Nuclear Criticality Safety Calc Analyses - Small-Diameter Containers

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Core design of long‐cycle small modular lead‐cooled fast reactor

For instance, the pin diameter of 1. Three types of assemblies—driver assembly, reflector assembly, and control assembly—are employed. Those geometries are referred from the ALFRED core 43 with the following modifications: removing the center hole and lengthening the fuel rod, using 91 fuel pins per assembly instead of fuel pins to reduce the assembly pitch, and changing the dimensions of the absorbing pins of the control assembly. Driver assemblies consist of fuel pins made of fuel pellets, claddings, and helium gaps between fuel pellets and claddings.

The large plenum aims at accommodating fission gas generated during the long fuel life, and it must be of a length at least equal to the length of active fuel. YSZ has been chosen as a reflector material due to its low neutron absorption cross section, low thermal conductivity, and high corrosion resistance under neutron irradiation.

The control assembly consists of a bundle of 19 absorbing pins inside a cylindrical tube, called a duct, cooled by LBE. The control rods move together to control the core reactivity. However, the main drawbacks of this material in the rod design are that Hf is heavy and expensive.

The core type considered in this paper is the onion zoning core. The core breeding ratio is the ratio of fissile material created to fissile material consumed either by fission or absorption. The onion zoning core consists of two regions: the blanket region and the LEU region. The blanket region is placed at the center of the core. Natural UN is used as the fuel of the blanket region. The LEU region encloses the blanket region radially and axially. As fission occurs, the conversion of U into Pu through neutron capture takes place in both regions of the reactor.

For this reason, the enrichment of the LEU region must be optimized to adjust the U loading and increase the core breeding ratio. As a result of previous sensitivity analyses, 42 two types of core were selected, with different numbers of driver and reflector assemblies.

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The core configuration was selected as the best performance for the breed and burn concept and for achieving an active core diameter less than the maximum value of 1. The two candidates are analyzed in the next section in terms of k eff and core breeding ratio trends during depletion for different values of enrichment in the LEU region. In this model, the active core height is divided into 20 axial meshes. All material compositions are homogenized assemblywise based on volume fractions. For both type I and type II cores, the depletion patterns of the fuel for different enrichment values in the LEU region are studied.

The burnup reactivity swing is defined in the following equation 49 : 1.

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The more k eff varies during the depletion, the bigger the reactivity swing is. One can notice that the core burns faster for higher U enrichment, that the breeding ratio increases during the depletion, and that the lower the U enrichment, the higher the breeding ratio and the lower the reactivity swing is. For the type II core, the enrichment of LEU region is reduced to minimize the burnup reactivity swing during 30 EFPY operation, making the most of the fact that the type II core has more igniter assemblies and a larger active core diameter than the type I core.

Finally, it is shown that the type II core with Based on these results, the proposed optimized core is the type II core with a This core achieves a lifetime of 30 EFPY and a small burnup reactivity swing. The optimization of this core and the enrichment of the LEU region were conducted by sensitivity analyses of k eff and breeding ratio trends over 30 EFPY cycle. The LEU region contains 66 igniter fuel assemblies with In total, the core consists of 78 driver assemblies, 13 control assemblies, and reflector assemblies.

Its task is to bring the reactor from any operating condition to a hot standby condition, leading to an improvement in overall shutdown reliability. Finally, the active core diameter and height are 1. The average specific power density, average volumetric power density, and linear power density are calculated from the design data. Although the core breeding ratio is less than 1. Since the breeding ratio remains smaller than unity, the designed core is a burner not breed and burn reactor core and the k eff decreases over the full operation time.

This location of maximum fluence does not change during depletion and remains the same throughout the entire cycle. The maximum total fluence estimated by the product of flux and time at EOC is The initial fuel loading mass is The average power density equals The Pu and Pu buildup masses remain small. A part of U is transmuted to fissile Pu so that criticality is maintained in the core. Overall, the average discharge burnup of the core is However, the rate at which this transfer of power occurs in the core from the periphery to the center remains small due to the small breeding ratio.

Overall, the axial power rate increases at the center and decreases at the bottom and the top of the active core height during depletion. The core height is divided into axial meshes 0. The gap size and plenum height are 0. Meanwhile, the axial fuel, cladding, and coolant temperatures of the hottest assembly tend to linearly increase from the bottom to the top of the active core coolant flows from bottom to top.

Therefore, the designed gap and plenum size are expected to accommodate for the fuel swelling of UN and the release of gaseous fission products throughout the cycle. To evaluate the accuracy of the safety parameters calculated with the deterministic code system ARC, a heterogeneous whole core is simulated with UNIST Monte Carlo code MCS, and its results for the safety study are compared to the homogeneous core results from the deterministic code system ARC.

The reliability of the control rod CR system and an accurate prediction of the rod worth are significant for safety assessments. The rod worth should be able to handle the burnup reactivity swing and temperature defect. This leads to the determination of the shutdown margin SDM. Total temperature defect: the reactivity reduction all control assemblies out from cold zero power CZP to hot full power HFP condition. The total rod worth as all control assemblies are inserted.

The worth of the worst stuck control assembly filled with coolant. The uncertainties and other margins. The available reactivity worth: the total rod worth minus the worth of the worst stuck control assembly. The shutdown margin, which is the difference between the available reactivity worth and the maximum required worth, ie, the sum of the burnup reactivity swing, the temperature defect, the uncertainties, and other margins.

Based on the approach developed in an LFR study of ANL, 58 other uncertainties that need to be considered are the criticality prediction, fissile load, and refueling possibility.

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  7. The total uncertainty is calculated as the root sum squared RSS of all the uncertainties considered. For the rod worth calculation, it is noted that the control assembly on the third ring has the highest rod worth value because it is located next to the LEU region. The individual rod worth of the six control assemblies on the third ring is equal due to the core symmetry. This large positive SDM value shows that the reactivity control system can cover the burnup reactivity swing, temperature defect, and other uncertainty effects during the operation.

    Because the high power rate region tends to slowly move from the peripheral region to the center of the core, the worth of the secondary control rod and the worth of the worst control assembly, located in the center region of the core, both increase during depletion. The coefficients considered in this work include the coolant density coefficient, the fuel Doppler coefficients, the axial core expansion coefficient, the radial core expansion coefficient, and the control rod driveline expansion coefficient.

    These coefficients are determined by direct eigenvalue differences between the base configuration and the perturbed state of the reactor. The reactivity at reference state is the one obtained at the normal operating state. A total of experiments were judged to be similar to application 1, and 68 experiments were judged to be similar to application 2. None of the experiments were judged to be adequately similar to applications 3 and 4. Discussion of the uncertainty analysis and similarity assessment is provided for each of the four applications.

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    Example upper subcritical limits USLs were. The study demonstrates the performance of the tools. This work has been a useful step towards verification of the existing and developed sensitivity analysis methods. Nuclear Criticality Safety Data Book. Safety Critical Mechanisms.

    Spaceflight mechanisms have a reputation for being difficult to develop and operate successfully. This reputation is well earned. Many circumstances conspire to make this so: the environments in which the mechanisms are used are extremely severe, there is usually limited or no maintenance opportunity available during operation due to this environment, the environments are difficult to replicate accurately on the ground, the expense of the mechanism development makes it impractical to build and test many units for long periods of time before use, mechanisms tend to be highly specialized and not prone to interchangeability or off-the-shelf use, they can generate and store a lot of energy, and the nature of mechanisms themselves, as a combination of structures, electronics, etc.

    In addition to their complexities, mechanism are often counted upon to provide critical vehicle functions that can result in catastrophic events should the functions not be performed. It is for this reason that mechanisms are frequently subjected to special scrutiny in safety processes. However, a failure tolerant approach, along with good design and development practices and detailed design reviews, can be developed to allow such notoriously troublesome mechanisms to be utilized confidently in safety-critical applications.

    A primer on criticality safety. Criticality is the state of a nuclear chain reacting medium when the chain reaction is just self-sustaining or critical. Criticality is dependent on nine interrelated parameters. Moreover, we design criticality safety controls in order to constrain these parameters to minimize fissions and maximize neutron leakage and absorption in other materials, which makes criticality more difficult or impossible to achieve.

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    The SAPs are primarily intended for use by HSE's inspectors when judging the adequacy of safety cases for nuclear facilities. The revised SAPs relate to all aspects of safety in nuclear facilities including the technical discipline of criticality safety. The purpose of this paper is to set out for the benefit of a wider audience some of the thinking behind the final published words and to provide an insight into the development of UK regulatory guidance.

    How can traceability of software safety requirements be created for legacy safety critical systems? Requirements in safety standards are imposed most times during contract negotiations. On the other hand, there are instances where safety standards are levied on legacy safety critical systems, some of which may be considered for reuse for new applications. Safety standards often specify that software development documentation include process-oriented and technical safety requirements, and also require that system and software safety analyses are performed supporting technical safety requirements implementation.

    So what can be done if the requisite documents for establishing and maintaining safety requirements traceability are not available? Nuclear criticality safety : 5-day training course. This compilation of notes is presented as a source reference for the criticality safety course. It represents the contributions of many people, particularly Tom McLaughlin, the course's primary instructor.

    criticality safety calculations: Topics by

    The NCSP maintains fundamental infrastructure that supports operational criticality safety programs. This infrastructure includes continued development and maintenance of key calculational tools, differential and integral data measurements, benchmark compilation, development of training resources, hands-on training, and web-based systems to enhance information preservation and dissemination. This paper also discusses the role Dr. Sol Pearlstein played in helping the Department of Energy lay the foundation for a robust and enduring criticality safety infrastructure.