1997 TMS Annual Meeting: Wednesday Abstracts

MATERIALS FOR SPALLATION NEUTRON SOURCES: Session IV: Neutronics

Session Chairperson: C.L. Snead, Brookhaven National Laboratory, Upton, NY 11973-5000

8:30 am

PRE-CONCEPTUAL DESIGN AND PRELIMINARY NEUTRONIC ANALYSIS OF THE PROPOSED NATIONAL SPALLATION NEUTRON SOURCE: J.O. Johnson, J.M. Barnes, L.A. Charlton, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6363

The Department of Energy has initiated a pre-conceptual design study for the National Spallation Neutron Source (NSNS) and given preliminary approval for the proposed facility to be built at Oak Ridge National Laboratory. The pre-conceptual design of the NSNS consists of an accelerator system capable of delivering a 1-2 GeV proton beam, with 1 MW of beam power, in an approximate 0.5 microsecond pulse, at a 60 Hz frequency onto a single target station. The NSNS will be upgraded in stages to a 5 MW facility with two target stations (a 60 Hz station and a 10 Hz station). There are many possible layouts and designs for the NSNS target stations. This paper gives a brief overview of the proposed NSNS with respect to the target station, as well as the general philosophy adopted for the neutronic design of the NSNS target stations. A reference design, based upon experience at existing sources and on designs for proposed new, high power, sources is presented, and some of the preliminary design neutronic results for the NSNS are briefly discussed.

9:00 am

CALCULATED NEUTRONIC PERFORMANCE AND RADIATION DAMAGE PARAMETERS FOR THE UPGRADED MANUEL LUHAN, JR., NEUTRON SCATTERING CENTER TARGET SYSTEM: P.D. Ferguson, G.J. Russell, E.J. Pitcher, J.D. Court, Los Alamos National Laboratory, Los Alamos, NM 87545

The upgraded MLNSC target system is designed to be a split target with two tiers of moderators. The original suite of moderators serving 12 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 4 additional flight paths. The upper moderators are coupled and viewed in backscattering geometry, as opposed to the decoupled moderators in the existing MLNSC target system which are viewed in transmission. Fabrication of this new target system is currently in progress and installation is expected in 1998. The neutronic performance of the target system s presented in the form of time and energy spectra for each of the planned moderators with comparisons to the existing MLNSC moderators. Results of several studies, including moderator thickness, upper target length, and reflector material, are presented. For the upper and lower targets, target canister material, and moderator structural material, we present neutron and proton energy spectra, helium production, and DPA calculations. Existing accelerator materials damage data are referenced, where applicable, to draw general conclusions on component lifetime.

9:30 am

CALCULATED NEUTRONIC PERFORMANCE OF A LONG-PULSE SPALLATION SOURCE: G.J. Russell, E.J. Pitcher, P.D. Ferguson, J.D. Court, D.J. Weinacht, Los Alamos National Laboratory, Los Alamos, NM 87545

Neutronic performance studies of a Long-Pulse Spallation Source (LPSS) at the Los Alamos National Laboratory show that a 1-MS LPSS has world-class neutronic performance with low technical risk. An LPSS uses coupled moderators (moderators that communicate neutronically at all energies with an adjacent reflector). There are potential gains of about a factor of 6 in time-averaged neutron brightness for a coupled moderator compared to a decoupled one; however, this gain comes at the expense of putting "tails" on the neutron pulses. The particulars of a neutron pulse from a moderator (e.g., rise time, peak intensity, pulse width as measured by the standard deviation or full-width at half maximum of the pulse, and decay constant(s) of the tails) are crucial parameters for instrument design/performance at an LPSS. Moderator neutronic performance can be altered in a variety of ways: a)target material and geometry; (b) moderator material and geometry; c) target-moderator geometry; d) reflector material; e) presence of decouplers and flight path liners; and f) the proton pulse width. We will discuss the neutronic performance of an LPSS and describe the variety of neutronic optimization studies that have been done to improve the neutronic performance of such a neutron source.

10:00 am BREAK

10:20 am

NEUTRONIC DESIGN OF THE APT MATERIALS IRRADIATION AT THE LOS ALAMOS SPALLATION RADIATION EFFECTS FACILITY: P.D. Ferguson1, W.F. Sommer1, M. S. Wechsler2, G.J. Russell1, E.J. Pitcher1, R.B. Kidman1; 1Los Alamos National Laboratory, Los Alamos, NM 87545; 2North Carolina State University, Raleigh, NC 27695-7909

The APT project is in the process of qualifying materials for use in the target/blanket assembly. As part of the process, an eight month irradiation of prospective target, blanket, beam entry window, and structural materials is taking place at LASREF in the 800-MeV, 1 mA proton beam. The irradiation is configured to produce samples at prototypic APT radiation environments, as well as samples at reduced damage rates to provide information as to how the materials age in an APT environment. In addition, three prototype lead blanket modules are being irradiated along with several aluminum tubes filled with 3He to experimentally determine the extent of tritium implantation in the APT system and to explore possible mitigation techniques. In this paper, we detail the methodology of the neutronic design of the irradiation. Neutron and proton spectra are presented for several irradiation locations and materials, as well as calculated gas production and dpa estimates.

10:50 am

PROGRESS REPORT ON THE ACCELERATOR PRODUCTION OF TRITIUM MATERIALS PROGRAM: S.A. Maloy, W.F. Sommer, Los Alamos National Laboratory, Los Alamos, NM 87545

Progress will be reported on the status of an irradiation by 800 MeV protons and spallation neutrons to determine the change in mechanical properties of materials to be used in the APT project. Materials will be irradiated for 8-9 months at the Los Alamos Radiation Effects Facility (LASREF). The irradiation matrix, developed by members of several laboratories nationwide, consists of specimens of candidate materials, scaled components and a closed-loop water system to measure rates of corrosion in irradiated water. The objectives are to determine the performance (particularly, mechanical and corrosion properties) of materials in APT-prototypic proton and neutron radiation and temperatures, to test manufacturing processes for producing components, and to develop a surveillance program to monitor the properties of materials during the life of the APT target/blanket.