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[en] 'Full text:' The ZED-2 low-power research reactor has been in operation at the Chalk River Laboratories in Canada since the seventh of September, 1960. For over fifty years, physicists have used it to measure the neutronic properties of numerous reactor fuel lattices for the development of heavy water moderated reactors. Today, the exponential growth of computing power makes numerical simulation a viable tool for reactor design, but we are then challenged to establish the accuracy of those simulations. When we assess the accuracy of computer codes for neutron transport analysis and reactor design today, we still compare them to ZED-2 measurements, which must be assessed with due care. Participation of Chalk River physicists in the International Reactor Physics Experiment Evaluation Project has improved the quality of uncertainty analyses applied to ZED-2 experiments. We assess the measurement uncertainty of experimental parameters with standard methods, and of uncertainty estimation are applied to based on sensitivity analysis for those simulations, which has been a powerful technique. The uncertainty of a reactor physics simulation can be directly estimated by using Monte Carlo sampling to simulate the uncertainty of input data. Simulations are repeated with parameters of the experimental configuration varied randomly within their probability distributions, and the effect on reactivity calculations is assessed. Horst Glaeser of GRS has formalized a simple method of assessment by limit statistics. We also compare reactor physics codes against each other, and Monte Carlo neutron transport codes such as MCNP have become a de facto standard for comparison. Monte Carlo codes trade theoretical approximations for the statistical analysis of many neutron histories, which is efficient on massively parallel computers. However, MCNP must still use measured data for the geometry and materials of an experimental configuration, and for nuclear properties. Thus, MCNP simulation results are still limited by the accuracy of experimental measurements. Monte Carlo sampling of a large number of full-core Monte Carlo cases can burden a modern computer cluster. We found it faster to sample cases with deterministic lattice cell codes, which run more quickly. While that approach only works for a uniform lattice, many important coolant voiding reactivity measurements were made with uniform lattices in ZED-2. Continued growth of computer power should enable us to sample multiple MCNP cases of complex ZED-2 experiments in the future. Finding the sensitivity to nuclear data is more difficult. We developed methods for nuclear data adjustment within MCNP, but the data set is large, and sensitivity to specific data would be difficult to extract from Monte Carlo sampling. Chalk River physicists have used TSUNAMI, which is a toolset for sensitivity and uncertainty analysis based on the KENO Monte Carlo neutron transport code; ERANOS is a deterministic neutron transport code with similar capabilities. These tools assess the sensitivity to specific nuclear data by calculation of the forward and adjoint neutron flux and application of first-order perturbation theory. Their estimates of nuclear data uncertainties provide a measure of code accuracy. They also show how well an experiment covers the uncertainties in a specific application. These methods encourage the closer examination of historical ZED-2 experiments, and support a better understanding of the data. Alternatively, the TSURFER module of TSUNAMI finds adjustments to the nuclear data that would correct the bias in simulation of an experiment, which also constrains the uncertainty. Direct adjustments of nuclear data in our MCNP simulations of the experiments largely confirmed TSURFER. When the bias is taken into account during analysis, the accuracy is improved. That also bridges the gap between ZED-2 and power-reactor simulations, based on the nuclear data that they share. TSURFER corrections may be based on multiple experimental cases, a feature which is essential for reactivity coefficients that were measured indirectly, through differences between experimental configurations in ZED-2. Since the coverage of nuclear data uncertainties may be improved by including additional experiments over a range of conditions, the remaining uncertainty in analysis may also be reduced. The adoption of modern methods for sensitivity analysis and the simulation of uncertainty in reactor physics computer codes greatly improve our understanding of code accuracy. Uncertainty estimates for our simulations been halved, but we can identify and reduce the remaining sources of bias and uncertainty. This increases our confidence in code accuracy assessments, as well as helping us plan better for new measurements in the ZED-2 reactor. (author)
[en] The concept of 'disruptive innovation' is a management tool that provides a framework for understanding the structure and dynamics of technology markets, especially their sometimes acute response to innovation. The concept was used in a trial assessment of a number of energy technologies, including renewable energy technologies and energy storage as well as nuclear technologies, as they interact in industry and the marketplace. The technologies were assessed and perspectives were provided on their current potential for innovation to disrupt the value networks behind various energy markets. The findings are summarized, and indicate that the concept may provide useful guidance for planning of technology development. (author)
[en] Accurate and complete nuclear data are a fundamental requirement for any nuclear reactor model. One major challenge to the modeling of advanced nuclear reactor systems is the lack of sufficient nuclear data for the operating conditions and materials relevant to the advanced systems. The Canadian Supercritical Water-Cooled Reactor (SCWR) is an advanced reactor concept which, like all advanced GEN-IV reactor concepts, differs significantly in operating conditions, fuel composition and non-fuel materials from conventional reactors. The Canadian SCWR is a pressure tube-based reactor with heavy water moderator and light water coolant, intended to operate with a coolant pressure of 25 MPa and temperatures ranging from 350 oC (inlet) to 625oC (outlet), with (Pu,Th)O2 fuel, using advanced fuel bundle and fuel channel designs. Because of these differences from conventional heavy water (HWR) and light water (LWR) reactors, it is not clear whether presently-used core modeling methods or nuclear data libraries are adequate for SCWR modeling. In this paper, an idealized model of an SCWR fuel channel with fresh fuel is modeled in order to examine the nuclear data contributions to the sensitivity and uncertainties in the neutron multiplication factor, k, and various lattice reactivity coefficients. (author)
[en] A 3-dimensional boundary-integral method has been developed for rf cavity mode analysis. A frequency-dependent, homogeneous linear matrix equation is generated from a variant of the magnetic field integral equation (MFIE) where the domain of integration is a closed surface specifying the rf envelope of the cavity. Frequencies at which the MFIE has non-zero solutions are mode frequencies of the cavity, and the solutions are the corresponding surface magnetic field distributions. The MFIE can then be used to calculate the electric and magnetic field at any other point inside the cavity. Forward iteration is used to find the largest complex eigenvalue of the matrix at a specific frequency. This eigenvalue is 1 when the frequency corresponds to a cavity rf resonance. The matrix equivalent of the MFIE is produced by approximating the cavity surface by a set of perfectly conducting surface elements, and assuming that the surface magnetic field has constant amplitude on each element. The method can handle cavities with complex symmetries, and be easily integrated with finite-element heat-transfer and stress analysis codes
[en] Elliptical beam shapes have been seen at the exit of a number of on-axis coupled electron linacs. These non-circular shapes have been attributed to the quadrupole effects produced by the coupling slots in the cell walls. Qualitative and detailed cavity calculations predict that the quadrupole effects cancel if the coupling slots are aligned across the accelerating cavities, as opposed to rotated through 90 degree as has normally been the case. Two short S-band linacs, identical except for the orientation of the coupling slots, have been built to test the predictions. The results of detailed measurements of the beam profiles at the exit of the two linacs are discussed
[en] This report describes the development of a mechanical design for a single-cell 476 MHz room-temperature rf cavity suitable for the PEP-II Asymmetric B-Factory Project at the Stanford Linear Accelerator Center. The work comprised preparation of a preliminary mechanical design of a single-cell 476 MHz rf cavity capable of handling 150 kW dissipation in the cavity walls. The results of extensive two dimensional and three dimensional heat transfer and thermal stress analyses of the cavity structure under high power operating conditions are presented, and a mechanical design and fabrication scheme is proposed. (Author) 9 refs., 38 figs., 4 tabs
[en] The concept of 'disruptive innovation' is a management tool that provides a framework for understanding the structure and dynamics of technology markets, especially their sometimes acute response to innovation. The concept was used in a preliminary assessment of a number of energy technologies, including renewable energy technologies and energy storage, as well as nuclear technologies, as they interact in industry and the marketplace. The technologies were assessed and perspectives were provided on their current potential for innovation to disrupt the value networks behind electricity markets. The findings indicate that this concept may provide useful guidance for the planning of technology development. (author)
[en] The ZED-2 (Zero Energy Deuterium) reactor is an experimental low-power critical facility located at the Atomic Energy of Canada Limited Chalk River Laboratories in Ontario, Canada. The facility is used to perform physics experiments in support of the CANDU and Advanced CANDU Reactor (ACR) programs. The reactor core is a large cylindrical vessel in which reactor fuel rods are positioned vertically. A heavy water moderator is pumped into the vessel to make the reactor critical. The ZED-2 design is very versatile: it can accommodate mixed fuel types in a variable number of fuel rods each with or without CANDU-type or ACR-type channels; channel coolants can be light or heavy water, or air, and can vary from channel to channel; lattices can be square or hexagonal with continuously variable lattice pitch; and some CANDU-type channels can be heated. Many of the experiments performed involve uniform cores containing the same type of fuel and channel in each fuelled location. However, at times a smaller number of fuel rods and channels are placed in the centre of a larger region of reference fuel to form a critical core assembly. These are called substitution experiments. The purpose of this paper is to describe why substitution experiments are performed, detail how they have historically been conducted and analyzed to extract the desired data from the test fuel, and finally how they are performed and analyzed today using specialized software.
[en] Validation of reactor physics codes requires the determination of bias and uncertainty in calculating parameters of importance (such as reactivity coefficients) in the analysis of nuclear power reactors. A challenge of this process is extending bias and uncertainty from validation against measurements in a test facility (such as AECL's ZED-2 critical facility at the Chalk River Laboratories) to the power reactor. AECL, with help from ORNL, is developing the use of sensitivity/uncertainty (S/U) analysis for bias extension for reactivity coefficient calculations (including coolant void reactivity, which is not a coefficient per se) to CANDU-type power reactors. This builds on methodology for validation of keff in criticality safety analysis . An underlying requirement of this method is that the physics codes model the reactor accurately with respect to the underlying nuclear theory, geometry and material composition. With a Monte-Carlo code and a high-fidelity model in which modelling uncertainties are minimized, the largest contributor to uncertainty in the calculation is from the nuclear cross section data. The main S/U analysis function is to assess the ZED-2 experiment representativity of the power reactor and to generate cross-section adjustments that increase consistency of results for the purpose of determining bias: Assessment of uncertainties and sensitivities of keff and reactivity coefficients, due to uncertainties in nuclear cross-section data libraries used in MCNP5  simulations. Estimation of representativity of the power reactor by the ZED-2 critical core experiments. This is assessed and quantified by the sensitivity of the keff calculation to variations of cross-section data within their uncertainties, as well as the sensitivities of reactivities. Extension of MCNP5 computational biases in keff and various reactivity coefficients based on simulations of ZED-2 experiments to the conditions of the power reactor.