# User Support **URL:** https://festim.discourse.group/c/general/4.md [Latest](https://festim.discourse.group/latest.md) · [Categories](https://festim.discourse.group/categories.md) · [Tags](https://festim.discourse.group/tags.md) --- ## [Welcome to FESTIM! 👋](https://festim.discourse.group/t/welcome-to-festim/5)
**Author:** [@system](https://festim.discourse.group/u/system)\ **Replies:** 0\ **Last updated:** [November 23, 2023, 8:33pm UTC](https://festim.discourse.group/t/welcome-to-festim/5 "2023-11-23T20:33:33Z")
We are so glad you joined us. FESTIM User support and development discussions for FESTIM Here are some things you can do to get started: :speaking\_head: Introduce yourself by adding your picture and information abou… --- ## [About the User Support category](https://festim.discourse.group/t/about-the-user-support-category/3)
**Author:** [@system](https://festim.discourse.group/u/system)\ **Replies:** 0
General questions about installing, using, and troubleshooting FESTIM --- ## [Mix material, Multilayer fusion blanket tritium transport coupling with OpenMC](https://festim.discourse.group/t/mix-material-multilayer-fusion-blanket-tritium-transport-coupling-with-openmc/188)
**Author:** [@approx-infinity](https://festim.discourse.group/u/approx-infinity)\ **Replies:** 1\ **Last updated:** [October 20, 2026, 2:36pm UTC](https://festim.discourse.group/t/mix-material-multilayer-fusion-blanket-tritium-transport-coupling-with-openmc/188 "2026-10-20T14:36:42Z")
I am trying to simulate the Tritium transport for a HCPB blanket sector. The blanket sector was generated using paramak. It has 7 layers. Most of the layers has mixed materials filled in. I have generated the Tritrium pr… --- ## [Question about kinetic surface model](https://festim.discourse.group/t/question-about-kinetic-surface-model/185)
**Author:** [@williamhayes123](https://festim.discourse.group/u/williamhayes123)\ **Replies:** 15\ **Last updated:** [October 14, 2026, 12:26pm UTC](https://festim.discourse.group/t/question-about-kinetic-surface-model/185 "2026-10-14T12:26:19Z")
In FESTIM verification, surface kinetic model gives the code like that, F.SurfaceKinetics( k\_sb=k\_sb, k\_bs=k\_bs, lambda\_IS=lambda\_IS, n\_surf=n\_surf, n\_IS=n\_IS, J\_vs=J\_vs, surfaces=1, initial\_condition=exact\_solu… --- ## [Understanding units for TotalVolume](https://festim.discourse.group/t/understanding-units-for-totalvolume/186)
**Author:** [@srichr](https://festim.discourse.group/u/srichr)\ **Replies:** 7\ **Last updated:** [October 1, 2026, 2:42pm UTC](https://festim.discourse.group/t/understanding-units-for-totalvolume/186 "2026-10-01T14:42:16Z")
Hi all, I’m investigating T inventory in a pipe. I originally used a 3D pipe and all was working fine until I played around with surface parameters and it began struggling to converge. I tried adjusting tolerances but it… --- ## [FESTIM using all cores of a shared machine (MUMPS / OpenMP threading) and how to limit it](https://festim.discourse.group/t/festim-using-all-cores-of-a-shared-machine-mumps-openmp-threading-and-how-to-limit-it/184)
**Author:** [@alevazcor](https://festim.discourse.group/u/alevazcor)\ **Replies:** 1\ **Last updated:** [September 1, 2026, 2:46pm UTC](https://festim.discourse.group/t/festim-using-all-cores-of-a-shared-machine-mumps-openmp-threading-and-how-to-limit-it/184 "2026-09-01T14:46:55Z")
Hi all, First time posting!! My colleague and I have been working with FESTIM2 for the past few weeks and ran into a behaviour on a shared server that I could not find documented anywhere on the forum, so I am writing i… --- ## [Materials with several hydrogen isotopes](https://festim.discourse.group/t/materials-with-several-hydrogen-isotopes/183)
**Author:** [@miklavrent](https://festim.discourse.group/u/miklavrent)\ **Replies:** 2\ **Last updated:** [August 27, 2026, 2:48pm UTC](https://festim.discourse.group/t/materials-with-several-hydrogen-isotopes/183 "2026-08-27T14:48:14Z")
Hi, I’m doing two isotopes in a multimaterial component. First I need to define materials (W, Cu, CuCrZr); next, volume subdomains with material for each of them. Finally, I define species (D, T). My problem is: before … --- ## [Solver does not converge for "Deuterium retention in self-damaged tungsten" with sharper drop in damage distribution](https://festim.discourse.group/t/solver-does-not-converge-for-deuterium-retention-in-self-damaged-tungsten-with-sharper-drop-in-damage-distribution/182)
**Author:** [@m2patino](https://festim.discourse.group/u/m2patino)\ **Replies:** 4\ **Last updated:** [August 19, 2026, 1:48pm UTC](https://festim.discourse.group/t/solver-does-not-converge-for-deuterium-retention-in-self-damaged-tungsten-with-sharper-drop-in-damage-distribution/182 "2026-08-19T13:48:43Z")
I’m trying to model deuterium retention in tungsten damaged by 20 MeV tungsten ions. Since the D retention is saturated when the damage is above 0.1 dpa, I want to use a following damage depth distribution shown in orang… --- ## [TDS example code crashes with higher flux](https://festim.discourse.group/t/tds-example-code-crashes-with-higher-flux/181)
**Author:** [@michael.komm](https://festim.discourse.group/u/michael.komm)\ **Replies:** 4\ **Last updated:** [August 18, 2026, 12:01pm UTC](https://festim.discourse.group/t/tds-example-code-crashes-with-higher-flux/181 "2026-08-18T12:01:51Z")
Hi, I am new here so I may have some trivial questions, my apologies in advance. I tried to run the TDS example script from the FESTIM tutorial: and it started to crash when I increased the incident flux. The tutoria… --- ## [How to include dissociation & recombination effects on tritium transport through 316 steel pipe](https://festim.discourse.group/t/how-to-include-dissociation-recombination-effects-on-tritium-transport-through-316-steel-pipe/178)
**Author:** [@srichr](https://festim.discourse.group/u/srichr)\ **Replies:** 2\ **Last updated:** [August 12, 2026, 1:01pm UTC](https://festim.discourse.group/t/how-to-include-dissociation-recombination-effects-on-tritium-transport-through-316-steel-pipe/178 "2026-08-12T13:01:42Z")
Hi all, I’m new to the community, and am running a simple diffusion problem for a purge gas system. As a first approximation to build up from, I have T2 at 100Pa inside a 5mm thick stainless steel pipe and am finding th… --- ## [Some questions about input](https://festim.discourse.group/t/some-questions-about-input/179)
**Author:** [@yafeng-lab](https://festim.discourse.group/u/yafeng-lab)\ **Replies:** 1\ **Last updated:** [August 10, 2026, 12:18pm UTC](https://festim.discourse.group/t/some-questions-about-input/179 "2026-08-10T12:18:51Z")
Hello, I am glad that PFC-TT has some amazing optimizations. I have some puzzles to ask. What is the role of mode in input.cvs. I understand that S. area parent bin (m^2), surface area (m^2) and f (ion flux scaling fac… --- ## [Problem with initial conditions](https://festim.discourse.group/t/problem-with-initial-conditions/177)
**Author:** [@miklavrent](https://festim.discourse.group/u/miklavrent)\ **Replies:** 1\ **Last updated:** [August 3, 2026, 10:45am UTC](https://festim.discourse.group/t/problem-with-initial-conditions/177 "2026-08-03T10:45:35Z")
Hi, Just wanted to attract your attention to what seems to be a bug: FESTIM cannot actually take a list of initial conditions. This is raised on github: Best wishes, Mikhail --- ## [Clarification on the Subdomain Formulation for F.Reaction](https://festim.discourse.group/t/clarification-on-the-subdomain-formulation-for-f-reaction/176)
**Author:** [@ee-nn](https://festim.discourse.group/u/ee-nn)\ **Replies:** 2\ **Last updated:** [July 20, 2026, 10:10pm UTC](https://festim.discourse.group/t/clarification-on-the-subdomain-formulation-for-f-reaction/176 "2026-07-20T22:10:21Z")
Hi everyone, I have a quick question on the Reaction class, upon which Trap is based. It appears that when assigning the subdomain, it explicitly imports the 1D subclass of VolumeSubdomain (link): from festim.subdomain… --- ## [Regarding the FESTIM 1.4 Tutorial Issues](https://festim.discourse.group/t/regarding-the-festim-1-4-tutorial-issues/175)
**Author:** [@liuliu-maker](https://festim.discourse.group/u/liuliu-maker)\ **Replies:** 4\ **Last updated:** [July 8, 2026, 1:36am UTC](https://festim.discourse.group/t/regarding-the-festim-1-4-tutorial-issues/175 "2026-07-08T01:36:02Z")
Dear developers, I downloaded FESTIM 1.4 last year and carried out some hydrogen diffusion calculations with it. I still need to use FESTIM 1.4 for other work, but I found that all the tutorials for version 1.4 are no lo… --- ## [Boundary conditions for HT in FESTIM2](https://festim.discourse.group/t/boundary-conditions-for-ht-in-festim2/164)
**Author:** [@miklavrent](https://festim.discourse.group/u/miklavrent)\ **Replies:** 8\ **Last updated:** [July 7, 2026, 3:12pm UTC](https://festim.discourse.group/t/boundary-conditions-for-ht-in-festim2/164 "2026-07-07T15:12:32Z")
Hi, I am trying to figure out how to apply boundary conditions in case of mixed isotopologues. If we have H2 and HT in gas, each with own partial pressure - is there a way to apply boundary conditions to find H and T co… --- ## [Problems on SurfaceReactionBC](https://festim.discourse.group/t/problems-on-surfacereactionbc/173)
**Author:** [@xinshen](https://festim.discourse.group/u/xinshen)\ **Replies:** 4\ **Last updated:** [July 7, 2026, 1:04am UTC](https://festim.discourse.group/t/problems-on-surfacereactionbc/173 "2026-07-07T01:04:52Z")
Hi all, I’m trying to use the SurfaceReactionBC in FESTIM v2.0 but the exported files are all zero. I’m confused with it. Here is the minimal script: import festim as F Alumina = F.HydrogenTransportProblem() import n… --- ## [How to create an initial distribution of trapped hydrogen?](https://festim.discourse.group/t/how-to-create-an-initial-distribution-of-trapped-hydrogen/174)
**Author:** [@EugZ](https://festim.discourse.group/u/EugZ)\ **Replies:** 2\ **Last updated:** [July 3, 2026, 4:58pm UTC](https://festim.discourse.group/t/how-to-create-an-initial-distribution-of-trapped-hydrogen/174 "2026-07-03T16:58:24Z")
Hello! I would like to calculate a desorption spectrum for a given initial depth distribution of trapped hydrogen. I. e., not to assume empty traps and fill them with implantation, but to start with a specified distribut… --- ## [Surface and Volume Exports in HydrogenTransportProblem DiscontinuousChangeVar](https://festim.discourse.group/t/surface-and-volume-exports-in-hydrogentransportproblem-discontinuouschangevar/172)
**Author:** [@ee-nn](https://festim.discourse.group/u/ee-nn)\ **Replies:** 1\ **Last updated:** [June 28, 2026, 12:19am UTC](https://festim.discourse.group/t/surface-and-volume-exports-in-hydrogentransportproblem-discontinuouschangevar/172 "2026-06-28T00:19:59Z")
Hi all, In HydrogenTransportProblemDiscontinuousChangeVar, the concentration fields themselves appear to be exported as I would expect (atoms/m \\!^{3-d} , where d is the dimension of the simulation). However, the TotalV… --- ## [Attempting Replication of Results in a FESTIM paper](https://festim.discourse.group/t/attempting-replication-of-results-in-a-festim-paper/163)
**Author:** [@ee-nn](https://festim.discourse.group/u/ee-nn)\ **Replies:** 4\ **Last updated:** [May 7, 2026, 1:03am UTC](https://festim.discourse.group/t/attempting-replication-of-results-in-a-festim-paper/163 "2026-05-07T01:03:10Z")
Hi there, I am attempting to replicate some results from a recent paper entitled entitled “Modeling hydrogen isotope transport behavior in the first wall: role of the bonding region in W-RAFM steel with an improved eval… --- ## [Temperature export in discontinuous problem](https://festim.discourse.group/t/temperature-export-in-discontinuous-problem/162)
**Author:** [@tez0rr](https://festim.discourse.group/u/tez0rr)\ **Replies:** 1\ **Last updated:** [April 17, 2026, 12:34pm UTC](https://festim.discourse.group/t/temperature-export-in-discontinuous-problem/162 "2026-04-17T12:34:16Z")
Hi, VTXTemperatureExport object does not seem to be implemented for the discontinuous case. I run into the error: NotImplementedError: Export type \ not implemented Wh… --- ## [Checkpoints not working in multi-material simulations](https://festim.discourse.group/t/checkpoints-not-working-in-multi-material-simulations/150)
**Author:** [@AdriaLlealS](https://festim.discourse.group/u/AdriaLlealS)\ **Replies:** 6\ **Last updated:** [April 16, 2026, 11:46am UTC](https://festim.discourse.group/t/checkpoints-not-working-in-multi-material-simulations/150 "2026-04-16T11:46:14Z")
Hello everyone, I’ve been using festim 2.0b0 (up to date to the latest commit in the fenicsx branch) to run 1D simulations in a single-material slab. I was restarting simulations from checkpoints and using the “read\_fun… --- ## [2d simulation breaks when introducing traps](https://festim.discourse.group/t/2d-simulation-breaks-when-introducing-traps/148)
**Author:** [@miklavrent](https://festim.discourse.group/u/miklavrent)\ **Replies:** 7\ **Last updated:** [April 13, 2026, 1:12pm UTC](https://festim.discourse.group/t/2d-simulation-breaks-when-introducing-traps/148 "2026-04-13T13:12:58Z")
Hi, I am trying to model 2d steel square inside another piece of steel, with traps in the inner piece of steel only. Initially, hydrogen is in inner steel. The code below works ok, but as soon as I uncomment the trap li… --- ## [Concentration-dependent diffusion coefficient](https://festim.discourse.group/t/concentration-dependent-diffusion-coefficient/154)
**Author:** [@cruiseraurora](https://festim.discourse.group/u/cruiseraurora)\ **Replies:** 4\ **Last updated:** [April 13, 2026, 12:51pm UTC](https://festim.discourse.group/t/concentration-dependent-diffusion-coefficient/154 "2026-04-13T12:51:45Z")
Hello! It is known that with increasing concentration the diffusion coefficient decreases. So is it possible to set up such a dependency in FESTIM? As far as I understand, it is only the temperature dependence of the dif… --- ## [The inverse problem for permeability](https://festim.discourse.group/t/the-inverse-problem-for-permeability/156)
**Author:** [@Gav](https://festim.discourse.group/u/Gav)\ **Replies:** 5\ **Last updated:** [April 13, 2026, 12:50pm UTC](https://festim.discourse.group/t/the-inverse-problem-for-permeability/156 "2026-04-13T12:50:24Z")
Hi! I am very new to Festim and am struggling to find documentation on whether I can use this program to get permeability, diffusivity, solubility and trap parameters from a dataset. Is this a capability that Festim pr… --- ## [Interface condition issue in multi-material diffusion with mixed solubility laws](https://festim.discourse.group/t/interface-condition-issue-in-multi-material-diffusion-with-mixed-solubility-laws/158)
**Author:** [@ChrisSo](https://festim.discourse.group/u/ChrisSo)\ **Replies:** 5\ **Last updated:** [April 13, 2026, 12:46pm UTC](https://festim.discourse.group/t/interface-condition-issue-in-multi-material-diffusion-with-mixed-solubility-laws/158 "2026-04-13T12:46:31Z")
Hi all, I recently switched to FESTIM2 (v2.0b1) and ran into an issue when running multi-material simulations using the discontinuous formulations. While benchmarking against FESTIM1, I found that in certain cases the … --- ## [Simple simulation (tutorial) with temperature gradient in the slab](https://festim.discourse.group/t/simple-simulation-tutorial-with-temperature-gradient-in-the-slab/157)
**Author:** [@Francesca](https://festim.discourse.group/u/Francesca)\ **Replies:** 1\ **Last updated:** [February 6, 2026, 1:10pm UTC](https://festim.discourse.group/t/simple-simulation-tutorial-with-temperature-gradient-in-the-slab/157 "2026-02-06T13:10:32Z")
Hi! I’ve just started using FESTIM. I installed version 1.4.1.post1 on windows via WLS. I tried to run the basic tutorial sample case from the website ( Simple simulation — FESTIM tutorial ) and it worked. Now I am tryi… --- ## [Mass balancing in FESTIM](https://festim.discourse.group/t/mass-balancing-in-festim/153)
**Author:** [@ChrisSo](https://festim.discourse.group/u/ChrisSo)\ **Replies:** 6\ **Last updated:** [January 5, 2026, 9:00am UTC](https://festim.discourse.group/t/mass-balancing-in-festim/153 "2026-01-05T09:00:57Z")
Hello everyone, I’m new to FESTIM and currently preparing some Tritium transport modelling work. Before starting, I discussed good practices with colleagues experienced in hydrogen transport (mostly using OpenFOAM), and… --- ## [Issues with 1D Hydrogen Diffusion Simulation Modeling](https://festim.discourse.group/t/issues-with-1d-hydrogen-diffusion-simulation-modeling/149)
**Author:** [@y5k4d6stjv-crypto](https://festim.discourse.group/u/y5k4d6stjv-crypto)\ **Replies:** 7\ **Last updated:** [November 26, 2025, 3:21pm UTC](https://festim.discourse.group/t/issues-with-1d-hydrogen-diffusion-simulation-modeling/149 "2025-11-26T15:21:57Z")
Hello everyone, I am trying to reproduce the study from the paper “Sensitivity study of hydrogen Soret transport in yttrium Hydride-Based nuclear fuel.” When calculating the radial hydrogen concentration variation in a 1… --- ## [Error defining time-dependent sources using dolfinx0.10.0](https://festim.discourse.group/t/error-defining-time-dependent-sources-using-dolfinx0-10-0/152)
**Author:** [@AdriaLlealS](https://festim.discourse.group/u/AdriaLlealS)\ **Replies:** 8\ **Last updated:** [November 26, 2025, 3:21pm UTC](https://festim.discourse.group/t/error-defining-time-dependent-sources-using-dolfinx0-10-0/152 "2025-11-26T15:21:18Z")
Hello everyone, I am currently working with hisp and PFC-Tritium-Transport in order to determine tritium inventory in ITER. I am running a custom version of hisp (AdriaLlealS/hisp at fix-b-bins) using the festim-fenicsx… --- ## [Issue with F.XDMFExport and F.VTXSpeciesExport](https://festim.discourse.group/t/issue-with-f-xdmfexport-and-f-vtxspeciesexport/151)
**Author:** [@Andrea](https://festim.discourse.group/u/Andrea)\ **Replies:** 1\ **Last updated:** [November 17, 2025, 4:59pm UTC](https://festim.discourse.group/t/issue-with-f-xdmfexport-and-f-vtxspeciesexport/151 "2025-11-17T16:59:32Z")
Hi all, I am working with three different materials — tungsten, EUROFER, and FLiBe — in a 2D geometry. I previously used FESTIM 1, but I was getting numerical errors, so I decided to move to FESTIM 2. When running a tr… [Next page](https://festim.discourse.group/c/general/4.md?page=1)