Conditions for effective utilization of the electronuclear blanket system as a neutron source

The efficiency of an intermediate-energy electronuclear setup with a blanket as an alternative source of neutrons is discussed on the basis of experience in designing the electronuclear neutron generator at the Institute of Theoretical and Experimental Physics. A classification of electronuclear setups is introduced. The factors determining the efficiency of the driver-target-multiplying blanket scheme at low and intermediate driver energies are examined. To obtain high neutron fluxes, the possibility of compensating an inadequate driver current by decreasing the subcriticality store is examined and the conditions for realizing such a possibility while preserving the fundamental requirement of nuclear safety are formulated. The concept of the criterion of dynamical safety, in contrast to the criterion of static safety ordinarily assumed for subcritical systems, is introduced. A program of precision investigations for studying operating regimes of a blanket under conditions of a low store of subcriticality is formulated on the basis of the criterion of dynamical safety. The results of an implementation of this program are important for the assessment of the technological possibility and desirability of replacing research reactors with subcritical setups based on an accelerator. 2 figures, 6 references. State Science Center of the Russian Federation-Institute of Theoretical and Experimental Physics. Translated from Atomnaya énergiya, Vol. 87, No. 4, pp. 255–262, October, 1999.     

Experimental Confirmation of the Concept of Two-Section Cascade-Type Blankets

In the last ten years, Russia and other countries have been showing a great deal of interest in two-section blanket reactors with unilateral neutron coupling of the sections (cascade-type blankets). These setups are intended to operate in power and transmutation electronuclear facilities, for which they permit decreasing substantially the required power of the proton accelerator. Theoretical and design works have been done on cascade-type blankets, but until very recently there were no experimental works.The results of the first experiment of this type, performed at the All-Russia Scientific-Research Institute of Experimental Physics, on compact deeply subcritical uranium–neptunium assemblies are presented. The experiment has confirmed the theoretical conclusion that cascade blankets have positive properties and ²³⁷Np is effective as a means for achieving unilateral coupling of the sections.     

Mathematical model of the electronuclear set-up on the beam of JINR synchrotron

On the basis of the Monte Carlo code CASCADE, developed at JINR, a mathematical model of the deep-subcritical set-up with the uranium blanket used in experiments underway at JINR using a 0.6–4 GeV proton beam, is created. The neutron spectra, yields and energies of generated particles are calculated and compared for several modifications of the set-up. The influence of paraffin and graphite moderators on the characteristics of the particles escaping the lead target is studied. The modelled set-up can be considered as a first step of the experiments to be designed at JINR U–Pu accelerator driven subcritical systems–subcritical assembly at Dubna (ADS–SAD) with a heat power of several tens of kW.     

Spatiotemporal Energy Distribution in a Pulsed Coupled Reactor System

The basic characteristics of nonstationary neutron transport in a subcritical component of a coupled pulsed reactor system are studied. The investigations are performed on the reactor-laser setup of stand B. The existence of a phenomenon which is unusual for nuclear reactors – a spherical wave of fission – in the subcritical assembly is confirmed experimentally. The basic characteristics of this wave are determined experimentally and confirmed computationally for a three-core pulsed reactor–laser system.     

Experimental Investigation of Models of a Cascade Blanket in an Electronuclear System

Using in an electronuclear system a two-section blanket with unilateral neutron coupling of the sections (cascade-type blanket) can decrease substantially the power requirements for the accelerator. Theoretical work confirms this supposition, but there are no experimental data in this field. An experimental investigation of cascade-type blankets is planned at the All-Russia Scientific-Research Institute of Experimental Physics. The results of a computational substantiation of models of a cascade blanket (primarily with a central section consisting of ²³⁷Np), which are suitable for performing experiments, are presented. The models chosen for the blanket are deeply subcritical (k _eff = 0.5–0.6) and contain a relatively small amount of fissioning materials. These models satisfy the nuclear-safety requirements and at the same time ensure that the experiments yield adequate information.     

Single-purpose electronuclear installation using natural uranium as fuel

The results of investigations of the parameters of an electronuclear setup, operating on solid fuel, for producing useful power are presented. The objective of the investigations is to show the attractiveness and practical possibility of producing a safe (subcritical) setup for producing energy with unlimited fuel resources. The setup contains an accelerator, two targets, and two blankets. The fissioning isotopes accumulate in one blanket, supplied with natural uranium. Actually, his blanket performs the function of enrichment for the uranium-plutonium fuel cycle in modern nuclear power. Power is generated mainly in the other blanket, which is supplied with fuel assemblies that are extracted from the first blanket. In contrast to reactors operating on natural uranium, in an electronuclear setup a high degree of fuel burnup can be achieved by converting part of the generated energy into neutrons. 1 figure, 9 references. State Science Center of the Russian Federation—Institute of Theoretical and Experimental Physics. Translated from Atomnaya énergiya, Vol. 87, No. 3, pp. 199–204, September, 1999.     

Variants of Aperiodic Pulsed Reactors with Boosted Pulse Parameters

Single (one-section) reactors, containing a neptunium–gallium or uranium–molybdenum alloy core, and coupled two-section systems, consisting of a single pulsed reactor and a driven subcritical assembly, consisting of a uranium–molybdenum alloy or dispersed uranium–graphite material, are studied. Calculations of the neutron and dynamical characteristics of these systems are performed. The information obtained, together with data from previous calculations, made it possible to draw a conclusion about the structure of reactor systems characterized by a short radiation pulse and large-volume cores and cavities for holding specimens. It is shown that a reactor with a single neptunium–gallium alloy core and a coupled cascade-type system consisting of this single driven reactor together with a driven subcritical uranium–graphite assembly have the best pulse parameters.     

Concept of electron accelerator-driven system based on subcritical cascade reactor

A concept of accelerator-driven system consisting of electron accelerator, neutron-generating target and two-core subcritical blanket with fast and thermal neutron spectrum has been presented. Some general features of the cascade neutron multiplication in the two-core subcritical blanket are discussed. Calculation results are demonstrated for the processes of electron–photon–neutron interactions of electron beam with the target material. Neutronic and heat engineering characteristics of the facility are also described. It has been shown that with the system's subcritical level of 2% and electron beam power of 4 MW, the facility power is as high as 50 MW.     

A Compact Fusion–Fission Hybrid Reactor

Up today, two hyper research projects to achieve nuclear fusion energy exist; inertial confinement fusion (ICF) driven by laser, called national ignition facility (NIF) and magnetic confinement fusion the international thermonuclear experimental reactor (ITER) project. In reaching the required temperature and pressure, to ignite nuclear fusion reactor, is technologically complex and economically expensive. Thus, a breakthrough and a short cut, other alternative methods should be considered. Pulsed power ICF driver with repetitive pulse operation, mainly dense plasma focus (DPF) machines for high yield fusion neutrons could be taken as drivers for the fission blanket operation. The setup can be a cost-effective and efficient. In this article, we consider a set of two medium energy sizes DPF to produce simultaneously dense plasma columns, operating as thermonuclear plasma driver, to pierce the pellet target for external nuclear fusion reactions. These DPFs produce sufficient fast neutrons for the fission process in the neutral uranium or thorium and/or weak enriched uranium blanket. The drive systems and the concept for delivering thermonuclear plasma to pellets target in the magnetic free zone of central region will be presented. The feasibility of such fusion–fission hybrid reactor will be discussed.     

Optimization of seed-blanket type fuel assembly for reduced-moderation water reactor

Parametric studies have been performed for a PWR-type reduced-moderation water reactor (RMWR) with the seed-blanket type fuel assembles to achieve a high conversion ratio, negative void reactivity coefficient and a high burnup by using MOX fuel. From the viewpoint of reactor safety analysis, the fuel temperature coefficients were also studied.From the result of the burnup calculation, it has been seen that ratio of 40–50% of outer blanket in a seed-blanket assembly gives higher conversion ratio compared to the other combination of seed-blanket assembly. And the recommended number of (seed+blanket) layers is 20, in which the number of seed (S) layers is 15 (S15) and blanket (B) layers is 5 (B5). It was found that the conversion ratio of seed-blanket assembly decreases, when they are arranged looks like a flower shape (Hanagara).By the optimization of different parameters, S15B5 fuel assembly with the height of seed of 1000 mm×2, internal blanket of 150 mm and axial blanket of 400 mm×2 is recommended for a reactor of high conversion ratio. In this assembly, the gap of seed fuel rod is 1.0 mm and blanket fuel rod is 0.4 mm. In S15B5 assembly, the conversion ratio is 1.0 and the burnup is 38.18 GWd/t in (seed+internalblanket+outer blanket) region. However, the burnup is 57.45 GWd/t in (seed+internal blanket) region. The cycle length of the core is 16.46 effective full power in month (EFPM) by six batches and the enrichment of fissile Pu is 14.64 wt.%. The void coefficient is +21.82 pcm/%void, however, it is expected that the void coefficient will be negative if the radial neutron leakage is taken into account in the calculation.It is also possible to use S15B5 fuel assembly as a high burnup reactor 45 GWd/t in (seed+internal blanket+outer blanket) region, however, it is necessary to decrease the height of seed to 500 mm×2 to improve the void coefficient. In this reactor, the conversion ratio is 0.97 and void coefficient is +20.81 pcm/%void. The fuel temperature coefficient is negative for both of cases.     

Measurement of the subcriticality of power-stressed reactors with an analog reactimeter

Conclusions A technique has been developed for measuring the effects of reactivity in a subcritical reactor with an analog reactimeter. It is based on the compensation of the current applied to the reactimeter input from the neutron detector. The compensation of current produced by neutrons of the subcritical multiplying assembly formalizes the algorithm for reactivity calculation, making it an adequate model of a reactor with a source and making it possible to determine the subcriticality without prior entry into the critical state. In this case the measurements are made in the presence of neutron sources characteristic of power-stressed reactors. The regular devices of the control and safety system could be used to produce unsteady variation of the neutron flux.All of this permits the proposed method to be extended to zero-power reactors and to power-stressed reactors. Once the subcriticality has been measured an analog of the neutron source is introduced into the reactimeter. This instrument measures the effects of reactivity in the subcritical state without the reactor being previously put into the critical state, monitors the entry of the reactor into the critical state by checking the reactivity, and makes all the measurements usually made with analog reactimeters. If the intensity of the source does not change during measurements (5–10 min) when chambers sensitive to rays (e.g., KNK-56 chambers) are used as neutron-flux detectors, then the accuracy of -ray compensation does not affect the results of the measurements.Translated from Atomnaya Énergiya, Vol. 45, No. 5, pp. 375–376, November, 1978.     

Prediction Method in Numerical Simulation of Dynamics Based on Prompt and Delayed Neutrons in Multiplying Systems

The basic elements of a method of numerical simulation of processes based on prompt and delayed neutrons in multiplying systems are presented. The method is based on predicting the contribution of the instantaneous state of the system to its state at subsequent definite times and summing the predicted contribution as a systematic transition is made to a new moment in time. The key element of the method is determining the initiation functions – the probabilities that a neutron emitted by a source in a prescribed volume of the system initiates a prompt fission neutron in a definite volume of the system sometime after emission. A procedure is proposed for determining the initiation functions; this procedure is based on the first-collision probability method and uses the standard stationary computer codes. The material presented in this paper comprises the basic results of the first stage in the development of the numerical model for full-scale simulation of the dynamics of the subcritical blanket of an experimental accelerator-driven subcritical system under construction at the Institute of Theoretical and Experimental Physics. It is noted that the model being developed can be used to analyze many important processes in other types of multiplying systems.     

Design and corrosion study of a closed spallation target module of an accelerator-driven system (ADS)

At the Forschungszentrum Karlsruhe (FZK) the characteristics of an accelerator-driven subcritical reactor system (ADS) are critically evaluated, mainly with respect to the potential of transmutation of minor actinides and long-lived fission products, to the feasibility and to safety aspects. The work is concentrating on system design, neutronics, thermalhydraulics, safety, materials and corrosion. This article describes the FZK approach to design a closed 4 MW(th) spallation target module with a solid beam window and eutectic lead–bismuth (Pb–Bi) as spallation material and cooling fluid, which is going to be implemented in the FZK three-beam concept of an ADS. This multi-beam concept shows significant improvements towards single-beam concepts from the literature with respect to power distribution in the subcritical blanket and thermal loads of heat removal from the beam window and the spallation region. For some selected martensitic and austenitic steels, corrosion tests in static lead are performed to examine their suitability as structural or window materials. Alloying aluminum into the surface layer by high-power electron beam treatment, corrosion can be reduced to nearly zero. One prerequisite to minimize corrosion is a proper oxygen control system (OCS) via the gas-phase to set the oxygen concentration in the liquid Pb–Bi. The dynamic behaviour of this oxygen control system is described. Finally, the KArlsruhe Lead LAboratory (KALLA) is introduced, the objectives of which are technological, thermal-hydraulic and corrosion investigations into the beam window, the spallation target module and the primary system of an ADS.     

SFR with once-through depleted uranium breed & burn blanket

This paper assesses the feasibility of Sodium-cooled Fast Reactor (SFR) cores that have TRU recycled seeds and once-through depleted uranium blankets. The design objective of these Seed-and-Blanket (S&B) cores is to maximize the power generated by the blanket. As the blanket fuel cost is significantly lower than the cost of the seed fuel and does not need reprocessing, increasing the fraction of reactor power generated by the blanket will reduce the total fuel cycle cost and the fuel reprocessing capacity required per unit of electricity generated. The S&B core is designed to have a prolate (“cigar”) shape seed (“driver”) to maximize the fraction of neutrons that radially leak into the subcritical blanket and reduce neutron loss via axial leakage. Both seed and blanket contain multiple batches; the blanket batches are gradually shuffled inward, while one third of the fuel batches in the seed are recycled. The preliminary study found that it is possible to design the seed to accommodate a wide range of TRU conversion ratios (CR) without significantly penalizing the burnup reactivity swing. The relatively small burnup reactivity swing enables to design the S&B core to operate at longer cycles and discharge its fuel at a higher burnup relative to conventional TRU transmutation cores with identical CR. The S&B cores can generate 1000 MW_th and fit within the S-PRISM reactor vessel. The fraction of core power generated by the blanket is between 40% and 50% without exceeding the radiation damage constraint of 200 Displacements per Atom (DPA); this fraction increases when the seed is designed to have a smaller CR. These features are expected to improve the economics of SFR.     

Characteristics of Two-Reactor Electronuclear Systems

The Monte Carlo method is used to simulate electronuclear systems consisting of two-cascade subcritical zones: a liquid-metal fast reactor, which is used as a booster, and a thermal reactor, where most of the energy is released. Reactors of the type VVÉR-1000, MSBR-1000, and CANDU-6 are considered. The systems considered, functioning in the safe regime (k _eff = 0.94–0.98), possess much higher maximum power in the entire range of k _eff than similar systems without an intermediate fast booster reactor. At the same time, for high thermal neutron flux and with both fast and thermal zones present nuclear wastes can be efficiently transmuted in them, decreasing the required proton current in the beam by approximately a factor of 10. This is especially important when the liquid-salt thermal breeding reactors are considered as the basic electricity producing zone.     

Comparison of Methods for Irradiating Prone Patients

The results of irradiation with an 18 MeV rotating gamma-ray setup and three variants of equipment for proton beam transport – horizontal beam, rotating universal GANTRI, and a planar system with irradiation direction limited to ±45° to the horizontal – are compared. The average values of three parameters averaged over the target size and position are obtained for each type of equipment – the fraction of the total dose that strikes the target, the ratio of the average (specific) irradiation dose to healthy tissue to the dose in the target, and the ratio of these quantities. Comparing the results shows that it is desirable to adopt simple planar systems in proton and ion therapy.     

聚变驱动次临界堆概念设计研究

在深入分析相关领域研究发展状况的基础上,提出一个可实现核废料嬗变、可裂变重金属核燃料和氚核燃料增殖、产能等多种功能的次临界反应堆概念。概念有托卡马克实验装置参数适量外推的等离子体物理和技术水平的聚变堆芯、高压He气/液态LiPb双冷却系统嬗变包层。介绍了系统基本概况和参考结构形式,阐述了系统聚变等离子体物理学、包层中子物理学和包层热工水力学设计的基本原则和主要工程约束限制条件,指出系统相关的安全和潜在环境影响问题,给出典型的参考设计参数。     

Long-Lived-Radionuclide Transmutation Scenarios

The results of multigroup calculations of continuous irradiation of Np, Am, and Cm in VVÉR-1000, PHWR-880, Superphoenix-1200, BREST-1000, and ÉLYaU-800 reactors are used to compare transmutation efficiency. The sources of continuous replenishment for the transmuters were Np, Am, and Cm extracted after a 3-yr holding period from the VVÉR and Superphoenix spent fuel. It is shown that the most effective transmuter is a subcritical liquid-fuel ÉLYaU system with an average thermal-neutron flux in the blanket 2·10¹⁵ sec^–1·cm^–2. For solid-fuel reactors, the continuous-irradiation model makes it possible to describe approximately the multiple transmutation regime. In the foreseeable future, one-time transmutation of Np, Am, and Cm in a solid-fuel reactor followed by storage in a long-term storage facility is feasible. The results of different computational variants for such regimes show that for transmutation in 10 yr in PHWR the radiotoxicity of Np, Am, and Cm accumulated in long-term storage reaches an equilibrium in no longer than 100 yr.     

聚变-裂变混合堆次临界能源包层结构的热-力耦合分析

探讨了一种新型聚变-裂变混合堆次临界能源包层的有限元建模方法。应用ANSYS Workbench软件建立了该次临界能源包层的3D结构模型,并对该模型进行了稳态热分析、热-力耦合分析,获得了包层各零件的应力分布及变形分布,分析了包层各零件的强度、刚度,利用热-力耦合分析找到了该次临界能源包层的薄弱环节。计算结果表明,该包层满足强度、刚度要求,为该次临界能源包层的设计和改进提供了理论依据。     

Expanded 233U Breeding in the Heavy-Water Blanket of an Electronuclear System

Comparative investigations are performed of the neutron-physical characteristics and their variations during burnup for two types of fuel Th–U and U–Pu with heavy- and light-water lattices. Analysis of the results gives the basic parameters of the electronuclear system operating in a thorium–uranium fuel cycle. It is shown that an external neutron source (accelerator + target) makes it possible to switch to the thorium–uranium fuel cycle with expanded ²³³U breeding without using fissioning uranium or plutonium isotopes. There are grounds for believing that with a higher accelerator current it is possible to achieve a regime where the heavy-water blanket can be replenished only with thorium with no ²³³U.