1,721,415 research outputs found
ITER waste management: the recycling and clearance option
No full textTo minimize the amount of radioactive waste requiring permanent disposal may strongly influence the environmental acceptability of fusion power. The waste management strategy applied here to the activated waste of ITER achieves this goal by maximizing recycling (reuse of the material) and clearance (declassification to non active waste). Limits of the surface dose rates of the waste after an interim storage of 50 years define various recycling procedures. The possibility of clearance is assessed from limits of the specific activity of the waste. These limits depend on the relative hazard of the radionuclides contained in the waste. It turns out that only a small part of ITER materials have such a radioactivity as to prevent its recycling or clearance (namely, first wall and front blanket). Most of the blanket and all the vessel may be recycled by remote handling. All the other components can be cleared or `hands-on` recycle
Advanced management concepts for fusion waste
No full textThis paper presents fusion waste management studies carried out under the long-term actions on Safety and Environment of the European Fusion Technology Programme. The fusion-specific strategy proposed here aims at reducing the permanent radioactive waste. Recycling is the solution investigated for in-vessel materials, which have high activation levels. Limits on surface dose limits define the feasibility of recycling by remote handling and by hands-on operation. The feasibility of clearance for materials having lower activation levels, is assessed with limits of the concentration of the radionuclides contained in the waste, weighting their respective potential hazard. This strategy is applied to two power reactor designs: PM-1, PM-2, representing advanced solutions or moderate progress on present technologies. It is shown that the amount of permanent radioactive waste can be reduced by recycling and clearance in both designs, but with significant advantages in the case of PM-1
Recycling and clearance of fusion activated waste
No full textThe irradiation conditions of ITER (International Thermonuclear Experimental Reactor) are taken as reference to analyze recycling (re-use of the waste material after suppression of noxious radionuclides) and clearance (declassification to non-active waste). Recycling is assessed, assuming limits for the surface dose rates of the waste. If alternative materials (reduced activation ferritic steel or Vsingle bondTi alloys) are used, the in-vessel components can be almost completely recycled. A vacuum vessel made of INCONEL and reduced activation steel can also be recycled. Clearance is assessed for the out-of-vessel components, using weighted averages of the clearance levels for single radionuclides proposed by recent IAEA studies. All the components of the outboard zones can be declassified to non-active waste after decay times from a few years to 50 y. The higher irradiation conditions of the inboard zone require the recycling of the coils and the use of reduced activation steel to allow declassification of the coil casings
Recycling and Clearance of Fusion Waste: (SEAL SUBTASK 10.1)
No full textSEAL (Safety and Environmental Assessments - Long-term), is a part of the European Fusion Technology Programme. It continues SEAFP (Safety and Environmental Assessment of Fusion Power) [4] where various designs of fusion power reactors have been analysed. Two of them, SEAFP Model 1 and 2 (SMI, SM2) are the object of this SEAL study aimed at defining a suitable management strategy for fusion activated waste. In SMI the breeder consists of Li20 and V-5Ti is the structural material of the in-vessel components. The SM2 configuration has a water cooled Pb-17Li blanket and the reduced activation ferritic steel LA12TaLC as structural material of the in-vessel components. The out of vessel components are the same in both models. The proposed waste management strategy envisages an interim storage of 50 years at the reactor site, then depending on the residual radioactivity, three options are possible: • Disposal as radioactive waste. • Recycling, i.e. reuse of the material in the nuclear industry. Both Remote Handling Recycling and Hands on Recycling are envisaged. • Clearance, i.e. the release of the materials from the regulatory contro
Criteria for defining low activation materials in fusion reactor applications
No full textCriteria are proposed for defining low-activation materials. These criteria take into account the three fundamental characteristics of the reactor which will be affected by the neutron-induced radioactivity: radioactive emissions in routine and off-normal conditions, maintenance operations after a shutdown, and finally waste management and disposal aspects. The activation of some typical candidate fusion reactor structural materials (reference steels, reduced activation steels and non-ferrous low-activation alloys) has been simulated in power reactor-relevant conditions. The compliance of the candidate materials with the proposed criteria has been examined. It turns out that only non-ferrous materials can fulfil all the proposed low-activation requirements
Nuclear fusion perspectives
No full textPhysical conditions for D-T fusion reactions in hot plasmas are reviewed, showing the difference between inertial and magnetic confinement. The principles of muon-catalized fusion are given as an example of alternative approach. The main features of the tokamak, i.e. the magnetically-confined plasma configuration which is most investigated in reactor studies are described. ITER, a 500 MW th tokamak reactor design, is an international project and represents the single step toward a DEMO, a demonstration electricity-generating fusion power station. Safety and environmental aspects of tokamak reactors, in particular their inherent safety, were investigated in the E.C. Safety and Environmental Assessment of Fusion Power-Phase 2 (SEAFP-2). Management options for tritiated -activated fusion waste are described, either with disposal in fission waste repositories, or according to other concepts. Data on fusion cost and time schedule are give
Reprocessing and clearance as ways for reducing radioactive waste from fusion reactors
No full textThe irradiated material chosen to investigate this concept is V-4Cr-4Ti, used as in-vessel structural material of PM-1, one of the three reactor models of SEAFP-2 assessments. The analysis performed deserves the following comments: in general, the modified concentrations of the parent isotopes have been assumed equal to the actual detection limits of the concerned elements. The nuclides investigated are those having the higher activities in the irradiated alloy (dominant nuclides). The contribution to the clearance index of other nuclides, present in the irradiated alloy and not yet examined should also be assessed. Even having reduced the concentrations of the impurities to the very low levels hypothesized, the ratios (A/Lc)m of some nuclides are too great. Beside K-42 and Ar-42, deriving from titanium, this happens for nuclides deriving from niobium, silver, nickel, copper, strontium. Hence the clearance index of the modified alloy is greater than the unity and clearance conditions are not achieved. Additional purification process have to be envisaged after the irradiation, with an elemental dilution of the noxious nuclides and then performing a purification process. As an example, it is found from table 2 that the sum of the ratios (A/Lc)m of Nb-93m, Nb-91 and Nb-94, nuclides deriving from a concentration of 2 x 10-2 ppm of niobium, is 7.75. An addition of 5/10 ppm of natural niobium to the molten irradiated material and a further purification of niobium to levels near to the initial one could achieve a 100-fold reduction of the ratios (A/Lc)m. 10000 t of V-4Cr4Ti, representing the total amount (maintenance + decommissioning) arising from the in vessel structures of a power reactor should be reprocessed with 100 kg of niobium, in the highly conservative hypothesis that all material is irradiated in first wall conditions. The secondary waste arising from the purification processes would not exceed a few ton which could be disposed of in an extremely safe wa
A model for intrusion dose calculations for radioactive waste disposal sites
No full textSafe management and disposal of radioactive waste is one of the main problems for nuclear energy, both for fission or fusion sources. High-level waste from nuclear reactors will have to be disposed of in deep underground repositories. The main purpose of this disposal, from the safety viewpoint, is to avoid the return of the radioactive waste into the biosphere, with possible interaction with the public. Intrusion is a way by which this could occur, that is, public inadvertent intrusion into a repository site, taking place after the site has lost its institutional control. The authors describe the assessment of a model for intrusion into a radioactive waste disposal site. An example of application to a fusion-specific repository, developed as part of the Safety and Environmental Assessment of Fusion Power (SEAFP)-2 activities, will be given, up to the evaluation of doses to the inadvertent intrude
Intrusion scenarios in fusion waste disposal sites
No full textResults of analyses on human intrusions into repositories of fusion radioactive waste are presented. The main topics are: duration of the institutional control, occurrence of intrusion, intrusion scenarios, acceptable risk limits and probabilistic data. Application to fusion waste repositories is implemented with a computational model: wells drilling is considered as the possible scenario. Doses and risks to intruder for different SEAFP-2 cases turn out to be very small. No intervention to reduce the hazard is necessar
Retroacetabular stress-shielding in THA
No full textRocco P. Pitto, Akanksha Bhargava, Salil Pandit, Jacob T. Munr
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