137Engineering Issues
net formation of each product nuclide that is specic for a given reactor. These values
(
the
l
ibrary
f
or
t
hat
r
eactor)
a
nd
t
he
d
ecay
c
onstants
o
f
t
he
r
eaction
p
roducts
m
ake
u
p
t
he
p
arameters
o
f
a
s
et
o
f
c
oupled,
l
inear,
rst-order
d
ifferential
e
quations
t
hat
a
re
a
f
unction
o
f
r
eactor
p
ower.
S
tarting
f
rom
a
n
i
nitial
c
omposition
o
f
f
uel,
d
ened
b
y
t
he
us
er,
t
he
c
ode
s
olves
t
hese
d
ifferential
e
quations
at
a
s
pecied
e
xposure
t
ime
a
nd
reactor power level to produce a total nuclide inventory.
What
i
s
n
ot
m
odeled
i
n
t
he
O
RIGEN2
c
alculation,
h
owever,
i
s
t
he
i
nhomogeneity
i
n
t
he
p
roduction
o
f
P
u
i
sotopes
a
t
d
ifferent
l
ocations
i
n
t
he
r
eactor
f
uel
b
ased
o
n
l
ocal
v
ari-
ations
i
n
n
eutron
uence
[
67].
D
uring
o
peration
o
f
a t
hermal