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head which are bounded by various thicknesses of
sodium.
Fairly accurate calculations have been made of
the heat-deposition rates in the lnconel filler
plates below the island and in the vicinity of the
fuel-to-NaK heat exchanger on the equatorial
plane of the reactor. These results were used
as a guide in estimating the heating in some
north-head regions, and new values were obtained
by compensating (by simple exponential attenu-
ation) for decreased beryllium thicknesses,
penetrations through additional fuel layers,
increased thermal-neutron leakage currents into
the north head, etc.
A neutron current of 7 x 10’3 neutrons/cm2*sec
was assumed to be escaping uniformly from the
upper portion of the core,’5 and it was assumed
that 1 Mw of fission power was being generated in
the fuel regions of the north head by neutrons
escaping into this region. The latter increased
the gamma rays in the fuel by about 30%.
The sources of gamma radiation considered
were those from the sodium and fuel in the north
head, the heat exchangers, boron, the fuel in the
core, core shells, beryllium, and lnconel shell
capture gammas. The sources of beta particles
considered were those from the gases in the
fuel-expansion tank, and the sources of alpha
particles were taken to be those from boron
captures. The average values of heat generation
obtained in these calculations are presented in
Table 1.2.2. The configuration of the north head
is shown in Fig. 1.1.5 of Chap. 1.1 of this report.
BETA- AND GAMMA-RAY ACTIVITY IN THE
FUELEXPANSIONCHAMBERANDTHE
OFF-GAS SYSTEM
R. B. Stevenson16
The power-source distribution of the acti
the gases in the space above the fuel in the fuel
expansion chamber and in the off-gas line has
’’AI M.- Parry, L, private communication to
H. W. Bertini.
160n assignment f
17J. J. Newgard, Fission Product Activity and Dec
Heat Distribution in the Circulating Fuel Reactor with
Fission Gas Stripping, TIM-205 (Sept. 28, 1955).
A =
volume flow rate of fuel through purging pumps
= total volume of fuel
PERIOD ENDING JUNE 10, 1956
been determined. The results obtained are to be
used in the calculation of the radiation heating
and the thermal stresses in this region of the
reactor.
The radioactive constituents of the gas in this
space are the gaseous fission products, xenon
and krypton, and their daughter products. There
is also a possibility that some volatile fission-
product fluorides will be formed in the fuel and
will escape into this area. However, it has been
shown l 7 that if all the fission-product fluorides
entered this space, they would add very little
activity to that already caused by the gaseous
fission products and their daughters. Thus, their
effect has been neglected here. Also, there is
some question as to whether the daughter products
of the fission gases will actually be carried
downstream by the off-gas system or whether they
will be deposited on the enclosing walls as they
are formed. In order to get a conservative estimate
of the power-source distribution, if was decided
to treat the daughter products of xenon and krypton
as gases (except insofar as their purging from the
fuel into the fuel expansion chamber is concerned).
The equilibrium amount of the gaseous fission
products in the fuel expansion chamber is given by
(approximate I y)
Yi’p
Ni =
(Ai + A,) (Ai + AS)
where Ni is the total number of atoms of type i in
the gas volume per fission per second, yi is the
saturation fission yield of the ith nuclide, A, is
the “purging” constant, As is the “sweeping”
constant, and Ai is the decay constant of the
ith nuclide. The “purging” constant is determined
by the volume flow rate of the fuel through the
purging pumps and the total volume of fuel. This
constant determines the amount of the gaseous
fission products which are purged from the fuel
into the expansion chamber. The “sweeping”
constant is determined by the flow rate of helium
through the expansion chamber and the volume of
the gas space. This constant determines the
dwell time of the radioactive nuclides in the gas
space and thus the number of disintegrations they
suffer there. The “purging” and “sweeping”
Constants are given by
volume flow rate of helium through expansion chamber
volume of gas space
,
35