Recycling Process For Clean Mox Fuel Pellet

:Water Channel

Rod Type

wt% Puf

wt% U235

wt%Gd203

# of Rod

©

3.9

0.2

46

«E»

2.8

0.2

8

®

3.1

4

®

4.9

2.0

10

®

4.9

1.5

4

Average

2.8

1.3

#Total

7?

FIG. 2 Lattice Enrichment Design, M39 (Discharge Burnup 39.5GWd/t)

_J ^ Control Rod Position

[yy :Water Channel

Rod Type

wt% Puf

wt% UZ35

wt%Gd203

# of Rod

9

4.5

0.2

44

©

3.2

0.2

8

©

3.3

4

®

4.9

2.0

16

Average

3.1

1.4

#Total

72

FIG. 3 Lattice Enrichment Design, M45 (Discharge Burnup 45. OGWd/t)

Table I Calculated Results of Equilibrium Core Performance

Uniform Core

Mixed Core

Core Design Parameter

M39

U45

M45

U45/M39

U45/M45

# of Reload Bundles

U02

164

120

112

MOX

196

172

56

56

Average .Discharge. Burnup

(GWd/t)

U02

45

45

45

MOX

40

45

39

45

MLHGR (kW/m)

35

40

39

39

39

MCPR

1.6

1.6

1.5

1.6

1.6

Shutdown Margin (%Ak)

2.5

1.6

1.6

1.9

1.8

Table II Examples of 17 x 17 PWR MOX Fuel Enrichment Design for Pu Enrichment Common Use with BWR MOX Fuel

Rod Type

# of Rod

Common Use Pu Enrichment (cf. Fig. 2, Fig. 3)

Case 1

Case 2

H

176

7.8

7.5

M

76

3.9

4.5

L

12

2.8

3.2

Remarks:

  • 1) Case 1 and 2 use the common Pu enrichments with the BWR design case M39 and M45, respectively, (cf. Fig.2, Fig.3)
  • 2) Both cases are designed for the maximum discharge burnup of 48 GWd/t with average Pu enrichment of 6.4 wt% Puf, and depleted uranium (0.2 wt% U235) for the MOX carrying material.

compares well with the U02 FA regardless of the full and partial insertions of the MOX FAs. Fig. 4 shows a comparison of the MLHGR envelope curves of the uniform core cases (U45, M39, M45). Each curve is an envelope of MLHGR vs. fuel pellet burnup. It is noted that the MOX FA in this study exhibits about 5 kW/m higher MLHGR than the UOj FA, but there is no remarkable difference between the MOX and U02 FAs on the power history as a function of burnup and the MOX fuel has a large operating margin of MLHGR over the fuel life time of peak pellet burnup of 65 GWd/t. Fig. 5 shows the envelope curves for the UOj and MOX FAs in a mixed core case (U45/M45). Notwithstanding relatively higher reactivity of the MOX fuel than the U02 fuel at high burnup, the mixed core cases were designed so that the MOX fuel gives a lower MLHGR in comparison with the U02 fuel at higher burnup (>50 GWd/t).

Sample Preschool Letter Parents
  1. 4 MLHGR Envelope Curves of Uniform Core Cases fuel pellet burnup (GWd/t)
  2. 4 MLHGR Envelope Curves of Uniform Core Cases
FIG. 5 MLHGR Envelope Curves of Mixed Core Case (U45/M45)

It has been demonstrated from the core performance calculation results that the advanced 9x9 MOX FA is feasible with the high burnup design with the full MOX core as well as the mixed core with the U02 fuel.

SAFETY CHARACTERISTICS OF ADVANCED 9x9 BWR MOX FUEL

Pu-240 in the MOX fuel makes the Doppler coefficient more negative than the U02 fuel. This is an augmented safety characteristic of the MOX fuel in the reactor accidents and abnormal transients, in particular the reactivity initiated accident (RIA). On the other hand, approximately 30% more negative void coefficient of the MOX fuel than the U02 fuel has a reverse effect in the case of core pressurization transient and core stability. However, the advanced 9x9 BWR FA gives about 20% less negative void coefficient than the standard 8 x 8 FA for the same enrichment. This feature partly offsets the more negative void coefficient of the MOX fuel. The mixed core of MOX and U02 fuels takes some intermediate value of the void coefficient depending on the fraction of the MOX FAs in the core. The control rod worth tends to become smaller with die increased neutron absorption of the MOX fuel, but the scram characteristic is also a function of the axial power distribution. More negative void coefficient skews the axial power distribution into a bottom peaked shape. The net effect of the MOX fuel on tihe scram characteristic is not much different from that of the U02 fuel.

Although somewhat more quantitative analysis is required when more specific boundary conditions including the plant design are taken into account, it may be concluded from the above discussions that there is no special technological issue for the use of MOX fuel related to the core performance and the safety characteristics.

  1. FUEL CYCLE COSTS OF MOX FUEL
  2. 1 GENERAL TRENDS IN THE MOX FUEL CYCLE COST

It is well known that the fuel cycle costs of MOX fuel strongly depend on the fabrication cost, because only this cost component comprises most of the front-end costs for MOX fuel. Moreover, in the current status of LWR fuel burnup, i.e. the average discharge burnup is less than 60 GWdlt, the fuel cycle costs decrease substantially with higher burnup, in particular for the MOX fuel [7], This is because all cost components of the MOX fuel decrease directly relative to the generated electricity, i.e. the cost decreases simply with the fuel burnup, whereas the uranium purchase and enrichment costs for U02 fuel remain almost constant with burnup.

Fuel cycle costs were calculated for the fuel design cases discussed above in section 2.3. The same economic input data as given in Table 9.1 of reference [7] was used, but no credit for Pu value was taken. Fig. 6 (a) and Fig. 6 (b) show the cost comparison of MOX cases (M39 and M45) against the U02 case (U45). As shown in Fig. 6 (a), if the MOX fabrication cost is below 4.0 times that of U02, the MOX fuel cycle with the same discharge burnup of 45 GWd/t becomes competitive to the U02 fuel cycle. If the MOX discharge burnup is lower than 40 GWd/t, the corresponding MOX fabrication cost is lower than 3.3 times that of U02. Based on the proposed BWR MOX fuel design, the importance of the MOX fuel discharge burnup as well as the fabrication cost was confirmed.

3.2 MOX FUEL FABRICATION COST

Taking it for granted that the MOX fuel equivalent to U02 fuel in fuel cycle costs is a measure of the MOX fuel economy, the key factor is the MOX fabrication cost. The fabrication cost depends on the throughput and the construction cost of the fabrication plant. If a simple enrichment design as presented in this study is used for the BWR MOX fuel, it seems obvious that both the throughput and number of the process lines will be optimized, particularly for the new MOX fabrication plant in Japan.

CD 3

U45(U02 fuel,45GWd/t)

U45(U02 fuel,45GWd/t)

M45 (MOX fuel, 45 GWd/t)

MOX fabrication cost (relative to U02 fuel fabrication)

FIG. 6a

Fuel Cycle Costs of MOX Fuel

FIG. 6a

U45 (U02 fuel, 45 GWd/l) M45 (MOX fuel. 45 GWd/t)

  1. 6b Fuel Cycle Cost Components
  2. COMMON USE OF PU ENRICHMENT FOR PWR AND BWR MOX FUELS
  3. 1 COMMON USE OF PU MATERIAL

It is of further benefit for the MOX fuel plant design that a common use of the Pu enrichments is made for the PWR and BWR MOX fuels. Since the PWR and BWR fuels use different dimensions and other specifications of the fuel pellet, only Pu enrichment can be commonly used. However, the common use saves the time required for the cleaning of the process line from the powder preparation to the pelletizing. Thus the process utilization is increased. Another merit of such common use is to make the process batch size more uniform so that the powder preparation process is utilized efficiently, since a small batch of the common enrichment for the PWR and BWR MOX rods can be combined to form a larger batch size. Such examples are presented below.

4.2 EXAMPLE OF COMMON USE OF PU ENRICHMENT

Table 11 and Fig. 7 show the PWR MOX fuel enrichment designs for maximum burnup of 48 GWd/t. In these designs, two enrichments of the BWR MOX fuel in Fig. 2 or Fig. 3 are commonly used, i.e. 3.9 wt% and 2.8wt% Puf (M39) or 4.5 wt% and 3.2wt% Puf (M45) are used in the PWR MOX bundle. Preliminary analysis has shown that both enrichment designs are compatible with the U02 fuel of the same discharge burnup.

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