JAERI 1287 JNDC Nuclear Data Library of Fission Products Fir

18 JNDC Nuclear Data Library of Fission Products JAERI 1287
very good.
In a critical reactor, a neutron of energy E, is required to perpetuate the chain reaction.
This reduces the average total energy released directly in the fission process to a net value
Q'r = Qf-Ei. (2.5.7)
The effective average total energy Q/(°°) absorbed in the reactor is the value Q'f substracted
by the amount Ea because of the low absorption probability of antineutrinos in the reactor;
QA°°)=Q'/-Ee. (2.5.8)
Also, the quantities End, Erd, £/?and Ea are time-dependent, and the full magnitude of the
latter three quantities is not realized for practicable irradiation and cooling times in a reactor.
This in turn changes the effective average total energy resulting directly from fission so that
where, AEa = AQfi-(AErd+AE^,
Qp - average Q value for beta decay.
Therefore, Qe// can be rewritten as
Qe//=Q'/-Ea+{AQ/3-2(AErd + AEl3)}, (2.5.9)
where the energies AQp, AE0 and AErd depend on the irradiation history of the reactor. In
addition to Qe// , energy Qc is liberated by the capture of the remaining (v—l) neutrons in
the reactor materials. This latter energy depends on the neutron energy spectrum and the
arrangement, amount, and constituent of reactor materials.
Finally the total energy QT released in fission and absorbed in a reactor is given by
Qr=Qeff + Qc (2.5.10)
The quantity Q'f, the net average energy released directly from the fission process, has
been calculated for various fissioning systems with known complete mass-yield distributions
by using: (1) Eqs. 2.5.6 and 2.5.7', (2) the fission product (FP) atomic masses in the Tables of
Isotopes and (3) fission mass-yield distributions compiled by Rider and Meek 41) . To compare
the energy release Q'f calculated from nuclear masses with that obtained by summation of the
Target
Nuclide
235 U
235 U
235 U
238 U
238 U
239pu
239pu
24lpu
233 u
232Th
Neutron
Energy
t a
fb
h c
f
h
t
f
t
t
f
Table 2.5.1 Q'f calculated from nuclear masses
Target
Mass Excess
MeV
40.92
40.92
40.92
47.31
47.31
48.59
48.59
52.95
36.91
35.45
a thermal neutrons.
b fission spectrum neutrons.
c 14-MeV neutrons.
d data from Ref. 52.
FP
Mass Excess
MeV
-173.23
-173.25
-173.97
-173.24
-173.72
-173.68
-173.50
-173.47
-173.20
-173.02
d
V
2.4229 ±0.0066
2.52 ±0.02
4.46 ±0.10
2.81 ±0.05
4.31 ± 0.08
2.8799 ±0.0090
3.01 ±0.05
2.934 ±0.0012
2.4866 ±0.0069
2.36 ±0.07
(v— 1 )«,
MeV
11.48
12.27
27.93
14.61
26.72
15.17
16.22
15.61
12.00
10.98
y /
MeV
202.67
201.90
201.96
205.94
194.31
207.10
205.87
210.81
198.11
196.49