127Engineering Issues
Operation of LWRs is generating increasing amounts of Pu. In the United States,
t
his
P
u
r
emains
i
n
t
he
f
uel
e
lements,
w
hich
a
re
s
tored
a
s
w
aste.
I
n
E
urope
a
nd
J
apan,
b
reeder-reactor
p
rograms
m
ay
u
ltimately
m
ake
u
se
o
f
P
u
r
ecovered
f
rom
s
pent
L
WR
f
uel.
H
owever,
t
here
h
ave
b
een
s
everal
s
tudies
o
f
r
ecycling
P
u
t
hrough
L
WRs,
r
eplacing
s
ome
f
raction
o
f
t
he
235
U as the primary ssile fuel [52]. Many
o
f
t
hese
s
tudies
a
re
c
entered
o
n
t
he
f
abrication
o
f
P
u–U
m
ixed
o
xide
(
MOX)
f
uel.
S
ignicantly,
a
n
i
nitial
i
ncorporation
o
f
P
u
i
nto
r
eactor
f
uel
r
esults
i
n
a c
ompletely
d
ifferent
P
u
i
sotopic
s
ignature
t
han
t
he
n
uclear
f
orensic
a
nalyst
w
ould
e
ncounter
i
n
t
he
U
S
m
aterials.
The
reactor types described earlier were designed to produc