poisoning
DESCRIPTION
Poisoning. Poisoning. Poisoning. Not anticipated! Reactor shut down!. Time scale: Hours and days. 135 Xe 10 6 b. 149 Sm 10 5 b. Poisoning. HW 28. Negative reactivity due to poison buildup. It is proportional to the amount of poison. Poisoning. small. Initial conditions? - PowerPoint PPT PresentationTRANSCRIPT
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
1
Poisoning
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
2
Poisoning
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
3
Poisoning• Not anticipated! Reactor shut down! Time scale:Time scale:
Hours and days.Hours and days.135Xe106 b
149Sm105 b
XeI
Ia Xe
a
mXe
a
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
4
HW 28HW 28
Poisoning
eratora
clada
fuela
poisona
poisona
eratora
clada
fuela
fuela
eratora
clada
fuela
fuela
f
f
kk
k
mod12
mod2
mod1
that Show
(critical)
reactor). (Infinite use uslet ,1
Reactivity
Negative reactivity due to poison buildup. It is proportional to the amount of poison.
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
5
Poisoning
),(),(),(),(),(),(
),(),(),(),(),(
trtrXetrXetrItrt
trXe
trtrItrItrt
trI
XeaXeIfXe
IaIfI
Initial conditions?Initial conditions?• Clean Core Startup.Clean Core Startup.• Shutdown (later).
constant.)0()( assume uslet and
Fuel.Fresh 0)0()0(
t
XeI
small
Assume no spacial dependence.
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
6
Poisoning
)(
)1()(
)(
)(
0
0
)(
0
0
0
0
ttXeaIXe
fI
tXeaXe
fXeI
IXeaXe
XeaXe
ee
etXe
)1()( 0 t
I
fI IetI
HW 29HW 29 Show that:
and
)(I)(Xe
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
7
Poisoning
)(I)(Xe
eratora
clada
fuela
Xea
eratora
clada
fuela
poisona tXet
modmod
)()(
• Now, we know Xe(t)
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
8
Poisoning• Shutdown. Shutdown. After the reactor has been operating for a “long” time.
.0)0()(
)()0(
)()0(
t
XeXe
II
),(),(),(
),(),(
trXetrIt
trXe
trIt
trI
XeI
I
),(),(),(),(),(),(
),(),(),(),(),(
trtrXetrXetrItrt
trXe
trtrItrItrt
trI
XeaXeIfXe
IaIfI
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
9
PoisoningHW 30HW 30 Show that
)()(
)()(
)()(
tt
XeI
It
t
IXeXe
I
eeI
eXetXe
eItI
Height of the peak depends on I() and Xe(), i.e. depends on .
> 0 ?
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
10
Poisoning
If, the available excess reactivity can compensate for less than 30 minutes of poison buildup, can’t startup again after ~30 minutes of shutdown, because you can’t achieve criticality. Need to wait some 40 hours (in this case) for Xe to decay down.
Shutdown Xe negative move control rods out try to add positive reactivity need to have enough reserve costly to do that.
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
11
Poisoning
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
12
PoisoningStrategiesStrategies• If you plan to shut down for “short maintenance”, think about stepback.• Examine different scenarios using this code from
http://www.nuceng.ca/ • Prepare your own report, code, calculations, graphs, comments, conclusions etc…..• Be creative and use whatever experience you gained during your study in this program.
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
13
PoisoningXe OscillationsXe Oscillations• (r,t) (spacial dependence) flux locally Xe burnup (reactivity) flux further control rods globally in flux elsewhere Xe burnup ….. Xe oscillation but limited by opposite effect due to increase (decrease) of I in the high (low) flux region.• In large reactors (compared to neutron diffusion length) local flux, power and temperature could reach unacceptable values for certain materials safety issues. • Think of one sensor and one control rod feel average flux apparently OK more sensors and control rods to locate and deal with local changes.
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
14
PoisoningPermanent PoisonsPermanent Poisons• 149Sm has sizeable but lower cross section than 135Xe.• It does not decay.
• Start from fresh fuel:
• Thus:
Constant . )0,()0,(),(),(),(
SmfSmfSm rrtrtrt
trSm
h time.Linear wit .Constant . )0,()0,(),( ttrrtrSm SmfSm
h time.Linear wit )0,()0,(),( trrtr fSmSma
Sma
Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).
15