| 简介 |
Source: Advances in Composite Materials for Medicine and Nanotechnology
Chapter 22 Composite Material for Shielding Mixed Radiation
ISBN 978-953-307-235-7
Edited by: Brahim Attaf
Publisher: InTech, April 2011
Pages:565-592
Huasi HU 1, *
1 School of Nuclear Science and Technology,Xi’an Jiaotong University (XJTU), Xi’an, 710049 Shannxi, China
ABSTRACT
Nuclear radiation shielding material is an important component of various types of nuclear facilities, and is one of the decisive factors to ensure the successful implementation of nuclear science and technology practice. At home and abroad traditional nuclear radiation shielding material is developed by determining material ratio through a large number of theoretical calculations and professional experience, then to conduct research process and create material samples, ultimately to select the approved products from the good shielding material samples by experiments. For example, the lead-borated polyethylene had been an excellent product for shielding the mixed neutron and γ-rays successively developed by the Reactor Experiments Inc. of American and the Nuclear Power Institute of China，R/X material # 202 and PB202 respectively. Although traditional method has made important contributions to the development of nuclear science and technology, but it has a long cycle of development, and a high cost of research resources, such as raw materials. What is more important, it is difficult to be expanded to nuclear radiation shielding material development of other areas. In this paper the studies on development of high performance nuclear radiation shielding materials were carried out methodologically.
A scientific and economical optimized design method of nuclear radiation shielding materials has been established innovatively; The modified craft of the epoxy resins in new types of nuclear radiation shielding materials by nano-TiO2 was studied，and the unstable temperature field and curing reaction kinetics model were established; A series of shielding material samples were made，such as the polyester sandwich (Interlayer) etc, and the correctness of optimal design method and trial-manufacture craft of shielding material has been verified by the experiments.
High performance materials optimized lightweight, compact and radiation shielding power were accomplished by genetic algorithms (GA) combined with the Monte Carlo N-Particle (MCNP) code. Firstly, through the appropriate choice of genetic algorithm parameters, the low optimize efficiency, the premature convergence, and other unfavorable factors in the genetic algorithm were to be overcome; Secondly, in the optimal design method basing on genetic algorithm the input cards automatically generating for the MCNP shielding calculation, MCNP calling, and the results feedback through the revision of the MCNP source code were realized to ensure proceeding of the optimal design controlled by the genetic algorithm; Thirdly, owing to the MCNP shielding calculation software were to be called by the genetic algorithm again and again, in order to give overall consideration of the accuracy of MCNP shielding calculation and the efficiency of optimal algorithm, a reliable and simple physical model for shielding calculation was established, the biased distribution of source was used, and the data precision control and other techniques in the genetic algorithm were enabled. By running the optimal design program, a series of optimized material samples had been obtained for mixed fission neutron and -ray shielding. They are Jxa1 and Jxa2 samples taking polyamide as curing agent, Pb6 sample taking anhydride as curing agent, Djy sample suited to powder forming with heat isostatic pressing (HIP)，and Interlayer samples also taking polyamide as curing agent without Fe, W and Pb. Deep penetrating simulation by using MCNP code further verified that the shielding performance of “Fe-Interlayer-Pb” sandwich structure Cake1 is better than the lead-borated polyethylene，and is even better than traditional optimum shield structure “Fe-CH2-Pb”，the other designed samples also have good radiation shielding performance.
New polymer nuclear radiation shielding materials in polymer evenly mixed with a lot of heavy-metal inorganic particles, so it does not belong to polymer matrix composites, or metal matrix composites, but of a polymer and metal powder mixture of the uniform. In trial-manufacture craft to overcome the precipitation phenomena of the heavy-metal inorganic particles in polymer is one of the difficulties. To solve the problem, the ways were adopted, such as to increase the polymer viscosity，reduce the curing time and so on. In forming process research of the new polymer nuclear radiation shielding materials, the characteristics of the new polymer was enhanced by adding a small quantity of nano-TiO2 particles. The parameters in the curing reaction kinetics in non-isothermally and isothermally curing process were determined according to the analysis of the differential scanning calorimeters (DSC)，then the unstable temperature field and curing reaction kinetics model were established. It was found that in the experiment the nano-TiO2 particles can effectively enhance curing heat release and reduce curing temperature, thereby reduce the curing time and increase viscosity. The glass transition temperature (Tg) of new polymer materials is also increased by nano-TiO2. The experimental results show that the glass transition temperature of the new polymer can be increased by 10K on condition that the mass content of nano-TiO2 is about 3wt% of the bisphenol A epoxy resin in the polymer, which is beneficial to enhance the toughness of new polymer shielding materials. The manufacture process flow has been established for the new polymer composite nuclear radiation shielding material basing on the trial-manufacture craft studies and sample trial-manufacture experiences.
In accordance with the optimized design results and established craft flow, a series of new polymer composite nuclear radiation shielding material samples, such as Jxa1, Jxa2, Pb6, and Interlayer etc, have been trial-manufactured. The performance appraisal of the trial-manufacture samples by experiments was carried out using tandem electrostatic accelerator neutron source (five energy points), spontaneous fission neutron source of 252Cf and γ-rays source of 60Co. By comparisons with experimental results, especially comparisons of Cake1 with “Fe-Interlayer-Pb” sandwich structure, traditional optimum shield structure “Fe-CH2-Pb” and MCNP simulation of Cake1, the shielding performance of trial-manufacture samples is the best，and is conformed to the results expected by optimal design. Thus the optimal design method of shielding materials and manufacture craft had been proved by the experiments.
The achievement in craft study in this paper has been applied to manufacturing thick pinhole used in fusion neutron penumbra imaging diagnosis supported by National Natural Science Foundation of China (10576022) and NINT Contract 200509006. A series of shielding material developed in this paper will be used in the collimating and shielding systems in nuclear diagnosis measurements, and can be popularized to the radiation shielding in fission reactors, particle accelerators and mobile nuclear facilities, etc. The optimal design method of nuclear radiation shielding materials and achievements in craft study can also be expanded to other fields, such as nuclear waste disposal, nuclear fusion engineering and aerospace engineering.
The authors would like to thank Zhiqiang WANG at the Metrology Department of the China Institute of Atomic Energy (CIAE), who provided accelerator and neutron dose monitoring. The authors also acknowledge valuable discussions with Professor Mingguang ZHENG at the Shanghai Institute of Nuclear Power Engineering, and Professor Yuangang DUAN at the Chengdu Nuclear Power Institute of China.
KEYWORDS:
Radiation shielding material；GA；MCNP code；Epoxy resin；Nano-TiO2
*This work was supported by the National Natural Science Foundation of China (Grant No.10576022,10975113), the National High Technology Research and Development Program of China (Grant No.2009AA050705), and NINT Contract 200509006.
WebPage: http://www.intechopen.com/articles/show/title/composite-material-for-shielding-mixed-radiation |
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