# Kinetic parameters calculation

**URL:** <https://openmc.discourse.group/t/kinetic-parameters-calculation/6043>\
**Category:** User Support\
**Created:** [October 10, 2025, 10:38am UTC](https://openmc.discourse.group/t/kinetic-parameters-calculation/6043 "2025-10-10T10:38:52Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Ste07](https://avatars.discourse-cdn.com/v4/letter/s/e9c0ed/32.png) [@Ste07](https://openmc.discourse.group/u/Ste07)\
**Post date:** [October 10, 2025, 10:38am UTC](https://openmc.discourse.group/t/kinetic-parameters-calculation/6043/1 "2025-10-10T10:38:52Z")

</div>

Hey there, i am new to openmc and i came across this novel feature in version 0.15.3 (installed using this procedure ( [2. Development Workflow — OpenMC Documentation](https://docs.openmc.org/en/stable/devguide/workflow.html#devguide-editable) )

> **[12. Kinetics parameters — OpenMC Documentation](https://docs.openmc.org/en/latest/usersguide/kinetics.html)**

I wanted to extract beta\_eff and Lambda, however while running the model i get  
“_what(): Invalid tally score “ifp-time-numerator”.”_

Is this feature still under development?

Thank you in advance, best

Stefano

Ps. i’ll attach part of the code if it is helpful

```python
_mc_model = openmc.Model(geometry, materials=materials, settings=settings , tallies=tallies)
_mc_model.add_kinetics_parameters_tallies(num_groups=6)
_mc_model.tallies.export_to_xml()
openmc.run()

```