NEUTRON SPECTRUM HARDENING IN CRITICAL AND SUBCRITICAL REACTORS COOLED WITH LEAD-208
G.L. Khorasanov, A.I. Blokhin
State Scientific Centre of the Russian Federation – Institute for Physics and Power Engineering named after A.I. Leypunsky (IPPE)
Paper presented by Dr. Georgii KHORASANOV Introduction
As known, the spent nuclear fuel of light water reactors contains approximately 1% of plutonium, 0.1% of neptunium, americium and curium and 4% of long-lived products of fission (technetium, cesium and others). The spent nuclear fuel contains radio nuclides which have to be isolated from the environment during a period more than 1000 years.
Among these nuclides the most dangerous from the radio toxicity point of view are plutonium and americium-241.
Meanwhile plutonium can be used as fuel for future FRs, as concerns the low fissile americium-241 it must be incinerated or transmuted into other short-lived radio nuclides at future ADSs or FRs. As known, the minimum of Am-241 fission in the hard part of neutron spectrum is around 0.1 MeV. In the intermediate and thermal parts of neutron spectra the Am-241 fission cross sections are great enough but at the same time radiation neutron capture are much greater that impacts to transmutation of americium into high order actinides rather than to its fission. Am-241 fission microscopic cross section:
101 Am-241(n,f)
100
10-1 Cross-section, barn
10-2 10-2 10-1 100 101 102 103 104 105 106 107 En, eV Radiation neutron capture cross section for Am-241
104
3 Am-241(n,g) 10
102
101
100
10-1 Cross-section, barn 10-2
10-3
10-4 10-2 10-1 100 101 102 103 104 105 106 107 En, eV
It can be seen that below En=0.1 MeV the radiation neutron capture cross sections are equal to 1 - 1000 barns. In the same region the fission cross sections are equal to 0.02 - 10 barns. Usually in ADSs and FRs the mean neutron energy of core does not exceed 0.5 MeV, while the mean energy of fission neutrons emitted by uranium-235, for example, is equal to 1.98 MeV.
100
-1 10
[a.u.] n -2 2 1
F 10
10-3
10-4 10-4 10-3 10-2 10-1 100 101 102 E [MeV] n One of the ways to enhance the neutron spectra hardening consists in using core materials – coolant, structural element, etc, - having small neutron moderation.
As such a coolant the molten lead enriched with lead stable isotope – lead-208 – was proposed by authors.
In the paper the possibility of neutron spectra hardening with the aim to enhance Am-241 fission probability is analyzed.
Blanket of the ADS with thermal power of 80 MW designed by authors, core and lateral blanket (LB) of the FR RBEC-M with thermal power 900 MW designed at the National Research Centre “Kurchatov Institute” are assumed. Method of calculations
It was calculated the neutron spectra of the 80 MW ADS blanket and of the reactor RBEC-M core and LB, and then on the basis of spectra obtained the mean energies of neutrons, one-group Am-241 fission and radiation neutron capture cross sections were found.
For hardening neutron spectra a coolant from Pb-208 instead of Pb-nat in the 80 MW ADS and instead of Pb-Bi in the RBEC-M were assumed. Code MCNP5 and input data for RBEC-M were used for determining the corresponding neutron spectra. Mean energies of neutrons were calculated due to expression:
<Еn>=∑Еnφn/∑φn, were Еn – is the mean neutron energy in the group g (number of groups g=28) of the ABBN-93 system, φn – is neutron fluxes into the group g, summation ∑ is made with respect all groups where neutron fluxes distinguishes from zero, practically.
Similarly Am-241 one-group fission and radiation neutron capture cross sections, <σfis> and <σс> , were calculated. The evaluated files of the library ENDF/B-VII.0 were used for determining microscopic cross sections of Am-241 fission and radiation neutron capture. Calculations and discussion
In Table 1 the mean energies of neutrons and probability of Am-241 fission along the subcritical blanket (H=110 cm, outer D=124 cm) of the ADS with thermal power of 80 MW are given.
Blanket was homogeneously supplied with uranium- plutonium nitride fuel in which the plutonium enrichment was equal to 15%. Pb-208 and Pb-nat were used as coolants.
In replacement of Pb-208 with Pb-nat coolant the effective neutron multiplication factor Kef was decreased approximately to 2%. Subzone 1 Subzone 2 Subzone 3 En=0.4254/0.4406 En=0.4438/0.3408 En=0.3346/0.2362 Fis=13.9982/11.3604 Fis=13.6897/9.8404 Fis=6.2326/3.8327
Target- Subzone 4 Subzone 5 Subzone 6 source of neutrons En=0.4820/0.5576 En=0.5377/0.4929 En=0.3723/0.3754 Fis=18.9701/21.5634 Fis=21.7887/17.6977 Fis=9.1580/11.9034
Subzone 7 Subzone 8 Subzone 9 En=0.3365/0.2554 En=0.3731/0.3811 En=0.3182/0.3285 Fis=8.6446/8.3228 Fis=11.2360/12.4424 Fis=6.0852/6.7810 The mean neutron energy averaged over the blanket is equal to 0.4026 MeV in using Pb-208 as coolant and 0.3787 MeV in using natural lead, Pb-nat.
Thus, the coolant replacement leads to neutron spectrum hardening on 6.3%.
Correspondingly on 5.8% increases the averaged over the blanket probability of Am-241 fission which is determined as the ratio Fis=<σfis>/(<σfis>+<σс>), where <σfis> - is one-group fission cross section and <σс> - is one-group radiation neutron capture cross section.
Probability of Am-241 fission in the central parts of blanket reaches 22% while at the periphery of blanket it falls down to 6%. Along 80 MW ADS blanket one-group Am-241 fission cross sections are of 0.1170–0.3724 barns while maximum cross section reaches at the central parts of blanket and minimum cross section falls down at the periphery of blanket . This dependence is in a good correlation with the dependence of mean neutron energy along the blanket.
In the reactor RBEC-M the replacement of its standard lead- bismuth coolant with Pb-208 coolant leads to hardening of neutron spectra of sub cores and lateral blanket on 6.4% and 6.1%, respectively.
In the next slide the neutron and physical parameters of the 900 MW thermal reactor RBEC-M are given. Reactor is cooled by its standard coolant from Pb-Bi (thin lettering) and by coolant from Pb-208 (bold lettering) as it was proposed by authors of this presentation. Parameters Inner core Middle core Outer core Lateral blanket
Mean energy 0.4246/0.3992 0.4408/0.4209 0.4433/0.4307 0.2662/0.2509
Relative increasing 6.3627 4.7280 2.8790 6.0980 of
Fuel volume 23.3 27.6 38.2 - share,%
Fuel plutonium 13.59 13.59 13.59 - enrichment, % Am-241 cross 0.2882/0.2629 0.2975/0.2779 0.2950/0.2829 0.1671/0.1521 section <σfis>, barns Relative increasing 9.6234 7.0529 4.2771 9.8619 of <σfis>, % Am-241 capture 1.5816/1.5967 1.5306/1.5366 1.5632/1.5627 2.4249/2.4958 cross section <σс>, barns Probability of Am- 15.4134/14.1374 16.2737/15.3155 15.8755/15.3283 6.4468/5.7442 241 fission, % For comparison: Am-241 fission probability in the spectrum of Pu-239 fission neutrons:
The mean energy of neutrons for Pu-239 spectrum of fission neutrons:
One-group Am-241 fission cross section in this spectrum of neutrons: <σfis> = 1.3676 barns
One-group Am-241 radiation neutron capture cross section in this spectrum of neutrons: <σc> = 0.2736 barns
Probability of Am-241 fission: Fis= <σfis>/<σfis>+ <σc>= 83.3% Conclusion
It might be concluded that replacement of lead or lead- bismuth coolant with lead-208 coolant in installations with fast neutrons leads to neutron spectrum hardening up to 6.3-6.4%. Under these conditions one-group Am-241 fission cross sections are increasing on 8-10%.
It was shown that in the ADS annular blanket (H=110 cm, outer D=124 cm) the Am-241 fission probability reaches 22% in the central parts of the blanket while at its periphery it falls down to 6%. The probability of Am-241 fission in the lateral blanket of the fast reactor RBEC-M does not exceed 5.7-6.4%, while in the sub cores of this reactor the probability of Am-241 fission is dramatically higher, 15-16%.
It might be mentioned once more that Am-241 fission in relatively hard neutron spectra is more preferable than its transmutation via neutron capture in the intermediate and thermal neutron spectra which leads to accumulation of curium and californium.
To pick up the 80 MW ADS blanket heat by means of the Pb-208 coolant about 60 tones (~6 m3) of this lead isotope are required.
To pick up the 900 MW RBEC-M core heat about 680 tones (~70 m3) of this lead isotope are required. At last I would like to announce a new book titled: “Application of stable lead isotope Pb-208 in nuclear power engineering and its acquisition techniques”. Editor G.L. Khorasanov. New-York: NOVA publishers, 2013, 194 p., (ISBN: 978-1-62417-653-1). Table of Contents: Preface pp. i-x
Chapter 1. Some Advantages in Using Lead-208 as Coolant For Fast Reactors and Accelerator Driven Systems (Georgy L. Khorasanov and Anatoly I. Blokhin, State Scientific Center of the Russian Federation – Institute for Physics and Power Engineering named after A.I. Leypunsky (SSC IPPE), Obninsk, Russian Federation)pp. 1-20
Chapter 2. Introductions of 208Pb Coolant to Innovative Fast Reactors (Hiroshi Sekimoto, Tokyo Institute of Technology, Tokyo, Japan)pp. 21-42
Chapter 3. Radiogenic Lead with Dominant Content of 208Pb: New Coolant, Neutron Moderator and Reflector for Innovative Nuclear Facilities (A.N. Shmelev, G.G. Kulikov, V.A. Apse, A.A. Chekin and E.G. Kulikov, National Research Nuclear University “MEPhI”, Moscow, Russia)pp. 43-98
Chapter 4. Photochemical Laser Separation of Lead Isotopes for Safe Nuclear Power Reactors (P.A. Bokhan, N.V. Fateev, V.A. Kim and Dm. E. Zakrevsky, A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia)pp. 99-124
Chapter 5. Assessment of Specific Cost of Highly Enriched Lead-208 Isotope by Gas Centrifuges Using Various Raw Materials (V.D. Borisevich, A. Yu. Smirnov and G.A. Sulaberidze, National Research Nuclear University "MEPhI", Moscow, Russia)pp. 125-136
Chapter 6. Method for Obtaining Isotopically Enriched Metal Lead from Monoisotopic Tetramethyllead and its Purification (Dmitry V. Akimov, Oleg S. Andrienko, Nikolay B. Egorov, Ivan I. Zherin, Denis V. Indyk and Mishik A. Kazaryan, Tomsk Polytechnic University, Tomsk, Russian Federation and others)pp. 137-176
Series: Nuclear Materials and Disaster Research Binding: Hardcover Pub. Date: 2013- February Pages: 194, 6x9 - (NBC-C) ISBN: 978-1-62417-653-1 Status: AV THANK YOU FOR YOUR ATTENTION! References
• D.A. Blokhin, E.F. Mitenkova, G.L. Khorasanov, E.A. Zemskov, A.I. Blokhin. Evolution of fast reactor core spectra in changing a heavy liquid metal coolant by molten Pb-208. In CD-ROM Proceedings of the International Conference PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, Knoxville, Tennessee, USA, April 15-20, 2012, Paper #219. • G.L. Khorasanov, A.I. Blokhin. One-group fission cross sections for plutonium and minor actinides inserted in calculated neutron spectra of fast reactor cooled with lead-208 or lead-bismuth eutectic. In CD-ROM Proceedings of the International Conference PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, Knoxville, Tennessee, USA, April 15-20, 2012, Paper #106. • D.A. Blokhin, E.F. Mitenkova, A.I. Blokhin. Generation of point wise nuclear data library on the basis of ENDF/B-VII.0, JEFF-3.1.1, JENDL-4.0. Preprint IBRAE-2011-08, 2011, Nuclear Safety Institute of RAS, Moscow. The advantages of the photochemical method of lead isotope separation consist in one- or two- photon excitation of atoms, a possibility of using commercially available highly effective semiconductor lasers and high efficiency of lead isotope separation in a reaction chamber.
The technique of selective photoreactions makes use of such working substance as lead vapor and does not require conversion of lead into a volatile substance and its back transformation into the target product which is the case with separating gas centrifuges.
All this gives good ground to expect in the years to come the production of 208Pb (with 99.0% enrichment) in large quantities (tones) for acceptable price, about $200/kg.