Zirconium hydride layer

The neutron spectrum of the Super FR is compared with those of LWRs and the sodium cooled fast reactor in Fig. 1.56. The blanket assemblies of the Super FR are equipped with zirconium hydride layer for the negative coolant void reactivity. The spectrum near the layer is similar to that of LWRs. Both fast and thermal neutron spectra are available in the Super FR. Availability of both will be suitable for the transmutation of long-lived fission products as well as minor actinides [95,96]. The improved core design for the high power density was reported [87]. 

Zirconium Hydride Layer Concept for Negative Void Reactivity... 

Placing a thin zirconium hydride layer between the seed and blanket fuel assemblies was found effective in changing the reactivity with steam density in the study of a steam cooled fast reactor [103, 104]. The typical geometry and calculation result are shown in Figs. 1.58 and 1.59, respectively. The effectiveness was explained in the subsequent studies [105,106]. The mechanism is described in Sect. 7.3. The fast neutrons are generated in the seed assemblies. They are moderated by the thin zirconium hydride layer between the seed and blanket. The layer is installed in the blanket assemblies in the present Super FR design. The moderated neutrons are effectively absorbed in the blanket fuel by the capture of U-238. The... 

Fig. 1.58 Original zirconium hydride layer concept of indirect cycle supercritical steam cooled fast reactor in two-dimensional core calculation model...

The mechanism of achieving negative reactivity is not whole-core spectrum softening by the moderator, but moderation through the zirconium hydride layer and absorption in the blanket. The breeding capability is not deteriorated much because the neutron spectrum of the remaining part of the core does not change much. 

The zirconium hydride layer concept is suitable for the Super ER, because the core shape stays normal, and is not flattened. The thickness of the RPV stays within... 

Concept of Blanket Assembly with Zirconium Hydride Layer... 

Effect of Zirconium Hydride Layer on Breeding Capability... 

T. Jevremovic, Y. Oka and S. Koshizuka, Effect of Zirconium-Hydride Layers on Reducing Coolant Void Reactivity of Steam Cooled Fast Breeder Reactors, Journal of Nuclear Science and Technology, Vol. 30(6), 497-504 (1993)... 

Calculations show that using a uranium dioxide fuel with 60% enrichment on with a zirconium hydride moderator makes it possible to obtain a core size of no more than 25 cm. The reactor is controlled by rotary steel drums with insertion from boron carbide, all drums are located in the reflector. The reactor shielding has a total thickness of 2 m, consisting of two layers light (1.6m) and heavy (0.4m) concrete. 

The local peaking factor is considered in the three-dimensional core depletion calculation of the Super FR, while it is separately considered by the assembly bumup analyses coupled with the subchaimel analyses in the Super LWR (see Chap. 2). The reason is that the local power peaking is mainly caused by the zirconium hydride (ZrHi 7) layers located in the blanket assemblies, introduced in Sect. 7.3. The local power peaking must be calculated along with the radial power distribution considering the arrangement of both the seed and blanket assemblies in the whole core, while it instead depends on the control rods and burnable poisons inside a fuel assembly in the Super LWR. 

Zirconium and Zircaloy-2 specimens exposed in solutions circulating in stainless steel systems collected some of the stainless steel corrosion products (iron and chromium oxides) in an outer layer of scale. This outer layer could be removed partially by a cathodic defilming operation. A sodium hydride bath treatment was required for complete removal. Table 5-8 lists values for long-term average corrosion rates observed in a solution 0.04 m in UO2SO4, 0.02 m in H2SO4, and 0.005 m in CUSO4 at 200, 250, and 300°C. 

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