ORNL-TM-7207 - the Molten Salt Energy Technologies Web Site

35
(Doppler effect), (2) changing the energy distribution of the thermal
neutron spectrum, and (3) causing expansion of the constituent materials.
The expansfon changes both the size and density of the core, as discussed
earlier. Table 28 shows the various cmponents of the total temperature
coefficient. The fuel coefficient is dominated by both a large, negative
Doppler component and a similar spectral component.
ple, that an increase of "IsC in fuel temperature would reduce reactiv-
ity by 6.009 essentially instantaneously.
Table 20. Temperature coefficients of
reactivity for DMSR
Fuel-salt Doppler 57
Fuel-salt density 30
Fuel-salt thermal spectrum 4 0
Total fuel salt 4 7
Moderator density
Moderator expansion
Moderator thermal spectrum
Total moderator
Total core
Reflector density
Reflector thermal spectrum
Reflector and vessel expansion
Total reflector
-2.2
7.2
14
19
4 8
0.1
1.2
-4.9
Total reactor -7 2
This means, for exam-
-%. 8
"he moderator effect is dominated by positive spectral and expansion
effects. This effect is relatively slow to appearo however, because the
time constant for conduction heating of the graphite fs on the order of
146 s.
If the temperature change were caused by a rapid power increase,
a small portion (-5%) of the excess power would appear in the m~de~ator