Impact flux of asteroids and water transport to the habitable zone in binary star systems

By now, observations of exoplanets have found more than 50 binary star systems hosting 71 planets. We expect these numbers to increase as more than 70% of the main sequence stars in the solar neighborhood are members of binary or multiple systems. The planetary motion in such systems depends strongly on both the parameters of the stellar system (stellar separation and eccentricity) and the architecture of the planetary system (number of planets and their orbital behaviour). In case a terrestrial planet moves in the so-called habitable zone (HZ) of its host star, the habitability of this planet depends on many parameters. A crucial factor is certainly the amount of water. We investigate in this work the transport of water from beyond the snow-line to the HZ in a binary star system and compare it to a single star system

Colliding Winds in Low-Mass Binary Star Systems: wind interactions and implications for habitable planets

Context. In binary star systems, the winds from the two components impact each other, leading to strong shocks and regions of enhanced density and temperature. Potentially habitable circumbinary planets must continually be exposed to these interactions regions. Aims. We study, for the first time, the interactions between winds from low-mass stars in a binary system, to show the wind conditions seen by potentially habitable circumbinary planets. Methods. We use the advanced 3D numerical hydrodynamic code Nurgush to model the wind interactions of two identical winds from two solar mass stars with circular orbits and a binary separation of 0.5 AU. As input into this model, we use a 1D hydrodynamic simulation of the solar wind, run using the Versatile Advection Code. We derive the locations of stable and habitable orbits in this system to explore what wind conditions potentially habitable planets will be exposed to during their orbits. Results. Our wind interaction simulations result in the formation of two strong shock waves separated by a region of enhanced density and temperature. The wind-wind interaction region has a spiral shape due to Coriolis forces generated by the orbital motions of the two stars. The stable and habitable zone in this system extends from approximately 1.4 AU to 2.4 AU. (TRUNCATED)Comment: 15 pages, 11 figures, to be published in A&

Asteroid flux towards circumprimary habitable zones in binary star systems: I. Statistical Overview

So far, multiple stellar systems harbor more than 130 extra solar planets. Dynamical simulations show that the outcome of planetary formation process can lead to various planetary architecture (i.e. location, size, mass and water content) when the star system is single or double. In the late phase of planetary formation, when embryo-sized objects dominate the inner region of the system, asteroids are also present and can provide additional material for objects inside the habitable zone (hereafter HZ). In this study, we make a comparison of several binary star systems and their efficiency to move icy asteroids from beyond the snow-line into orbits crossing the HZ. We modeled a belt of 10000 asteroids (remnants from the late phase of planetary formation process) beyond the snow-line. The planetesimals are placed randomly around the primary star and move under the gravitational influence of the two stars and a gas giant. As the planetesimals do not interact with each other, we divided the belt into 100 subrings which were separately integrated. In this statistical study, several double star configurations with a G-type star as primary are investigated. Our results show that small bodies also participate in bearing a non-negligible amount of water to the HZ. The proximity of a companion moving on an eccentric orbit increases the flux of asteroids to the HZ, which could result into a more efficient water transport on a short timescale, causing a heavy bombardment. In contrast to asteroids moving under the gravitational perturbations of one G-type star and a gas giant, we show that the presence of a companion star can not only favor a faster depletion of our disk of planetesimals but can also bring 4 -- 5 times more water into the whole HZ.Comment: Accepted for publication in A&

Reactor physics calculation of BWR fuel bundles containing gadolinia

"January 1977.""YAEC-1126."Includes bibliographical references (pages 142-144)A technique for the calculation of the neutronic behavior of BWR fuel bundles has been developed and applied to a Vermont Yankee fuel bundle. The technique is based on a diffusion theory treatment of the bundle, with parameters for gadolinia bearing pins generated by transport theory, and converted to effective diffusion- theory values by means of blackness theory. The method has been used to examine the dependence of various bundle average parameters on control rod insertion history

An analysis of plutonium recycle fuel elements in San Onofre-1

"May 1974."Also issued as an Nucl. E. thesis by the first author, MIT, Dept. of Nuclear Engineering, 1974Includes bibliographical references (pages 167-171)A method has been developed to allow independent assessment of the use of plutonium recycle assemblies in operating reactors. This method utilizes Generalized Mixed Number Density (GMND) cross sections (based on Breen's Mixed Number Density cross sections) and the spectrum code LASER. LASER is modified to form LASER-M by adding ENDF/B-II thermal cross sections for the plutonium isotopes; adding edits to output G-aND cross sections, approximate microscopic removal and transport cross sections; and increasing LASERs compatibility with commonly used diffusion theory codes such as PDQ. Plutonium critical experiments for a number of lattices of 1.5 w/o and 6.6 w/o plutonium are analysed with LASER-M which is found to give better criticality agreement than LASER (without the ENDF/B-II plutonium cross sections) and other published data. Unit assembly power distributions are calculated for a uranium assembly and a constant and graded enrichment plutonium assembly both surrounded by uranium assemblies. The use of LASER-M with GMND cross sections is found to give excellent agreement with the published calculations of power distributions for the uranium assembly and good agreement for the plutonium assemblies. A quarter core depletion calculation of the San Onofre reactor containing four plutonium recycle demonstration assemblies is performed using the diffusion theory computer code PDQ-7. Use of PDQ-7 with GMND cross sections from LASER-M is shown to give excellent agreement with quasi experimental power distributions at cycle burnups of 0 MWD/MTM, 3342 MWD/MTM, and 6045 MWD/'MTM. Also, the calculated value of k-eff versus cycle burnup is determined to be in excellent agreement with the actual operating condition of k-eff = 1 .000

Neutronic analysis of a proposed plutonium recycle assembly

Statement of responsibility on title-page reads: George M. Solan David D. Lanning Bruce F. Momsen, and Edward E. Pilat"August 1975."Also issued as a Nucl. E. thesis, MIT Dept. of Nuclear Engineering, 1975Includes bibliographical references (pages 271-275)A method for the neutronic analysis of plutonium recycle assemblies has been developed with emphasis on relative power distribution prediction in the boundary area of vastly different spectral regions. Such regions are those of mixed oxide (Pu0 2 in natural U02 ) fuel pins relative to enriched uranium pins, or water regions relative to fuel pin regions. The basic analytical methods for determination of spectrum averaged constants are given in the following descriptions: (1) Generalized Mixed Number Density (GMND) group constants (based on Breen's Mixed Number Density Method) are generated by a modified version of the spectrum code LASER, called LASER-M. (2) THERMOS Corrected LASER-M (TCL) group constants are based on mixed oxide- uranium oxide and water region boundary modeling in one dimensional (slab) geometry with the integral transport code THERMOS.The LASER-M model, as modified by addition of ENDF/B-II thermal cross sections for the plutonium isotopes, is used to predict the criticality of experimental lattices of U02 - 2 w/o Pu0 2, and fair agreement is shown. LASER-M unit cell depletion calculations with Yankee Core I data (3.4 w/o U-235) to 40,000 MWD/MT and Saxton Core II data (6.6 w/o Pu02 in natural U02) to 20,000 MWD/MT show good isotopic agreement. Saxton Critical Reactor Experiment (CRX) lattice cores (19 x 19 rod array) consisting of a single fuel type region (mixed oxide or uranium oxide) or multiregions of both pin types were analyzed for relative power distribution comparisons. Cores with water slot regions were included. LASER-M Normal, LASER-M GMND and TCL two group constants were used with PDQ-7 in the calculations. GMND results were in excellent agreement compared to the good agreement of TCL for these cases of isolated spectral disturbances in an asymptotic core region.The methods were applied to a proposed plutonium recycle "island design" assembly in which a large control rod water region is in close proximity to a zoned mixed oxide region. The TCL method yielded significantly greater power peaking and mixed oxide region average power owing to the spectral influence of the water region explicitly accounted for in this method. Such a result is consistent with published calculations. It is concluded that infinite lattice spectrum calculations are insufficient to deal with spectrum effects more complex than those in the Saxton CRX experiments