Moderators using liquid and solid methane and liquid hydrogen are currently in use at major spallation neutron sources. Los Alamos Neutron Scattering Center (LANSCE) is planning the use of liquid methane as part of a major update program planned in about three years time. This report presents a general overview of some of these devices and outlines the general engineering design of the proposed LANSCE moderator, including some suggested solutions to the radiation damage problems of methane. Also included is a brief overview of a possible combined H2/Ch4 moderator for high intensity proton beams. 15 figs.

The Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory is a spallation neutron source dedicated to materials research. Its three cryogenic methane moderators provide twelve neutron beams to fourteen instruments and test facilities. IPNS has begun a program to enhance the effectiveness of its target, reflector, and moderator system. This program will involve the examination of many different potential system modifications and their various interactions. The first component of such a task is the assessment of the current performance of the target, reflector, and moderator system, and the verification of the computational model used to evaluate the system. To that end, we have developed a Monte Carlo model of the IPNS neutron generation system as currently configured, and are in the process of validating that model with corresponding measurements. This paper describes the Monte Carlo model and analysis, as well as some of the experimental comparisons we use to validate our model. (auth).

The Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory is a spallation neutron source dedicated to materials research. Its three cryogenic methane moderators provide twelve neutron beams to fourteen instruments and test facilities. This report concerns ongoing activities for benchmarking our Monte Carlo model of the IPNS neutron generation system. This paper concentrates on the techniques (both experimental and calculational) used in such benchmarking activities.

The upgraded Lujan Center target system is designed to be a split target with two tiers of moderators. The original suite of four moderators serving twelve flight paths has been optimized and an additional pair of moderators, one water and one LH2, have been added in a new upper moderator tier serving four additional flight paths. The upper moderators are partially coupled and viewed in backscattering geometry, as opposed to the decoupled moderators in the existing Lujan Center target system, which are viewed in transmission geometry. Fabrication of this new target system is currently in progress and installation is expected in 1998. The decoupling scheme for the upper moderator tier is documented. The neutronic performance of the two cold moderators is presented in the form of time and energy spectra with comparisons to the existing Lujan Center LH2 moderator. Neutronic performance of a partially-coupled flux trap LH2 moderator is also presented.

Global warming, shortage of low-cost oil resources and the increasing demand for energy are currently controlling the world's economic expansion while often opposing desires for sustainable and peaceful development. In this context, atomic energy satisfactorily fulfills the criteria of low carbon gas production and high overall yield. However, in the absence of industrial fast-breeders the use of nuclear fuel is not optimal, and the production of high activity waste materials is at a maximum. These are the principal reasons for the development of a new, fourth generation of nuclear reactors, minimizing the undesirable side-effects of current nuclear energy production technology while increasing yields by increasing operation temperatures and opening the way for the industrial production of hydrogen through the decomposition of water. The construction and use of such reactors is hindered by several factors, including performance limitations of known structural materials, particularly if the life of the projected systems had to extend over the periods necessary to achieve low costs (at least 60 years). This book collects lectures and seminars presented at the homonymous NATO ASI held in autumn 2007 at the Institut d’Etudes Scientifiques in Cargèse, France. The adopted approach aims at improving and coordinating basic knowledge in materials science and engineering with specific areas of condensed matter physics, the physics of particle/matter interaction and of radiation damage. It is our belief that this methodology is crucially conditioning the development and the industrial production of new structural materials capable of coping with the requirements of these future reactors.