Notes:
(1) Direct capture in Cm243 yields
Cm244.
(2) Direct capture in Cm242 yields
Cm243.
(3) Beta decay of Am242 yields
Cm242.
Branching ratio (BCm2 =
82.7%) is accounted for by an effective (reduced) concentration of Am242,
which
is treated as a fission product (i.e. it has no fission cross section).
The positron emission branch
producing Pu242 is ignored.
(4) Am242m decays by isomeric
transition into Am242. The concept of a reduced 242Am concentration
can
not be implemented for the production by
the decay of Am242m because a yield for decay can not be
specified in the WIMSD library.
(5) Capture in Am241 results
in Am242m with a branching ratio BAm2. The branching
ratio is energy
dependent. Calculations based on ENDF/BVI
Rev.5 data produce values ranging from 0.132 for the
Plutonium recycling benchmark to 0.109
for the BAPL2 benchmark. A value (BAm2 =0.12) is retained
as in the 1986 WIMSD library. It
approximately corresponds to the DIMPLES01 benchmark.
(6) Reduced Am242
is produced from capture in Am241. Since only one nuclide
can be specified as the
capture product (and this is Am242m
under the previous item), Am242 is treated as a fission product
with the yield proportional to the capture
to fission (c/f) ratio. Unfortunately the ratio strongly depends
on the neutron spectrum. Calculations
based on ENDF/BVI Rev.5 data produce c/f ratios ranging from
42 for the Plutonium recycling benchmark
to 124 for the BAPL2 benchmark. A value (c/f = 92) is adopted,
which approximately corresponds to the
DIMPLES01 benchmark. The expression for the reduced yield of
Am242 is given by:
(c/f)*(1
BAm2)*BCm2
The fission in Am241 is predominantly
a threshold reaction with a small subthreshold contribution. From
the reactivity point of view the fission
in Am241 is not important. To make the yield of Am242g exact,
the
fission cross section of Am241 in the
WIMSD library is forced to be proportional to the absorption cross
section, normalised to conserve the above selected
c/f ratio. The effective reduced 242Am yield is 67 atoms
per fission, based on the same data for
BCm2 and BAm2 as for items (3) and (5), respectively.
(7) Am241 decays by alpha emission
into Np237.
(8) Cm decays by alpha emission
into Pu240.
(9) Cm decays by alpha emission
into Pu239.
(10) Cm242 decays by alpha emission
into Pu238.
(11) Pu241 decays by beta emission
into Am241.
(12) On capture in Np239 the
resulting Np240 is assumed to decay instantly by beta emission into Pu240.
(13) Np239 decays by beta
emission into Pu239.
(14) On capture in Np237 the resulting
Np238 is assumed to decay instantly by beta emission into Pu238.
(15) Pu238 decays by alpha emission
into U234.
(16) On capture in U238 the resulting
U239 is assumed to decay instantly by beta emission into Np239.
(17) To account for the production
U237 from the (n,2n) reaction of U238, a pseudo fission product
(ID=4927) is defined, which decays
instantly into U237. The yield is equal to the ratio of (n,2n)/(n,f)
reactions of U238. This ratio is
sensitive to the detailed shape of the spectrum and hence difficult
to determine. The reaction contribution
above 10 MeV is significant. The value for the yield per fission
(n,2n)/(n,f) =0.06 is adopted.
(18) The capture product of Pa233 is assumed to decay instantly into
U234.
(19)U237 decays by beta emission into Np237.
(20) The capture chain from U232 up to U238 is represented explicitly.
(21) To account for the production U232 from the (n,2n) reaction in U233,
a pseudo fission product
(ID=4927) is defined, which decays
instantly into U232. The yield is equal to the ratio of (n,2n)/(n,f)
reactions.
(22) To account for the production U232, the fission product Pa231 is
introduced (i.e. the fission cross
section is deleted from the cross
section set). Its fission yield is equal to the ratio of (n,2n)/(n,f)
reactions of Th232. The capture
product of Pa231 is assumed to decay instantly into U232.
(23) The capture product of Th232 is assumed to decay instantly into
Pa233.
