Solid Radioactive Waste Strategy Report.pdf - UK EPR

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EPR UK N° NESH-G/2008/en/0123 REV. A PAGE 218 / 257 Shielding The TN DUO design features have been chosen to comply with the following storage and transport requirements: TABLE 42: DOSE RATES FROM THE TN DUO FLASK Activity Contact (mSv/h) 2 meters (mSv/h) Storage < 0.50 (average) < 10 (maximum) < 0.1 (maximum) Transport < 2 (maximum) < 0.1 The radial shielding has the following features: · Neutron shielding is mainly provided by a layer thick resin poured outside the secondary containment barrier, between the aluminium heat exchangers; · Gamma shielding is provided by the rolled and welded steel shells of the two containment boundaries and also by the high density resin neutron shielding; · Additional neutron shielding is provided near the hollowed plates of the handling device to reduce doses to operators. The axial shielding is assured by the following features: · The neutron shielding layer is added to the primary lid to reduce dose rates to operators during handling operations; · Gamma shielding is provided by the steel material of the two lids and the flask base. Heat dissipation The TN DUO has been designed to cater for the general trends of spent fuel in Europe: higher enrichment and heat power, higher burn-up. The heat dissipation capacities of the TN DUO flask and variations will evolve accordingly with the operators’ fuel characteristics over the life of a power plant. The basket aluminium plates build heat conducting pathways to the cavity inner surface. The cavity is backfilled with helium - a gas with a high heat conduction coefficient (10 times that of nitrogen). The hottest fuel rod cladding temperature will thus be always kept below the maximum allowed temperature in transport and storage configurations. Aluminium heat exchangers are pinned on the outer surface of the secondary containment shell to conduct decay heat to the outer surface of the flask. These heat exchangers are manufactured in wave corrugated aluminium plates to ease fabrication. The outside paint coating is specified for high thermal emissivity. Handling and operations The TN DUO has been designed to offer, as much as possible, similar handling procedures and tools as the TN 24 flask family. The TN DUO handling procedures will never prove to be an issue.
EPR UK N° NESH-G/2008/en/0123 REV. A PAGE 219 / 257 The primary lid is equipped with a single orifice allowing all the operations needed after the fuel assemblies have been loaded into the flask: draining water from the cavity, venting, drying, vacuum drying and back-filling with helium. This orifice is connected to a draining tube reaching the lowest part of the cavity. The primary lid is positioned precisely to ensure the connection of the orifice tool with the draining tube. The flask primary lid has been designed with a conical form, to reduce the risk of jamming the lid in the cavity during in-pool operations. Loadings and unloadings should be performed underwater or in a dry environment hot cell. For loadings performed in a pool, a gasket will seal the gap between the primary and secondary containment barrier. Furthermore this space between these barriers will be pressurised in order to prevent water ingress into this gap. The TN DUO incorporates an innovative handling system. Trunnions are no longer located on the flask but on a handling tool serving as interface between the flask and the lifting beam. These trunnions will be fitted to hollow cavities designed on the top and bottom of the flask, for vertical or horizontal handling and tilting operations. The validity of this solution has been verified with competent experts. FIGURE 85: THE TN DUO WITH ITS INTERFACE TOOLS AND TRUNNIONS
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Solid Radioactive Waste Strategy Report.pdf - UK EPR

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