Spent fuel | Radwaste management
Russia’s dry store24 August 2010
A facility currently under construction near Krasnoyarsk, Siberia will accept spent fuel currently stored under water from RBMK, VVER and plutonium research reactors, and store it in dry, air-cooled conditions for 50 years.
Russia currently has 10 operating nuclear power stations, which generate about 15% of Russian electricity output. They consist of 1000MW water-cooled VVER-1000 reactors at Balakovo, Kalinin, Novovoronezh and Rostov NPPs, and 1000MW light-water cooled, graphite-moderated RBMK-1000 reactors at the Leningrad, Kursk and Smolensk NPPs. The VVER-1000 consists of more than 162 nuclear fuel assemblies, and the RBMK-1000 has 1700 assemblies. After three to four years of operation these assemblies are extracted from the reactor and transferred to temporary storage in fuel ponds on site. After a period of between 10-20 years, depending on the type of fuel assembly, their energy has reduced by 10-15 times, so they may be transferred to dry storage, where they are cooled by air.
Since 1985 an 8600 t capacity spent fuel pond has operated on the site of the three Gornochimicheski Combinat plutonium production reactors in the former Soviet secret city of Krasnoyarsk. Since then, Russian nuclear specialists have accumulated extensive experience of its operation. But something will soon need to be done. The Krasnoyarsk pond still holds fuel elements that were extracted from reactors between 15-20 years ago. And spent fuel ponds in a number of Russian nuclear power plants, such as Leningrad and Kursk, are nearly full up.
This problem could be resolved in two ways; either to construct new fuel ponds at nuclear power plants—which will soon also fill up—or to construct a centralized storage facility next to a plant that will reprocess spent nuclear fuel in the future. In the long term, a geological repository for nuclear waste is also planned. For these reasons, it was decided to construct a dry storage facility at the Zheleznogorsk Mining and Chemical Plant on the eastern shore of the Yenisei River in Zheleznogorsk, 60km from Krasnoyarsk.
Development work on the construction project began in the early 2000s. St. Petersburg-based design and research institute VNIPIET drafted a project according to which an interim fuel store would need to hold 30,000t of waste; 20,500t of RMBK-1000 fuel, and 9,500t of VVER-1000 fuel. Construction of the facility began in 2003 by the main contractor of the mining and chemical reactors, Sibhimstroy. But for a number of reasons, including construction delays, the project was not completed.
As a result, the Russian government retendered for the job, and in August 2008,E4 Group won the contract to be general contractor of the facility. Subsidiaries of the privately-held E4 Group have designed or helped commission 20 reactors; five subsidiary companies are located at Kursk, Smolensk and Novovoronezh NPP, and the company is also participating in the Chernobyl safe confinement project.
The tight schedule of construction and assembly works calls for the first stage of construction to be finished by mid-2010, and work completed by 2015, according to the project documents. The first stage of the store would begin operation in 2011.
The scope of works includes an unprecedented amount of work for the general contractor, including construction management of the building and guardhouse, bomb shelters and towers, construction of roads and drives, including an asphalted road more than 18km long. The contract also includes dismantling of an existing precast concrete building no. 3, which includes dismantling of 5700m3 of precast reinforced M400 concrete with a 30,000m3 stainless steel-lined pool. Demolition of another, larger building no. 2 will involve dismantling of precast and monolithic concrete on the order of 30,000- 40,000m3 each. Performing this work requires hundreds of skilled employees,specialized machinery and equipment. Today the Group E4 workforce on site involves more than 1500 workers.
The new building will consist of two bays with overall dimensions of 249.5 m x 51 m. The intermediate storage facility will be divided into three main zones. Zone I will be a remotely-operated storage area where the processing equipment, and the main sources of radiation and radioactive contamination are kept. Zone II is the regularly-serviced premises for the repair of equipment and other work related to opening contaminated processing equipment. Zone III will be working premises for staff.
The administrative building block will adjoin the spent nuclear fuel reception area, which will unload containers that come into the building via rail. The building will be linked to the railway, on which the spent fuel will be delivered directly into the repository. A section of the spent fuel storage facility is a hall that spans 33 m with a length of 42 m, equipped with a bridge crane. This area will handle the main process of receiving spent fuel and transferring it to storage in the bowels of spent fuel store.
Spent fuel will be repacked at its current location into dry transport/storage containers according to specific procedures. One package holds 32 fuel assemblies; two packages will be stored in a single cluster in the repository.
Given the specificity of the design and the presence of hundreds of tons of nuclear fuel, a particularly acute issue is environmental safety. But the complex in Zheleznogorsk will be one of the most advanced and modern in the world. Cutting- edge engineering solutions, protective mechanisms, automated control systems and sensors detecting any deviations from standard indicators all guarantee the safety and durability of the spent fuel, and will prevent any negative impact on the environment and residents, E4 said.
The use of dry nuclear fuel storage technology has several advantages compared with wet storage technology. For example, dry storage improves the conditions of the spent fuel. Unlike wet storage, which requires a special pool, dry storage casks are more reliable; they are designed to withstand impacts and the temperature change between outdoors and internal heating. Moreover, the E4 group is designing systems to prevent explosion and fires, as well as waterproofing that eliminates leakage from the storage facility, and its possible spread in the environment or the atmosphere.
The comprehensive radiation prevention system at Zheleznogorsk deserves special attention. Structures in hazard areas being erected by E4, are made from monolithic concrete with a stainless steel cladding. Steel structures are made from stainless steel, and designed to enable decontamination. Premises, depending on destination, have pressure-seal doors and radio-protective doors, specifically designed gateways. Many processes are fully automated, to reduce the risk of human error.
Because the spent fuel storage building is made completely from reinforced concrete, large-panel shuttering from German supplier DOKA was used, as well as DOKA scaffolds. For the monolithic girder coating, the contractor used the systems Statiko Szn and Formas A180, mounted on mobile platforms. The painting and decorating contractor intends to apply fireproof materials, which can also reduce the activity of nuclear fuel.
Modern equipment and automation systems are all very nice, but what about the people who live near the facility? Will the spent fuel store affect them? The E4 Group answers this question unambiguously. “Even at full load, the store will not affect the health of the inhabitants of the region. This complex will be the most reliable and most secure place to store spent nuclear fuel. In construction we use the most advanced engineering solutions and advanced safety systems,” said Danil Nikitin, general director of E4 Group.
Estimated surface concentrations and radiation doses from radioactive aerosol emissions from the dry storage cells in normal operation and during design-basis accidents would not exceed allowable dose limits for radiation workers and the public, E4 said. To monitor the effect of dry storage of spent nuclear fuel on the environment and the population, the store will have a modern system of continuous monitoring of emissions of radioactive and hazardous chemicals.
E4 Group is confident that dry storage cells fully satisfy the requirements of Russian federal rules and regulations, and will not adversely impact on the staff, population and environment.
With further development of nuclear energy, the need for modern, safe and environmentally-friendly complexes such as the spent fuel store in Zheleznogorsk will multiply. Ensuring its satisfactory performance and safety could greatly contribute towards the further development of nuclear energy in Russia.