ORNL-5388 - the Molten Salt Energy Technologies Web Site

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3. Refueling System Modifications - A t the end of each operating cycle, spent fuel
must be discharged and fresh fuel inserted into the reactor (typically 1/3-of the core
loading is replaced each year), and the light water present at end of cycle must be
replaced with a D20-H20 mixture before the reactor can be returned to power operation.
Refueling procedures and equipment must be developed which will allow these operations to
be performed with minimum D20 inventory requirements. Minimizing the D20 inventory is
important to the economics and commercial feasibility of the SSCR, since the cost of D20
represents roughly 75% o f the additional capital expenditures required to realize spectral-
shift control.
times because of the adverse effect on capacity factor and the resulting increase in power
cost.
Care must also be taken to ensure that refueling does not increase outage
The exposure of personnel to tritium qenerated in the coolant must also be mini-
mized during refueling operations.
4. D20 Upgrader Design - Although D20 upgraders have yet to be employed in con-
junction with spectral-shift control , similar units have operated on CANDU reactors, and
vacuum distillation columns are also utilized in heavy-water production facilities. Thus,
the technical feasibility of the D20 upgrader can be considered as demonstrated. However,
a conceptual upgrader design optimized for the specific demands of the SSCR must be
developed so that its cost can be determined. The upgrader is probably the single most
significant and costly piece of equipment which must be added to realize spectral-shift
control.
5. Licensability and Safety - Although the spectral-shift-controlled reactor is
not expected to raise any new safety, licensing or environmental issues except the basic
issue of tritium production and containment, a number of core physics parameters are
changed sufficiently that the response to postulated accidents must be evaluated.
most significant of these appears to be the somewhat different moderator temperature co-
efficient of reactivity, which could lead to a number of potentially more severe accidents
early in cycle when the D20 concentration is relatively high. The D20 dilution accident
must also be addressed; this accident is analogous to the boron dilution accident in the
poison-controlled PWR, but the response to D,O dilution may be more rapid and hence the
accident may be potentially more severe than its counterpart in the PWR.
Finally, it should be pointed out that while the relationship of the SSCR to the
I
LWR gives it market advantages, it also gives it some disadvantages relative to other
alternatives. Although the SSCR demand for U308 will be less than that of the conventional
LWR, the basic properties of light water and the LWR design characteristics inherent in
the SSCR will limit its fuel utilization efficiency to lower levels than those achievable
with other alternatives such as the HWR. On the other hand, the prospect for early and
widespread deployment may mean that it could effect a more significant reduction in over-
all system U308 demand than might be achievable with other alternatives, even though the
inherent resource utilization of an individual SSCR plant may be less than that of other
systems. Employing denatured SSCRs would allow additional time to develop effective
The