Transcript Neutronic Model of a Mirror Based Fusion

Safety And Power Multiplication Aspects Of
Mirror Fusion-Fission Hybrids
K. Noack1, O. Ågren1, J. Källne1, A. Hagnestål1, V. E. Moiseenko2
1Uppsala
2Institute
University, Ångström Laboratory, Division of Electricity,
Box 534, SE 751 21 Uppsala, Sweden
of Plasma Physics, National Science Center “Kharkiv Institute of Physics and Technology”,
Akademichna st. 1, 61108 Kharkiv, Ukraine
 Articel:
Annals of Nuclear Energy 38, 578 (2011)
FUNFI workshop, Varenna, Italy, September 12-15, 2011
2/17
CONTENT
1. Present Neutronic Model
2. Safety Considerations
3. Discussion and Conclusions
3/17
1. Present Neutronic Model
 Modified radial structure:
TABLE 1.
Two hybrid options:
A
B
keff
0.95
0.97
Core thickness (cm)
21.8
22.8
Fission power (GW)
3
1.5
Fusion power (MW)
35-75
11-20
New component: Reactivity modulator (RM)
LBE-cooling loop
T-breeding New component: Shield
• Thickness • (60:40) vol% steel&water
decreased • Steel with 1.75 wt% Bnat
• 20 wt% of
Li-6
4/17
1. Present Neutronic Model
 Standard axial dependence of the neutron source:
: Length of the core = 25 m !
5/17
1. Present Neutronic Model
 Reactivity effect of the „Reactivity modulator“ (RM):
# Calculation model:
• 2 B4C-annuli at the outer core surface
at both ends
• Thickness = 1 cm, height = 2.5 m
• Boron is 90% enriched in 10B
~4000 pcm
: Reactivity range = 4000 pcm (10-5)
6/17
1. Present Neutronic Model
 Disadvantage & Advantages:
 Disadvantage:
Reactor technology has no experience with such long systems.
 Advantages:
1) Highly efficient utilization of the neutron source.
2) First wall problem is considerably mitigated.
3) The shielding of the magnetic coils is a fission shielding
4)
5)
6)
7)
problem.
The vertical installation could enable natural circulation of
the LBE-coolant.
See talk O12 of H. Anglart, this workshop.
The long system implies a small leakage and hence a
relatively small effect of the thermo-structural expansion.
Low average fission power density of 76 W/cm3 and low
average linear pin power of 80 W/cm.
Low radial peaking factor of 1.15 and of 1.30 over the whole
core.
7/17
2. Safety Considerations
 Steady-state power amplification:
● Demand: The generation of the fission power must be
manageable in any case to prevent the system from
damage!
PAF
Fission power
Fusion power
E fis 1
keff
J c ,1
Pfis 


 Pfus
E fus  ( 1  keff ) S
Meff
*appr
: Three possibilities to control the fission power:
PAF
• Pfus
• *appr
• Meff
(fusion driver)
(fusion driver)
(fission blanket)
Reactivity feedback effects!
: The blanket must remain sub-critical in any case!
8/17
2. Safety Considerations
 Temperature feedback effects at start-up & switch-off:
# Calculation model: • Fuel
400 K  1100 K
• LBE, structure 400 K  900 K
Δkeff /(keff·ΔT) (10-6 1/K)
Δkeff (pcm)
-1.05  30%
▬73
2) LBE-coolant density effect
-7.4  5%
▬350
3) Axial core expansion
~0
4) Radial expansion of fuel pins
0.4 (from Ref. 12*)
19
5) Radial core expansion
-6.8 (from Ref. 12)
▬320
Effect
1) Doppler effect of the fuel
*[12]
0
(?)
W. M. Stacey, Nuclear Reactor Physics, 2004. Data given for a Na-cooled FR with oxide fuel.
: Expected maximal total temperature effect for start-up/switch-off (or
„loss of plasma“):
~ ▬/+800 pcm
9/17
2. Safety Considerations
 Coolant void effects − Voided radial areas within the core:
# Calculation model:
LBE-voided radial core areas (cm)
1
2
3
4
5
[115 < r < 122]
[113 < r < 124]
[111 < r < 126]
entire core
buffer&core&expansion zone
~1445 pcm  3%
: Expected maximal reactivity effect by radial LBE-voiding: ~ +1500 pcm
10/17
2. Safety Considerations
 Coolant void effects − Loss of LBE-coolant:
# Calculation model: • vertically installed hybrid
• united volume of buffer, core, exp. zone
• different LBE-levels
: Loss of the LBE-coolant results in a negative reactivity effect!
11/17
2. Safety Considerations
 Reactivity effects of water in the coolant loop and in
the vacuum chamber:
Cases: 1 – H2O within the core
3 – H2O within buffer, exp. zone
2 – H2O within core, buffer, exp. zone
4 – H2O within the vacuum chamber
: • Case 1 must be excluded by design!
• All the other „water effects“ are negative.
12/17
2. Safety Considerations
 *-Effect of the axial distribution of the neutron source:
Standard axial dependence of the neutron source
# Calculation model: Deformations of the axial dependence.
Deformation of the n-Source
Ratio of fission heatings
(def./stand.)
1) Peak height reduced by factor 2
1.03
2) Source length compressed to 20 m
1.13
3) Full intensity concentrated at z=0
1.42
13/17
2. Safety Considerations
 Axial dependence of the specific fission heating:
hfis(z)= Fission heating per source neutron emitted at z
hfis = 1513 (MeV)
Pfis   h fis( z )S ( z )dz
14/17
3. Discussion and Conclusions
 With regard to the blanket (A – keff=0.95, B – keff=0.97):
1) Response to changes of Pfus.
• To reduce thermal shocks the Pfis should respond gradually.
# In this respect, option B is not worse than A!
2) Response to inadvertant insertion of (+)-reactivity.
• Worst case:
„Inflow of cold LBE“ + „Ejection of the inserted RM“
+800 pcm
 Restriction: ≤ ~1000 pcm
# Then, even B is in deep sub-criticality!
3) Responses to start-up and switch-off at the beginning of the cycle.
• Start-up (▬800 pcm):
 Withdrawal of the RM to meet the nominal criticality in the
operation state.
• Switch-off (+800 pcm):
 Insertion of the RM to fulfill keff ≤ 0.95 (0.97).
# No safety relevant disadvantage of option B compared to A!
15/17
3. Discussion and Conclusions
 With regard to the blanket (A – keff=0.95, B – keff=0.97):
4) Response to „unprotected“ transients.
• Incidence: Driver cannot be shut off on demand.
T- increase
 insertion of (▬)-reactivity
T-increase is slowed down.
# In this respect, option B is more advantageous than A!
 Further reduction of the PAF by completely inserting the RM.
# In this respect, option B is more advantageous than A!
Our position:
The shut-off of the driver definitely takes place after a
minimal delay!
 Quantitative estimates of possible core damage need
dynamic calculations!
16/17
3. Discussion and Conclusions
 With regard to the blanket (A – keff=0.95, B – keff=0.97):
5) Response to coolant void effects.
• Loss of coolant:
 negative effect.
• Voided areas within the core:  <+1500 pcm < 2300 pcm
+ cooling down the blanket
 + 800 pcm
• The RM could be used to compensate reactivity.
# Both hybrid options remain sub-critical!
6) Response to filling the LBE-coolant loop with water:
• Incidence: For example, intended misuse.
 Negative effects, provided that buffer, core and exp. zone
form a united volume!
# No safety relevant difference between both hybrid options!
7) Comparison of the hybrid options A and B:
 The study revealed that option B does not exhibit substantial
disadvantages with regard to safety!
17/17
3. Discussion and Conclusions
 With regard to the mirror driver:
8) Minimal value as low as possible < Pfus < definite maximal value.
9) The driver must be equipped with several redundant, quick
shut-off techniques.
10) Pfus should be supplied gradually tunable and stable.
11) If Pfus is fluctuating, the frequencies should be clearly
above 10 Hz.
12) The probability of plasma collapses must be minimal.
13) The neutron source should have the axial peaks at stable
positions.
In case of fluctuations, the frequency range should be clearly
above 10 Hz.
Thank you for your attention!