Dynamical Modeling of the Nuclear Fission Process at Low Excitation Energies

Two recipes for modeling the dynamics of the nuclear fission process are known in literature. The underlying equations contain the driving, dissipative, and random forces. The two recipes are mostly different in the prescriptions for the driving force. In this work we carefully compare these driving forces and the resulting fission rates. It turns out that the rates may be very close or strongly different depending on the value the shell correction to the nuclear deformation energy. We give arguments in favor of one of the recipes.

Project New Orion: Pulsed Nuclear Space Propulsion Using Photofission Activated by Ultra-Intense Laser

Project New Orion entails a pulsed nuclear space propulsion system that utilizes photofission through the implementation of an ultra-intense laser. The historical origins derive from the endeavors of Project Orion, which utilized thermonuclear devices to impart a considerable velocity increment on the respective spacecraft. The shear magnitude of Project Orion significantly detracts from the likelihood of progressive research development testing and evaluation. Project New Orion incorporates a more feasible pathway for the progressive research development testing and evaluation of the pulsed nuclear space propulsion system. Photofission through the application of an ultra-intense laser enables a much more controllable and scalable nuclear yield. The energy source for the ultra-intense laser is derived from a first stage liquid hydrogen and liquid oxygen chemical propulsion system. A portion of the thermal/kinetic energy of the rocket propulsive fluid is converted to electrical energy through a magneto-hydrodynamic generator with cryogenic propellant densification for facilitating the integral superconducting magnets. Fundamental analysis of Project New Orion demonstrates the capacity to impart a meaningful velocity increment through ultra-intense laser derived photofission on a small spacecraft.

Sensitivity impacts owing to the variations in the type of zero-range pairing forces on the fission properties using the density functional theory

Using the Skyrme density functional theory,potential energy surfaces of^(240)Pu with constraints on the axial quadrupole and octupole deformations(q_(20)and q_(30))were calculated.The volume-like and surface-like pairing forces,as well as a combination of these two forces,were used for the Hartree–Fock–Bogoliubov approximation.Variations in the least-energy fission path,fission barrier,pairing energy,total kinetic energy,scission line,and mass distribution of the fission fragments based on the different forms of the pairing forces were analyzed and discussed.The fission dynamics were studied based on the timedependent generator coordinate method plus the Gaussian overlap approximation.The results demonstrated a sensitivity of the mass and charge distributions of the fission fragments on the form of the pairing force.Based on the investigation of the neutron-induced fission of^(239)Pu,among the volume,mixed,and surface pairing forces,the mixed pairing force presented a good reproduction of the experimental data.

Numerical analysis on element creation by nuclear transmutation of fission products

A burnup calculation was performed to analyze the Apr`es ORIENT process, which aims to create highlyvaluable elements from fission products separated from spent nuclear fuels. The basic idea is to use nuclear transmutation induced by a neutron capture reaction followed by a β-decay, thus changing the atomic number Z of a target element in fission products by 1 unit. LWR(PWR) and FBR(MONJU) were considered as the transmutation devices. High rates of creation were obtained in some cases of platinum group metals(44Ru by FBR,46 Pd by LWR) and rare earth(64Gd by LWR,66 Dy by FBR). Therefore, systems based on LWR and FBR have their own advantages depending on target elements. Furthermore, it was found that creation rates of even Z(= Z + 1) elements from odd Z ones were higher than the opposite cases. This creation rate of an element was interpreted in terms of "average 1-group neutron capture cross section of the corresponding target element σc Z defined in this work. General trends of the creation rate of an even(odd) Z element from the corresponding odd(even) Z one were found to be proportional to the 0.78th(0.63th) power of σc Z, however with noticeable dispersion. The difference in the powers in the above analysis was explained by the difference in the number of stable isotopes caused by the even-odd effect of Z.

Fission Fragment Decay Heat by Using the Most Recent Evaluated Nuclear Data Library ENDF/B-VIII

In this paper, a home-made code was designed to calculate the decay heat emitted by fission fragments as a result of successive radioactive emissions after a fission burst. The nuclear data necessary for the calculations was extracted from the latest version of the Evaluated Nuclear Data Library ENDF/B-VIII.0. The code can calculate the decay heat of thermal and fast neutron-induced fission reactions on the isotopes of Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, California, Einsteinium, and Fermium. A numerical method was used in this work to calculate the decay heat of all fission fragments due to the individual thermal or fast fissions of the isotopes of the previous ten actinides. The most influential nuclei in the decay heat were also identified at different times after the fission event. Moreover, the code showed high capability in calculating the fission fragments inventories and decay heats due to the decay of fission fragments of 31 fissionable nuclei.

Prediction of the Average Decay Heat per Fission for MOX Nuclear Fuel

MIXED Oxide Nuclear fuel (MOX) contains both uranium and plutonium in oxidized form. It is important to calculate the nuclear decay heat due to the single thermal fission (fission due to 0.0235 eV neutron) for all fissile nuclei in the MOX fuels (U235, Pu239, and Pu241). These fissile nuclei are the main source of the decay heat in MOX fuel. Decay heat calculation of the weighted fissile material content in MOX fuel is also important. A numerical method was used in this work to calculate the concentrations of all fission products due to the individual thermal fission of the three fissile materials as a function of time N(t). The decay heat calculations for the three fissile materials are directly calculated using the summation method by knowing the different concentrations of fission products over time. The average decay heat of the MOX fuel in induced thermal fission is also concluded. The most influential nuclei in the decay heat were also identified. The method used has been validated by several comparisons before, but the new in this work is using the most recent Evaluated Nuclear Data Library ENDF/B-VIII.0. Calculations of decay heat show very common trends for a period of 107 sec after the fission burst of thermal fissions of individual fissile nuclei. Moreover, the code showed high capability in calculating the fission fragments inventories and decay heats due to the decay of fission fragments of 31 fissionable nuclei.

Proposal of a Deuterium-Deuterium Fusion/PWR Fission Hybrid Reactor

This article proposes to associate a Deuterium-Deuterium (D-D) fusion reactor with a PWR (fission Pressurized Water Reactor) in a hybrid reactor. Even if the mechanical gain (Q factor) of the D-D fusion reactor is below the unity and consequently consumes more energy than it supplies, due to the high energy amplification factor of the PWR fission reactor, the global yield is widely superior to 1. As the energy supplied by the fusion reactor is relatively low and as the neutrons supplied are mainly issued from D-D fusions (at 2.45 MeV), the problems of heat flux and neutrons damage connected with materials, as with D-T fusion reactors are reduced. Of course, there is no need to produce Tritium with this D-D fusion reactor. This type of reactor is able to incinerate any mixture of natural Uranium, natural Thorium and depleted Uranium (waste issued from enrichment plants), with natural Thorium being the best choice. No enriched fuel is needed. So, this type of reactor could constitute a source of energy for several thousands of years because it is about 90 more efficient than a standard fission reactor, such as a PWR or a Candu one, by extracting almost completely the energy from the fertile materials U238 and Th232. For the fission part, PWR technology is mature. For the fusion part, it is based on a reasonable hypothesis done on present Stellarators projects. The working of this reactor is continuous, 24 hours a day. In this paper, it will be targeted a reactor able to provide net electric power of about 1400 MWe, as a big fission power plant.

Nuclear Energy and Its History: Past Consequences, Present Inadequacies and a Perspective for Success

An attempt is made to locate nuclear technology within a logical context considering history, risks, societal catastrophes and perspectives: the need is identified for a new direction in the exploitation in order to restore the role in energy production. We depict the situation coming from a marvelous history of discoveries started at the beginning of the XX century;heroes are recalled who made possible something that is inconceivable today: design, construction and production of electricity in a few years;that history was tainted by intentional nuclear explosions, i.e. the original sin that we are now paying. Then, we attempt to show that the societal risk is an inherent part of the civilization. Restoring the public trust (towards nuclear fission technology) by matching nuclear safety with the current technological status and advancers in risk assessment is the key objective. The “independent assessment”, or a principle for the exploitation of nuclear energy already stated in the 50’s of the previous century, shall then re-appear. This is used to erect the signpost for a “dynamic barricade” to further reduce the risk of operation of nuclear reactors and to match the design with current technological capabilities and with the frontiers of the research.

Fundamental Architecture and Performance Analysis of Photofission Pulsed Space Propulsion System Using Ultra-Intense Laser

Photofission enables a unique capability for the domain of non-chemical space propulsion. An ultra-intense laser enables the capacity to induce nuclear fission through the development of bre- msstrahlung photons. A fundamental architecture and performance analysis of a photofission pulsed space propulsion system through the operation of an ultra-intense laser is presented. A historical perspective of previous conceptual nuclear fission propulsion systems is addressed. These applications use neutron derived nuclear fission;however, there is inherent complexity that has precluded further development. The background of photofission is detailed. The conceptual architecture of photofission pulsed space propulsion and fundamental performance parameters are established. The implications are the energy source and ultra-intense laser can be situated far remote from the propulsion system. Advances in supporting laser technologies are anticipated to increase the potential for photofission pulsed space propulsion. The fundamental performance analysis of the photofission pulsed space propulsion system indicates the architecture is feasible for further evaluation.

A desktop-computer simulation for exploring the fission barrier

A model of a fissioning nucleus that splits symmetrically both axially and equatorially is used to show how one can predict the presence of a fission barrier of several tens of MeV for nuclides of mass number A ~ 90 and of ~ 10 MeV for elements such as uranium. While the present model sacrifices some physical realism for the sake of analytic and programming simplicity, it does reproduce the general behavior of the run of fission barrier energy as a function of mass number as revealed by much more sophisticated models. Its intuitive appeal and tractability make it appropriate for presentation in a student-level “Modern Physics” class.

Viewing the Future of Nuclear Power Plants Following the 2011 Disaster in Fukushima Nuclear Power Plant

Concerning the increasing global energy demand, the current paper considers nuclear energy as a solution. Within this context, the 2011 disaster in Fukushima Nuclear Power Plant and, particularly, the technical disorders in boiling water reactors are explained. The deficiency of safety technique in boiling water reactors is explained. The deficiencies in safety procedure of this type of reactors manifested during 2011 earthquake and subsequent tsunami are explained. To complete the discussion, the newer technologies of reactors enabling them to act more safely during natural disasters are introduced. These investigations indicate that despite improvement in the fission reactor technologies, the danger embedded in them still remains. Therefore, the nuclear fusion using Deuterium-Tritium reaction is the best way forward for energy production in the future, and the best candidate of this type of reactors is Tokamak.

A Developed Material as a Nuclear Radiation Shield for Personal Wearing

A new composite of silicone rubber and boric acid was developed to be used as a personal wearing for protection from nuclear radiation. The capability of this material for absorbing thermal neutrons of different intensities followed by a detonation of nuclear weapon has been investigated. This investigation was performed by using californium-252 neutron source of like fission spectrum. The thermal neutron flux was measured behind different thicknesses of the developed material using a BF3 detector. Two positions of measurements were performed;at position near the detonation where the intensity of thermal neutron flux is low and at position far from the detonation where the intensity of thermal neutron is high. For both cases, the contribution of total thermal, initial incident and new produced thermal neutron fluxes are measured. The obtained results indicated that, addition of boron with concentration of about 17% to the silicon rubber tends to decrease the flux by more than 70%.

Student-level numerical simulation of conditions inside an exploding fission-bomb core

This paper describes a freely-available spread-sheet that has been developed to simulate the conditions of reaction rate, core acceleration and velocity, energy generation, and pressure within a detonating fission-bomb core. When applied to a model of the Hiroshima Little Boy bomb, the spreadsheet predicts a yield of 12.7 kilotons, a figure in reasonable agreement with published values.

A method for 3D simulation of internal gas effects on thermal-mechanical behaviors in nuclear fuel elements

A new method for three-dimensional simulation of the interaction between the gas and the solid around is developed.The effects of the gas on the thermal-mechanical behaviors within the surrounded solid are performed by replacing the internal gas with an equivalent solid in the modeling,which can make it convenient to simulate the thermal-mechanical coupling effects in the solid research objects with gases in them.The applied thermal expansion coefficient,Young's modulus and Poisson's ratio of the equivalent solid material are derived.A series of tests have been conducted;and the proposed equivalent solid method to simulate the gas effects is validated.

Shaping the Future of Energy:A Path toward Zero-Emission and Sustainable Solutions

In the age of rapidly growing global population and escalating energy demands,the pursuit of sustainable,zero-emission energy sources has become critical.This article explores the interplay between environmental concerns,such as global warming and the greenhouse effect,and the need for innovative energy solutions.The melting polar ice caps exemplify the urgent need for reducing carbon emissions.ARCs(advanced reactor concepts)in both fission and fusion technologies offer promising paths to zero-emission energy.Advanced fission reactors,including SMRs(small modular reactors)and Generation IV reactors,provide improved safety,efficiency,and waste management.Fusion energy,despite being in the experimental stage,holds potential as a nearly limitless clean energy source.AI(artificial intelligence)significantly enhances these technologies by optimizing design,operations,maintenance,safety,and grid integration.AI-driven innovations are pivotal in accelerating the development and deployment of ARC technologies,ensuring they are safe,reliable,and efficient.The article underscores the vital role of policy support,global cooperation,and strategic investments in shaping a sustainable energy future that can mitigate the effects of climate change,support economic growth,and protect our planet.

基于灵敏度/不确定度方法的快中子裂变的衰变热不确定度分析

针对传统轻水堆衰变热的计算标准不适用于快堆的问题,为此,本文采用灵敏度/不确定度(S/U)方法,在分析衰变热计算过程中由于核数据引入的不确定度的基础上,开展了快中子裂变的裂变产物衰变热不确定度计算方法研究,得到了1~10^(13) s时间范围内^(235)U和^(239)Pu的快中子裂变产物衰变热不确定度及其与半衰期、平均能量、裂变产额、分支比不确定度的关系。结果表明,在1~10^(3) s以及10^(8)~10^(10) s时间范围内,^(235)U和^(239)Pu的快中子裂变产物衰变热不确定度为2%~10%;在10^(3)~10^(8) s时间范围内,衰变热不确定度小于2%。本文建立的^(235)U和^(239)Pu的快中子裂变产物衰变热不确定度分析的方法流程以及不确定度标准数据,为后续钠冷快堆、铅冷快堆和气冷快堆衰变热的不确定度分析评价奠定了基础。

^(252)Cf自发裂变K X射线发射与动能-电荷关系

原子核裂变后多物理量间的关联测量是认识裂变过程直接有效的实验手段,然而由于初级裂变产物准确的电荷鉴别仍面临技术困难,电荷相关的多参数研究相对匮乏.为此,通过高分辨的低能高纯锗探测器和金硅面垒探测器开展了^(252)Cf自发裂变的裂变碎片K X射线和动能的符合测量.利用K X射线可以很好地鉴别电荷数Z=39—62的裂变碎片,电荷分辨ΔZ≈0.7,K X射线产额呈现强烈的电荷相关性.借助K X射线给出了碎片平均动能和平均总动能及其分布宽度随核电荷数的分布,轻碎片动能分布具有鲜明的奇偶效应,偶Z碎片的动能比奇Z碎片的高约0.48 MeV;平均总动能在Z=52—53处达到峰值,总动能分布宽度在Z=56附近呈现凹坑,这反映了形变壳结构对断点形状的显著影响.裂变碎片K X射线发射的信息及动能-电荷关系研究可为裂变独立产额测量和裂变理论模型的检验提供必要的参考数据.

热中子诱发^(239)Pu裂变气体产物核Xe产额的评价

裂变产额数据是核反应堆设计与运行、核装置设计与测试以及乏燃料处理与核废料管理等应用中的重要数据,同时也是裂变物理研究的基础数据。采用基于Zp模型的裂变产额统一评价方法,对中子诱发^(239)Pu裂变气体产物核Xe的A=131~135,138,140等7个同位素核所在质量链上的产物核产额进行了分析评价,获得了能量为0.0253 MeV(T)、裂变谱(F)和14 MeV(H)的中子诱发^(239)Pu裂变产物核Xe的7个同位素核的独立产额和累积产额评价结果,并建立了ENDF/B-VI格式数据库。与传统评价方法比较,统一评价方法考虑了同一质量链上的独立产额、累积产额的相互关联,给出的产额相互自洽,增加了产额评价数据的可靠性。其中^(131-133)Xe考虑了先驱核碘的贡献,累积产额比JEFF-3.3和ENDF/B-VIII.0有所增加。^(134)Xe的产额存在分歧,通过分析,采用了较高的实验数据,认为该数据比较合理。

反应堆中子通量测量用裂变电离室探测装置研制

为建立一套用于反应堆中子通量测量的监测装置,以实现核电站堆外核测量系统测量要求,研制了一种长灵敏区、宽量程、高灵敏度和强γ抑制能力的裂变电离室探测装置。同时对该裂变电离室探测装置的热中子灵敏度、高压坪特性、甄别特性和γ感应度等典型核性能指标进行了试验验证。试验结果表明,该裂变电离室综合性能能够满足AP1000系列核电站堆外核测量系统中间量程测量通道的应用需求。

堆外核测量系统裂变电离室线性响应研究

为满足先进反应堆堆外核测量系统中间量程测量通道灵敏度高、探测器灵敏区长、反应堆线性响应好的需求,采用多支灵敏区长度具有一定比例关系、同时机械结构完全相同的裂变电离室,进行热中子灵敏度标定和反应堆线性响应研究,以为核电厂实际所需长灵敏区裂变电离室提供一种在现有试验堆条件下进行其核性能试验的方法。通过测量不同灵敏区长度的裂变电离室热中子灵敏度和反应堆高中字注量率下的线性响应,对其热中子灵敏度随灵敏区长度的线性变化和反应堆线性响应进行试验验证。测量结果表明,裂变电离室热中子灵敏度随灵敏区长度呈线性关系,且在反应堆热中子注量率1.23×10^(2)~3.10×10^(10)nv(1nv=1n·cm^(-2)·s^(-1))范围内进行计数率模式和MSV模式线性拟合,裂变电离室最大线性度为-1.23%。