FFTF RELATED STUDIES IN THE ORNL--LMFBR SHIELDING PROGRAM. Page: 6 of 55
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II. THE HEAD COMPARTMENT PROBLEM
The problem of calculating the neutron dose rates above the reactor
cover is by far the more difficult of the two problems which have been
considered in this design. An idea of its complexity can be obtained from
Fig. 1, which shows an artist's drawing of the FFTF reactor. There are
multiple paths through which radiation reaches the lower surface of the
reactor head and multiple paths for streaming and transmission through
the head and cover. The design objective is to provide for the total dose
level of 2 mrem/hr directly above the reactor vessel head. Approximately
1 mrem/hr is allocated for gamma-ray dose from the sodium coolant in the
branch arm piping; therefore, the desired neutron dose level is only
Although the most important part of the problem is the determination
of the source distribution incident on the head, the construction schedule
required a design evaluation for the clearance gaps around the major pene-
trations of the head at an early date. These evaluations were performed
using a crude estimate of the source from one-dimensional transport calcu-
lations and a detailed two-dimensional transport calculation for the head
Figure 2 shows the DOT R-Z geometry for a model of a main rotating
plug. A doubly offset clearance gap is shown having widths of 1/2 in.,
3/8 in., and 1/4 in., the larger gaps being required in locations having
more several thermal gradients. In order to accurately calculate the
streaming in the void gaps, a highly biased 315-angle quadrature was used
in the 50-group, P1 DOT calculations. Several DOT calculations were per-
formed for various slit configurations using the one-dimensional source
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Mynatt, F.R.; Clifford, C.E.; Muckenthaler, F.J.; Maerker, R.E.; Gritzner, M.L.; Williams, L.R. et al. FFTF RELATED STUDIES IN THE ORNL--LMFBR SHIELDING PROGRAM., report, January 1, 1972; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1030630/m1/6/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.