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2. Burnable absorber for HYPER<br />

2.1 The HYPER core<br />

HYPER is a Pb-Bi-cooled ADS under development at KAERI with the aim of transmuting both<br />

TRUs and LLFPs such as 99 Tc and 129 I. The HYPER system is rated at 1 000 MW th thermal power and<br />

the minimum required sub-criticality is k eff = 0.97. Figure 1 shows a schematic configuration of the<br />

evolving HYPER core. In HYPER, a linear accelerator produces the proton beam of 1 GeV and the<br />

proton impinges on the Pb-Bi target in the core central region, generating about 28.84 spallation<br />

neutrons a proton. The proton beam is delivered to inside of the core through a beam tube to maximise<br />

the source neutron importance and also to obtain favourable axial power distribution. For emergency,<br />

3 locations are reserved for safety zones. The fuel blanket region is divided into 3 TRU enrichment<br />

zones (low, medium, high) to obtain acceptable radial power distribution. The low and high TRU fuels<br />

are loaded in the innermost and outermost zones, respectively.<br />

A unique feature of the HYPER core is transmutation of 99 Tc and 129 I in a localised thermal<br />

neutron zone. Inner region of the FP (Fission Product) assembly is composed of I and moderator<br />

(CaH 2 ) rods to produce thermal neutron and 99 Tc-is placed in the peripheral region to block the<br />

thermal neutron leakage into the neighbouring fuel assemblies [6]. Currently, two fuel types are<br />

considered for HYPER, one is the TRU-Zr metal and the other one is the TRU-Zr dispersion fuel,<br />

where TRU-Zr particles are dispersed in Zr matrix. In this work, the dispersion fuel is assumed. Spent<br />

fuels from PWRs of 33 GWD/MTU burn-up, after 30-year cooling time, are reprocessed with a<br />

pyrochemical processing and then recycled into the HYPER core. In the present work, a uranium<br />

removal rate of 99.9% is assumed. Consequently, the HYPER core is not completely free from<br />

uranium elements, instead, uranium occupies about 9 w/o in the fuel as shown in Table 1.<br />

Table 1. Feed fuel composition in weight percent<br />

(33 GWD/MTU, 30-year cooling)<br />

Isotopes<br />

234 U<br />

235 U<br />

236 U<br />

238 U<br />

237 Np<br />

238 Pu<br />

239 Pu<br />

240 Pu<br />

241 Pu<br />

242 Pu<br />

241 Am<br />

242m Am<br />

243 Am<br />

243 Cm<br />

244 Cm<br />

245 Cm<br />

246 Cm<br />

Weight percent (w/o)<br />

0.2000E-2<br />

0.7894E-1<br />

0.3840E-1<br />

0.8920E+1<br />

0.4449E+1<br />

0.9909E+0<br />

0.4756E+2<br />

0.2168E+2<br />

0.2689E+1<br />

0.4101E+1<br />

0.8649E+1<br />

0.3868E-2<br />

0.7591E+0<br />

0.1207E-2<br />

0.6604E-1<br />

0.7321E-1<br />

0.8515E-3<br />

783

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