Radiation Barrier Research Articles

THE EFFECT OF RADIATION SHIELDS ON OPERATOR EXPOSURE DURING CONGENITAL CARDIAC CATHETERISATION.

Cardiac catheterisation personnel are exposed to occupational radiation and its health risks. Little data exist regarding the efficacy of radiation-protective equipment from congenital catheterisation laboratories (CLs). The authors retrospectively reviewed data in which CL operators wore a radiation dosemeter during catheterizations on patients of >20 kg. A leaded under-table skirt was present in all cases. Three additional radiation-protective devices were utilised at operator discretion: a top extension to the under-table skirt, a ceiling-mounted shield and a disposable patient drape. Case details, operator position, fluoroscopy time, incident air KERMA in the patient plane (K, mGy) and dose-area product (DAP, µGy·m2) were recorded. A total of 136 catheterizations over 8 months were included. Median operator dose (OpD) was 12 µSv (range 0-930) and indexed to K and DAP to correct for patient factors and case times. Indexed OpD decreased significantly with each additional shield used (14.8 vs. 1.3 nSv µGy-1 m-2 and 124 vs. 14 nSv mGy-1 with one and four shields, respectively, p < 0.001). This trend was not significant with operator at head-of-bed. Combinations that included the ceiling shield had the lowest indexed OpD. The patient drape did not further reduce OpD when all other shields were used (1.3 vs. 2.2 nSv µGy-1 m-2, p = 0.5; 14 vs. 17 nSv mGy-1, p = 0.4) and was associated with higher patient exposure indexed to weight and fluoroscopy time (4.5 vs. 3.1 µGy m2 kg-min-1, p = 0.009; and 0.51 vs. 0.38 mGy kg-min-1, p = 0.01). Supplemental radiation barriers can decrease operator-absorbed radiation. A ceiling-mounted shield may provide greatest benefit. The authors do not recommend routine use of disposable patient drapes.

Fast reactors and nuclear nonproliferation problem

The growing number of countries wishing to use nuclear energy, and the expansion in the geography of NPPs entails the risk of nuclear weapons proliferation, given that political leaders in some countries may want to purchase or develop sensitive nuclear technologies. A certain risk of proliferation through nuclear power technologies and materials cannot be excluded altogether. In the nuclear fuel cycle there are large inventories of nuclear materials, including fissile materials, (many hundreds and thousands of tons). The problem of spent nuclear fuel with plutonium in it, especially for novice countries and countries with small nuclear power program, also increases the risk of proliferation, including the growing risk of actions on the part of subnational or terrorist organizations because of the proliferation of nuclear technologies and materials as respective protection measures are insufficient in these countries.In the event of thermal reactors, uranium enrichment is indispensable to production of fuel. Long-term storage of SNF from thermal reactors in an open fuel cycle, which is a common practice nowadays, entails an increased risk of proliferation due to the weakening of the radiation barrier over time and the potentiality of unauthorized removal of fuel by the proliferator state and its theft by criminals and terrorists.Fast-neutron reactors started up and operating on plutonium fuel do not require uranium enrichment. There is no long-term storage of SNF in the closed fuel cycles of fast reactors. Gradual replacement of thermal reactors by fast reactors, due to natural uranium being in short supply, creates prerequisites for phasing out uranium enrichment. However, countries having small nuclear power programs and, therefore, a limited number of nuclear units will use thermal reactors still for a long time, which will require uranium enrichment.Creation of nuclear weapons based on energy-grade plutonium using a simpler “gun-type” design is practically impossible because of a high neutron background inherent in this kind of plutonium. However, this does not exclude the potentiality of terrorist attempts to fabricate a primitive nuclear explosive device.Both sensitive technologies (uranium enrichment and SNF processing with separation of plutonium) will be used to start up fast reactors on uranium fuel with the subsequent transition to plutonium fuel. In this case, plutonium with a small content of higher isotopes will be bred not only in the blanket, but also in the reactor core in much greater quantities.The paper considers various technological and institutional approaches to solving the problem of fast reactor blankets in terms of ensuring a strong proliferation resistance.

A model of multi-pass absorption of external EC radiation at initial stage of discharge in ITER

A model is developed for multi-pass absorption of external electron cyclotron radiation (ECR) in tokamaks, which is used at initial stage of discharge to overcome the impurity radiation barrier (burn-through). Model is based on a semi-analytical solution of the ECR transport problem in the case of multiple reflection of radiation from the wall of the vacuum chamber. We estimate the efficiency of absorption of injected radiation for typical values of the electron temperature and density at the initial stage of discharge in ITER.

Ceramic Photonic Glass for Broadband Omnidirectional Reflection

We report on the fabrication and properties of ceramic photonic glass, a disordered arrangement of monodisperse ceramic spheres with diameters in the range of the wavelengths of incident light. These novel materials are produced as solid thin films which can be used for a wide range of applications, such as broadband visible reflectors, thermal radiation barrier coatings, high temperature stable structural coloration, resonant random lasers and media for photonic Anderson localization. Large nearly monodisperse spheres of different sizes were obtained by methods of sol–gel chemistry. Photonic glass films with layer thickness varied in the range 7–100 μm were deposited by drop casting from suspensions in ethylene glycol. Larger particles demonstrate a larger spectral window of broadband reflection. For thermal barrier coating applications strong reflection in the wavelength range of 1–6 μm is obtained with particles close to 3 μm diameter.

Correcting radiation survey data to account for increased leakage during intensity modulated radiotherapy treatments

Intensity modulated radiotherapy (IMRT) treatments require more beam-on time and produce more linac head leakage to deliver similar doses to conventional, unmodulated, radiotherapy treatments. It is necessary to take this increased leakage into account when evaluating the results of radiation surveys around bunkers that are, or will be, used for IMRT. The recommended procedure of applying a monitor-unit based workload correction factor to secondary barrier survey measurements, to account for this increased leakage when evaluating radiation survey measurements around IMRT bunkers, can lead to potentially costly overestimation of the required barrier thickness. This study aims to provide initial guidance on the validity of reducing the value of the correction factor when applied to different radiation barriers (primary barriers, doors, maze walls, and other walls) by evaluating three different bunker designs. Radiation survey measurements of primary, scattered, and leakage radiation were obtained at each of five survey points around each of three different radiotherapy bunkers and the contribution of leakage to the total measured radiation dose at each point was evaluated. Measurements at each survey point were made with the linac gantry set to 12 equidistant positions from 0° to 330°, to assess the effects of radiation beam direction on the results. For all three bunker designs, less than 0.5% of dose measured at and alongside the primary barriers, less than 25% of the dose measured outside the bunker doors and up to 100% of the dose measured outside other secondary barriers was found to be caused by linac head leakage. Results of this study suggest that IMRT workload corrections are unnecessary, for survey measurements made at and alongside primary barriers. Use of reduced IMRT workload correction factors is recommended when evaluating survey measurements around a bunker door, provided that a subset of the measurements used in this study are repeated for the bunker in question. Reduction of the correction factor for other secondary barrier survey measurements is not recommended unless the contribution from leakage is separately evaluated.

Fundamental Study of the Potential Application of Steel Fiber Reinforced Concrete to Enhance the Impact Resistance of Nuclear Power Plant Structures

Concrete has been used as one of the major building materials for nuclear power plant (NPP) structures. While NPP structures of conventional concrete mixtures are considered to provide sufficient shielding capacities in terms of both structural containment and radiation barrier, further demands have been added to ensure and enhance the structural safety with considerations of aircraft impacts and/or earthquakes. To improve the impact resistance of the concrete itself, this paper presents the potential application of steel fibers as additives with no variation of the concrete mixture proportions that are currently used for NPP structures in Korea. Different types of steel fibers with variations of addition volumes were applied to the concrete mixtures and various kinds of mechanical properties such as strength, toughness, and fracture energy were evaluated. From the experimental results, a practical addition proportion and a type of steel fiber were chosen for the potential application to NPP structures. .

A novel complete radiation protection system eliminates physician radiation exposure and leaded aprons

Background: Occupational health hazards associated with fluoroscopic-based procedures are well known, including a high prevalence of orthopedic problems and those related to radiation exposure, particularly cancer and cataracts. This article reports the “first-in-man” clinical experience with a novel radiation protection system designed to eliminate radiation exposure to operators and thereby obviate the need for orthopedically burdensome leaded aprons. The Trinity Radiation Protection System consists of a combination of fixed shields, radiation drapes, and interconnecting flexible radiation resistant materials creating a complete radiation protection environment for the operators, yet maintaining full and unimpeded contact with the patient and total control of all operational elements of the catheterization equipment. Methods and results: This report constitutes an analysis of 19 nonrandomized cases in which operator radiation exposure data were collected (Trinity Radiation Protection System n = 10 cases versus standard shielding alone n = 9). In all cases performed with the Trinity System, there was neither any measurable significant radiation exposure in any anatomic region nor for the total case, whereas operators performing cases with standard shielding were exposed to radiation in all regions of their bodies (total per case exposure differences p < 0.0001). Conclusion: The novel radiation protection system described is the first to provide a complete radiation barrier that eliminates radiation exposure to operators, thereby obviating the need for orthopedically burdensome leaded aprons. This approach to radiation protection has promise to enhance the safety and occupational health of medical personnel in the catheterization laboratory. © 2012 Wiley Periodicals, Inc.

Study on containment safety systems for Korean fusion DEMO plant

The purpose of this study is to review the strategy for radiation barriers in the fusion power plants and to produce simulation data for the conceptual design of safety features to maintain the integrity of such barriers as a part of R&D program through the National Fusion Research Institute of Korea. Even though the amount of radioactive source term in fusion power plants should be much less than that of fission power plants, internal as well as external events can result in damage to facilities such that public can be critically exposed by radiation. In the first part of this study, we reviewed and compared the multiple defenses to protect radioactive hazard in fission and fusion power plants. Containment was characterized as an indispensable physical barrier and the integrity of containment particularly enveloping a fuel cycle which is a major radioactive source term, tritium, should be secured. Since water is assumed as one of the coolant options in the Korean fusion DEMO plant, the thermo-hydraulic analysis was carried out using computer simulations to produce key parameters related with the integrity of containment in the second part. The performance of both of active and passive safety features to control the key parameters was compared to take recent fission technologies into account.

PSI effects on plasma burn-through in JET

Plasma Surface Interaction (PSI) effects on plasma burn-through are compared for the carbon wall and the ITER-Like Wall (ILW) at JET. For the carbon wall, the radiation barrier and C2+ influx have a significant linear correlation whereas the radiation barrier in the ILW does not have such a linear correlation with Be1+ influx. The JET data are explained by the simulation results of the DYON code. The radiation barrier in the carbon wall JET is dominated by the carbon radiation, but the radiation barrier in the ILW is mainly from the deuterium radiation rather than the beryllium radiation.

МОДЕЛЬ МНОГОПРОХОДНОГО ПОГЛОЩЕНИЯ ВНЕШНЕГО ЭЦ-ИЗЛУЧЕНИЯ НА НАЧАЛЬНОЙ СТАДИИ РАЗРЯДА В ИТЭР

A model is developed for multi-pass absorption of external electron cyclotron radiation (ECR) in tokamaks, which is used at initial stage of discharge to overcome the impurity radiation barrier (burn-through). Model is based on a semi-analytical solution of the ECR transport problem in the case of multiple reflection of radiation from the wall of the vacuum chamber. We estimate the efficiency of absorption of injected radiation for typical values of the electron temperature and density at the initial stage of discharge in ITER.

A novel complete radiation protection system eliminates physician radiation exposure and leaded aprons

Occupational health hazards associated with fluoroscopic-based procedures are well known, including a high prevalence of orthopedic problems, and those related to radiation exposure, particularly cancer and cataracts. This article reports the "first-in-man" clinical experience with a novel radiation protection system designed to eliminate radiation exposure to operators and thereby obviate the need for orthopedically burdensome leaded aprons. The Trinity Radiation Protection System consists of a combination of fixed shields, radiation drapes, and interconnecting flexible radiation resistant materials creating a complete radiation protection environment for the operators, yet maintaining full and unimpeded contact with the patient and total control of all operational elements of the catheterization equipment. This report constitutes an analysis of 19 nonrandomized cases in which operator radiation exposure data were collected (Trinity Radiation Protection System n = 10 cases versus standard shielding alone n = 9). In all cases performed with the Trinity System, there was neither any measurable significant radiation exposure in any anatomic region nor for the total case, whereas operators performing cases with standard shielding were exposed to radiation in all regions of their bodies (total per case exposure differences P < 0.0001). The novel radiation protection system described is the first to provide a complete radiation barrier that eliminates radiation exposure to operators, thereby obviating the need for orthopedically burdensome leaded aprons. This approach to radiation protection has promise to enhance the safety and occupational health of medical personnel in the catheterization laboratory.

Intraoperative radiotherapy in previously augmented patients with early-stage breast cancer.

186 Background: Breast conservation therapy (BCT) is the preferred treatment for early stage breast cancer (ESBC), providing equivalent survival to mastectomy with improved quality of life (QOL). Nevertheless, previously augmented women (PAW) with ESBC are often denied access to BCT due to potential complications arising from capsular contracture from exposure to whole breast radiation therapy (WBRT). Instead of BCT, PAW are commonly advised to undergo total, skin-sparing, or nipple-sparing mastectomy with or without breast reconstruction to eliminate the need for WBRT. These more extensive procedures alter the form and function of the breast, increase the risk of perioperative morbidity, prolong postoperative recovery, and add incremental costs. Intraoperative radiotherapy (IORT) emerged as a strategy for delivering breast radiotherapy that preserves the option of BCT in PAW with ESBC. IORT confines the effects of radiotherapy to the quadrant of the breast and to the portion of the prosthesis in proximity to the cancer. Since IORT is administered at the time of BCT, it permits insertion of a radiation barrier to further shield the prosthesis from effects of radiotherapy. Methods: We present several examples of PAW who underwent BCT combined with IORT for the treatment of ESBC. Results: Four women with an average age of 51.8 years (range: 47-57) were treated with BCT and IORT for ESBC using the Intrabeam System (Carl Zeiss-Meditec, Inc., Oberkochen, GE). All women had either saline (SA), silicone (SI), or combination retropectoral implants (RP). All pathological margins were clear and IORT was administered without complications. Average follow-up was 26 months (range: 1-72 months). None experienced a recurrence and breast cosmesis was acceptable in all women. Conclusions: IORT preserves the option of BCT in PAW by reducing the impact of radiotherapy on the breast. This radiotherapy approach eliminates the physical burden, impact on QOL, and cost of more extensive breast procedures. Consequently, IORT should be considered a preferred treatment for PAW facing a diagnosis of ESBC. [Table: see text]

Starch films from a novel (Pachyrhizus ahipa) and conventional sources: Development and characterization

Biodegradable films from ahipa, cassava and corn native starches were developed by casting method and their physicochemical, mechanical and barrier properties were analyzed taking into account the different starch botanical sources. Filmogenic suspensions were prepared; their rheological behaviors were studied and all of them exhibited film-forming ability. However, mechanical assays demonstrated that unplasticized films were too rigid, limiting their technological applications. Thus, 1.5% w/w of glycerol as plasticizer was added to filmogenic suspensions and film flexibility and extensibility were improved, this effect was more significant for ahipa and cassava starch films. Furthermore, thickness, moisture content and water solubility of the developed films were increased when plasticizer was incorporated. Glycerol addition reduced film water vapor permeability and the lowest reduction corresponded to cassava starch films due to the high viscosity of its filmogenic suspensions. Plasticized starch films resulted to be UV radiation barriers; ahipa starch films had the lowest light absorption capacity and higher transparency than cassava and corn starch films. Dynamic-mechanical analysis indicated that plasticized films were partially miscible systems exhibiting two relaxations, one attributed to the starch-rich phase and the other to the glycerol-rich one. Likewise, it could be demonstrated that glycerol exerted a major plasticizing effect on ahipa starch matrixes.

The Effect of Inorganic Nanoadditives on the Thermal, Mechanical and UV Radiation Barrier Properties of Polypropylene Fibres

The objective of this study of modified polypropylene (PP) fibres using nanoadditives (nano-CaCO3 and Cloisite 30B) was to determine the influence of these additives on thermal and mechanical properties, but especially on the barrier properties of the nanocomposite fibres against UV radiation. The DSC data obtained from measurements of PP/CaCO3 or PP/C30B nanocomposite fibres were used for determination of the constants n and K of the Avrami equation and in the estimation of other thermal properties of the fibres, such as their crystallization half-time t1/2, rate of crystallization t1/2, the necessary time for maximum crystallization tmax and free energy per unit area of surface in the lamella perpen-dicular to the axis of a high-molecular chain se. The nano-CaCO3 or Closite 30B fillers (pre-treated separately in three different solvents: glycerine, acetone and water) did not influence the melting temperatures but caused an increase in PP crystallization temperatures in comparison with the pure PP fibres. The pre-treatments of nanoadditives resulted in increase of n, K, t1/2 values and decrease of t1/2, tmax as well as the values of free surface energies per unit area of the modified PP fibres. There was also observed a decrease in the mechanical properties, however, there was an increase of barrier properties against UV radiation of nanocomposite PP fibres in comparison with neat PP fibres, which was one of the main objectives of the study.

Improvement of evaluation methodology of plutonium for intrinsic feature of proliferation resistance based on its isotopic barrier

The present paper is prepared for the peaceful use of the nuclear energy. It is important to develop the methodology to evaluate the proliferation resistance of nuclear energy systems, and the concept of evaluation function “ Attractiveness (ATTR)” has been proposed as a new evaluation function for one of the intrinsic features of proliferation resistance, fissile material characteristics based on its isotopic barriers. In the present paper, the improvement of the function ATTR to evaluate plutonium is examined and performed. The terms of the characteristics of potential explosive energy and the technical difficulty for fission explosive device use in the evaluation function ATTR are both improved to refer their physical nature. The effect of compression on Rossi-alpha is introduced to improve the term of the characteristics of potential explosive energy. A relation between Rossi-alpha and potential explosive energy is also studied theoretically for the improvement of the evaluation function ATTR. Radiation barrier of plutonium is also introduced as a new technical difficulty factor. The improved evaluation function ATTR is applied for the categorizations of plutonium produced in typical reactors.

Analysis of a nano-porous multi-layer film for thermal radiation barrier coatings

A highly reflective thermal radiation barrier coating (TRBC) made of a multi-layer film is studied for high temperature applications. The multi-layer film with a periodic microstructure consisting of cylindrical nano- pores acts a photonic band gap (PBG) crystal. The coating is constructed such that pores are arranged periodically along the in-plane directions and axes of the pores are parallel to the thickness direction. The pore diameter is varied periodically through the thickness to form a multi- layer film of alternating low and high porosities. The pri- mary motivation behind considering this microstructure is that it can be fabricated from aluminum dioxide, which remains stable at high temperatures. The reflectivity of a single layer with uniform porosity is computed by numerically solving Maxwell's equations, by considering both the microstructure explicitly and a homogenized layer to gain insights into the effect of pore size on the reflec- tivity of the nano-porous layer. Based on the study of the single layer, two microstructures with different arrange- ments of pores are designed to exploit the effect of microstructure to widen the band gap of the PBG crystal and to increase the reflectivity of the TRBC. Results of numerical simulations reveal that a wider band gap and higher reflectivity can be achieved by making the inter- pore distance of alternate layers of the multi-layer film comparable to the wavelength of the incident thermal radiation. A TRBC, which is made of a microstructure with a wider band gap and has increased reflectivity, will reflect a greater amount of incident heat energy over a wider range of frequencies.

Reduction of low-Z impurities during plasma start-up

Reduction of low-Z impurities is essential during the plasma start-up in tokamaks. For plasma start-up using the method of Coaxial Helicity Injection (CHI) it has been found that conventional wall conditioning methods have been inadequate to generate a plasma with acceptably low levels of low-Z impurities. NSTX has now used a new combination of techniques to improve CHI start-up performance. These are the use of high-current discharge cleaning of the lower divertor surfaces, which function as the CHI electrodes, to remove loosely bound impurities, controlling the poloidal magnetic field to avoid plasma wall contact and the use of evaporated lithium coatings of the electrodes and other plasma-facing surfaces. Together, these techniques have enabled significant improvement in NSTX CHI performance leading to a saving of central solenoid flux and the first observation of electron temperatures during CHI exceeding the oxygen radiation barrier temperature.

Effect of secondary processes on material hardening under low temperature radiation

Evolution of radiation barrier (vacancies and interstitials) clusters is analyzed under low temperature radiation in the presence of the most important secondary effects: recombination and formation of divacancy complexes. It is proposed a barrier hardening model in that mechanisms of mutual annihilation of the vacancy and interstitial barriers and their clusterization play a main role. It is taken into account reducing barrier densities due to barrier mutual annihilation of two different types and developing the large clusters by interconnection of two barriers of the same type.

ECR heating power modulation as a means to ease the overcoming of the radiation barrier in fusion devices

A method is proposed to ease the overcoming of the impurity radiation barrier during current drive in tokamaks, as well as in alternative fusion and plasmochemical systems with ECR plasma heating. The method is based on the fact that the dependence of the ionization rate on the electron temperature is strongly nonlinear and the dependence of the recombination rate on the latter is weaker. The result is that, during temperature oscillations, the effective temperature for ionization-recombination processes is higher than that in a steady state, so the ionization equilibrium is shifted and strongly emitting ions are stripped more rapidly. Thereby, ECR plasma heating in the initial discharge stage can be made more efficient by modulating the heating power at a low frequency. The evolution of the electron temperature in a homogeneous hydrogen plasma with a carbon impurity and in small ISX-scale tokamaks is simulated numerically, as well as the evolution of the electron and ion temperatures and of the current during discharge startup in the ITER device. Numerical simulations of the effect of modulation of the ECR heating power on the rate of heating of nitrogen, oxygen, and argon plasmas were also carried out. The assumption of coronal equilibrium is not used. It is shown that the low-frequency modulation of the heating power can substantially ease the overcoming of the radiation barrier.

Lead attenuation characteristics models

Lead attenuation characteristic curves are often consulted in premises radiation shielding assessments employing the non-destructive testing (NDT) method. This study developed lead attenuation characteristics mathematical models for the radionuclide Co-57. These models take into account the statistical variation of the attenuation characteristics. The results are a set of equations that a NDT assessor can use to predict the range of transmission factors for the NDT measurement or, using the inverse functions, to gauge the lead equivalence (with the associated uncertainty) of a radiation barrier. This study showed that the combined effect of types of statistical variations can form an uncertainty region on the transmission characteristics such that the relative uncertainty decreases for values of lead mass per unit area up to approximately 20 kg/m2 and 15 kg/m2 for the Ludlum 18 and Ludlum 2241-2 survey meters respectively but thereafter increases.