Spherical cold neutron moderator

FIELD: physics.

SUBSTANCE: auger unit is replaced with a funnel with an outlet tube with a special shape, placed in the bottom end part of a moderator chamber and providing quasi-uniform release of spheres under the force of gravity. The average frequency of release of the spheres is defined by the diameter and length of the neck of the funnel and its angle of inclination to the horizontal.

EFFECT: simple design of the unit due to continuous removal of spent spheres from the moderator chamber and high reliability and long service life thereof.

1 cl, 2 dwg


The invention relates to inhibitors of neutron research reactor and neutron-producing target accelerators, and is intended for receiving the external neutron beams of low energy (cold neutrons). In most cases, the active ingredient of cold moderators are hydrogen-containing substance in the liquid phase, but to achieve low temperatures is the use of substances in the solid phase (methane, aromatic hydrocarbons, solid deuterium). Solid hydrogenous substances subject to strong radiation decomposition under the action of fast neutron source, with the attendant undesirable effects. Therefore, the substance of the retarder must be periodically replaced with fresh, the neutron source has to halt, if the replacement is made simultaneously throughout the chamber of the retarder. The dispersed, ball structure of the working substance of a cold neutron moderator allows continuous shifts slow neutrons substances and allows the use of the retarder indefinitely unlike traditional moderators.

Known ball cold neutron moderator with a continuous change of the solid balls of methane, consisting of the cryogenic chamber of the retarder located near intense source of restricnational - nitrosopropane target accelerator tract continuous supply of fresh solid balls of methane in the camera node removal of the spent balls from the chamber and the regeneration system of methane and production of beads described in the work of A.T. Lucas, G.S. Bauer, C.D. Sulfredge, A pelletized solid methane moderator for a medium-to-high power neutron source, Proc. of the 13th Meeting of the International Collaboration on Advanced Neutron Sources, ICANS XIII, Villigen, Switzerland, November 1995, published: G.S. Bauer, R. Bercher (Eds.), Paul Scherrer Institut Proceedings 95-02, vol. II, 1996, p.644-652.

The outline of this well-known moderator presented in Appendix 1 - camera retarder, 2 - tract fresh balls of generator balls, 3, 4 - site removal of waste beads, made in the form of a screw.

The disadvantage of this device is the presence of mechanical active node of the rotating auger. This determines the unreliability of the auger site because of its work in conditions of strong fields of fast neutrons and a low temperature (20-40 K), and difficult access to prevention, repair or replacement. The failure of the auger site will lead most likely to a complete replacement camera retarder with the adjacent parts of the path of submission and selection of balls.

The objective of the invention is to provide a high reliability of the site selection of the spent balls preserving the continuity and periodicity (or quasi) release the balls from the chamber.

The village is Alanna task is solved by that ball in cold neutron moderator, including cryogenic chamber of the retarder located near intense source of fast neutrons' (for example, a research nuclear reactor or nitrosopropane target accelerator), the generator "fresh" solid balls of slow neutrons substances tract continuous supply of fresh solid balls into the camera and the host of the continuous removal of the spent balls from the camera node to the continuous removal of the spent balls from the chamber made in the form of a funnel with a curved outlet tube at the bottom end of the chamber of the retarder, and the size and shape of the funnel and the outlet tube are calculated by the methods of mathematical modeling of the conditions for ensuring the desired average speed release beads with subsequent experimental validation.

Schematic diagram of the construction of the proposed site, the continuous removal of solid waste balls shown in Fig. 1, where 1 is the cylindrical section (compartment camera moderator), 2 - funnel, 3 - direct a portion of the outlet tube 4 is bent part of the tube 5 is inclined upward part of the tube, α - the angle of the ascending part of the outlet tube.

The principle of the proposed site, the continuous removal of solid waste balls that is. In the chamber of the cold moderator harikesanallur substances (mesitylene, methane) fill the compartments of the chamber of the retarder to a certain height. Under the influence of gravity and the dynamic pressure of flow of the cooling helium through the cone and pipe section of the site selection process, they are removed from the chamber with a defined frequency, and with the same frequency in the camera spiked fresh balls (the principle supply of balls in the chamber can be the same or different; it is not the purpose of this paper), so that the height of the backfill remains constant. The diameter of the discharge tube must be selected so that there are no blockages in the movement of the balls. After passing through the straight part of the tube beads are experiencing gradually increasing the resistance in the curved part of the tube, and then in the course of the inclined part of the tube, the resistance becomes maximum. Thus, by selecting the height and slant of the tube it is possible to achieve a dynamic balance between resistance balls and gravity load from all the balls, filling compartment of the camera. In this case, obviously, the average consumption of balls reaches a stable, desired values.

For the balls of solid methane with a diameter of 4 mm, extracted with average frequency 1 ball/s, figure 1 shows the dimensions calculated by the PCF program, should be approximately the same as in Table 1. Detailed description of the calculation methodology, see what the Annex 2.

Table 1
Site settings selection of ballsSize mm
The minimum inner diameter of the discharge tube13 mm
The height of the cone plots (L1)50 mm
The height of the straight part of the discharge tube (L2)30 mm
The radius of the curved part of the discharge tube(R)70 mm
The horizontal projection of the length of the portion of the inclined tube (L3)90 mm
Vertical projection length of the portion of the inclined tube (H)19 mm
The angle of the discharge tube (α)α≈12°

Schematic diagram of ball offer of a cold neutron moderator with a continuous change of the solid balls of methane is given in Fig. 2, where 1 is the source of fast neutrons, 2 - water prejudicial, 3 - camera cold moderator, 4 - pneumotach fresh balls of methane in the chamber 5 to the generator of the solid balls of methane, 6 - master the ü supply of liquid methane, 7 - liquefier purified gaseous methane, 8 - enriching camera, 9 - heater unit, 10 - tract disposal of waste beads, 11 - cold trap radiolytic hydrogen 12 - helium ventilator, 13 - node dosed selection of exhaust balls from the chamber.

The device operates as follows. From the generator the balls of solid methane 5 (its principle and design not described here) with a certain frequency beads are pneumotach 4 moving cold helium gas To 20-30 in the upper part of the chamber of the retarder 3, immediately adjacent to the neutron source 1 and the water prejuidices 2. The temperature of the helium is supported helium refrigeration machine (not shown) through the heat exchanger 11. To flat bottom rectangular or oval in horizontal section of the chamber adjacent few (3 - 5) funnels conical shape with drainage tubes - site selection 13 (see also Fig. 1). Balls, poured from drainage pipes with a frequency equal to the frequency of submission of fresh balls, common pipe 10 fall within the heating unit 9 with a temperature of 90-100 K, which serves as a separator of radiolytic hydrogen. From block 9 of gaseous hydrogen and helium pumped through a helium liquefier hydrogen 11 is a heat exchanger between the helium refrigerating machine and helium of pneumata the transportation path of the balls of methane. The cooled helium is passed through the path of feed of the balls and the chamber of moderator ventilator-circulator 12. Liquid methane from the heavier products of decomposition from the hopper 9 is poured in enriching the chamber 8 with a temperature of more than 120 K, where the removed gaseous methane after liquefaction liquid nitrogen 7 is returned to the generator 5 through the pipe 6. The cycle repeats.

Reliability of continuous operation of such a retarder is provided by the absence of moving mechanical parts in the zone of high radiation, and the presence of several selected craters in the case of locking balls in one or two selected tubes bulbs will continue to be discharged from the other, and the first performance is easily restored by heating the tubes to the melting point of methane (tubes can be provided with electric heaters).


1. K.D. Wilkinson, A.T. Lucas, A combined H2/CH4cold moderator for a short-pulsed neutron source. Proceedings of the 10th Meeting of the International Collaboration on Advanced Neutron Sources (ICANS X), Institute of Physics Conference Series Number 97, Los Alamos National laboratory. Institute of Physics, October 1988, p.559.

2. H. Stelzer, H. Bamert-Wiemer and N.Bayer. J.Neutron Res., 11 1-2 (2003), p.99. Full Text via CrossRef.

3. G.S. Bauer. Pulsed Neutron Source Cold Moderators: Concepts, Design and Engineering. In: Proc. of International Workshop on Cold Moderators for Pulsed Neutron Sources. ANL, USA, Sept. 29 - Oct. 1997. Edition of the OECD. 1998, pp.27-42.

4. Shabalin, E.P., et al., Pelletized Cold Neutron Moderators for the IBR-2M reactor. In: Proc. of the 6thInternatinal Workshop on UCN& CN Physics and Sources, S. Petersburg-Moscow, 1-7 July 2007: http://cns.pnpi.spb.ru/ucn/articles/Shabalin.pdf.

5. Kulikov, S.A., Shabalin, E.P. "New Complex of Moderators for Condensed Matter Research at the IBR-2M Reactor". Rom. Journ. Phys., Vol. 54, No 3-4, pp.361-367, Bucharest, 2009.

6. Kulikov, S.A., et al., R&D of productive pelletized cold neutron moderators (status), Proc. of the Second Research Co-cordination Meeting, IAEA, Kuala Lumpur, Malaysia, p. 171-175, 2009.

7. Physics of Particles and Nuclei Letters, 2010, Vol. 7, No. 1, pp.57-60.

Ball cold neutron moderator, including cryogenic chamber of the retarder located near intense source of fast neutrons, for example, a research nuclear reactor or nitrosopropane target accelerator generator "fresh" solid balls of slow neutrons substances tract continuous supply of fresh solid balls into the camera and the host of the continuous removal of the spent balls from the chamber, characterized in that the node is continuous removal of the spent balls from the chamber made in the form of a funnel with a curved outlet tube at the bottom end of the chamber of the retarder, and the size and shape of the funnel and the outlet tube are calculated by the methods of mathematical modeling of the conditions for ensuring the desired average speed release beads with subsequent experimental validation.


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