76
The age of neutrons from
by a MODRIC multigroup diff’usion c a l c u l a t i o n ) .
t h e d i f f e r e n t sources was assumed t o be proportional t o t h e lethargy; t h a t is,
Computed values of
T
i
a r e given i n Table 6.1.
Table 6 . 1 .
1
2
55.7
22.7
Group Precursors h a l f - l i f e ( s e e )
Delayed Neutron Data
3
4
5
6
6.22
2.30
0.61
0.23
F r a c t i o n a l y i e l d of precursors, 1 0 4 p i (neutrons per io4 neutrons )
2.11
14.02
12.54
25.2%
7.40
2.70
Neutron mean energy (Mev)
0.25
0.46
0.40
0.45
0.52
0.5
Neutron age i n MSRF: (em2)
6.2.4
256
266
264
266
269
26%
MSRE Dimensions
The computation of B2 f o r t h e nonleakage p r o b a b i l i t i e s used R = 27.75 i n . and H = 68.9 i n . ft3.
The volume of f u e l w i t h i n t h e s e boundaries i s 25.0
A t a c i r c u l a t i o n r a t e of 1200 gpm, residence times a r e 9.37
t h e core and 16.45 see i n t h e e x t e r n a l loop.
see i n
A thermal neutron d i f f u s i o n
l e n g t h appropriate f o r a core with highly (-93%) enriched uranium and no thorium was used (L2 = 210 em2).
6.3
Results of Computation
The core residence t i m e , i n u n i t s of precursor h a l f - l i v e s ,
from 0.2 t o 41.
Because of t h i s , t h e shapes of t h e delayed neutron
sources i n t h e core vary widely, as shown i n Fig. 6.1, circulating.
ranges
when t h e f u e l i s
(The source s t r e n g t h i s normalized t o a production r a t e of