A genetic algorithm (GA)-based optimizer (GAOPT) has been developed for in-core fuel management of advanced gas-cooled reactors (AGRs) at HINKLEY B and HARTLEPOOL, which employ on-load and off-load ...refueling, respectively. The optimizer has been linked to the reactor analysis code PANTHER for the automated evaluation of loading patterns in a two-dimensional geometry, which is collapsed from the three-dimensional reactor model. GAOPT uses a directed stochastic (Monte Carlo) algorithm to generate initial population members, within predetermined constraints, for use in GAs, which apply the standard genetic operators: selection by tournament, crossover, and mutation. The GAOPT is able to generate and optimize loading patterns for successive reactor cycles (multicycle) within acceptable CPU times even on single-processor systems. The algorithm allows radial shuffling of fuel assemblies in a multicycle refueling optimization, which is constructed to aid long-term core management planning decisions. This paper presents the application of the GA-based optimization to two AGR stations, which apply different in-core management operational rules. Results obtained from the testing of GAOPT are discussed.
This paper is concerned with the reactivity during a transient of a layered MOX, and moderating lubricant (zinc stearate) mixing system which is used as part of fuel processing. The reactivity ...effects with increases in temperature and mixing (moderation) are investigated here. The transient and static simulations reveal that large increases in reactivity and temperature are possible. The nuclear criticality modelling of powders is performed using the Finite Element Transient Criticality (FETCH) code. This models criticality transients in spatial and temporal detail using a continuum multi-fluid model of the gas and solid-powder phases. The neutronics model in FETCH solves the neutron transport in full phase space. In this study a number of hypothetical criticality scenarios with the same generic mixing device and MOX powder are investigated in order to gain an understanding of the dynamics of powder criticality. An additive zinc stearate is also introduced. The zinc stearate, can act as a moderator and thus, on mixing, a ramp reactivity can be introduced. The mixing device is introduced into the simulations to help investigate this ramp reactivity.
A homogenized whole-reactor cylindrical model of the Dounreay Fast Reactor has been constructed using both deterministic and Monte Carlo codes to determine neutron flux distributions inside the core ...and at various out-of-core components. The principal aim is to predict neutron-induced activation levels using both methods and make comparisons against the measured thermal reaction rates. Neutron transport calculations have been performed for a fixed source using a spatially lumped fission neutron distribution, which has been derived from measurements. The deterministic code used is based on the finite element approximation to the multigroup second-order even-parity neutron transport equation, which is implemented in the EVENT code. The Monte Carlo solutions were obtained using the MCNP4C code, in which neutron cross sections are represented in pointwise (or continuous) form. We have compared neutron spectra at various locations not only to show differences between using multigroup deterministic and continuous energy (point nuclear data) Monte Carlo methods but also to assess neutron-induced activation levels calculated using the spectra obtained from both methods. Results were also compared against experiments that were carried out to determine neutron-induced reaction rates. To determine activation levels, we employed the European Activation Code System FISPACT. We have found that the neutron spectra calculated at various in-core and out-of-core components show some differences, which mainly reflect the use of multigroup and point energy nuclear data libraries and methods employed, but these differences have not resulted in large errors on the calculated activation levels of materials that are important (such as steel components) for decommissioning studies of the reactor. The agreement of calculated reaction rates of thermal neutron detectors such as the
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Mn(n,γ)
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Mn against measurements was satisfactory.
INTRODUCTIONMucormycosis following hematopoietic stem cell transplant (HSCT) carries a very high mortality rate. Pulmonary mucormycosis often leads to systemic dissemination and eventual death. It is ...imperative for transplant providers to have a high level of suspicion for mucormycosis and initiate early treatment. Here, we present a 64-year-old woman who died of disseminated mucormycosis 13 days following her allogeneic HSCT.CASE PRESENTATIONA 64-year-old female with a history of acute myeloid leukemia (AML) presented for allogeneic HSCT and passed away from intracerebral hemorrhage secondary to mucormycosis infection 13 days following her transplant. On autopsy, it was found she had angioinvasive mucormycosis in her frontal lobe leading to cerebral edema which eventually led to tonsillar herniation and brainstem infarction. Her lungs were the likely source of infectious dissemination.DISCUSSIONThis case represents an unusual course of events following HSCT in that no other published case shows tonsillar herniation resulting from mucormycosis-related intracerebral swelling. We also report this case because it is believed mucormycosis in HSCT patients is underreported. Additionally, our case highlights the importance of increased vigilance for mucormycosis in patients with prolonged neutropenia prior to HSCT and the potential link of voriconazole prophylaxis and increased risk for mucormycosis.
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