Small nuclear power plants based on ship-propulsion nuclear reactors

NIKIéT. Translated from Atomnaya énergiya, Vol. 77, No. 6, pp. 407–414, December, 1994.     

Fixation of radioactive chemical sludge in a matrix containing cement and additives

The radioactive chemical sludge stored in a clariflocculator (CF) at CWMF has to be fixed in cement before disposal in Near Surface Disposal Facilities (NSDF). The gross β–γ and ¹³⁷Cs content associated with the sludge were typically of the order of 10³–10⁴ Bq/g while the α content was about 10² Bq/g. The total solid content of the sludge varied in the range 3–13% by weight. Experiments were carried out to optimize the ratio of sludge to cement, study the effect of additives like vermiculite and bentonite and characterize the resulting cement blocks with respect to leaching and compressive strength. Results indicated that the blocks obtained on mixing the sludge only with cement in the ratio 1.0:1.5 by weight showed good compressive strength but poor leaching characteristics in tap water. Addition of bentonite or vermiculite (5% of weight of cement) reduced the compressive strength but improved the leaching behaviour. The effects were subdued in case of bentonite but were very significant in case of vermiculite. The effect of addition of both bentonite and vermiculite (each 5% of weight of the cement) was comparable to that of vermiculite alone and hence, addition of only vermiculite to cement was recommended in order to keep the leaching minimum.     

Study on a concrete filled structure for nuclear power plants

The feasibility of a new structural system for nuclear power plant buildings utilizing concrete filled steel structures, termed ‘SC structural system' was studied. SC wall test specimens (1/5 scale) were manufactured and compressive loading tests were carried out to determine how to prevent buckling. Also, bending shear tests were performed using H-section wall specimens to determine the shear and bending characteristics of SC walls. This paper presents an outline of the feasibility study, and the various structural properties resulting from the experiments.     

Regulation of nuclear power plants a multi objective approach

The regulation of nuclear power plant (NPP) is evolving in a direction to harmonize probabilistic safety criteria in the near future. The utilities will not only have to demonstrate that they are operating below a target risk level but also to demonstrate that the unavailability of some of the critical safety systems are below a specified level. In order to satisfy the Technical Specification and Maintenance (TS&M) requirements in a cost effective manner multi-objective optimization of TS&M requirements is of profound interest. The constrained multi-objective optimization of the TS&M requirements of a nuclear power plant (NPP) based on risk and cost gives the pareto-optimal solutions, from which the utility can pick suitable decision variables. The paper presents a multi objective genetic algorithm (GA) technique to investigate a trade-off between risk and cost both at the system and the plant level for Loss of Coolant Accident (LOCA) and Main Steam Line Break (MSLB) as initiating events in a NPP.     

Economic potential of modular reactor nuclear power plants based on the Chinese HTR-PM project

Modular reactors with improved safety features have been developed after the Three-Mile Island accident. Economics of small modular reactors compared to large light water reactors whose power output is 10 times higher is the major issue for these kind of reactors to be introduced into the market. Based on the Chinese high temperature gas-cooled reactor pebble-bed module (HTR-PM) project, this paper analyzes economical potentials of modular reactor nuclear power plants. The reactor plant equipments are divided into 6 categories such as RPV and reactor internals, other NSSS components and so on. The economic impact of these equipments is analyzed. It is found that the major difference between an HTR-PM plant and a PWR is the capital costs of the RPV and the reactor internals. The fact, however, that RPV and reactor internals costs account for only 2% of the total plant costs in PWR plants demonstrates the limited influence of this difference. On the premise of multiple NSSS modules forming a nuclear power plant with a plant capacity equivalent to a typical PWR plant, an upper value and a target value of the total plant capital costs are estimated. A comparison is made for two design proposals of the Chinese HTR-PM project. It is estimated that the specific costs of a ready-to-build 2 × 250 MW_th modular plant will be only 5% higher than the specific costs of one 458 MW_th plant. When considering the technical uncertainties of the latter, a 2 × 250 MW_th modular plant seems to be more attractive. Finally, four main points are listed for MHTGRs to achieve economic viability.     

Management of radioactive wastes from the operation of nuclear power plants

A prerequisite for the acceptance of the nuclear energy system is the effective management of the rad-wastes. Among the wastes to be considered, there are the wastes from the operation and decommissioning of nuclear power plants, as well as those from the nuclear fuel cycle. For the management of operating wastes, processes and facilities optimized in the course of several decades, are available, with which the raw solid and liquid wastes can be reduced in volume and turned into products which are physically and chemically stable and thus suitable for final disposal. The management of spent fuel can be done either by direct final disposal or reprocessing. The required interim storage facilities are ready for operation. The methods and a facility for packaging spent fuel for direct final disposal are in an advanced stage of development and construction. If fuel assemblies are to be reprocessed abroad, the wastes generated from the process must be taken back. Decommissioning wastes have technical properties which correspond essentially to the various groups of operating wastes and can thus be processed with similar methods; however since large quantities of them are generated in relatively short times, they present particular logistic problems. All waste types end up in final disposal sites to be built under the responsibility of the federal government. A final disposal site for low level wastes is in operation. In addition, two final disposal projects for accommodating higher level wastes including spent fuel for direct disposal and vitrified wastes from reprocessing, are being pursued.     

Chemical analysis of fuel crud obtained from Korean nuclear power plants

Crud samples were obtained from two different kinds of used fuels in PWRs. The constituent elements were analysed according to the shapes of crud particles by SEM and EPMA. The principal elements of octahedral crystal particles were identified as Ni and Fe, where the ratio (Fe/Ni) was approximately 2. The major element of the observed needle-like structures was determined to be Ni. In addition, Zr composed the main element of particles shaped like broken fragments sized at 10-50 μm in diameter. The round particles less than 20 μm in diameter were identified as Si-containing compounds. We also found the Zn element in a series of fuel crud samples obtained from a plant. Zn was mainly detected in the hard crud, inner layer of crud, but not on the surface of crud. It was observed that there is an inverse relationship between the Ni and Zn contents in the hard crud.     

Forced vibration tests and analyses of nuclear power plants

Methods for conservatively predicting the response of a constructed nuclear power plant to earthquake excitations are presented. This approach is based on experimental testing of the reactor plant and using test results to develop a mathematical model of the system. First, steady state forced vibration tests are conducted using structural vibrators attached to the reactor structure to determine dynamic response characteristics. Second, modal analysis applied on a digital computer is used to create a linear multiple-degree-of-freedom model that has dynamic response characteristics nearly the same as the physical system for the experimental inputs. Finally, the input force levels are extrapolated from the levels of the inertial vibrators to earthquake levels and the response of the model is calculated for strong-motion earthquakes.Tests have been conducted on three nuclear power plants: the experimental gas-cooled reactor (EGCR) at Oak Ridge, Tennessee; the Carolinas-Virginia tube reactor (CVTR) at Parr, South Carolina; and the San Onofre Nuclear Generating Station (SONGS), San Onofre, California. Analyses in varying detail have been performed; the most extensive work has been done at San Onofre. This article summarizes test results, dynamic models, and the results of seismic response calculations for each plant.     

核反应堆棒控电源电路仿真与优化

棒控电源是核电站反应堆燃料棒的驱动机构的电源,核电站内的棒控电源柜通常与驱动机构相距较远,通过电缆相连接。为了提高设备的集成度,棒控电源柜中多个直流斩波模块共用一个整流模块,这种设计大大增加了直流母线的长度。直流母线和电缆的分布电感和分布电容,会产生电压过冲、增加开关损耗、产生高频振荡,并对电源控制产生巨大干扰。通过对电源电路的分析,计算直流母线的分布电感和电缆的分布电容,建立棒控电源系统PSIM仿真模型,得到了与样机测试波形近似的仿真结果。然后提出了减小直流母线分布电感的优化方法,经理论推导和仿真验证,可有效改善高频振荡和电压过冲等问题,显著提高电路性能指标。     

Inservice measurements on piping systems and components in nuclear power plants

A special program has been developed and applicated by TÜV Rheinland to control the behaviour of pipes in power plants during service. Therefore on one hand it is possible to demonstrate the safe behaviour of the pipe on the other hand it is possible to find out unexpected loads before leading to problems. Measurements are taken over years and therefore moreover long time changes can be detected. The four phases of the program allow its application to the actual problem with basic measurements, temporary measurements or continuous measurements.     

Automated recordkeeping of nuclear materials at electric power plants powered with a water-moderated-water-cooled nuclear reactor

Conclusions The automated nuclear-material recordkeeping system based on the NUMIS-2 program is at present being introduced at the Novororonezh electric power plant. Concurrently, the program is being modified in order to allow its use by the computer model being created in the COMECON member-nations. In the long term, it is expected that the recordkeeping program will become a component part of a single automated control systems of individual electric power plants.The NUMIS-2 program was approved for nuclear-material recordkeeping use after it was tested on the first fuel load of the fourth unit of the Novovoronezh electric power plant. The experiment confirmed the feasibility of automating the processing and storing of nuclear-material information and of recording that information and on the standard computer carriers of information. In principle, these same records can be submitted to the national recordkeeping service (or to the International Atomic Energy Agency) for their further immediate processing by means of the computer program employed by the service. In this manner, the recordkeeping system becomes closed, which makes it promising.We note that the propesed nuclear-material recordkeeping system satisfied the basic requirements of recordkeeping by computer laid down by the International Atomic Energy Agency as well as the required order of reporting by the plants under the control of the Agency.Translated from Atomnaya Énergiya, Vol. 45, No. 4, pp. 267–270, October, 1978.     

Methods of mathematical modeling and optimization of nuclear power plants

Conclusions Theoretical research and practical experience indicate that there are large and still far from completely disclosed possibilities of the method of mathematical modeling as applied to technical and economic analyses and the choice of optimum solutions in the development of prospective types of nuclear power plants.From accumulated favorable experience the use of the method of mathematical modeling and a computer can be recommended for solving most problems of this class.A further increase in the effectiveness of the method of mathematical modeling requires the development of scientific research directed toward improving methods of the study, processing, and predicting information, the development of methods of obtaining solutions for incompletely specified data, the automation of the construction of mathematical models, and the creation of an automated system of development and optimum design of nuclear power plants.Translated from Atomnaya Énergiya, Vol. 40, No. 2, pp. 145–151, February, 1976.