LMFBR fuel design

Figure 10.29 shows the principal steps in applying the Purex process to irradiated LMFBR fuel, step 7 of Fig. 10.28. The flow scheme and the compositions and locations of solvent, scrubbing, and stripping streams have been taken from the process flow sheet of a 1978 Oak Ridge report [Oil] describing a planned experimental reprocessing facility designed for 0.5 MT of uranium-plutonium fuel or 0.2 MT of uranium-plutonium-thoiium fuel per day. As that report gave process flow rates only for the uranium-plutonium-thorium fuel. Fig. 10.29 does not give flow rates for the uranium-plutonium fuel of present interest. This flow sheet shows the codecontamination step, in which flssion products are separated from uranium and plutonium the partitioning step, which produces an aqueous stream of partially decontaminated...

The calculated elemental composition, radioactivity, and decay-heat rate for discharge fuel are shown in Table 8.7 for the uranium-fueled PWR (cf. Fig. 3.31), in Table 8.8 for the liquid-metal fast-breeder reactor (LMFBR) (cf. Fig. 3.34), and in Table 8.9 for the uranium-thorium-fueled HTGR (cf. Fig. 3.33). These quantities, expressed per unit mass of discharge fuel, are useful in the design of reprocessing operations. For the purpose of comparison, all quantities are calculated for 150 days of postirradiation cooling. 

TOSHINSKY, V, SEKIMOTO, H., TOSHINSKY, G., "Self-Fuel-Providing LMFBR Design Problems and Their Possible Solutions", Proc. ICENES 98, Tel-Aviv, Israel, 1998), Vol.l, p. 43. 

ANSI/ANS-54.2-1985, "Design Bases for Facilities for LMFBR Spent Fuel Storage in Liquid Metal Outside the Primary Coolant Boundary."... 

ZPPR is designed to be used for physics studies of power breeder reactor systems in support of the AEC s lMFBR program, and can accommodate mockups characr terlstic of the proposed 300- to 500-MW(e) demonstration pltmts and lOOO-MW(e) commercial plants- Compositiph simulation is accomplished by assembling fuel, coolant, and structural materials, In the form of small plates, Into drawers which are, In turn, loaded into the reactor matrix. 

To provide Uiese data, a research effort has been initiated At the Critical Mass liaboratory at Battelle-Northwest. Fuels Currently of interest in the LMFBR PO am Plan Involve Uranium enriched with between 8 aiid 30 Pu. Consequently, the initial series of experiments was designed to obtain criticality data on bydrogetious intxtures of PuOt-UOa at concentrations that vdll provide over the widest possible range in the 8 to 30 wt% enrichment region. 

Subcriticality Design Considerations for LMFBR Spent Fuel Shipping Casks, /. S. Phil bin, S. A. Dupree (Sandia Labs)... 

The most important advantage of these gas core concepts, however, may lie in the fact that they can be designed as breeders but with minimal initial fissile feed requirements. This point is significant for two reasons (a) the rate at which these gas core reactors could be brought on line would not be dependent oh the rate of fuel being discharged from LWRs as would be the case fpr LMFBRs and b) the estimated easily recoverable U.S. uranium resources will probably be sufficient to fuel 500 to 1000 LWRs of 1000 MW(e) each, while this same amount of uranium could be used to fuel approximately... 

J. A. VlTTl et al., Preconceptual Study of 1000 MWe Carbide Fueled LMFBR Designs, ESG-DOE-13244, Rockwell International (1978). 

CAHALAN, J., et al.. Accommodation of Unprotected Accidents by Inherent Safety Design Features In Metallic and Oxide-Fueled LMFBRs, Proc. ANS International Topical Meeting on reactor Safety, Knoxville. 

Tables 1 and 2 tabulate the above mentioned fuel cycle dynamic response characteristics for selected open cycle and closed cycle concepts of small reactors without on-site refuelling, based on the inputs provided by designers in the corresponding annexes. For comparison. Table 3 lists the corresponding values for typical LWRs [2] and projected high-breeding LMFBRs [3]. IHM is for initial heavy metals and CR is for conversion (or breeding) ratio.

As indicated by Table 2 and several design descriptions given in the annexes, achieving a CR >1 appears feasible in the several concepts of small fast-spectrum reactors with lead and lead bismuth coolant, especially when dense nitride fuel is employed. Should it work out in practice, such reactors will not loose to larger-size LMFBRs in the efficiency of uranium ore... 

Fuel Rod Design Table 7.4 Fuel rod design criteria for LMFBRs. (Taken from [1]) 455... 

The coolant flow velocity, which is usually determined by flow experiments, has been limited in LMFBR designs in order to prevent excessive vibration of the fuel rods. Smaller fuel rod diameters are advantageous for a high power density concept with fixed average linear heat rate, but this concept requires more mass flux to keep the cladding surface temperature below the limit. High mass flux, that is, high flow velocity, raises a concern of FIV. 

Strain controlled limit has been applied in LMFBRs rather than load controlled limit. Inelastic or creep strain have been used as design criteria in LMFBRs. In the Fast Flux Test Facility or CRBRP fuel rod designs, inelastic hoop strain was limited to 0.1% on average and 0.2% as the peak for normal operation conditions, 0.3% at an anticipated transient, and 0.7% at an unlikely event [14]. Inelastic strain limit was an earlier approach used for a failure criterion and is a straightforward concept. 

---