**3. On the possibility of acquisition of radiogenic lead enriched with lead-208**

#### **3.1 On the sources of radiogenic lead enriched with lead-208 in Russia**

The problem of acquisition of radiogenic lead enriched with lead-208 is coupled with perspectives of involving thorium into nuclear power engineering of Russia. As it is noted in Ref.16 to develop the thorium nuclear energetic it is necessary to obtain at least 10-13 thousand tones of thorium per year at the stage of 20-30 years of this century.

Content of lead-208 in thorium ores and minerals can reach 0.3-0.5% wt of thorium mass. In acquisition 10-13 thousand tones of thorium per year it will be possible to recover about 65 tones of radiogenic lead per year. This quantity of lead is insufficient to cover the needs in lead coolant of large scale nuclear power which requires approximately 2000 tones of lead per 1 GW of electrical power. But 65 tones of lead are sufficient to cool the blanket of 80 MWth ADS. About 700 tones of lead can be enough to cool the reactor RBEC-M delivering 340 MW electrical.

As an illustration, in Fig. 6 and 7 the results of burning 1 kg of uranium-238 placed in the one part of ADS 80 MW subcritical blanket (cell 3 near the blanket far margin) and corresponding accumulation of plutonium-239 are given. Calculations have been performed

0 2 4 6 8 10

Irradiation time, years

Fig. 7. Mass burning of 1 kg of U-238 in the neutron spectra of 80 MW ADS blanket, in the cell 3 which is near far blanket's margin. The solid curve corresponds to the case, when the blanket is cooled with lead-208, the dash curve – to the case, when the blanket is cooled with

**3. On the possibility of acquisition of radiogenic lead enriched with lead-208** 

The problem of acquisition of radiogenic lead enriched with lead-208 is coupled with perspectives of involving thorium into nuclear power engineering of Russia. As it is noted in Ref.16 to develop the thorium nuclear energetic it is necessary to obtain at least 10-13

Content of lead-208 in thorium ores and minerals can reach 0.3-0.5% wt of thorium mass. In acquisition 10-13 thousand tones of thorium per year it will be possible to recover about 65 tones of radiogenic lead per year. This quantity of lead is insufficient to cover the needs in lead coolant of large scale nuclear power which requires approximately 2000 tones of lead per 1 GW of electrical power. But 65 tones of lead are sufficient to cool the blanket of 80 MWth ADS. About 700 tones of lead can be enough to cool the reactor RBEC-M delivering

**3.1 On the sources of radiogenic lead enriched with lead-208 in Russia** 

thousand tones of thorium per year at the stage of 20-30 years of this century.

on the basis of code ACDAM [15] developed at the IPPE Centre of nuclear data.

 U-238, ADS+Pb208, cell=3 U-238, ADS+Pbnat, cell=3

875

900

925

950

Mass accumulation (gram/kg U-238)

lead natural.

340 MW electrical.

975

1000

As it is shown in Ref. 16, the main source of thorium in Russia is the Lovozerskoe deposit at Kola Peninsula. Estimations show that in reprocessing 2 mln tones of loparit ore per year 500-600 thousand tones of Ln2O3 and TiO2, 100 thousand tones of Nb2O5, 10 thousand tones of Ta2O5, 13 thousand tones of ThO2 and 65 tones of radiogenic lead can be produced. In Ref 16 the conclusion was made that is possible to extract in near future large quantities of thorium from the progress of industry and as co-product of rear metal raw.

The separate problem is the level of lead-208 enrichment of lead-208 in various deposits. It can be strongly different. For example, in Brazil monazites radiogenic lead is enriched by lead-208 up to 88.34% [17]. For FRs and ADSs it can be desirable the following isotopic composition of radiogenic lead: lead-208-93% and lead-206-6% with minimum content of lead-207 – the isotope with large cross section of neutron capture. In Ref. 18 the data concerning thorium-containing ores and monazites in the world scale are given. The authors of this paper pointed out that as a rule radiogenic lead contains very small quantities of lead-204 and lead-207–isotopes with large cross sections of neutron capture.

It can be noted that the advantages of lead-208 can be used, besides nuclear power plants, in other branches of nuclear science and technology. It seems that lead-208 as low moderating material will be preferable in the lead slowing down neutron spectrometers [19] and also in the spallation neutron sources to have the harder neutron spectra under interaction of high energy protons with liquid proton target from lead-208 [2, 20].

#### **3.2 Prospects of ancient monazite from placers and bed-rock's deposits of Ukraine as the raw materials to produce highly enriched 208Pb**

Monazite is the phosphate containing mainly ceric rare earths ((Ce, La, Nd …, Тh) PO4) and is the main natural concentrator of thorium. It is widely spread (though usually in small amounts) in rocks and some types of ores. Owing to chemical and mechanical durability monazite is accumulated in placers.

The crystal structure of monazite can be presented as three-dimensional construction of oxygen nine apex polyhedron with rare-earth center atoms and oxygen tetrahedrons with the central atom of phosphorus. Nine-fold coordination allows a wide occurrence of relatively large ions of the light rare earths and thorium in mineral structure. The total content of thorium in a mineral can reach 28 wt%, and concentration of 5-7 wt% is usual. Though there are no experimental data about the form of radiogenic lead presented in the monazite structure, the numerous data, summarized for example in work [21], argued for its good stability in a monazite crystal matrix that allows monazite to be used for isotope dating.

In Ukraine monazite contains in developed fine-grained titanium-zirconium placers. By the explored easily enriched titanium-zirconium ores Ukraine comes to the forefront in Europe and in the CIS. The resources of zirconium in Ukraine make more than 10% of world ones. Now the largest Malyshevsky (Samotkansky) placer is developed and the working off of the Volchansky placer has been started.

Owing to the marked paramagnetism monazite at existing capacity of mines can be taken in passing by working out of placers in quantity of about 100 tons per year that corresponds

New Coolant from Lead Enriched with the Isotope Lead-208 and

and by the extraction from raw materials in complex deposits.

FRs and ADSs instead of lead natural, natPb.

smaller than those for the coolant consisted from natPb.

**4. Conclusions** 

others.

0.8%.

and transmutters.

Possibility of Its Acquisition from Thorium Ores and Minerals for Nuclear Energy Needs 67

For extraction of thorium and the lead enriched with 208 isotope Russia has a great opportunities by preparation the fine-grained titanium-zirconium placers for development

The paper is dedicated to the proposal of using lead enriched with the stable isotope 208Pb in

It seems that unique neutron features of 208Pb make it as one of the best among the molten metal coolants now assumed for FRs and ADSs: sodium, lead-bismuth, lead natural and

The main advantage of 208Pb is its low neutron absorption ability: for neutron energies En=0.1-20.0 MeV the microscopic cross sections of radiation neutron capture by 208Pb are by 1.5-2.0 times smaller as compared with natPb, and for energies, En<50 keV, the difference in the cross section values reaches 3-4 orders of magnitude. Averaged over neutron spectra of the LFR or ADS the one-group cross sections for a coolant from 208Pb are by 5-6 times

The second advantage of using 208Pb consists in achievement the core neutron spectra hardening on 5-6% due to low energy losses. Low neutron absorbing and moderating features of 208Pb permit to reach the gain in the multiplication factor Kef on 2-3% for critical or subcritical core fueled with U-Pu mix. In this case to have the multiplication factor Kef =1.01 for the LFR or Keff =0.97 for the ADS, both cooled with lead-208, the enrichment of power grade Pu in the U-Pu fuel can be reduced approximately on 0.7-

The third important advantage of using 208Pb is coupled with increasing the small share of neutrons of low energies, 5-10 eV in spite of the neutron spectra hardening in whole. In this region of neutron energies the microscopic cross sections for such nuclides as 238U and 99Tc are maximum and very high, and the one-group cross sections for these nuclides averaged over neutron spectra of LFRs and ADSs cooled with lead-208 are equal to 0.6 and 0.8 barn respectively which are comparable with the one-group cross sections for typical breeders

The possibility of using 208Pb as coolant in commercial fast critical or subcritical reactors requires a special considering but relatively high content of this isotope in natural lead, 52.3%, and perspectives of using high performance photochemical technique of lead isotope separation permit to expect obtaining in future such a material in large quantities and under economically acceptable price. In the paper it is shown that principal possibility of acquisition of radiogenic lead containing high enriched lead -208, up to 93%, exists. Nowadays in Russian Federation and Ukraine thorium- containing loparit ores and monazite minerals are reprocessed for production of rаre metal raw. Thorium and lead are not required now and they are deposited in sludge. Nevertheless, the scales of future thorium and radiogenic lead production for innovative nuclear reactors have some prospects in near-term future. The conclusion is made that to obtain the minimum amount of required in future radiogenic lead (65 t/year) for small sized FRs and ADSs the very large

approximately to 3.5 tons of thorium and 0.5 tons of the lead enriched with 208 isotope. Now monazite is considered as a harmful radioactive impurity and it is not produced.

The composition of monazite from the Malyshevsky placer as to the amounts of U, Th and Pb for dating purposes is well studied in work [21] by means of X-ray-fluorescent technique specially developed for individual grain analysis. In Table 3 the data about the contents of thorium, uranium and about isotope contents of lead for monazite of the Malyshevsky deposit is cited. The average composition of lead is confirmed by direct mass spectrometry determinations.


Table 3. Contents of thorium, uranium, lead and isotopic composition of lead for monazite of the Malyshevsky placer (Ukraine)

As is seen from Table 3, enrichment by 208Pb in the average for all monazite is insufficiently high. However, there is a probability of monazite separation by the flotation, magnetic or other characteristics with release of low uranium fraction of the mineral.

Extraction of total monazite concentrate by working out of the Malyshevsky placer scattering of an average almost won't demand additional costs and its price as at first approximation can be accepted as the equal to zircon concentrate, i.e. ~ 1 US \$/ kg. Cost of hydrometallurgical emanation of lead from monazite by analogy with similar processes can be estimated as (2430 US \$/ kg). The removal of differences with low U/Th ratio and the high content of 208Pb from monazite concentrate will require additional researches and will cause some rise in price of a product.

In Ukraine there are insufficiently studied shows of monazite in ancient radical breeds, their barks of aeration and in placers, i.e. enriched 208Pb. According to the available analytical data there is a possibility to detect monazite with highly enriched 208Pb.

For extraction of thorium and the lead enriched with 208 isotope Russia has a great opportunities by preparation the fine-grained titanium-zirconium placers for development and by the extraction from raw materials in complex deposits.
