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GKN-ZL Interim Storage at Neckarwestheim Nuclear Power Station

An interim storage for spent nuclear material is being set up at the Neckarwestheim nuclear power plant. The facility has a service life of 40 years and is designed to house up to 151 Castor containers in 2 caverns. The facility was set up underground on account of local conditions. The intermediate storage consists of 2 parallel caverns, which are linked by a cross-passage. The cross-passage is divided horizontally and serves as an escapeway and for ventilation. Upslope there are 2 shafts, which house the escape structure and the exhaust air chimney. The entrance building at the front mainly serves to transfer Castor containers on to transport vehicles. Both caverns are located in Upper Shell Limestone, which is covered by quaternary Neckar gravels and loam soils. The excavation is being carried out conventionally using excavators and picks. The crown for the cavern located towards the north linking up with the construction shaft as well as the first 50 m of the southern cavern was driven as a full-face excavation. The crown drive with a 140 m² cross-section was undertaken protected by extensive advance supporting measures: a fan-shaped expanded pipe umbrella and GfK bundled bolts secure the face in soft ground. Immediate supporting was undertaken using steel fibre shotcrete. HEB 240 girders were used as support arches. On account of the great weight of the arch - 1.9 t - an arch setting device was employed. The crown was divided into part-cross-sections in order to underpass the existing administrative building with the advance supporting concept being adhered to. Micro-piles in the crown zone, a temporary shotcrete floor in the side walls as well as a lance umbrella for the inner walls represent supplementary supporting measures. The bench with a 150 m² cross-section reappears beneath the crown abutments and runs with a constant width along the entire length of the cavern. A closely-knit SN bolt system with cross-sections varying from 40 to 63.5 mm was chosen to secure the bench walls. A redundant system is used for waterproofing. It comprises an external large-area drainage system and a bituminous seal that is point-fixed to the waterproofing surface. The umbrella seal drains in the form of dry gravel packs beneath the watertight floor. The wall sections including the crane way are divided vertically into 2 stages. In keeping with the vault, the block lengths amount to 10 m. Lattice girders support the reinforcement in the vault. In each case, four of these girders are prefabricated in the open sector together with the upslope reinforcement layer and then moved into the cavern. The formwork carriage runs along the floor so that it is suitable for completing the walls as an installation carriage for waterproofing and reinforcement in the vault. The fresh concrete loads from the 80 to 150 cm thick vault blocks are diverted via the crane way brackets. Altogether, 26,000 m³ of in situ concrete will be installed.

 

  • Country: Germany
  • Region: Baden-Württemberg
  • Tunnel utilization: Utilities
  • Type of utilization: Interim Storage for spent Fuel Elements
  • Client: EnBW Kernkraft GmbH
  • Consulting Engineer: Gähler & Partner AG, IMM Prof. Dr.-lng. B. MaidI- Dipl.-lng. R. MaidI
  • Contractor: Baresel AG Niederlassung Tunnelbau
  • Main construction method: Trenchless
  • Type of excavation: Excavator
  • Lining: Shotcrete
  • No. of tubes: 2
  • Tunnel total length: 2 x 90 m
  • Cross-section: 2 caverns each with 290 m² cross-section and 90 m long
  • Underground excavation: 60,000 m³
  • Total excavation: 30,000 m³
  • Contract Volume: approx. € 20 million (roughwork)
  • Construction start/end: November 2003 to April 2006