit 2, and in 2000, its capacity was increased from 756 spent fuel assemblies to 1,779 spent fuel assemblies. Dominion anticipates that it will be able to store the spent fuel produced at the unit there until 2025.

Further information about spent fuel pools and dry cask storage is available at an NRC website, http://www.nrc.gov/waste/spent-fuel-storage.html. Another NRC website, http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/dry-cask-storage.html, provides additional information on dry cask storage.

KM: ek