Authors & Affiliations
Grabezhnoi V.A., Dulin V.A., Dulin V.V.
A.I. Leypunsky Institute for Physics and Power, Obninsk, Russia
Abstract
The neutron coincidence method is widely used to determine plutonium parameters in samples. Their acquisition is based on the approximation of the point kinetics model, i.e. on the assumption of small geometrical sizes of the samples and, thus, their low mass and neutron multiplication. It is quite obvious that in the course of mass measurement of extended samples with significant neutron multiplication, it is necessary to take into account the spatial effect, i.e. the dependence of probability (efficiency) of detector recording on its position and the position of a generated neutron. At the same time, the state of these samples can be far from critical. This fact does not allow the standard approach to be used for consideration of spatial effects and calculation, with making use of the solutions of adjoint conventionally-critical homogeneous equation, how it is usually done, for example, for subcritical states that are not deep (≤ βeff). Experimental determination of 239Pu mass fraction and Pu mass, with sets of disks of various isotopic compositions and with the use of method of double and triple neutron coincidences was implemented by means of a highly effective active well neutron coincidence counter AWCC. The aim of this work was to determine the following: the solution of what equation is the most applicable for the analysis of the results of measurements of multiplying media parameters with significant neutron multiplication, namely, an adjoint nonhomogeneous equation, whose solution shows the detector probability to record (detect) a neutron appeared in point - x,; an adjoint nonhomogeneous equation that considers neutrons from induced fissions of media nuclei, or the solution of adjoint conventionally-critical homogeneous equation.
Key words
Plutonium, transfer equation, neutron-neutron coincidences, point kinetics model, subcritical state, spatial effect, neutron multiplication
Article Text (PDF, in Russian)
References
1. Böhnel K. The Effect of Multiplication on the Quantitation Determination of Spontaneously Fissioning Isotopes by Correlation Analysis. Nucl.Sci.Eng. 90, 1985, pp. 75-84.
2. Peter A. Santi. Review of multiplicity analysis. LA–UR–05–8866, 2005.
3. Takeshi Sakurai, Shigeaki Okajima, Experimental core for experiments of effective delayed fraction βeff. Progress in Nuclear Energy, Special Issue, Vol 35, no.2, 1999, ISSN 01149–1970. Aut.: pp. 140-156.
4. Grabezhnoj V.A., Dulin V.V., Mihajlov G.M., Pavlova O.N. Opredelenie gluboko podkriticheskikh sostoyanij razmnozhayushhikh sred metodom Rossi - al'fa [Alfa-Rossi Determination of Deeply Subcritical States of Multiplying Media]. Atomnaya energiya - Atomic Energy. 2006, no. 2, pp. 140–148.
5. Dulin V.A., Dulin V.V. Opredelenie umnozheniya nejtronov utechki i massy delyashhegosya veshhestva v glubokopodkriticheskikh sistemakh [Determination of Multiplication of Leackage Neutrons and Fissile Material Mass in Deeply Subcritical Systems]. Atomnaya energiya - Atomic Energy. 2009, no. 1, pp. 3-9.
6. Bell D., Glesston S. Teoriya yadernykh reaktorov [Theory of Nuclear Reactors]. Moscow, Atomizdat Publ., 1974. 201 p.
7. Marchuk G.I., Orlov V.V. K teorii sopryazhennykh funkcij [On the Theory of Conjugate Functions]. Moscow, Gosatomizdat Publ., 1961. pp. 31–34.
8. Bulanenko V.I., Dulin V.A. Opredelenie umnozheniya nejtronov v dvuokisi plutoniya [Determination of Neutron Multiplication in Plutonium Dioxide]. Trudy trjohstoronnego seminara Evroatom – Rossiya – SShA, po uchjotu i kontrolyu yadernykh materialov [Proc. of the Trilateral NMC&A Workshop (Euratom – Russia – USA]. Obninsk, 2009.
9. Smelov V.V. Lekcii po teorii perenosa nejtronov [Lectures on Neutron Transfer Theory]. Moscow, Atomizdat Publ., 1978. pp. 166-176.
10. Kazanskij Yu.A., Matusevich E.S. Eksperimental'naya fizika reaktorov [Experimental Reactor Physics]. Moscow, Energoatomizdat Publ., 1994. pp. 116-119.
11. Tsutomu Iijima. On the background counts in the Rossi – alfa experiment. Nukleonik, Band 11, Heft 3, 1968, p. 157.
12. Dulin V.A. Izmerenie effektivnoj doli zapazdyvayushhikh nejtronov βeff metodom α–Rossi v vodorodosoderzhashhikh sredakh [Measurements of Effective Fraction of Delayed Neutrons βeff by the α– Rossi Method in Hydrogenous Media]. Atomnaya energiya - Atomic Energy. 2006, no. 5, pp. 393-399.
UDC 539.125.523
Problems of Atomic Science and Technology. Series: Nuclear and Reactor Constants", issue 4:9, 2014
