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3. REFERENCE-CONCEPT DMSR
A preliminary conceptual design has been developed for a DMSR oper-
ating on a 30-year fuel cycle. The emphases to date have been on the re-
actor core design and fuel cycle, with less attention to other aspects of
the system. Although thfs design establishes the basis concept and char-
acterizes its major properties, it is tentative and would be subject to
major refimement and revtsion if a substantial design effort were under-
taken.
3.1 Neutronic Properties
The basic features of this BMSR concept which distfnguish it from
other MSRs are established primarily by the reactor care design and its
ass~ciated neutronic properties. 'Phe design described here represents
the results of a first-round effort to balance some of the many variables
invo%ved in a reactor COT@, but it is by PPO means an opthized design.
3.1.1 Weutronics core model
Prom a neutranics point of view, the core is simply designed as f ~l-
EoWs (FJg. 2).
1. The core and r@f%e~tor fill a right circular cylinder that is
18 rn in diameter and 18 m high. The core, which is a cylinder 8.3 m in
diameter and 8,3 m high and centered inside the larger volume, fs filled
with cylindrical graphite logs in a triangular array of 8.254-m pitch.
Approximately 95X of the CQF~ (core B) has log diameter of 0.254 m, with
the fluid fuel filling the interstftial volume to praduce a fuel volume
fraction of 9.31%. An axial cyLindrieal hole of 0,851-m diam in the een-
ter of each log admits another 3.63% fuel for a total of 12.94 voP %. To
achieve flatteni~g of the fast flux and thus maximize the lifetime of the
graphite moderator, the remaining 5% of the core (core A>, a cylinder 3 m
in dfameter and 3 m hfgh, has a log diameter of 0.24 m, resultfng in a
total fuel volume fraction of 20.00% in this zone.