Nuclear Related Facilities Research Articles

Using water pool as cushion to mitigate ground vibration due to collapse of cooling tower with simulation of complete debris distribution

Large-scale cooling towers in inland nuclear power plants (NPPs) may collapse under extreme conditions. The collapse-induced ground vibrations threat the safety operations of the adjacent nuclear related facilities. Therefore, prediction and possible mitigation of the ground vibrations are significant in the NPP planning. This study proposed a novel method to arrange a water pool as a cushion underneath the cooling tower to mitigate the ground vibrations. The planar dimension of the water pool is determined by the debris distribution of the collapsed cooling tower. To achieve this, first, the mitigation effect was tested using a steel ball impacting on a concrete pedestal. Then, to obtain the complete debris distribution, a technique was developed to reproduce the disappearing elements in the finite element method-based simulation, and was validated against the tests of vase debris. Finally, the “cooling tower-water pool cushion-soil” models were established to demonstrate the vibration mitigation using the water pool cushion. For the concerned case with the water pool of 6 m depth, the vibration reduced by 56 % and 59 % for the maximum and average of the ground peak accelerations in the horizontal direction, as well as by 65 % and 60 % for those in the vertical direction, respectively.

Evaluating the effectiveness of security systems regime of a hypothetical radiological facility using a risk calculation

This paper presents how security effectiveness can be measured by considering the cost involved in providing security for a radiological center and measures to improve security through risk analysis. The expansion of nuclear technologies and the possible use of nuclear and radioactive materials continues to grow. This increase comes with potential risk of radioactive materials being used for the wrong reasons; thus it is important to provide physical protection of nuclear related facilities to counter these threats and use atomic energy for peaceful purposes. The effectiveness of the security systems put in place at the facility can be assessed by making analysis of the risks associated to the facility.

Reproduction strategy of radiation data with compensation of data loss using a deep learning technique

In nuclear-related facilities, such as nuclear power plants, research reactors, accelerators, and nuclear waste storage sites, radiation detection, and mapping are required to prevent radiation overexposure. Sensor network systems consisting of radiation sensor interfaces and wxireless communication units have become promising tools that can be used for data collection of radiation detection that can in turn be used to draw a radiation map. During data collection, malfunctions in some of the sensors can occasionally occur due to radiation effects, physical damage, network defects, sensor loss, or other reasons. This paper proposes a reproduction strategy for radiation maps using a U-net model to compensate for the loss of radiation detection data. To perform machine learning and verification, 1,561 simulations and 417 measured data of a sensor network were performed. The reproduction results show an accuracy of over 90%. The proposed strategy can offer an effective method that can be used to resolve the data loss problem for conventional sensor network systems and will specifically contribute to making initial responses with preserved data and without the high cost of radiation leak accidents at nuclear facilities.

Selective Poisoning Attack on Deep Neural Networks †

Studies related to pattern recognition and visualization using computer technology have been introduced. In particular, deep neural networks (DNNs) provide good performance for image, speech, and pattern recognition. However, a poisoning attack is a serious threat to a DNN’s security. A poisoning attack reduces the accuracy of a DNN by adding malicious training data during the training process. In some situations, it may be necessary to drop a specifically chosen class of accuracy from the model. For example, if an attacker specifically disallows nuclear facilities to be selectively recognized, it may be necessary to intentionally prevent unmanned aerial vehicles from correctly recognizing nuclear-related facilities. In this paper, we propose a selective poisoning attack that reduces the accuracy of only the chosen class in the model. The proposed method achieves this by training malicious data corresponding to only the chosen class while maintaining the accuracy of the remaining classes. For the experiment, we used tensorflow as the machine-learning library as well as MNIST, Fashion-MNIST, and CIFAR10 as the datasets. Experimental results show that the proposed method can reduce the accuracy of the chosen class by 43.2%, 41.7%, and 55.3% in MNIST, Fashion-MNIST, and CIFAR10, respectively, while maintaining the accuracy of the remaining classes.

Safety Assessment of Aircraft Crash Accident Into Spent Nuclear Fuel Dry Storage Facility – A Review With Focus on Structural Evaluation

Since the 1970s, aircraft crash accidents have been considered as one of the severest external events that should be evaluated for license application of nuclear reactors. After the 9.11 terrorist attacks, many countries have performed safety assessment against intentional or targeted aircraft crashes into nuclear related facilities. In some countries, assessment against targeted aircraft crash was enforced by regulation and considered an important task for license approval. Safety assessment against aircraft crash is a technically difficult task and many countries manage R&D programs to improve its reliability. In this paper, regulations of many countries regarding safety assessment against aircraft crash are summarized, separating regulations for accident aircraft crash and those for targeted aircraft crash. Research performed in various countries on safety assessment of nuclear facility against aircraft crash are summarized, with a focus on spent nuclear fuel dry storage facilities.

Investigation on the gamma sources integrity inside a dry pit storage

One of the primary concerns in the operation of nuclear related facilities is the safety of the system. Worldwide publicity on a few nuclear accidents as well as the notorious Hiroshima and Nagasaki bombing have always brought about public fear on anything related to nuclear. Thus, investigation and analysis on the safety system shall be continuously conducted to determine the safety condition of the facilities. In the early days, analytical and experimental methods were employed. However, this approach is limited to low risk experimentation. With the advancement of computer technology, specific computer codes were used to predict and analyse high risk safety issues such as the fall-out from a nuclear explosion or analysis of melt down occurrence in a reactor core. This paper discusses a prediction model on a gamma irradiation facility source pit which having failure on its air cooling system. The CFD model predicts the temperature of the gamma sources under such situation to determine its integrity.

Development and Improvement of Human Resource Development in Nuclear Engineering for National College Students in Japan

Human resource development program in nuclear engineering has been developed and carried out for national college students in Japan. It consists of (a) remote lectures and e-Learning contents on radiation and nuclear related subjects, and (b) on-site workshops and visits at nuclear related facilities or Nagaoka University of Technology. In approximately 10 years since it was started, more than 10 thousand of students participated in the program, which, we believe, was effective to enhance their understanding in these fields. However, as an educational system, it seems possible to be improved through utilization of ICTs etc. From our understanding that the problem is the lack of bidirectional feature in our program. In the future, we are planning to provide substantial amounts of exercises base on Active-learning with ICTs to deepen the understanding of the subjects carried out in the workshops or facility visits.

Design-oriented acceleration response spectrum for ground vibrations caused by collapse of large–scale cooling towers in NPPs

Abstract Nuclear-related facilities can be detrimentally affected by ground vibrations due to the collapse of adjacent cooling towers in nuclear power plants. To reduce this hazard risk, a design-oriented acceleration response spectrum (ARS) was proposed to predict the dynamic responses of nuclear-related facilities subjected to ground vibrations. For this purpose, 20 computational cases were performed based on cooling tower-soil numerical models developed in previous studies. This resulted in about 2664 ground vibration records to build a basic database and five complementary databases with consideration of primary factors that influence ground vibrations. Afterwards, these databases were applied to generate the design-oriented ARS using a response spectrum analysis approach. The proposed design-oriented ARS covers a wide range of natural periods up to 6 s and consists of an ascending portion, a plateau, and two connected descending portions. Spectral parameters were formulated based on statistical analysis. The spectrum was verified by comparing the representative acceleration magnitudes obtained from the design-oriented ARS with those from computational cases using cooling tower-soil numerical models with reasonable consistency.

The contested politics of the Asian atom: peripheralisation and nuclear power in South Korea and Japan

ABSTRACTSouth Korea and Japan have been unwaveringly committed to a nuclear-focused energy supply system despite the contested nature of that technology and the Fukushima accident in 2011. The socio-political consequences of four nuclear-related facilities (Ulju, Gyeongju, Futaba, and Rokkasho) are explored through the lens of social peripheralisation. This framework suggests that nuclear facilities will migrate to communities that are geographically remote, economically marginal, politically powerless, culturally defensive, and environmentally degraded. Nuclear infrastructures in the four cases are imposed on peripheral regions, impairing not only the structure of local economies and political power, but also creating a discriminative structure in terms of social and environmental inequality. Peripheralisation suggests a deeper dynamic by which pro-nuclear attitudes become ‘locked in’ socially and culturally so that communities come to depend on the very processes that made them peripheral. Community dynamics, subnational struggles, and contests over local power relations may determine the future of nuclear power.

Mitigation of Ground Vibration due to Collapse of a Large-Scale Cooling Tower with Novel Application of Materials as Cushions

Ground vibration induced by the collapse of large-scale cooling towers in nuclear power plants (NPPs) has recently been realized as a potential secondary disaster to adjacent nuclear-related facilities with demands for vibration mitigation. The previous concept to design cooling towers and nuclear-related facilities operating in a containment as isolated components in NPPs is inappropriate in a limited site which is the cases for inland NPPs in China. This paper presents a numerical study on the mitigation of ground vibration in a “cooling tower-soil-containment” system via a novel application of two materials acting as cushions underneath cooling towers, that is, foamed concrete and a “tube assembly.” Comprehensive “cooling tower-cushion-soil” models were built with reasonable cushion material models. Computational cases were performed to demonstrate the effect of vibration mitigation using seven earthquake waves. Results found that collapse-induced ground vibrations at a point with a distance of 300 m were reduced in average by 91%, 79%, and 92% in radial, tangential, and vertical directions when foamed concrete was used, and the vibrations at the same point were reduced by 53%, 32%, and 59% when the “tube assembly” was applied, respectively. Therefore, remarkable vibration mitigation was achieved in both cases to enhance the resilience of the “cooling tower-soil-containment” system against the secondary disaster.

Determination of strontium-90 from direct separation of yttrium-90 by solid phase extraction using DGA Resin for seawater monitoring

It is important for public safety to monitor strontium-90 in aquatic environments in the vicinity of nuclear related facilities. Strontium-90 concentrations in seawater exceeding the background level have been observed in accidents of nuclear facilities. However, the analytical procedure for measuring strontium-90 in seawater is highly demanding. Here we show a simple and high throughput analytical technique for the determination of strontium-90 in seawater samples using a direct yttrium-90 separation. The DGA Resin is used to determine the abundance of strontium-90 by detecting yttrium-90 decay (beta-emission) in secular equilibrium. The DGA Resin can selectively collect yttrium-90 and remove naturally occurring radionuclides such as 40K, 210Pb, 214Bi, 238U, and 232Th and anthropogenic radionuclides such as 140Ba, and 140La. Through a sample separation procedure, a high chemical yield of yttrium-90 was achieved at 95.5±2.3%. The result of IAEA-443 certified seawater analysis (107.7±3.4mBqkg−1) was in good agreement with the certified value (110±5mBqkg−1). By developed method, we can finish analyzing 8 samples per day after achieving secular equilibrium, which is a reasonably fast throughput in actual seawater monitoring. By processing 3L of seawater sample and applying a counting time of 20h, minimum detectable activity can be as low as 1.5mBqkg−1, which could be applied to monitoring for the contaminated marine environment. Reproducibility was found to be 3.4% according to 10 independent analyses of natural seawater samples from the vicinity of the Fukushima Daiichi Nuclear Power Plant in September 2013.

NPP planning based on analysis of ground vibration caused by collapse of large-scale cooling towers

Ground vibration induced by collapse of large-scale cooling towers can detrimentally influence the safe operation of adjacent nuclear-related facilities. To prevent and mitigate these hazards, new planning methods for nuclear power plants (NPPs) were studied considering the influence of these hazards. First, a “cooling tower-soil” model was developed, verified, and used as a numerical means to investigate ground vibration. Afterwards, five critical factors influencing collapse-induced ground vibration were analyzed in-depth. These influencing factors included the height and weight of the towers, accidental loads, soil properties, overlying soil, and isolation trench. Finally, recommendations relating to the control and mitigation of collapse-induced ground vibration in NPP planning were proposed, which addressed five issues, i.e., appropriate spacing between a cooling tower and the nuclear island, control of collapse modes, sitting of a cooling tower and the nuclear island, application of vibration reduction techniques, and the influence of tower collapse on surroundings.

Comparison of Decontamination Standards

Abstract The quality of materials used in nuclear-related facilities is critical, especially the ease of decontamination of different paints and coatings. Standards describe different testing methods for classification. Nevertheless, compliance with these standards cannot be carried out negligibly from a safety point of view. In this study, a withdrawn Hungarian (MSZ-05 22.7662-83), an international ISO (ISO 8690:1988), and Russian (GOST 25146- 82) decontamination standard were compared. Four different paints were tested as part of this survey. The ease of decontamination varied mainly from poor to fair levels in the case of the Hungarian standard, while the ISO standard exhibited very good level. In the case of the Russian standard, only a theoretical comparison was carried out. Based on the results, it was found that a special epoxy-based coating can be recommended for isotope laboratories due to being the best material from an ease of decontamination point of view. From comparison of the standards considered here, it was found that the application of ISO standard is significantly faster and simpler than the withdrawn Hungarian standard. However, in the case of the Hungarian standard the data described the ease of decontamination in more details. The use of water or some other cleaning agents can be effective to remove 137Cs and 60Co contamination right after early identification. Isotope 137Cs and 60Co contamination of a surface can be cleaned quickly and effectively using distilled water for the 137Cs isotope removal from the surfaces being several times easier than that of 60Co.

Prediction of ground motion due to the collapse of a large-scale cooling tower under strong earthquakes

The ground motion owing to the collapse of a large-scale cooling tower under strong earthquakes was appropriately predicted using a comprehensive approach. The predicted results can be used for the safety evaluation of nuclear-related facilities adjacent to the cooling tower as well as in the planning of nuclear power plant construction in China. In this study, a cooling tower–soil model was first developed based on a falling weight–soil model, which the authors verified by falling weight tests. Then the collapse process of a cooling tower was simulated, and the collapse-induced ground vibrations were assessed by using the proposed model. Finally, the ground motion, which was a combination of the earthquake-induced ground motion and the collapse-induced ground vibrations, was estimated based on the superposition principle of waves. It was found that the cooling tower may collapse under strong earthquakes with the peak ground accelerations (PGAs) in the range of 0.35–0.45 g in x (EW) and y (NS) directions, respectively. These PGAs are far beyond the PGA range of major earthquakes in the common seismic design in China. The types of the site geologies of towers can significantly affect the collapse-induced ground vibrations. For a typical hard soil consisting of strongly weathered sandy slate, moderate ground vibrations may occur in the considered region. The collapse-induced PGAs were in the range of 0.017–0.046 g for the observed points at distances of 350 m in radial direction. For a rock-like foundation, the collapse-induced radial PGAs may be as high as 0.08 g at distances of 350 m, indicating that the effect of the collapse-induced ground vibrations on the nuclear-related facilities should be seriously assessed in certain scenarios.

Prediction of ground vibration due to the collapse of a 235 m high cooling tower under accidental loads

A comprehensive approach is presented in this study for the prediction of the ground vibration due to the collapse of a 235m high cooling tower, which can be caused by various accidental loads, e.g., explosion or strong wind. The predicted ground motion is to be used in the safety evaluation of nuclear-related facilities adjacent to the cooling tower, as well as the plant planning of a nuclear power station to be constructed in China. Firstly, falling weight tests were conducted at a construction site using the dynamic compaction method. The ground vibrations were measured in the form of acceleration time history. A finite element method based “falling weight-soil” model was then developed and verified by field test results. Meanwhile, the simulated collapse processes of the cooling tower under two accidental loads were completed in a parallel study, the results of which are briefly introduced in this paper. Furthermore, based on the “falling weight-soil” model, “cooling tower-soil” models were developed for the prediction of the ground vibrations induced by two collapse modes of the cooling tower. Finally, for a deep understanding of the vibration characteristics, a parametric study was also conducted with consideration of different collapse profiles, soil geologies as well as the arrangements of an isolation trench. It was found that severe ground vibration occurred in the vicinity of the cooling tower when the collapse happened. However, the vibration attenuated rapidly with the increase in distance from the cooling tower. Moreover, the “collapse in integrity” mode and the rock foundation contributed to exciting intense ground vibration. By appropriately arranging an isolation trench, the ground vibration can be significantly reduced.

Dynamical modeling investigation for economy of nuclear power plants (NPPs) in global nuclear energy market

Non-linear dynamical analysis for the global nuclear energy market is investigated. Currently, the market means a different characteristics comparing to the past situation which had been done before two severe accidents as the Three Mile Island nuclear power plant (NPP) accident in the United States and the Chernobyl NPP disaster in the Soviet Union. For the nuclear related facility, the environmental and safety aspects are the important issues of the analysis. Fundamentally, the economic factor is still a critical matter for the commercial trade between two countries which depend on the energy demand and uranium price. The dynamics simulations show the trend of trade is affected by the several kinds of the aspects. Using system dynamics (SD) method, the event quantification is performed for the event flows, stocks, and feedback where the single and double arrow lines are incorporated.

Experimental Study on Gamma Ray Shielding with Cracked Concrete Panels

In nuclear-related facilities, many reinforced concrete shielding panels are used against radioactive rays. Some shielding panels simultaneously serve as structural slabs or walls. Reinforced concrete shielding plates may crack due to the drying shrinkage of concrete, earthquakes, and other factors. The shielding performance of a cracked reinforced concrete panel against radioactive rays should be clarified. In the design process, engineering safety is based on knowledge of research. If the knowledge is short, conservative assumptions and large safety factors compensate the shortage of knowledge. On the other hand, it has to be recognized that the mental security of the people does not always correspond with the physical safety. In order to avoid misunderstanding and obtain the assurance of society, scientific data should be accumulated. Experimental results are the most fundamental. Therefore, in this study, gamma ray radiation tests on cracked concrete panels were carried out. In the tests, Co-60 and an ionization chamber were used as the source of gamma ray radiation and to measure the dose rate, respectively. A cracked concrete panel was placed between the radiation source and the ionization chamber, and the dose rate was measured. The purpose of this study is not only for the engineering safety but also for the mental security of the people. The previous tests were already reported [1]. The tests were carried out on six concrete panel specimens. Parameters of the tests were crack shape, panel thickness, and crack width. The crack shapes were natural crack and pre-made slit, the thicknesses were 50, 100, and 150 mm, and crack width was varied from 0 to 10 mm. In this paper, subsequent tests are reported. Two additional panel specimens 400 mm thick were prepared that have natural crack and pre-made slit, respectively. The useful data on the gamma ray shielding performance of cracked concrete plates were accumulated.

Special Issue on Structural Engineering of Nuclear Related Facilities

Since it was first used, nuclear energy’s control has been an important issue. With the generation of electricity as a major nuclear energy application, the improvement of nuclear power generation technology has been required by society, including power plant design, construction, and maintenance and radioactive waste disposal. Nuclear facilities must also take into account disaster prevention, as in the case of earthquakes and terrorist attacks, particularly because of the extensive potential and actual range of effects. This has made nuclear energy issues important considerations in JDR editorial meetings. In the July 16, 2007, case of the Niigataken Chuetsu-oki Earthquake, quake ground motion equaled or exceeded that presumed in the design of the Tokyo Electric Power Company’s Kashiwazaki-Kariwa Nuclear Power Station, the world’s largest nuclear power station. Specific safety objectives for nuclear power plants include stopping the nuclear reaction, cooling the nuclear reactor, preventing radioactive material emission, and shielding surroundings from radiation - all of which were almost completely achieved in this case. Many problems were also revealed, however. JDR examined a special issue on Kashiwazaki-Kariwa Nuclear Power Station earthquake resistance at an editorial meeting but determined that such a topic remains premature. In its stead, we have planned a number featuring the structural engineering of nuclear related facilities as a first step in a series of special issues on nuclear energy. The papers for this number were submitted mainly by the presenters of 20th International Conference on Structural Mechanics in Reactor Technology, held in Espoo, Finland, in 2009 with the catch phrase “Challenges Facing Nuclear Renaissance.” We greatly appreciate the many contributions to this issue, and would like to thank the reviewers, without whose cooperation this number could not have been published. Please note that, independent of special numbers such as this one, JDR looks forward to receiving papers on a wide range of fields related to disaster.

Experimental study on pullout strength of anchor bolt with an embedment depth of 30 mm in concrete under high temperature

Many anchor bolts are used in nuclear-related facilities in order to fast some equipments and pipes. About these anchor bolts, the possibilities should exist in being exposed to high temperature due to accident. However, little information is available regarding the effects of high temperatures on the behavior of anchor bolts. To obtain basic experimental data and to examine the response of cast-in-place anchor bolts to high temperature exposure, pullout strength of an anchor bolt during heating and after heating was examined. The maximum temperature in this test is 500 °C and two different rate of heating were prepared. Tests results show that pullout strength decreases with increasing surface temperature. Regardless of different rate of heating in this experiment, identical ratio of pullout strength of anchor bolt was obtained when the same temperature of concrete surrounding the bolt head was applied.

Empirical investigation on buckling and post-buckling behaviour of cell liners

In nuclear-related facilities, many concete walls and slabs are lined with thin stainless steel plates in order to insure against the risk of accidental air leakage during a severe earthquake. These liners are forcibly deformed with the deformation of the concrete walls and slabs during an earthquake. The purpose of this paper is to obtain basic empirical data on the shearing behaviour of thin steel plates attached to concrete, especially to understand the relationship between the shear strain of the plate and its lateral displacement, as fundamental research on the safety of lining plates. A new apparatus for measuring the lateral displacement of a lining plate by continuously scanning its surface is tested. The apparatus proves to be quite effective for understanding the buckling wave of the lining plate and the essential behaviour of a thin steel plate attached to a concrete wall subject to a shear force is clarified.