R&D of productive pelletized cold moderators

1. R&D of productive pelletized cold moderators The First Research Coordination Meeting on Improved Production and Utilization of Short Pulsed, Cold Neutrons at Low-Medium Energy Spallation Neutron Sources Shabalin E., Shabalin D., Kulagin E., Kulikov S. Joint Institute for Nuclear Research, Dubna, Russia

2. Swelling of irradiated solid methane during annealing Before annealingAt annealing Solid methane Hydrogen bubbles walls

4. Experimental Facility URAM-2 • Figure 1: Conceptual design of the URAM-2 irradiation facility • the IBR-2 reactor; (2) irradiation capsule; • (3) carrying bowl with a cart in ‘near of the reactor’ position; • (4) helium pipelines; (5) evacuated transport passage; (6) nitrogen cryostat; • (7) carrying bowl with a cart in ‘out of the reactor’ position; • (8) charging tube with plug; (9) vacuum lock

5. Head part of URAM-2 facility Copper capsule; (2) thermal bridge; (3) a helium tube (heat exchanger); (4) thermocouples ; (5) blue color marks solid methane, condensed onto the capsule inner surface.

6. Methane Layer, 5 mm, T irrad.= 20-21K, Time of irrad. = 11.12 h

7. Water ice Segment 7.5 mm, Time of irrad. = 11 h Segment 7.5 mm, Time of irrad. = 10.5 h

8. Evacuated chamber with a sample, elevation along diameter 1 – cylindrical shell of the chamber; 2 – coaxial cables of displacement gauges (3); 4 - steel membrane; 5 – steel shell of a sample chamber; 6 – the sample (aluminum sponge filled with solid methane); 7 – coil of copper tube (heat exchanger); 8 – steel tube for filling and evacuation of methane and hydrogen gases.

9. Front end of the irradiation rig, elevation through central plane of the sample 1 – cylindrical shell of the chamber; 6 – aluminum foam filled with solid methane; 7 - coils of copper tube; 8 – steel tube for filling and evacuation gases; 9 – pockets for temperature sensors; 10 – steel string suspender of the sample chamber; 11- helium pipes inside an evacuated 3 m-long tube.

10. Temporal behavior of parameters during heating of the irradiated sample , exp # 7 Irradiation time 30 h*) 1 hour of irradiation ≡ 0.81 MGy

11. Solid mesitylene as a material for cold moderators m-xylene Mesitylene Tm = 227 K Tm= 225K Mixture with m-xylene or pseudocumene is of glassy structure, and has good neutron thermalization property.

12. Solid mesitylene cold moderator Density of vibrational states (by I. Natkaniec) 0

13. Solid mesitylene cold moderator Density of states for methane and TMB mixture

14. Solid balls of the frozen mixture of mesitylene and m-xylene Method of solid ball production is based on freezing of droplets in liquid nitrogen. Diameter of balls is ~5 mm

15. Complex of moderators for the IBR-2M reactor

16. Water pre-moderator Grooved water moderators Membrane of cold moderator for beams7, 8and10 Flat water moderator Moderator complex for beams # 7,8,10,11

17. Differential flux density at the direction of the beam # 7 at 4.5 m off the source

18. Gain on cold neutron flux from mesitylene moderator at 20K compare to water grooved moderator at 300K

19. Principal scheme of the IBR-2M moderator system

20. 1. By computer simulation of gas flow with a separate ball inside cylindrical tube, characteristics of hydrodynamics at both stationary and non-stationary motion of a ball has been calculated. Fig.1. Gas velocity pattern around a ball in a pipe (computer simulation). Averaged velocity of gas is 10 m/s; Averaged velocity of gas is 8 m/s; the ball is stopped . the velocity of the ball – 3 m/s .

21. 2. General ball transport equation for sliding bead along straight and inclined tube can be written as • where α is a degee of inclination of a transport tube, Cx and Cy are the drag coefficients for streamwise and transverse hydrodynamical forces, correspondingly , μ is sliding friction coefficient, ρ is density, d is diameter, and v is velocity; subscripts are easy to recognize.

22. Streamwise (left) and transverse (right) forces onto a ball by flowing gas (open circles is for sliding, closed circles- rolling of balls).

23. Transportation of mesitylene balls Simplified, analytically soluble equation for transport of a ball in the straight pipe is: where factor А<1 is weakly depend on Re anddball/dpipe, and С(0) is a drag force factor for the stopped ball. It is clear that it’s possible to simulate mesitylene beads transport by 80 K helium gas with transportation of glass beads of the same size with flow of room temperature nitrogen due to equality of the complex in the brackets.

24. Transportation of ideal solid balls Computer hydrodynamic model: Speed of a ball (d=5 mm) moving in a straight pipe (d=17 mm) with gas flow 11 m/s versus time . Black curves – sliding of the ball with friction factors k=0.05 and k=0.1; the blue curve – rolling of the ball. Magenta –analytic calculation for k=0.05

25. 2 1 3 4 5 6 8 7 6 5 4 3 2 1 0 1 8 13 7 10 8 11 12 9 Schematic installation for study of transport of glass balls through a glass tube by nitrogen gas flow 9 1 – glass pipe of 17.4 mm diameter, 3.6 м length; 2 – sluice with a valve for charging of balls; 3 – tube inside the sluice, 15 mm diameter, length 9 см; 4 – terminal part of the feeding, flexible gas pipe of low pressure, 14 mm in diameter, 4.5 м length; 5 – flowmeter; 6 – part of the feeding gas pipe of high hydraulic resistance; 7 – accumulating capacity 63 l (in combination with the load 6, it filtrates gas flow oscillations); 8 – pressure regulator; 9 - high pressure (about 10 bar) part of the feeding gas pipe as long as 50 m; 10 – cylinder with compressed nitrogen (Р~30-60 bar) ; 11 – searchlights; 12 – digital movie cameras; 13 – scale ruler

26. Balls transport (one experiment) gas flow is 5 m/с X =41.66+1134 t+223 t2 Coordinate of ball, mm Model: user3 Equation: (1117-P1)/P2*(1-exp(-x*P2))+P1*x+43 Chi^2/DoF = 1.36281 R^2 = 1 P1 3159.36656 ±176.30728 P2 0.25535 ±0.02403 Time, sec

27. Acceleration versus velocity of a ball for the case 11 m/s gas velocity. Red and black symbols – experiment, green –theory for rolling of ideal ball along a pipe with ideally smooth walls.

29. Clip 8.02.07 P2080007cam1

30. Plans of work to the end of this year • Measurement of values of terminal velocity of a ball and their fluctuation for different gas flow rates. • Derivation of a theory of transporting a ball with account for its bouncing, and extracting semiempirical factors of the transport equation.