Transport Of Fissile Material Research Articles

Impact of control rod insertion during burnup on PWR fuel assembly isotopic composition

Abstract Criticality analysis of spent fuel assumes that the fuel material is unburned which means that it is in its most reactive condition. In fact, this is not the real situation for fuel as it is burned during reactor operation causing reduction in the reactivity. Considering the reduction in reactivity during spent fuel calculations is the Burn-up Credit concept (BUC). In addition, the control rods radial and axial positions have an effect on the reactivity which can be considered in the criticality safety analysis. This paper studies the effect of burnup and control rods (CRs) movement on reactivity and isotopes inventory. Calculations are carried out in two phases, first kinf is calculated for different burnup profiles with control rods are either fully withdrawn or fully inserted. In the second phase keff is calculated for different control rods insertion levels. For both phases, burnup calculations are performed for a UO2 assembly then multiplication factor calculations of burned UO2 assemblies in cold state are done. The burnup calculations are performed using MCNP6 code and ENDF/B-VII library for different burnup levels up to 45 GWd/tU. The results obtained can be taken in consideration in criticality safety analysis performed for the spent fuel to improve the economic efficiency for manufacture, storage and transportation of fissile materials.

On-Site Nuclear Fuel Cycle of “BREST” Reactors

Dynamic developing of modern nuclear industry demands meeting the following requirements: improved safety, reduced capital costs, radioactive waste (RW) management issues, independence of limited resources. Efficiency of uranium resources used in "BREST" reactors based on a closed fuel cycle is about 160 times higher than for VVER, RBMK reactors [1], which makes it possible to stop searching for new deposits and uranium mining. The need for periodical fuel regeneration and fabrication in a closed cycle includes reproduction of plutonium in the core without the uranium containing screens (breeding ratio is approximately 1,05, ensuring a high level of safety and support of the non-proliferation regime) and transmutation of the most dangerous long-lived actinides and high refining of RW, achieving the radiation balance of buried RW and extracted uranium ore. The manufacturing is located directly at the NPP to avoid transportation of fissile materials. This approach provides economic efficiency of the entire complex.

Experimental investigation of the MSFR molten salt reactor concept

Abstract In the paper experimental modelling and investigation of the MSFR concept will be presented. MSFR is a homogeneous, single region liquid fuelled fast reactor concept. In case of molten salt reactors the core neutron flux and fission distribution is determined by the flow field through distribution and transport of fissile material and delayed neutron precursors. Since the MSFR core is a single region homogeneous volume without internal structures, it is a difficult task to ensure stable flow field, which is strongly coupled to the volumetric heat generation. These considerations suggest that experimental modelling would greatly help to understand the flow phenomena in such geometry. A scaled and segmented experimental mock-up of MSFR was designed and built in order to carry out particle image velocimetry measurements. Basic flow behaviour inside the core region can be investigated and the measurement data can also provide resource for the validation of computational fluid dynamics models. Measurement results of steady state conditions will be presented and discussed.

Heterogeneity versus homogeneity effects in neutron absorbers used in transport packages

AbstractMany fissile material transport packages incorporate boron as a neutron poison [predominantly as a boron–metal matrix composite (MMC)] to maintain criticality safety. The MMC contains a prespecified proportion of Boron ‘homogeneously’ distributed throughout the metal matrix. Uncertainty arises as to the meaning of ‘homogeneous’, in the context of providing the neutron absorbing properties assumed in the safety case for a package and the potential effect on criticality. During criticality analyses, it is usual for homogeneous materials to be assumed as uniform, without irregularities, with equal properties in all directions, at the atomic level. Since the boronated materials are ‘alloys’, the constituents are not chemically combined but finely mixed, with the boron particles, of various sizes, viewable via a microscope. This signifies that at the atomic level, the material is not homogeneous, but a heterogeneous mixture with size and distribution of boron within the MMC being not strictly uniform.D...

'Design to manufacture': journey through criticality considerations for new design fissile material transport packages

The development of new fissile material transport packages is an increasingly complex and costly business. The IAEA regulations stipulate performance requirements for the behaviour of the package under both normal and accident conditions. The principal performance drivers are: impact/structural, thermal, shielding and criticality safety. The needs of these disciplines can often compete, with refinements becoming necessary to optimise the design of the package. Maximising the payload while achieving the required levels of safety can be time consuming and expensive. Early communication with the criticality safety analysts can frequently speed up the design process. Numerous variables are significant to criticality safety, (e.g. mass, geometry and spacing of fissile material, presence of moderators, presence of fixed poisons, potential damage to package, etc.). Small changes in the design can result in big changes in the reactivity and this may lead to a very large number of scoping calculations. Increased computing power and improved code abilities can make criticality scoping calculations much more efficient. The development of software to enable a single parameterised input to analyse multiple variations of a basic model provides significant benefits in the production of the criticality analysis and to the overall design process. Criticality analysis of a specific design and of variations in that design can now be performed more quickly and efficiently. Through frequent interaction between members of the design team, a 'fluid' design can be created, and an iterative process can then optimise the package configuration. Retaining the criticality input throughout the design, development, prototype manufacture and testing ensures that the key safety principles are progressed to the manufactured package. In turn, the time and cost of the overall project in producing an acceptable package may be much reduced. The paper presents experience from a criticality viewpoint of the development of new package designs for transport of fissile materials, emphasising the benefits of the utilisation of software/computing developments in this process, with statistics illustrating the efficiencies now achievable.

DETERRENCE OF NUCLEAR TERRORISM WITH MOBILE RADIATION DETECTORS

The United States has multiple nuclear detection initiatives to secure against a terrorist nuclear attack, including the Container Security Initiative, installation of radiation detectors at U.S. border points of entry, and establishment of the Domestic Nuclear Detection Office (DNDO). The current nuclear detection system architecture falls short of being able to reliably catch fissile nuclear material in transit, specifically shielded Highly Enriched Uranium (HEU) and Plutonium (Pu), both within the US and abroad. Checkpoints at border crossings can be circumvented, and no adequate system is under development to deter the transport of fissile materials. Using nuclear link-budget calculations, we show why a network relying primarily on handhelds, fixed detectors, and portals is not sufficient. We examine the technical, economic, and operational feasibility of a comprehensive national network incorporating in-vehicle detectors to reliably detect and deter the transport of fissile material inside the vehicle itself.

Thorium-Fueled Underground Power Plant Based on Molten Salt Technology

This paper addresses the problems posed by running out of oil and gas supplies and the environmental problems that are due to greenhouse gases by suggesting the use of the energy available in the resource thorium, which is much more plentiful than the conventional nuclear fuel uranium. We propose the burning of this thorium dissolved as a fluoride in molten salt in the minimum viscosity mixture of LiF and BeF2 together with a small amount of 235U or plutonium fluoride to initiate the process to be located at least 10 m underground. The fission products could be stored at the same underground location. With graphite replacement or new cores and with the liquid fuel transferred to the new cores periodically, the power plant could operate for up to 200 yr with no transport of fissile material to the reactor or of wastes from the reactor during this period. Advantages that include utilization of an abundant fuel, inaccessibility of that fuel to terrorists or for diversion to weapons use, together with good economics and safety features such as an underground location will diminish public concerns. We call for the construction of a small prototype thorium-burning reactor.

The 1996 IAEA Regulations for the Safe Transport of Radioactive Materials—The Transport of Fissile Material

In September 1996 the Board of Governors of the International Atomic Energy Agency (IAEA) approved the publication of the 1996 edition of the Regulations of the Safe Transport of Radioactive Materials. The requirements for the transport of fissile material differ significantly in this document from the requirements of the previous (1985) edition of the Regulations. Changes have been made to the materials which are subject to the additional requirements for fissile material and to the way in which packages containing fissile material are tested, assessed and labelled. Specific requirements for the carriage of fissile material by air and for uranium hexafluoride have also been introduced.

Nuclear Transport Approvals and Practice in Sweden

AbstractThis paper describes the transport related part of the Swedish integrated system for supervision of the movement of nuclear materials. The legal framework is described as well as the unique role of SKI being both the regulatory body for safety at the nuclear installations and the national Competent Authority for transport of fissile material. The general outlines of the SKI provisions for transport, physical protection and quality assurance are presented. Practice in terms of Package Design Approvals, certificate revalidations, transit shipment approvals, import/export licenses are described. Finally experience from the implementation of the system is presented.