Fusion energy calorimeter for the tokamak fusion test reactor Page: 4 of 7
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amount of energy lost from the calorimeter by the
=scaoe of ganma rays produced in endothermic reac-
tions nas been estimatea'to be less than 5% of the
enery associated with inelastic colisions, and
is probably comparable with the energy gained by
enothernic capture reactions.
Maximizing the lateral extent of the moder-
ator, rather than adding shielding or reflecting
material, aopears to be the optimal method for in-
suring adequate isolation of the central region
from boundary effects. The half-width of the mod-
erator in the TFTR calorimeter can be as large as
In cm in each direction (see Fig. 2). Two-dimen-
sional calculations made with the 00T-3.5 code'
demonstrate that this half-width is sufficiently
large so that scattered low-energy neutrons en-
tering the sides, either by reflection of mod-
erator neutrons :r from the TFTR ambient, have
iess than 10a effect on the total energy depos-
ition aong the major radial axis.
Except at the front face, ambient gammas
from the TFTR structure can be stooped by approx-
imately 6 cm of lead shielding. However, addit-
ional gammas will be produced in the lead by
imoirtng fast neutrons.
The 2-0 calculation gives nearly the iden-
tical total energy deposition profile along the
major radial axis as predicted by the !-0 ANISN
calculation. However, the 2-0 calculations shows
that at cistances beyond atout 40 cm from the
front 'ace, the fast-neutron population below la
MeV make io a larger contribution, am' the gamas
a smaller contribution to the total enermv
dePoltiOrn, than predicted by the 1-0 calculation.
Conclus ans Concerning Power Deposition
Dther aspects of the power deposition cal-
culition; are given +n Ref. 3. The principal
concl..wcss 'rnm the 1-0 and 2-D analyses are the
A '- neutronics model is adeotate for calcul-
..'t the energy deposition along the central
^a'al axis of the calorimeter up to the dec-
ace coint; beyond, the 1-D model introduces
errors because of the non-representation of
neutron streaming to Doints away from the
rnt 'ace. However, ir integ-ating the total
Sower deposition aicng the central axis, the
5verml integrated error is less than 10%.
2, The torondai-field coils provide additional
attenuation of neutrons entering the sides
of the calorimeter, and thus increase the is-
olation of trae central axis. Scattering off
ta coils, and extra gamma rays produced in
tne coils are not significant additions to the
total Dower deposition along the central axis.
(31 Externally generated gamria rays deposit sig-
nificant amounts of energy in the calorimeter,
so that it might be desirable to install a
lead shield around the sides. With sucth a
shield in place, the central axis is isolated
from all gamnmas except those produced in the
vacuum vessel in front of the calorimeter.
It is estimated that the maximum error int-
roduced by neglecting gammas produced in the
vacuum vessel is 5%; by neglecting loss from
the calorimeter of gammas produced by inelastic
collisions in the moderator - also 5n; and by
neglecting exothermic capture gammas in the
moderator - again 5%.
(4) Assuming no errors in the measurement of tem-
oerature changes in the moderatorthe "equivalent-
fusion-neutron"fluence incident on the calorimeter
front face can be determined with an uncer-
tainty of less than 10A simply from integ-
ration of the measured profile of temperature
increase along the central axis. The fusion
neutron source strength can then be inferred
by accounting for attenuation through the
vacuum vessel and certain geometrical factors.
If each of the latter calculations has an un-
certainty of !7%, for example, then the source
neutron production can be estimated "absolutely"
with an uncertainty of t15%, on the basis of
the measured profile of temperature increase
along the central axis.
Conclusion n(a) may be altered if the surface
of the vacuum vessel, all around the torus, is
sufficiently reflective so that the current of
reflected neutrons into the calorimeter is much
larger than accounted for by our neutronics cal-
culations, While in such a case the neutron par-
rent may oe substantially higher than calculated
the actual power deposited is unlikely to experience
a major increase.
In view of the above conclusions, the spatially
averaged temperature increase in the moderator,
per fusion pulse, can be calculated 'rom a. 2
as a function of equivalent-fusion-neutron fluence
incident on the calorimeter face. Lino power 0e0-
osition profiles such as those it Fig, 3, one an
calculate the expected AT in each regirn of the
Figure 5 shows the expected temoeroture in-
crease within the front 10 cm of the ooderater,
for the various TFTR operating modes listed in
Table 2. Using one of the most sensitive hydrac-
arbons as the working medium, -T operation in
the TFTR with fusion power amplification Q -
for 1.0 s will giua T = 0.3"C near the front
face, which would produce an easily measured 0.2.
change in resistance of a resistance thermometer.
(Mode Ill operation is assumed.) With oulses of
several seconds length, as in Mode V, a vell-
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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/m1/4/: accessed March 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.