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Blokhin, A.I.

Paper Title Page

TUEO01

 Neutronic And Physical Characteristics Of An Accelerator Driven System With A Target And Core Coolant From The Lead-208 Isotope 

  • G.L.Khorasanov, A.P.Ivanov, A.I.Blokhin
    Institute for Physics and Power Engineering, Obninsk, Russia

Presently, several research centers of the European Community are planning to construct in 2025-2030 an Accelerator Driven System (ADS), named as EFIT, with the aim to transmutate minor actinides (MA), wastes of nuclear power plants. It is supposed that thermal capacity of the EFIT subcritical core will be equal to several hundreds of MW and it will be driven by a proton beam of energy Ep=1000 ÌeV and current about Ip=20 mA. In supporting this project, in 2001-2004 in Europe the facilities PDS-XADS with 80 MW thermal capacity and XT-ADS (MYRRHA) with 50 MW thermal capacity were considered within a design phase. In these facilities a conventional eutectic of natural lead (Pb-nat) and bismuth, Pb-nat(45%)-Bi(55%), was proposed as a coolant material for the target and core. With the aim of hardening the ADS target neutron spectrum, earlier an opportunity of using the modified lead-bismuth eutectic consisted from (80-90)% of the slow neutron moderating lead isotope, Pb-208, and (20-10)% of Bi-209 has been proposed by authors, that was presented at the ICONE 13 and GLOBAL 2005 International conferences on nuclear science and engineering. In this paper a possibility of using molten pure Pb-208 as the coolant for the subcritical core of 80 MW thermal capacity of the PDS-XADS type facility is considered. Calculations of neutronic and physical characteristics of the ADS were performed using Monte Carlo code. The following initial data were chosen: the annular core with the target in its center; the core coolant Pb-208(100%); a fuel, a mix of mono nitrides of depleted uranium and power plutonium with a small share of neptunium and americium; the target coolant, the modified eutectic, Pb-208(80%)-Bi(20%); proton beam energy 600 MeV; effective multiplication factor of the core Keff = 0.97; thermal capacity of the core N = 80 MW. From calculations follows that in using Pb-208 as the core coolant the intensity of external source of neutrons to deliver 80 MW thermal capacity is equal to S = 2.29·1017 n/s, that corresponds to proton beam current Ip = 2.8 mA and beam capacity Ðp = 1.68 ÌW. In using natural lead instead of Pb-208, effective multiplication factor of the core in normal operating regime falls down to the value equal to Keff =0.95. In these conditions multiplication of external neutrons in the core and thermal capacity of the core are below nominal by 1.55 times. For achievement the rated core power N=80 ÌW it is required on ~20-30 % to increase the fuel loading and volume of the core, or by 1.55 times to increase intensity of external source of neutrons. In the last case, the required parameters of proton beam and its target are following: intensity of external source neutrons S = 3.55·1017 n/s., beam current Ip = 4.32 mA, beam capacity Ðp = 2.59 ÌW. Thus, replacement of the coolant from natural lead by the coolant from lead-208 results in economy of capacity of the proton beam on the value of Pp=0.91 MW, and using the uranium - plutonium nitride fuel allows to establish the worth of capacity of the proton beam on burning out the fuel in limits of less than 10 %, due to the core breeding ratio equal to ~1. It allows in the ADS core with thermal capacity equal to 80 MW to lower capacity of the required proton beam to the value about 2 MW instead of capacity of the proton beam equal to 3.6 MW considered the PDS-XADS project. Hence, the proposed variant of the ADS allows to save capacity of the proton beam about Pp=1.6 MW. To exploit the accelerator with this lower proton beam current it will be required about ~ 56 tons of Pb-208, as a minimum, for the core coolant. Charges for it obtaining can be recovered at the expense of the economy of the proton accelerator construction cost. In this case, the accepted price of the lead isotope Pb-208 must be less than $2,860/kg.