REPORT ON IN NAVAL NUCLEAR JUNE, 1995

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A redesigned reactor vessel and reactor compartment arrangement for this LEU core would require
lengthening the ship by eight feet, and would increase the construction costs of the reactor core, reactor
and plant heavy equipment, and the ship itself, The economic impact of this option is explored in detail in
Section C.
3. I~act of Increased Core Volume on Reactor ReliabilitY: A submarine or aircraft carrier LEU
reactor providing the same ship perfornlance would have many more fuel modules and therefore many
more moving parts than the REU reactor, employing up to three times as many control rods and drive
mechanisms, and requiring more support equipment such as power supplies, instrumentation and circuit
breakers. While these parts today are individually very reliable, they do require maintenance and
occasional repair or replacement. Doubling to tripling the number of these parts would increase the cost of ;
emergent majntenance and the potential for operational problems.
4. IIrn)act of 5% LEU on Attack Submarine Design: The above analyses used 20%, the highest
level of enrichment within the internationally recognized definition of LEU. This was done to assess use of
LEU at the enrichment level that would cause the least adverse impact on Naval reactors. To assess the
sensitivity of submarine characteristics to a lower enrichment level, a life-of-the-ship core with 5%enriched
LEU was studied.
The fissile content of5% LEU is one-fourth that of20% LEU, so the volume of uranium required in this
core to power the submarine for its lifetime is roughly four times that of the 20% LEU case, or twelve
times the HEU design base case. The increase in the reactor equipment weight, hull dimensions and
displacement are shown below:
TABLE 5
Impact of 5% LEU on a Modern SSN
Change for a
Attribute 5% LEU Core
Machinery weight, % increase + 119%
Hull displacement, % increase +70%
Hull diameter, feet +6
Hull lenQ:th, feet +54
The impact on a submarine reactor becomes more pronounced with enrichment levels below 20%. The
size and displacement of the 5% LEU submarine would make it unacceptable for an attack mission, and its
cost would be prohloitive.
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