Transcript TITRE DE LA PRESENTATION

MOX Recycling in PWR
Zone
Vidangée
3.7% UOX
Giovanni B. Bruna
IRSN – DSR dir
Summary
•
MOX (Mixed Oxide) Fuel Recycling in
PWRs
1. French Context
2. Physics of Pu Recycling in PWRs
3. Void Effect in PWR cores with Plutonium
3. Codes 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:
Open UOX Cycle
Pu Rec.
With FBR
Pu Recycling in France :
a Year-Lasting Experience
• 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
Current MOX Assembly
Gd-poisoned Assembly
Low-enrichment pins
CYCLADES L.S. – 12 Gd2O3 pin/ass.
Intermediate-enrichment pins
High-enrichment pins
Water tubes
Water tubes eau
8 % C Gd2O3 pins
Physics of MOX Recycling in PWR
• 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.

-
An increased epi-thermal efficiency,

-
Shorter prompt neutron lifetime,
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
• MOX fuel in PWRs 3/4 :
1. A smaller Delayed-neutron Fraction (b 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 from
main Isotope
Families to reactivity
swing
vs. Fuel Burn-up
60
40
20
0
Fission
Products
Heavy Structural
Minor
Isotopes Materials Actinides
Physics of MOX Recycling in PWR
• 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
Original assembly
design
Physics of MOX Recycling in PWR
• 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
242Cm
Possible
simplification
b
243Cm
244Cm
32 years
- 25 minutes
Real process
163 days
16 hours
18,1 years
n - 2n
241Am
242Am
243Am
n

~ 5 hours
Fission products and energy
production by fusion
13 years
238Pu
239Pu
240Pu
2,10 days
2,35 days
241Pu
33 minutes
237Np
5,57 days
235U
236U
237U
23,5 minutes
238U
239U
242Pu
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

*Lower than 0.5 *Lower than 0.5

TOTAL
100
100
100

Typical Reactivity
swing
8500
4300
3500

(Annual cycle 10 Gwd/ t pcm -)
Physics of MOX Recycling in PWR
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°
Moderator Coefficient
> UOX
Physics of MOX Recycling in PWR
• Sensitivity of PWR core to the Plutonium
content:
a.
b.
c.
d.
e.
f.
Reactivity
Quite Low ( 600 pcm / % Pu)*
Void Effect
Very High (5 000 pcm / % Pu)*
Control Rod Worth
Medium
Soluble Boron Worth
Medium
Burnable Poison Worth
Medium
Power and Temperature Effects
Low
*1% increase of Plutonium content (RG Pu)
Physics 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 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.
Void effect in MOX fueled cores
• 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 cores
• Reactivity swing in a Voided core:
The reactivity swing in a Voided core results from
compensations among a large number of huge
individual isotope and reaction-rate contributions
having opposite sign:
- Every isotope contributes through several
rates (absorption, fission, 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 cores
• Moderator vs. Void Effect in UOX & MOX Fuel
Void Effect
0
100
Void Fraction
Moderator Effect
MOX
Reactivity
UOX
Full Void
Reactivity
depending on
Plutonium content
Void effect in MOX fueled cores
Fission Rates vs. Lethargy (MOX fueled Assembly in
Infinite Medium, no leakage)
Unités
arbitraires
O Elastic Scattering
U238Resonance
Traps
Pu239 Fission
U238
Inelastic
Scattering
Fission
Spectrum
Region
Epi-thermal
Region
Pu240
Capture
Thermal
Capture
Léthargie
Void effect in MOX fueled cores
• X.S. Behavior vs. Energy
Zone 1/v
Pu240
Fission à seuil
U235,
Pu239
Résonances
U238,
Pu240,
…
U238
0.2 0. 1.0 1.8
3
6
60 100
8E5
Log E
Void effect in MOX fueled cores
• Thermal Absorption X.S.
Void effect in MOX fueled cores
• Thermal Fission X.S
Studies on Heterogeneous Void
Infinite Medium Assembly Calculation

Homogeneous Void
Heterogeneous Void
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 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 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 Void
Computation sample : the central region can contain a
MOX assembly
Homogeneous Void
Heterogeneous Void
Studies on Heterogeneous Void
OCDE Benchmark sample
UO2
MOX
Études 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
b.MMOX
c.LMOX
d.(UO2
14.40
9.70
5.40
3.35)
Studies 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 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 Void
K Inf with water
Void

1. UO2 M. Inf
1.3697*
2. MOX M. Inf.
1.1447*
0.7738*
-41900*
3. Sample
1.3427*
1.3458*
+ 170*
a.*Rounded-off values
0*

« Envelop »
Heterogeneous Void
Homogenous Void
Void effect in MOX fueled cores
Void effect in MOX fueled cores
• 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 cores
• Qualification basis. Quite rich, including:
a.GODIVA
b.JEZEBEL
c.EOLE
- ERASME S, R, (L)
- EPICURE
d.VENUS
- VIPO
series
e.[SUPR series
U35,
Pu39, Pu40,
Pu hard spectrum
U38, Pu,
U38, Pu
WG Pu]
Qualification of Void calculations:
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:
MOX 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:
MOX fueled cores
Voided Zone
3.7% UOX
EPICURE mock-up Experiment
MOX
3.7%
UOX
Low and High
Enrich.
UOX-MOX EPICURE
Qualification
of Void
calculations:
MOX fueled
cores
Qualification of Void calculations: MOX fueled cores
( EPICURE LE (Low-Enrich) UOX-UOX)
20
21
22
23
24
25
26
27
-0.2
28
2.9
-0.2
-0.6
1.7
2.3
-2.9
-0.7
-1.4
-1.6
-1.7
-2.6
-5.0
-3.1
27
26
25
-2.7
24
-1.3
23
-3.1
0.0
22
-3.7
-2.5
21
20
1.4
20
1.3
21
22
23
24
25
26
27
--3.0
-5.0
-2.5
-1.6
-4.6
0.2
-1.6
-0.3
-1.8
2.8
-0.7
-1.9
-3.9
-1.9
1.2
2.6
0.1
-1.5
-0.5
4.2
1.1
1.2
3.1
-1.6
27
26
25
24
2.1
23
21
20
28
-3.3
28
22
28
2.0
5.2
Qualification of Void calculations: MOX fueled cores
( EPICURE LE (Low-Enrich) UOX-UOX)
20
21
22
23
24
25
26
27
2.0
28
-1.0
2.2
2.7
0.3
2.3
3.2
-1.0
-1.4
1.3
0.7
-2.9
1.7
0.0
27
26
25
4.7
24
1.6
-1.5
23
2.9
0.7
22
-3.7
2.7
21
20
0.9
0.0
20
21
22
23
24
25
26
27
28
-7.0
28
--6.0
-6.2
-4.8
-6.0
-5.5
-2.7
-4.0
-7.0
-4.0
-0.8
-0.7
-1.8
-0.3
-1.6
-3.0
-2.1
-2.2
-0.7
0.0
-2.0
-1.4
-2.3
-1.1
0.7
-1.5
-2.3
-1.4
-4.3
27
26
25
24
23
-2.8
22
-0.4
21
20
28
0.0
-1.4
Qualification 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 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 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.
Void effect in MOX fueled cores
• 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 ….