ORIG. RUSSIAN: CALCULATION OF SLOW ENERGY NEUTRON SPECTRA

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP88-00904R000100110013-5
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 17
• Document Creation Date: December 22, 2016
• Document Release Date: August 26, 2009
• Sequence Number: 13
• Publication Date: May 1, 1964
• Content Type: STUDY

 Approved For Release 2009/08/26: CIA-RDP88-00904R000100110013-5
t~~A Oise
Third United Nations
International Conference
on the Peaceful Uses
of Atomic Energy
Confidential until official release during Conference
A/CONF o 28/P/365
USSR
May 1.964
Original: RUSSIAN
CALCULATION OF SLOW ENERGY NEUTRON SPECTRA
G.1.Illarchuk, G. A.lljasova, V.N.Mlorozov, V. V.Srnelov, V.A.Hodalcov.
There-are-three most essential aspects in the-neutron thermalization problem: the'develop-
ment of the theory of neutron-matter interaction and the-evalution of corresponding constants,
needed for calculation; the development of the computational algorithms for solving of
mathematical problems with needed accuracy; and, at last, the-problem of the, interpretation of
slow neutron flux-spectral data. On the whole, in the present paper the questions of second
aspect of the problem will be considered.
The-slow energy neutron scattering problem was formulated by Hurwitz and Cohen [1,2].
The,most complete solution of this problem was obtained in the theory of neutron scattering by
nuclei of monoatomic gases [1-4]. In the last years the necessity turned out of a more
careful analysis of neutron scattering mechanism, taking into account the molecular binding
effect. The-results of these, investigations were reported in detail at the Brookhaven
Conference,on Neutron Thermalization [5].
It should be noted then that in the last years some important experimental data on the
neutron thermalization problem have been obtained [5-7]. After these investigations the-more
careful comparison of experimental data with the theory based on different physical models is
possible, It should be,also observed that progress of our knowledge of physical processes in
nuclear reactors makes the development of more perfect and exact methods of the solution of
neutron transport equation evident.
The peculiarity of the,problern of calculating the thermal neutron distribution lies in the
fact, that the low energy neutrons not only lose their energy, but acquire it. Due to this
effect, the integral operator in the transport equations is Fredholm-type operator. The
transport equation may be solved by spherical harmonics method in 1'-approximation,
by Sn-method, by the method of characteristics, by Vlonte Carlo method, and others [8-15].
The-survey of some mathematical methods of solution of the transport equation, their
confrontation and comparison of the theory with the-experiment [6-71 are, given in present
paper. spe-Hial attention is paid to the problem of calculating neutron flux,angular distribu-
tion;, r('t01' cell,
Approved For Release 2009/08/26: CIA-RDP88-00904R000100110013-5
 Approved For Release 2009/08/26: CIA-RDP88-00904R000100110013-5
1. CALCULATION Ol? NEUTRON FLUX AND NEUTRON IMPORTANCE BY THE
SPHERICAL HARMONICS METHOD.
The,stationary slow neutron flux,in the 'case - of a cylindrical cell inay'be-described by the
following integro-differential transport equation:
sine(cosgi - sin ) +a (r, v) q (r, v, B, ~i) -?
Vgroup
--
dv' fdl1'as (r;v'-Iv, Q1' -- ~) c~i (r, v', O', ,') . q(r, v)
(1)
whereas (r; v'-+ v, St'-s) is the,differential scattering cross-section;. a(r, v).as(r, v)+aa(r, v)
is : the total cross-section; 6 and to are the meridional and azimuthal angles, respectively (Fig.t).
Let the, function' , (r,:v, 0, fir) be, in the, form
(r. v, 6,,c) "p(v)v(r : v, 0,(A) (2)
where.p(v) is chosen to take a more complete-account of the, neutron flux,d,(r, v, 0, ear)
character of variation in variable v. The energy spectrum of formally homogenized 'cell was
used, as the ,function p(v). From above,one 'may . conclude] that v(r, v, 0, PG) is slightly
dependent on the velocity v over the entire, thermal ization range, O