Enhanced Performance of Solid Methane Moderators in Neutron Sources

1. Solid methane moderators: thermodynamics and chemistry O Kirichek, CR Lawson, GL Draper, DM Jenkins, DJ Haynes, S Lilley ISIS Facility, STFC, Rutherford Appleton Laboratory, Harwell, Didcot, UK The 23rd meeting of the International Collaboration on Advanced Neutron Sources 13th - 18th October 2019, Chattanooga, Tennessee

2. TS2 Solid Methane Moderator WISH diffractometer Cryostat Electronics Dilution fridge IGH Cryostat Gas Panel High Pressure Panel Leak detector WISH publications: Nature family journals - 11 Science - 3 Phys. Rev. Lett. - 12 Phys. Rev. B – 78 Total number - 236 CCR compressor IGAn Vacuum Pump Cryostat Trolley Gas cylinder LC Chapon, P Manuel et al, Neutron News22 (2011) 22-25

3. Solid methane adhesion and viscosity Bond breaking force Dynamic viscosity F/A, MPa µ , Pa s T, K Andesite lava: 106 – 107 Pa s OK, AJ Church, MG Thomas, D Cowdery, SD Higgins, MP Dudman, ZA Bowden Cryogenics52 (2012) 325 T-1, K-1

4. Solid methane under exposure to neutron radiation “Burp” Phenomenon J Carpenter Nature330, (1987) 358 Intense Pulsed Neutron Source (IPNS) Argonne National Laboratory, USA H + H → H2 + 218 kJ/mol CH3 + CH3 → C2H6+ 368 kJ/mol Analysis of volatile products from the solid methane moderator EP ShabalinJINR Commun. (1995) E17-95-142 IBR-2, Dubna, Russia

5. ISIS Facility neutron spallation Target Station II (2009) Solid Methane Moderator Target

6. Temperature dependences of Thermostimulated exoelectron emission (TSEE) and Post-desorption from solid methane pre-irradiated by electrons EV Savchenko, OK, CR Lawson, IV Khyzhniy, SA Uyutnov, MA Bludov Nuclear Inst, and Methods in Physics Research B433 (2018) 23

7. Model based on the theory of thermal explosion (based on Carpenter’s approach) The process of accumulation and recombination of radiolysis defects can be described by the equations: T is temperature; N1,2 - number of defects; R1,2 - defect production rate, (R1 ≂ R2); M - mass of the system; C - heat capacity of solid methane; H - thermal conductivity; A - heat-exchange area; Tcool is the coolant temperature; P - heating power provided by the external source. Isochoric pressure derivative can be determined using the cyclic relation that: (1/V)∂V/∂TP term is related to the isobaric thermal expansion coefficient of solid methane and -V∂P/∂VP to the isothermal bulk modulus OK, CR Lawson, DM Jenkins, CJT Ridley, DJ Haynes Cryogenics88 (2017) 101

8. Comparison of the model based on the theory of thermal explosion with moderators test data J Carpenter Nature330, (1987) 358 IPNS (a) Nature published data (dots) and (b) the spontaneous event as outcome of our model showing both temperature (blue line) and pressure (red line). ISIS TS2 solid methane moderator test data (dots) and simulation showing both temperature (blue line) and pressure (red line). For more details please visit Chris Lawson’s poster

9. TS2 Solid Methane Moderator operation data Max Pressure: 30 bar One fill ~ 200 gr 1140 min (19 h) or 650 μAmps 150 K 93 K 60 K 47 K 47 K ~2.5 h Life time of moderator: 1 – 2 cycles (up to 60 days)

10. Methane radiolysis products Methyl Ethyl Ketone (MEK) For more details please visit Gemma Draper’s poster Large hydrocarbon molecules

11. Conclusions • Solid methane moderator could be comfortably operated above 45K. • There is an optimal compromise between neutron flax, moderator vessel’s wall thickness and time between methane changes. • Small empty space left in the moderator during methane change may allow to reduce pressure on vessel walls (solid methane behaves like a viscous liquid above 60 K). • Usage of optimal solvent(s) for vessel cleaning may extend the moderator’s life-span. Another benefit could be improvement of Health & Safety aspects of moderator cleaning procedure. • The solid methane moderator operations could be highly atomised liberating valuable technical resources.

12. Area of Solid Methane Moderator suitability ESS SNS J-PARC ISIS TS2 SNS TS2 CSNS neutron flux IBR-2 IPNS KIPT NS LENS HUNS RANS CPHS SCANS ESS-Bilbao

13. Cryo volcanoes Short-period comets orbit the sun over a period of less than < 200 years. In Kuiper Belt and Oort Cloud the temperature of a comet could be as low as 30K

14. On behalf of my co-authors I would like to thank: • Zoe Bowden, Matt Fletcher, Dennis Cowdery, Steve Wakefield, Andy Church, Rajesh Gupta, Sean Higgins, Richard Down, Rob Major, Chris Goodway, Rob Done, Mike Dudman and all others involved in the “methane” project. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 645660 Thank you very much for your attention!