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MOX Recycling in PWR
Giovanni B. BrunaIRSN – DSR dir
Zone Vidangée
3.7% UOX
Summary
• MOX (Mixed Oxide) Fuel Recycling in PWRs
1.1. French ContextFrench Context
2.2. Physics of Pu Recycling in PWRsPhysics of Pu Recycling in PWRs
3.3. Void Effect in PWR cores with Plutonium Void Effect in PWR cores with Plutonium
3.3. Codes and methodsCodes and methods
Pu Recycling in France :a Year-Lasting Experience
• In 1976 France adopted a « partially closed » cycle in 900MWe PWRs aiming at
• Improving the fossil fuel utilization• Limit Pu build-up• Use the huge amount of depleted
Uranium,• Reduce the amount of wastes (and their
activity
• Concentrate Pu in reactors:
Pu Rec.
With FBR
Open UOX Cycle
• MOX loading in 900 MWe PWR cores:
a. Three-zoned assembly, b. At equilibrium, 1/3 of the core assemblies
contain MOX fuel,c. Average Pu enrichment of the fuel : 7,0%,d. Objective burn-up : 50000 MWd/ton heavy
metal
Pu Recycling in France : a Year-Lasting Experience
Gd-poisoned Assembly
Water tubes eau
CYCLADES L.S. – 12 Gd2O3 pin/ass.
8 % C Gd2O3 pins
Current MOX Assembly
Low-enrichment pins
Intermediate-enrichment pins
High-enrichment pins
Water tubes
Pu Recycling in France : a Year-Lasting Experience
• MOX fuel in PWRs 1/4: • A grain-structured fuel
• Pin power distribution,• Pin thermo-mechanical behavior,• Volatile F.P. release,
• A lower number of fission per MWth •Fission energy release•Pu : 210 Mev / fission, vs. U : 200 Mev / fission
• P.F Build-up• Short-term Residual power
Physics of MOX Recycling in PWR
• MOX fuel in PWRs 2/4:• A Fission efficiency (per gram)
•~ U235 for WG Pu,•< U235 for RG Pu
• A roughly equivalent Doppler Coefficient,• A slightly higher Moderator Coefficient,• A reduced absorber worth (up to 60 – 70 % for
the assembly):•Soluble boron, •Control clusters, •Poisons (burnable and not-burnable).
Physics of MOX Recycling in PWR
• MOX fuel in PWRs 3/4 :
- An increased competition among fuel, structural materials and moderator, and a slightly increase of leakage.
Shorter prompt neutron lifetime,
- An increased epi-thermal efficiency, A reduced capacity to escape traps.
- A lowered thermal fission,- An increased epi-thermal and fast fission,
Improved fast neutron utilization.
Physics of MOX Recycling in PWR
Physics of MOX Recycling in PWR
• MOX fuel in PWRs 3/4 :
1. A smaller Delayed-neutron Fraction (eff),
2. An almost absent Xenon poisoning,
3. A smaller reactivity swing vs. Burn-up (higher Internal Conversion ratio ~0.75 vs. 0.60)
Contribution frommain Isotope Families to reactivity swing vs. Fuel Burn-up 0
20
40
60
FissionProducts
HeavyIsotopes
StructuralMaterials
MinorActinides
• Pin-wise Power Control• Compensation of physical effects through the
assembly design
FISSION REACTION RATES vs. LETHARGY(Infinite medium calculations)
Physics of MOX Recycling in PWR
• Pin-wise Power Control• Compensation of physical effects through the
assembly design
Physics of MOX Recycling in PWR
Original assembly design
• Pin-wise Power Control• Compensation of physical effects through the core
loading strategy
OUT-IN
Physics of MOX Recycling in PWR
• Fuel Burn-up / Breeding Process• Actinide build-up chain
Possiblesimplification Real process
n - 2n
n
Fission products and energy production by fusion
242Cm 243Cm 244Cm
243Am
240Pu 241Pu 242Pu239Pu238Pu
237Np
236U 237U 238U235U
242Am241Am
- 25 minutes32 years
16 hours 18,1 years163 days
13 years~ 5 hours
2,10 days 2,35 days 33 minutes
5,57 days 23,5 minutes
239U
Physics of MOX Recycling in PWR
• Fuel Burn-up / Breeding Process •Contribution of Actinide families to the reactivity swing vs. Fuel burn-up [MOX] UO2 MOX RCVS
Uranium 80 5 1
Plutonium - 20 41 26
Minor Actinides 3 7 16
Fission Products 33 47 57
4
TOTAL 100 100 100
Typical Reactivity swing
(Annual cycle 10 Gwd/ t - pcm -)
8500 4300 3500
*Lower than 0.5
Physics of MOX Recycling in PWR
*Lower than 0.5
Xenon-poisoning Effect at equilibrium 1500 pcm
Soluble Boron Worth ( per ppm) 7 pcm
Black Control Rod Worth (per Rod) 600 pcm
Gray Control Rod Worth (per Rod) 450 pcm
Doppler Coefficient 3 pcm/K°
Physics of MOX Recycling in PWR
Moderator Coefficient > UOX
• Sensitivity of PWR core to the Sensitivity of PWR core to the Plutonium contentPlutonium content::
a. Reactivity Quite Low ( 600 pcm / % Pu)*b. Void Effect Very High (5 000 pcm / %
Pu)*c. Control Rod Worth Mediumd. Soluble Boron Worth Mediume. Burnable Poison Worth Mediumf. Power and Temperature Effects Low
*1% increase of Plutonium content (RG Pu)
Physics of MOX Recycling in PWRPhysics of MOX Recycling in PWR
1.Transient sensitiveness to Plutonium content
-LOCA -RIA-Main Steam Line Break (RTV)
2.Additional Control Rods,
3.Constraints on the Loading Strategy,
4. System Modification
Physics of MOX Recycling in PWR
• Design constraintsDesign constraints:
Limit the Plutonium enrichment in the fuel and its core content to guarantee the safe operation against:
- The Soluble Boron and Control Rod Worth decrease,
- The Modified et more sensitive Operating conditions,
- The Increased Uncertainty.
Physics of MOX Recycling in PWRPhysics of MOX Recycling in PWR
• Neutronics behavior of PWR cores in case of LOCA is sensitive to the Plutonium content because:
- The MOX Moderator Coefficient is slightly different compared to UOX
- The Void Effect depends on the core
◊ Overall Plutonium content,
◊ Plutonium isotope composition,
◊ Heterogeneity.
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
• Reactivity swing in a Voided core:Reactivity swing in a Voided core:The reactivity swing in a Voided core results from The reactivity swing in a Voided core results from
compensations among a large number of huge compensations among a large number of huge individual isotope and reaction-rate individual isotope and reaction-rate contributions having opposite sign: contributions having opposite sign: - Every isotope contributes through Every isotope contributes through
several rates (absorption, fission, several rates (absorption, fission, slowing-down …)slowing-down …)
- Every individual component worth can be far bigger than the whole Void Worth,
- Big Uncertainty- Very large Sensitiveness of Void Worth
to the base data and the computation methodology.
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
• Moderator vs. Void Effect in UOX & MOX Fuel
MOXUOX
Reactivity
Void Fraction
0 100
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
Full Void Reactivity depending on Plutonium content
Moderator Effect
Void Effect
Fission Rates vs. Lethargy (MOX fueled Assembly in Infinite Medium, no leakage)
Léthargie
Unités arbitraires
O Elastic Scattering
U238Resonance Traps
Pu239 Fission
Thermal Capture
Pu240
Capture
U238
Inelastic Scattering
Fission Spectrum
Region
Epi-thermal Region
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
• X.S. Behavior vs. Energy
0.2 Log E60 100
Résonances
Zone 1/v
1.0
Fission à seuil
0.3
1.8 8E56
Pu240
U238, Pu240,
…U238
U235,Pu239
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
• Thermal Absorption X.S.
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
• Thermal Fission X.S
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
Studies on Heterogeneous VoidStudies on Heterogeneous Void
Homogeneous Void
Heterogeneous Void
Infinite Medium Assembly Calculation
Studies on Heterogeneous Void
1.Homogeneous Void : Progressive et uniform void of the sample,
2.Heterogeneous Void : Non-uniform, spotted Void of the sample; some regions are privileged,
3.The void fraction is the same but the reactivity swing is far different.
Studies on Heterogeneous VoidStudies on Heterogeneous Void
1.Accounting for leakage effect reduces the reactivity swing significantly
2.For sake of conservatism, the design calculations are always performed in an infinite medium, no leakage modeling approximation.
Studies on Heterogeneous VoidStudies on Heterogeneous Void
1.Coupling Effect
a. The reactivity of each region changes with the void fraction,
b. The neutronics importance of the region (i.e., the asymptotic contribution of the region to the reactivity) changes too, in the meantime.
2.The actual reactivity of the sample depends on region-wise importance (as a weighting function).
Studies on Heterogeneous VoidStudies on Heterogeneous Void
Homogeneous Void Heterogeneous Void
Computation sample : the central region can contain a MOX assembly
Studies on Heterogeneous VoidStudies on Heterogeneous Void
OCDE Benchmark sample
UO2
MOX
Études de Vidange HétérogèneÉtudes de Vidange Hétérogène
1. OCDE Benchmark
2. 3*3 assembly sample with 10*10 pins/ass.; (1.26 cm pitch): Inf. Medium Calc. with a variable Pu enrichment central MOX assembly:
a.HMOX 14.40b.MMOX 9.70c.LMOX 5.40
d.(UO2 3.35)
Studies on Heterogeneous VoidStudies on Heterogeneous Void
1.In the MMOX sample with water, typical parameter values are respectively:
2.Zone Kinf*Imp*.
3.UO2 1.3697 0.88
4.MOX 1.1447 0.12
5.Sample 1.3427
a.*Rounded-off values
Studies on Heterogeneous VoidStudies on Heterogeneous Void
1. In the central-void MMOX sample, typical parameter values are respectively:
2. Zone Kinf *Imp*.
3. UO2 1.3697 0.96
4. MOX 0.7738 0.04
5. Sample 1.3458
*Rounded-off values
Studies on Heterogeneous VoidStudies on Heterogeneous Void
K Inf with water Void
1. UO2 M. Inf 1.3697* 0*
2. MOX M. Inf. 1.1447* 0.7738* -41900*
3. Sample 1.3427* 1.3458* + 170*
a.*Rounded-off values
Homogenous Void
Heterogeneous Void
« Envelop »
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
• Main calculation challenges:Main calculation challenges:
a.Space and Energy Heterogeneity;b. Streaming inn the voided regions;c. Self-shielding and dependence on the
temperature of epi – thermal resonances:- Pu39, Pu41 0,3 eV,- Pu40 1,0 eV,- Pu 42 1.8 eV;
d. Mutual resonance self-shielding.
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
• Qualification basis. Quite rich, Qualification basis. Quite rich, including:including:
a.GODIVA U35,b.JEZEBEL Pu39, Pu40,c.c.EOLEEOLE
- ERASME S, R, (L) ERASME S, R, (L) Pu hard spectrumPu hard spectrum- EPICUREEPICURE U38, Pu,U38, Pu,
d.VENUS - VIPO series U38, Pu
e.[SUPR series WG Pu]
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores
• Pin-power distribution measurement technique 1/2:
• A very careful characterization of the fuel is to be performed (to avoid effect of fabrication uncertainties);
• Activity is measured pin by pin through gamma spectrometry (relative values);
•But U and Pu R.R. are different (due to X.S. );•Thus gamma-scanning activities in U and Pu regions
are inhomogeneous: absolute values are necessary•Activities of some F.P. the Yields of which (both U
and Pu) are very well known (with equivalent uncertainty level) are measured independently as tracers,
•Y-scanning activity distribution are re-normalized to obtain absolute distributions;
•To obtain the power distribution from the activity, a suitable normalization is performed via a “ P/A ” conversion factor experimentally measured in reference mock-ups.
Qualification of Void calculations: Qualification of Void calculations: MOX fueled coresMOX fueled cores
Qualification of Void calculations: Qualification of Void calculations: MOX fueled coresMOX fueled cores
• Pin-power distribution measurement technique 2/2:
• The process of measurement is very hazardous and complex,
• It is not fully independent from data and computation,
• The quality of the pin-wise experimental distribution depends on:
•The fuel fabrication process (homogeneity of composition and density),
•The representativeness of the experimental mock-ups The experimental techniques,
•The base-data used (Yields);•The robustness of the overall reconstruction process.
Qualification of Void calculations: Qualification of Void calculations: MOX fueled coresMOX fueled cores
Qualification of Void calculations: Qualification of Void calculations: MOX fueled coresMOX fueled cores
Qualification of Void calculations: Qualification of Void calculations: MOX fueled coresMOX fueled cores
Voided Zone
3.7% UOX
EPICURE mock-up Experiment
MOX
3.7% UOX
Low and High Enrich.
UOX-MOX EPICURE
Qualification Qualification of Void of Void
calculations: calculations: MOX fueled MOX fueled
corescores
20 21 22 23 24 25 26 27 28
28 -0.2
27 2.9 -0.2
26 -0.6 1.7 2.3
25 -2.9 -0.7 -1.4 -1.6
24 -2.7 -1.7 -2.6 -5.0 -3.1
23 -1.3 -3.1
22 0.0 -3.7
21 -2.5
20 1.4 1.3
20 21 22 23 24 25 26 27 28
28 -3.3
27 --3.0 -5.0
26 -2.5 -1.6 -4.6
25 0.2 -1.6 -0.3 -1.8
24 2.8 -0.7 -1.9 -3.9 -1.9
23 2.1 1.2 2.6 0.1 -1.5 -0.5
22 2.0 5.2 4.2 1.1 1.2 3.1 -1.6
21
20
Qualification of Void calculations: MOX fueled coresQualification of Void calculations: MOX fueled cores( EPICURE LE (Low-Enrich) UOX-UOX)
20 21 22 23 24 25 26 27 28
28 2.0
27 -1.0 2.2
26 2.7 0.3 2.3
25 3.2 -1.0 -1.4 1.3
24 4.7 0.7 -2.9 1.7 0.0
23 -1.5 1.6
22 0.7 2.9
21 2.7 -3.7
20 0.0 0.9
20 21 22 23 24 25 26 27 28
28 -7.0
27 --6.0 -6.2
26 -4.8 -6.0 -5.5
25 -2.7 -4.0 -7.0 -4.0
24 -0.8 -0.7 -1.8 -0.3 -1.6
23 -3.0 -2.1 -2.2 -0.7 0.0 -2.0
22 -2.8 -1.4 -2.3 -1.1 0.7 -1.5 -2.3
21 -0.4 -1.4 -4.3
20 0.0 -1.4
Qualification of Void calculations: MOX fueled coresQualification of Void calculations: MOX fueled cores( EPICURE LE (Low-Enrich) UOX-UOX)
• Analysis of results:
• Despite
•The same experimental techniques are used a for all measurements
•The same schemes and options are adopted for computations,
• The discrepancies C/ E increase significantly with the sample Pu enrichment.
Qualification of Void calculations: MOX fueled coresQualification of Void calculations: MOX fueled cores( EPICURE LE (Low-Enrich) UOX-UOX)
• Possible explanation 1/2:
• Differences in the C/ E results can be explained by the effect of :
•Measurement uncertainties •Computation precision,
•Which both are sensitive to the spectrum hardiness (Pu enrichment).
Qualification of Void calculations: MOX fueled coresQualification of Void calculations: MOX fueled cores( EPICURE LE (Low-Enrich) UOX-UOX)
• Possible explanation 2/2 :•Measurement are less precise with increasing enrichment, because:
•R.R. decrease,•Yield uncertainty increases;
•Computation precision is reduced with increasing enrichment because:
•The worth of the non-resolved resonance region increases;
•This region is generally far less well described in the libraries;
•Improvements to be made both in measurement techniques and computation.
Qualification of Void calculations: MOX fueled coresQualification of Void calculations: MOX fueled cores( EPICURE LE (Low-Enrich) UOX-UOX)
• CONCLUSION CONCLUSION
The complexity of physical problems and the difficulty in the modeling increase with MOX fueling, which demands:
- A huge effort to improve the base-data and the computation tools,
- New qualification needs,- A conservative approach at the design
stage,- Several modification in the design and
operation- A wide integration of the operational
experience feed-back:- That’s history, now ….That’s history, now ….
Void effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled coresVoid effect in MOX fueled cores