MULTIPHYSICS MODELING OF PRECURSORS IN MOLTEN SALT FAST REACTORS USING PROTEUS AND Nek5000

The goal of this work was to calculate the impact of the delayed neutron precursor drift in fast spectrum Molten Salt Reactors (MSRs) using coupled solutions from the neutronics code PROTEUS and the computational fluid dynamics code Nek5000. Specifically, using a multiphysics approach to solve the effective delayed neutron fraction (βeff) or delayed neutron precursor distribution for reactors with flowing fuel salts would provide valuable information for transient simulations and safety assessments. Given the multiple options for the flux solution and geometric resolution/fidelity in PROTEUS, two approaches were developed and applied to various test cases: PROTEUS-NODAL/Nek5000 and PROTEUS-SN/Nek5000. For the former, the precursors are tracked in the built-in precursor drift model in PROTEUS-NODAL, whereas in the latter, Nek5000 directly tracks the precursors. Both approaches were used to solve a single test channel problem and showed excellent agreement in the calculated βeff. Separately, a 3D hourglass-shaped core was modeled using the PROTEUS-SN/Nek5000 approach. This problem was designed to demonstrate the capability of the discrete ordinates (SN) solver and Nek5000 to model complex core designs with axially varying geometries and the ability for Nek5000 to track the precursors and calculate the resulting βeff. In addition, the Nek5000 calculations revealed the presence of recirculation zones in the hourglass design, which could lead to significant temperatures in the fuel salt and surrounding materials. These first coupled solutions show why these approaches may be necessary for not only predicting the precursor drift effect in fast MSRs but also for reactor design and performance assessments.

The effect of mode of delivery on the perinatal outcome in fetuses with abdominal wall defects

A descriptive study of 125 infants with abdominal wall defects was undertaken to determine the effect of mode of delivery on outcome. Fifty-six infants had gastroschisis and 69 had omphalocele. Overall, there were no differences between the omphalocele and the gastroschisis groups in either cesarean section rate (22% vs 26%) or prematurity rate (26% vs 30%). However, the omphalocele group had a significantly higher infant death rate (22% vs 7%, p less than 0.001), a significantly higher incidence of associated major congenital anomalies (29% vs 5%, p less than 0.001), and a higher incidence of long-term infant morbidity (14.5% vs 8.9%). Within either group there was no significant difference between vaginal and cesarean delivery regarding either infant mortality, acute or long-term infant outcome, or frequency of associated major anomalies. We conclude that vaginal delivery of infants with abdominal wall defects does not adversely affect infant outcome.

Labial adhesions in a postpartum patient

The occurrence of labial adhesions in a patient in the immediate postpartum period is described. The adhesions did not respond to topical estrogen therapy, and sharp separation was required. Factors related to possible etiology as well as management of this condition are discussed.

Functional aspects of T-lymphocyte subsets in pregnancy

Several recent reports have suggested that a decrease in circulating T helper cells may contribute to the relative immunodeficiency of pregnancy. To investigate the significance of these findings, 90 pregnant women were evaluated. The results of this study indicate that although pregnant women have a decreased proportion of T helper cells, they do have adequate T helper cell function as determined by an in vitro immunoglobulin synthesis assay and a T-lymphocyte colony-forming assay. Based on these studies it is unlikely that decreased numbers of T helper cells are primarily responsible for the immunodeficiency of pregnancy.