Venting of Fission Products and Shielding in Thermionic Nuclear Reactor Systems. Page: 6 of 7
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X T 0.53
Qp 1.17 973 0.61
Xe13 (5.3d) 0
Q -0.428 0.081
Fig. 5. Decay schemes for 133Xe and Xe.
isotopes of greatest interest, 133Xe and 135Xe, have
half-lives of 9 h and 5.3 days, respectively, the
large uncertainty in the value of the escape life-
time can significantly affect the calculated radia-
tion level. Experimental investigations of escape
rates out of emitters are required before a satis-
factory value can be assigned to the radiation
level. In any case, the storage of fission gases in
a lightly shielded gas chamber can pose design
Absorption in a Charcoal Trap
Normally, absorption traps are thought to
operate at very low temperatures; however, at pres-
sures of 20 Torr a charcoal trap can be useful even
at moderate temperatures. For the example of a 1 MW
thermal reactor, the volume of charcoal required to
store the xenon and krypton at 20 Torr can be cal-
culated as a function of temperature.1 As shown in
Fig. 6, this charcoal volume is considerably smaller
than the original volume of 1.2 x 103 liters with-
out charcoal as shown in Table III. At a tempera-
ture of 100*C the charcoal volume is about 15 liters.
Although 15 liters is not a trivial volume to shield,
it may represent a compromise solution. At 100*C,
the use of heat pipes may prove feasible for con-
trolling the charcoal trap temperature.
The two methods discussed above of handling
fission gases have their disadvantages. If the
charcoal-trap temperature rose appreciably, the
fission-gas pressure could increase and pose a
hazard to reactor operation. On the other hand the
liglrtly shielded gas-chamber system could pose a
radiation hazard after reactor shutdown. Figure 7
100 200 300 400 500 600
Fig. 6. Amount of xenon absorbed in charcoal
as a function of temperature.
TIME AFTER REACTOR SHUT DOWN, days
Fig. 7. Rare-gap activity following reactor
shutdown after 1.2 years of operation.
shows the rare-gas activity expected following
reactor shutdown after 1.2 years of operation. The
curve shows that after one month the activity has
fallen by a factor of 100. At this time the activity
is due mainly to 5Kr which has a ten-year half-life.
Although this activity is small compared to the
previously cited values, it is a 5-R/h radiation
source at a distance of 1 m. With a ten-year half-
life it does not disappear suddenly. If poorly
shielded, it might pose a hazard for any crew work-
ing near the reactor after shutdown.
,'g. 7. pare-goy eetvity T0cong rector
<Ltdo,., aeTEe 1.2 year. of opertltm.
i 0 20 30 40 50 60
, . . . .
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Salmi, E. W. Venting of Fission Products and Shielding in Thermionic Nuclear Reactor Systems., report, January 1, 1972; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1036131/m1/6/: accessed May 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.