Fusion reactors : Radiation hazards and risk

Power exhaust is a crucial issue for future fusion reactors. Divertor detachment and the required power dissipation fractions of about 95% are foreseen to be achieved by impurity seeding. In a tokamak, at high seeding levels the radiation often concentrates in a small region inside the confined plasma near the X-point. In early observations the so-called X-point radiator (XPR) often led to back-transitions to L-mode or disruptions. In metal tokamaks or with higher available heating power, these regimes can be stabilized and are now established on AUG, JET, TCV, KSTAR and WEST. The XPR is a cold, dense plasma inside the confined region in the vicinity of the X-point, that breaks the paradigm of poloidal symmetry of density and temperature on closed flux surfaces. On AUG, the poloidal extent of the XPR is a few centimeters and it is observed up to 15 c m above the X-point. The long connection length in this region and the access of neutral particles from the divertor region facilitate the creation of the XPR, as predicted by an analytical model. Numerical simulations with SOLPS-ITER match the observations at AUG and TCV and allow predictions towards a power plant, where a lower impurity concentration is required to trigger an XPR. Since the XPR greatly reduces power and particle fluxes to the targets, simpler and more efficient divertor concepts, such as the compact radiative divertor, can be envisaged for future devices. A scenario with an XPR, however, comes at the cost of an increased impurity concentration and a potential reduction in confinement, which has to be further quantified. The XPR location can be well detected by various diagnostics, enabling responsive real-time control, even through large transients like an LH transition. The active control helped to access a new regime of ELM suppression at AUG, which is now also observed at TCV and JET. The observation of the XPR on multiple tokamaks, the demonstration of its active control, and the emergence of theoretical models that scale favourably towards fusion reactors have opened up a new phase of advanced power exhaust research. • X-point radiators (XPR) are observed at almost all operational tokamaks. • Earlier observations did not identify it as a stable operational regime. • In JET D–T discharges, an XPR could be created and successfully be controlled. • Future reactors would benefit from its controllable full detachment and ELM suppression. • The XPR enables detached ramp-up & -down and the novel compact radiative divertor (CRD).

Protecting Lunar Colonies From Space Radiation

With current designs of future fusion power plants, it is evident that a significant quantity of operational radioactive waste will be produced over the lifetime of the plant. This waste will be mostly due to the replacement of in-vessel components (IVCs) on a regular basis, currently assumed to be every five years. This potentially large quantity of waste raises issues about its ultimate disposal, particularly the nature of the disposal facility required to accommodate it. The term invessel component includes the divertor and the breeding blanket, the “fuel” in a fusion reactor. In this perspective only, the waste resulting from IVC replacement is analogous to the fuel waste arising from fission power plants, and this comparison, whether justified, or not, could prejudice the fusion waste disposal solution. As fusion in-vessel component waste is significantly and fundamentally different from fission reactor fuel waste, it is essential that the fusion disposal solution be based solely on its needs. To highlight this fundamental difference between the fusion and fission operational waste, a radio toxicity index has been defined, which may prove to be of value in defining appropriate requirements for the disposal of fusion operational waste. Uranium has been the basis of the fission power industry and it is found in nature in concentrations varying, typically, from 0.1 to 1%, and in some cases ore bodies with concentrations up to 25% have been found. Because uranium is a radioactive element, and is quite common in the earth’s crust, it offers an opportunity to be used as a benchmark for comparing potential fusion and fission power reactor radioactive waste. As U-238 is the most abundant isotope of uranium found in nature (>99%), it is proposed that the radio toxicity of U-238 be used to assess the relative radio toxicity of relevant fusion and fission waste. The ratio of the radio toxicity of a given material to that of U-238 is referred to as the radio toxicity index. Therefore, a waste material with a radio toxicity index equal to one would be considered acceptable for disposal in the earth’s crust, in the same manner that uranium tailings are disposed of in the mining industry. The results of studies performed for typical fusion breeder material indicate that there is no compelling economic reason for reprocessing. Furthermore, the radio toxicity index for such materials indicates that there are no technical reasons — i.e., there does not appear to be a need for deep, geological disposal of spent fusion breeder material. On the contrary, the application of the radio toxicity index to spent fission fuel has demonstrated, from a waste disposal perspective, that there are compelling reasons for reprocessing to separate low radio toxicity fission products from the high radio toxicity actinides, which can be reused. This conclusion augurs well for a future fusion power industry and goes a significant distance in demonstrating the potential environmental advantages of fusion power.

The National Radiological Protection Board (NRPB) is an independent statutory body which was created by the 1970 Radiological Protection Act. Its responsibilities are to advance knowledge about the protection of mankind from radiation hazards and to provide information and advice to individuals and organisations in the UK with responsibilities relating to protection against radiation hazards. The NRPB coordinates and represents UK interests in radiation protection internationally; in the UK, it advises on the adoption of international standards and defines emergency criteria. It is an advisory body as opposed to a regulatory one. It conducts research, provides services to industry and makes assessments of situations involving exposure of the public both through normal operations and under accident conditions. The present paper is concerned mainly with its assessments methods.

This article presents the results of the review of scientific and technical information on the use of a risk-based approach (RBA) in providing personal protective equipment (PPE) at an enterprise. Regulatory documents, scientific works and developments of domestic and foreign scientists on the use of PPE against industrial health and safety hazards and their selection based on RBA were used as the theoretical and methodological basis for the study. Scientific works are considered in the Science Direct, Dergi Park, Web of Science (Publon), Elsiever, Google Scholar databases, on professional industry platforms on labor protection ILO, EU-OSHA, NEBOSH, IOSH. The study contains information retrieval, descriptive, experimental and effective research stages. The information retrieval stage includes the study of scientific and methodological literature, national and interstate standards. This article covers the entire range of theoretical and methodological substantiation of the use of PPE in the provision of RBA, including regulatory standards for the use of PPE, in force in the Republic of Kazakhstan in comparison with international practice.

Materials recycling aspects including contact gamma dose rates and cooling times were investigated for the first wall, blanket, and shield components of future fusion power reactors. Candidate stru...

All superconductors exhibit thermal and EM instabilities because of their poor thermal conductivity and worst electrical conductivity in their normal state. These instabilities lead to premature quench in superconducting magnets. To circumvent the problem, practical superconductors are produced in the form of fine filaments in high conductivity copper matrix. Most popular superconductor Nb-Ti had been produced this way by co-processing it with Cu and used universally up to a field of 8–9 T. To meet the stringent requirement of high \(J_{\text{c}}\) and low AC losses for accelerator and fusion reactor magnets, impressive improvements have been made in the production techniques of Nb-Ti. Conductors with fine filaments 1–5 µm diameter cladded with diffusion barriers, with low filament spacing to dia. ratio (~ 0.15), resistive matrix to reduce filament coupling and low fraction of Cu have been produced. Conductors carrying large \(J_{\text{c}}\) of 50–70 kA in Rutherford and cable-in-conduit conductor (CICC) configuration have been produced. For future accelerators and fusion reactors, high-field A-15 Nb3Sn superconductor cables with high \(J_{\text{c}}\) have been produced by bronze technique, internal tin (IT) method, improved distributed tin (DT) method, RRP and the jelly roll (JR) methods. The DT technique has yielded Nb3Sn wire with 2–3 µm filament dia. with \(J_{\text{c}}\) = 105 A/cm2 (12 T, 4.2 K) and AC loss = 300 kJ/m3 (± 3 T, 4.2 K) suitable for ITER application. JAERI has produced CICC Nb3Al cable by JR technique, which produces a field of 13 T at a current of 46 kA. NRIM, KEK and FNAL have jointly developed Nb3Al Rutherford cable (14 × 1.84 mm) using 27 strands prepared by the so-called rapid heating quench technique (JR-RHQT) for the luminosity upgradation of the LHC. V3Ga conductors too are being developed by PIT technique for the future DEMO fusion power reactor to take care of the induced radioactivity by the 14 MeV neutrons released by the D + T reaction.

future experimental power reactors. The benefits of developing radiation resistant structural materials, insulators, and tritium handling systems suitable for use in fusion reactors would be substantial and far outweigh the nominal environmental impacts associated with construction and operation of this facility. The principal environmental impacts of the proposed facility result from routine construction activities including clearing approximately six acres of land for the building, parking areas and an access road. Liquid waste discharges consist primarily of cooling tower blowdown during operations. Significantly contaminated liquid and solid waste will be disposed at the existing LASL waste disposal area. Very small quantities (less than 100 curies per year) of tritium and traces of other radioactivity will result in site boundary doses not exceeding 5 mrem per year, or less than 5 percent of applicable radiation protection guidelines and less than 5 percent of the natural radiation background from naturally occurring radioactivity. Alternatives considered included abandoning or postponing the project, selecting alternative designs, and selecting alternative locations for the facility.

The radiation hazards currently of primary concern to public health are fallout of radioiodine from testing nuclear weapons and excessive x-ray exposures performed by careless and sometimes poorly trained physicians. Because of the relatively short half life of I/sup 131/(8 days), it might be expected to be of little consequence as a public health hazard following nuclear weapons testing. However, the yield of I/sup 131/ from a nuclear weapon is sufficiently high that considerable contamination of the environment takes place, and the hazard to the general population becomes greatest when the weapon is detonated at low altitude. The ground contamination problem increases as the altitude of detonation decreases. After the USSR tests of 1961, levels of I/sup 131/ contamination rose rapidly-in a few communities to a level which, if continued over a period of several months, would cause a dose in excess of the Federal Radiation Council's (FRC) radiation protection guide of 0.5 rem. The meteorologic aspect is of interest to public health authorities because it clearly indicates the manner in which variation in the weather pattern may cause fallout to occur from time to time in quite unexpected places. As a result of later detonations, estimates indicate that inmore » some regions of the United States the radiation dose received by the thyroid glands of children may reach a level of 1.5 rem/yr, which represents the ingestion of 100,000 mu mu C of radioiodine. This amount is 3 times the quantity of radioiodine recommended by the FRC as a maximum limit. The FRC has announced that its radiation standards, applicable to the peacetime uses of radionuclides, do not apply to environmental contamination from fallout. The political implications of this decision, as well as the confusion it has introduced among public health authorities, are discussed. Reduction of the I/ sup 131/ hazard by the use of dried or stored fresh milk by infants and lactating mothers, and addition of stable iodide to the diet, are also discussed. Problems of medical overexposure to radiation are, in general, the result of the use of unsafe x-ray equipment or careless use of x-ray equipment. It is recommended that exposure dose values to such tissues as the reproductive organs be reduced to 15 mr/yr or about 15% of the exposure dose from natural background sources, as an The duties and experiences encountered during the 4-yr operation of a radiation control agency are recounted. The most important part of a comprehensive radiation control program, in terms of overall exposure of the population, is the effort to minimize the radiatlon exposure from the medical and dental use of x-rays. The fact that much of the equipment is installed in apartmert houses, other multiple dwelling structures, and office buildings means that a more critical evaluation of the structural shielding is necessary. An inspection of existing x-ray installations showed that much equipment had been installed in multiple dwellings without having the basic structural shielding considered standard practice for many years. Public health considerations relating to siting nuclear reactors in cities are discussed, particularly with respect to nuclear-powered vessels entening the harbors of large cities. The problem of safeguarding the public from hazards associated with the transportation of radioactive materials in a large city is also discussed. Dosimetry tests showed that many watches being sold with luminous dials exceeded permisnible dose rates, and many jewelry and department stores have been restrained from selling such watches. Other tests showed that, under normal use, television equipment does not emit a sufficiently hlgh dose rate of x-rays to constitute a health hazard. (BBB)« less

The presence of radionuclides and heavy metals in soil is responsible for various health hazards. This research summarizes the potential radiological risks posed by naturally occurring radionuclides and heavy metals in the soil samples of Noida and Greater Noida regions (India), using NaI (Tl) detector. The activity concentrations of 226Ra, 232Th, and 40K in the studied area ranged from 12 ± 3 to 29 ± 4Bqkg-1, 14 ± 7 to 34 ± 7Bqkg-1, and 253 ± 48 to 408 ± 61Bqkg-1, respectively, reflecting the variation in natural radioactivity across the sites. Radiological risk parameters, including radium equivalent (Raeq), absorbed dose rate (AD), and annual effective dose (AED), were estimated for the health risk assessment. The absorbed dose rates for 226Ra, 232Th, and 40K across the study locations varied from 5 to 13 nGy h-1, 9 to 21 nGy h-1, and 28 to 50 nGy h-1, respectively. The annual effective doses were estimated to be 0.14 to 0.24mSv year-1 (indoor) and 0.03 to 0.06mSv year-1 (outdoor). The mean concentrations of the analyzed trace elements in the examined areas followed the sequence: Pb (0.12mg kg-1) > Cu (0.07mg kg-1) > Cr (0.06mg kg-1) > Ni (0.04mg kg-1) > Co (0.03mg kg-1).

Background: Health hazards are associated with exposure to ionizing radiations such as x-rays. Many private x-ray diagnostic clinics in Lagos State operate with inadequate safety and protection devices, which make the conditions unsafe to patient and environment. Objective: To assess the working conditions, protection measures put in place, safety awareness and attitudes of both employees and employers to safety and protection in radiodiagnostic centers in Surulere and Ikeja Local Government Areas. Methodology: Questionnaires were used for collecting information on socio-demographic data, occupational history, activities, working conditions, knowledge and experience of radiation hazards in x-ray centers. Interviews were conducted with Heads of Departments and Radiologists using the checklist adapted from the International Atomic Energy Agency. Results: 88.9% of the participating centers had adequate space and some safety assessment performed prior to installation of the facility. 81.5% had few basic protection devices. Only 40.7% employed adequate and qualified staff while 25.9% provided personnel training and 22.2% had quality control programme. 14.8% had radiation protection programme. 60.2% of respondents were aware of health hazards associated with radiation exposures, 57.8% of which were males. Conclusion: Operation conditions in most private diagnostic centers are below standard due to grossly inadequate provision of safety and protection devices. Employment of qualified staff and continuous education need be emphasized and enforced. Keywords: x-ray exposure; radiation hazards; Safety awareness Nigerian Journal of Health and Biomedical Science Vol. 6 (1) 2007: pp. 62-72

For broad antero-posterior beams of monoenergetic (0.1-10 MeV) electrons organ doses per unit fluence were computed through Monte Carlo simulation in a reference male and female adult and a 7 year old girl. Effective doses (E) per unit fluence were calculated for the three phantoms and for an average adult. E increases from about 8x10 -14 to about 1.2 x 10 -10 Sv.cm 2 with increasing electron energy. Uncertainties were (often much) better than 6% for the adults, and 18% for the child. E as calculated for the average adult-may be used for both males and females as under- or overestimations stay within 25% from E for the average adult. The child's radiation risk is underestimated for electron energies in the range of 0.6 to 3 MeV. This underestimation up to a factor of about 20 is unacceptable for radiological protection purposes. The present results were compared with literature data on operational quantities associated with radiation hazard from weakly penetrating radiation. Neither directional nor personal dose equivalent appears to be a realistic quantity in this case. Both would yield an unnecessarily large safety factor for radiological protection.

目的 综述国内外航天辐射危害及防护剂研究的进展,提出加强防护剂研究的建议. 资料来源与选择国内外有关航天辐射剂量、生物效应的数据以及航天辐射防护剂研究的文献. 资料引用相互和独立地引用文献资料,共引用23篇参考文献. 资料综合就载人航天辐射危害、航天辐射损伤的生物学效应以及航天辐射防护剂研究发展方向等3个方面进行综合. 结论航天辐射防护剂研究应予加强。

This paper presents the design feasibility of a 1 MW, CW, 204 GHz conventional cavity gyrotron, for probable plasma heating application in future thermonuclear fusion reactors (DEMO like machines). A careful study of the mode selection process followed by the resonator design, and RF behavior studies will be presented in this paper.

This chapter begins with a brief presentation of future nuclear reactors. Next, current uses of ceramics in the nuclear industry are reviewed, which, with the exception of graphite moderators and B4C control rods, rely largely on oxides or silicates. Then, the potential for using non-oxide Ultra-High Temperature Ceramics (UHTCs) and MAX phases in future (so-called Generation IV) fission and fusion reactors is discussed.