Fusion energy calorimeter for the tokamak fusion test reactor Page: 6 of 7
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the resistance measurement is automated,
then the time response for the calorimeter system
is essentially toe time for the thermopile to come
into equilibrium with the working meciun, or a
period of several seconds. Thus it would not be
:psssle to monitor changes in the fusion energy
production during a single pulse in TFTR, even
for Mode I oeration. In any event, transient
noise caused Oy gama radiation night prevent
useful temperature measurements antil immediately
after the power sulse.
Neutronics results such as chose illustrated
in Fig. 3 indicate that the depth of the working
medium should be at least 60 co to absorb more
than 95 of the incident neutrons and also the
gannes that are both incident and produced in the
moderator. The moderator legion should be enclose:
.n a thin material that has a low affinity for
neutrons o moderate to high energy and that also
has a low tnernal conductivity.
The moderator must be surrounded by thermal
insulation (see Fig. 2, to prevent temperature
changes in the liquid due to variations in ambient
temperature, and to minimize heat loss from the
moderator so that the full value of 8T on the cen-
tral axis will be measured. The thermal insulation
can be a solid such as Johns-Manville Mill-K.
Another approach is to enclose the absorbing medium
in a controlled-temperature bath of oil or other
fluid that would maintain the container wall at a
constant temperature. (In this case, the container
wall should have high conductivity.) This tech-
nique would be especially applicable to the case
of a working medium with a boiling point below
room temper ture lsee Table 1).
There are two asocts st the calorimeter cal
'li -he response of the device to a given ab-
so'ed energy. For this calibration, heating el-
ements would be placed at a number of positions in
-he working medium, to simulate the expected nuc-
lear energydeosition profile. The response of
tee measurement system would be determined for a
known amount of energy dissipated in these heating
f2; The relation of the incident neutron and
gamma energy to tne total fusion neutron produc-
?ton. As a check dn the conclusions of the neut-
ronics analyses discussed in earlier sections,
the device could be caliorated against a known
neutron source by integrat'ing the neutron intensity
and ;pec-rum, and ganna-ray atensity at the cal-
orimeter front face, when a deuterium beam bon-
barts a tritiated target inside the torus (as is
planned for calibration of the TFTR nestrnn det-
ectors). An integration period of at least sev-
eral hours would be required 'or this calibration.
Advantages of the Neutron Calorimeter
' The detection equipment is simple and robust.
No pneumatic transport tubes are necessary to
get pulse-by-oulse measurements.
(2) The measurement equipment is simple. Long
decay times allow easy collection and storage
(3) The detector response is limited and cannot
(4) The system is insensitive to tack-scattered
low-enerqy aeutrons which usay enter thec cal-
(5) The method is capable of providing a direct
measurement of fusion power Production, rather
d than oy inference from flyx and socctral
(6) The method will become increasingly aporcoriate
as experimental fusion reactors produce arger
neutron yields oer pulse.
Disadvantages of the Neutron Calorimeter
(1) Th lower limit to useful detection is bout
ll fusion neutrons per cm2.
(2) Considerable space is required to accommodate
the bulk moderator needed to prevent fast neut-
rons and gammas from entering the central region
of the calorimeter from the sides.
(3) Time resolution is poor - of the order of l to
Application to Long-Pulse Test Reactors
The demonstration of the ability to correlate
the power deposition in an isolated "blanket mod-
ule" to the total fusion power Production, as Well
as the testing of the ability of neutronict codes
to predict the measured Dower deposition profiles,
will provide valuable information for the design
of experimental power modules for next-gerrration
tokamak test reactors. In toroidal geometry,
reflected neutrons may have a significant effect
on the power deposition in an isolated module.
The ability of neutronics codes to describe toe
correct neutron field can be tested only ir the
TFTR, in the 1980s.
In the ErF/INTOR type of test reactor, tne
0-0 neutron flux is expected to be of the order of
4x1011 n/cm2/s. Then a 100-s pulse would produce
a temperature increase of about 1C in a calorim-
eter of the type discussed here, and slaw variations
in power output during the pulse could be followed.
Hence a neutron calorimeter could find valuable
application in the shakedown phases receding 3-
oporation, an well as for monitoring the neutron
power generated during the more intense 3-' noer-
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Jassby, D.L. & Imel, G.R. Fusion energy calorimeter for the tokamak fusion test reactor, report, April 1, 1981; New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc1211995/m1/6/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.