Safe and Secure Transport and Storage of

CHAP/£.K &

-from:

Packaging, transport, and storage of high-, intermediate-, and low-level radioactive wastes

Woodhead Publishing Series in Energy: Number 78

Safe and Secure Transport and Storage of Radioactive Materials (pp-

2 3/- 270)

Edited by

Ken B. Sorenson

15

B. Droste

BAM Federal Institute for Materials Research and Testing, Berlin, Germany

15.1 15.1.1

Radioactive waste categories General introduction to radioactive waste forms

Radioactive wastes are generated by research and medicine (e.g., the use of radioisotopes), industrial use of radioisotopes (e.g., for nondestructive materials testing), different activities related to nuclear power plant (NPP) operations (e.g., mining of uranium and thorium ores, manufacturing of fuel assemblies, operational waste generation during NPP Operation), reprocessing of spent nuclear fuel, and dismantling of nuclear installations. With respect to final disposal and potential impacts of heat onto geological formations, radioactive wastes are generally divided into the following categories: • •

Non-heat-generating or negligibly heat-generating waste Heat-generating waste

With respect to their radiological potential, wastes are divided into three other categories: • • •

Woodhead Publishing is an imprint of Elsevier 80 High Street, Sawston, Cambridge, CB22 3HJ, UK 225 Wyman Street, Waltham, MA 02451, US A Langford Lane, Kidlington, 0X5 1GB, UK Copyright © 2015 Elsevier Ltd. All rights reserved. ISBN: 978-1-78242-309-6 (print) ISBN: 978-1-78242-322-5 (online) British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Libraiy Library of Congress Control Number: 2015939628

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Low-level waste (LLW) Intermediate-level waste (ILW) High-level waste (HLW)

Low- and intermediate-level wastes (in most cases) typically are non-heatgenerating, whereas HLW is always heat generating. For that reason, associated with equivalent differences in radioactive inventory, the techniques of conditioning, pack­ aging, storage, and disposal of LLW and ELW are very much different from those for HLW. According to Newstead (Newstead, 2002), in the United Kingdom, LLW are defined as wastes containing radioactive materials other than those suitable for disposal as ordinaiy refuse but not exceeding 4 GBq/t of alpha or 12 GBq/t of beta/ gamma activity. Intermediate-level wastes are those with levels exceeding the upper boundaries for LLW, but which do not need heating to be taken into account in the design of storage and disposal facilities. High-level wastes are those in which the temperature may rise significantly as a result of their radioactivity, so this factor has to be taken into account in storage and disposal facilities.

Safe and Secure Transport and Storage of Radioactive Materials. http://dx.doi.org/10.I016/B978-l-78242-309-6.000I5-0

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Safe and Secure Transport and Storage of Radioactive Materials

Packaging, transport, and storage of high-, Intermediate-, and low-level radioactive wastes

15.1.2 Low- and intermediate-level radioactive waste forms The acceptance criteria for LLW and ILW and their packages strongly depend on national requirements resulting from decommissioning and disposal strategies. Similar to the above-mentioned UK criteria, in France for the above-ground disposal site “Centre de 1 ‘Aube,” maximum LLW activity limits for the disposal site capacity and maximum package activity concentrations, specifically attributed to relevant radioisotopes, are given in Dutzer (2002). Radioactive waste covers a wide ränge of materials. Primary waste (i.e., waste resulting from the first steps of operations) can be of the following forms: • • • • • • • •

Liquids, coneentrates, and sludges Ion exchanger resins Compressible and/or combustible materials Dimensional ly stable solids Filters and multiple tube filters Ashes, powders, and granules Metal scrap, insulating materials, debris, rubble, and contaminated soil Other waste forms.

According to the selected decommissioning strategy, various pre-treatment and conditioning techniques have to be applied to transfer the primary waste into waste forms acceptable for storage and/or disposal (Brennecke, 1995). After collection and selection, a pre-treatment is done. Principal pre-treatment methods are decontamination, crushing, compression, evaporation, distillation, rectification, decantation, dewatering, filtration, incineration, and pyrolysis. For most cases ' of storage and disposal, it is necessary to provide solid, inert, and nonreactive waste forms to prevent waste reactions and radioisotope mitigation. For combustible wastes, incineration is obligatory to reduce the volume and to transfer those into inorganic and inert waste forms; however, off-gas treatment and secondary waste must be taken into account. Figure 15.1 shows a flowchart of the incineration process as it is operated in the central decontamination department of WAK (a German pilot reprocessing plant) in Karlsruhe, Germany (Lausch and Rittmeyer, 2011). The incineration facility is constructed for solid and liquid bumable wastes with low radioactive contamination. Solid wastes are collected in foil bags or cardboard boxes, then are transferred to a fumace. Liquid wastes are collected in tanks, analyzed for activity and halogenated hydrocarbons, and transferred in batches to incineration in the afterbuming chamber. The radio­ active pollutants in the wastes end up either in ash or in the incinerator’s exhaust gas. The ash is filled into barreis and then high-pressure-compacted. The exhaust gas is fed into a multilevel cleaning System with scrubbers, absorbers, and filters. The radioactive waste treatment in such an incineration facility, followed by ash compaction, reduces the waste volume by a factor of up to 100 (Lausch and Rittmeyer, 2011). Cementation of LLW and ILW is an often-used immobilization process for solidification of liquids, as well as to embed scrap and other solid parts. Liquid inorganic wastes, such as Chemical effluents, are evaporated. The pollutants are concentrated in the evaporation residue. The evaporator coneentrates are solidified by homogeneous mixing with cement and filled into dmms. Figure 15.2 shows a flowchart of the

233

HDB incineration plant Furnace > 800 °C 850 °C 100 MPa). Figure 15.24 shows the test arrangement for one of the drop tests. Detailed Information on this test program is given in Quercetti et al.

(2010).

Figure 15.23 5-m flat bottom drop of a ductile cast iron waste Container: (a) view of the experimental test set-up (BAM TTS), (b) finite element model of the test specimen for numerical calculation (Zencker et al., 2007b).

The drop of cubically shaped waste Containers onto an unyielding or a stiff real target can cause extremely high stresses, which may be not acceptable in some cases, such as in combination with fracture mechanics considerations. This is nearly always the case for the 9-m drop test according to the transport regulations. Waste Containers requiring an approval as Type B(U) packages have to be equipped with additional impact-limiting package components. Figure 15.25 shows a cubic ductile iron Container (WACOII from Siempelkamp, Germany) encased in an overpack consisting of a welded pipe construction. In the 9-m drop (Figure 15.25(a)), this kind of impact limiter works quite well; however, in a 1-m puncture drop (Figure 15.25(b) and (c)), its

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Safe and Secure Transport and Storage of Radioactive Materials

Figure 15.25 Drop tests at B AM drop test fadlity (Lehre) with a WACOII Container, equipped with a Steel pipe impact limiter: (a) in a 9-m drop onto a comer, (b) before 1-m puncture drop test onto the lid side, (c) after 1-m puncture drop test.

protection function is limited, and most of the impact force acts onto the Container lid or walls. Other technical concepts with respect to material selection or construction features to withstand the extremely high mechanical impact are possible (Sievwright et al., 2005). The fire test for radioactive waste Containers can be another important pari of the safety case. For Type B(U) packages, a 30 min fire has to be investigated; for German Konrad repository Waste Container Class II packages, a 60 min fire has to be investi­ gated. When we had to assess that problem in a licensing procedure for a thick-walled cast iron Container (Konrad Type VI, 2.0 x 1.7 x 1.6 m, 150 mm wall thickness, net mass 10.3 mg, maximum gross weight 20 Mg), we performed a full-scale fire test with that Container filled with an inactive spherical ion exchanger resin (Bayer LEWATIT S100 KR/H free of chlorine) with a moisture content of 50%. The Container was instrumented with thermocouples in the fire, at Container suifiace points, and inside the con­ tent fixed at three Symmetrie Container axes. The 1-h fire test was performed in an open BAM fire test facility using propane bumers, providing a total heat flux of ~75 kW/m2, as estimated in a calibration fire test with a calorimeter Container before (Wieser et al., 1998). Justification for performing a fire test was to address two uncertainties that could be answered only by a fullscale experiment. The first reason was that clarification was needed on the function of the elastomeric lid seals at high temperatures and high pressure; and the second question was related to the expected overpressure by water vapor and resins decomposition gases.

Packaging, transport, and storage of high-, intermediate-, and low-level radioactive wastes

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Figure 15.26 One-hour fire test at BAM fire test facility (Lehre) with a ductile cast iron Container filled with ion exchanger resin: (a) view of the Container inside the fire, (b) fire temperatures, (c) temperatures measured inside the Container.

Figure 15.26(a) shows the Container engulfed by fire. Figure 15.26(b) shows the fire temperatures measured around the Container in 10-cm distances from the Container walls. The temperatures measured inside the Container during the fire test and 3 h of the cooling phase are shown in Figure 15.26(c). The helium leakage rate of the lid System was