Space Reactor Radiation Shield Design Summary, for Information Page: 3 of 70
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The Manager, SNR
Enclosure (2) contains the results of preliminary thermal analyses to determine whether each of
the material temperature limits can be met for each material set under consideration, and begins
to assess the overall thermal management of the shield, piping, reactor control drive
mechanisms, and the energy conversion region of the Reactor Module.
The shield design work done to date focused on evaluating alternative material sets, potential
configurations of these material sets within the shield, and overall shield configuration
alternatives. The objective was to provide the required radiation attenuation to protect spaceship
equipment, minimize mass, and ensure the shield itself would perform its function throughout
long duration, deep-space missions. Summary findings from this design work are as follows:
" The NRPCT had narrowed the slate of candidate shield materials to five primary materials
(lithium hydride (LiH), beryllium (Be), boron carbide (B4C), tungsten (W), and water
(H20)) and one potential alternate material (10B metal) (see Reference (a)). Four basic
shield material sets were under consideration: 1) Be/B4CIW, 2) Be/10B/W, 3) Be/B4C/W/LiH,
and 4) Be/B4CIW/H20.
" Minimizing mass of the flight shield is a primary objective. Studies by ORNL (Reference (b))
showed that the mass of the shadow shield was higher than previous estimates. This was
true despite the material composition of the shield. Careful integration of reactor, piping,
energy conversion equipment, and spaceship interfaces will be needed to minimize shield
mass. Key methods to minimize mass include minimizing reactor size and reflector
operating envelope, and maximizing the shielding benefit of other required components (e.g.
energy conversion and spaceship components).
" The gas coolant piping is an important factor in designing the shield configuration and
thermal design. Minimizing the number and diameter of coolant pipes will minimize shield
mass. Pipe shield caps would not be necessary for piping shield penetrations if the pipes
spiral azimuthally through the shield just inside the outer radial surface. Investigation of
shield masses for pipes going around the shield should be completed as part of future work.
" The lifetime average release of short lived volatile fission products to the coolant must be
limited (estimated at < 103 release to birth ratio) so a second gamma shield segment is not
required between the coolant loops and the payload, which would significantly increase the
reactor radiation shield mass. This level of fission product retention is a reasonable design
assumption. Fission product and corrosion/erosion product irradiation affects on the
alternator require further investigation.
" Gamma radiation interactions at the outer surface of the reactor or reflector could drive
electrons off the surface. This interaction needs to be further investigated as both a
potential electron radiation source that could bypass the shield and as a potential spaceship
electrical charging source. Resolution of this concern will require close integration with
A significant next step that had not been performed prior to program closeout was the
performance of spaceship level trade studies that would provide an initial balance among
equipment radiation dose limits, local equipment radiation shield requirements, spaceship boom
length, and reactor radiation shield requirements.
PRE-DECISIONAL - For planning and discussion purposes only
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Pheil, EC. Space Reactor Radiation Shield Design Summary, for Information, report, February 17, 2006; Niskayuna, NY. (digital.library.unt.edu/ark:/67531/metadc873954/m1/3/: accessed March 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.