This report was prtparad as an account of work sponsoreti by the United States Government. Neither the United States nor the United States Atomic Enerfy Comnvuton. nor any of their employees, nor any of mew contractors, subcontractors, or their employees, makes any warranty, eapress or implied, or assumes any legal liability or responsibriitv for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not irfnneje privately owned nejhcv ORHL-4880 UC-79d-Liquid Metal Fast Breeder Reactors Physics Contract No. W-7l*05-eng-26

This paper documents an oral presentation given in the special session on Fast Reactor Shielding Sponsored by the Shielding and Dosimetry Division at the October 1971 meeting of the American Nuclear Society in Miami, Florida. The progress to date on neutron transport calculational studies of FFTF shielding design is presented, including the analysis of supporting integral experiments. The major FFTF shielding problems considered were the predictions of (1) neutron dose rates above the reactor head and (2) neutronvfluence intensities at the core support grid plate.

The DOT-III computer program solves the energy and angular dependent Boltzmann equation with general anisotropic scattering for rectangular, polar, or cylindrical geometries. Principal applications are to neutron and/or gamma-ray transport problems in either forward or adjoint mode. Both homogeneous and external source problems can be solved and searches on multiplication factor, time absorption, nuclide concentration, and zone thickness are available. However, the code is particularly designed and suited to the solution of deep penetration radiation transport problems.The discrete ordinates, or Carlson's S , method is utilized to solve the Boltzmann equation. A good account of the historical de\'elopment and application of this method is included by Mynatt e£ al. in a description of the development and verification of two-dimensional transport theory for radiation shielding applications. l Briefly, the discrete ordinates method involves the solution of difference equations derived in a term-wise manner by integrating the analytic form of the Boltzmann equation over a fivedimensional finite cell defined in terms of location, direction, and energy phase space variables. Supplementary difference equations are required to obtain a solution to the flux. These equations relate the average flux for a cell with each pair of associated cell face fluxes. The equations should provide a good approximation to the true variation and at the same time be easily and quickly solved on the computer. Two forms of the supplementary equations which have been utilized in earlier versions of DOT are "diamond difference" and "step function" equations.The cross sections required by DOT-III are of the multigroup, P n , expansion type generated by codes such as AMPX, which is described in Mrs. Maskewitz's paper. The utilization of this type of multigroup cross-section data allows the solution of coupled neutron and secondary gamma-ray transport problems with anisotropic scattering.Various versions of DOT and related computer programs have been developed over the years and several have been placed at RSIC. Some examples of fResearch sponsored by Union Carbide Corporation under contract with the U. S. Atomic Energy Commission.•Present address: United Aircraft Corp., Hartford, Conn.

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The elements of a shielding program based on a fundamental approach are discussed with a brief evaluation of the present status of the technology. A procedure is presented for utilizing the best features of Monte Carlo, discrete ordinates, and diffusion theory in coupled calculations providing good accuracy at minimum expense. As an example, results are presented from a four-step coupled two-dimensional discrete ordinates calculation for determination of the neutron and secondary gamma-ray dose rates in the FTR head compartment. An assessment of computational methods development plans is presented.

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