Decommissioning and dismantlement of the Stade nuclear power ...

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24 Plant dismantlement: waste material categories Based on its experience of past decommissioning projects and its intimate knowledge of the Stade facility, E.ON Kernkraft GmbH is able to estimate with considerable accuracy the volume and percentages of materials that will be allocated to each clearance category, as shown in the chart below. Materials categories: percentages and volumes Area in Mg (megagrams) Clearance (restricted and unrestricted) 272,100 Mg Non-nuclear area 127,540 Mg Nuclear area Controlled re-use Detailed view: Nuclear area Radioactive waste 97,2 % Safety clearance 0,4 % Controlled re-use 2,4 % Radioactive waste Nuclear area 124,005 (97.2 %) 545 (0.4 %) 2,990 (2.4 %) 127,540 (100 %) Non-nuclear area 272,100 - - 272,100 Total 396,105 545 2,990 399,640 Total
Mechanical breakdown of materials During the dismantlement process large plant components need to be cut up into smaller sections. Conventional tools such as large blade saws, hydraulic shears, cutting torches, and metal shredders are used for this purpose. Slow-running machinery is employed wherever possible to prevent the creation of aerosols. The tools and equipment are set up in the necessary configuration in the areas designated for dismantling/cutting, decontamination, and waste treatment. Minimizing the decommissioning personnel’s exposure to radiation is the paramount criterion for selecting which tools and methods to use. The work processes are also designed to prevent the buildup of dust and grime. Certain processes are even performed in sealed areas with their own, separate air handling systems or in containers. In these areas, the air is extracted and filtered, thereby preventing the spread of radioactivity within the plant and protecting the environment from radioactive emissions. Wherever possible, the plant components are broken down into pieces small enough to fit into special containers, which are then transported to further treatment stations. After disassembly and cutting, each item is thoroughly cleaned. Extremely sensitive measuring instruments are then used to determine each item’s level of radioactivity or surface contamination. Depending on the outcome of these measurements, each item is either submitted for final clearance testing or is first decontaminated and then submitted for final clearance testing. Decontamination In most cases, radioactivity is confined to mere surface contamination. When the Stade plant was built, many of the components used were coated with a special sealant designed to facilitate decontamination. These types of components can in most cases be completely decontaminated by thorough washing or abrasion. Where contamination has penetrated deep into the material via cracks and pores it is removed by mechanical or chemical means. The following decontamination methods are used: _ steel grit blasting, _ water blasting, and _ chemical flushing. Dry steel grit blasting is a highly effective decontamination method for disassembled and cut-up components with readily accessible surfaces. It involves grinding the surface off the components by bombarding them with a jet of pin-head-sized steel grains traveling at nearly the speed of sound. Chemical flushing, on the other hand, is used for decontaminating whole systems and assemblies prior to disassembly. The final decontamination step is a simple matter of isolating the contaminated particles from the steel grit or chemical solution. Decontamination keeps the volume of secondary radioactive waste to an absolute minimum and significantly reduces the amount of radiation to which the plant’s personnel are exposed during subsequent dismantling work. The decontamination methods used are specially tailored to the method of disposal. 25
Page 1: Decommissioning and dismantlement o
Page 5 and 6: The Stade nuclear power station - a
Page 7 and 8: Why is the Stade plant being decomm
Page 9 and 10: Dismantlement methods Germany’s n
Page 11 and 12: Decommissioned and dismantled nucle
Page 13 and 14: The Stade nuclear power station: sp
Page 15 and 16: Most plant components and systems t
Page 17 and 18: Dismantlement Phase II 1 Steam gene
Page 19 and 20: Dismantlement Phase IV 1 Polar cran
Page 21 and 22: Timeframe When the Stade nuclear po
Page 23 and 24: Different workforce structures requ
Page 25: Disposal methods There are a range
Page 29 and 30: Radioactive waste E.ON Kernkraft pl
Page 31 and 32: Green fields In Germany two nuclear
Page 33 and 34: The permit process Permit applicati
Page 35 and 36: Publisher E.ON Kernkraft GmbH Corpo

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