# How to run OpenMC without the production of delayed neutrons **URL:** \ **Category:** User Support\ **Created:** [January 10, 2019, 7:24am UTC](https://openmc.discourse.group/t/how-to-run-openmc-without-the-production-of-delayed-neutrons/389 "2019-01-10T07:24:11Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Shyne](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@Shyne](https://openmc.discourse.group/u/Shyne)\ **Post date:** [January 10, 2019, 7:24am UTC](https://openmc.discourse.group/t/how-to-run-openmc-without-the-production-of-delayed-neutrons/389/1 "2019-01-10T07:24:11Z")
Hello everyone: I want to calculate the beta\_eff by the two separated MC simulations, with and without the production of delayed neutrons. However, I have no idea about how to run the simulation without the production of delayed neutrons. I found the variable “emission\_mode” in the class “openmc.data.Product” in user’s docs. Is it the control switch for the production of delayed neutrons? Thanks in advance for your replies! Best Regards, Shyne ---
**Author:** ![Ajay\_Rawat](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Ajay\_Rawat](https://openmc.discourse.group/u/Ajay_Rawat)\ **Post date:** [January 10, 2019, 9:43am UTC](https://openmc.discourse.group/t/how-to-run-openmc-without-the-production-of-delayed-neutrons/389/2 "2019-01-10T09:43:28Z")
Dear Shyne, You can find the diff patch for doing these calculations. [https://gist.github.com/paulromano/2b9d2d4a80dc53625f209a4bdf0801f5](https://gist.github.com/paulromano/2b9d2d4a80dc53625f209a4bdf0801f5) with regards Ajay ---
**Author:** ![Shyne](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@Shyne](https://openmc.discourse.group/u/Shyne)\ **Post date:** [January 11, 2019, 7:15am UTC](https://openmc.discourse.group/t/how-to-run-openmc-without-the-production-of-delayed-neutrons/389/3 "2019-01-11T07:15:32Z")
Dear Ajay, Thanks for your replay.And it took me some time to modify the source following your suggestion and recompile the code. But the modifed code got the identical results of keff with the original one at the same random seed. The test case is the simple case “Modeling a Pin-Cell” in user’s docs([https://openmc.readthedocs.io/en/latest/examples/pincell.html](https://openmc.readthedocs.io/en/latest/examples/pincell.html)). It seems the modifed code still runs with the production of delayed neutrons? Or I misunderstood the function of the diff patch? Best Regards, Shyne 在 2019年1月10日星期四 UTC+8下午5:43:29，Ajay Rawat写道： ---
**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\ **Post date:** [February 1, 2019, 1:41pm UTC](https://openmc.discourse.group/t/how-to-run-openmc-without-the-production-of-delayed-neutrons/389/4 "2019-02-01T13:41:35Z")
Hi Shyne, It looks like there was one line missing in that diff, namely a change in nuclide\_header.F90. I’ve just updated the diff at the link that Ajay sent. Have a look at it again and give it a try. Best regards, Paul ---
**Author:** ![cp-f](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/cp-f/32/2266_2.png) [@cp-f](https://openmc.discourse.group/u/cp-f)\ **Post date:** [December 9, 2022, 1:02am UTC](https://openmc.discourse.group/t/how-to-run-openmc-without-the-production-of-delayed-neutrons/389/5 "2022-12-09T01:02:07Z")
Dear Paul, is there may an updated version of this patch which works with the current OpenMCversion? Thanks already a lot. Best Christopher ---
**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\ **Post date:** [December 13, 2022, 3:20pm UTC](https://openmc.discourse.group/t/how-to-run-openmc-without-the-production-of-delayed-neutrons/389/6 "2022-12-13T15:20:38Z")
Yes, someone by the name of Christopher just submitted a pull request to make this a proper feature 😄 > > > This new feature should allow users to simulate the prompt criticality of their …system. Which is the criticality based only on the prompt fission neutrons. Therefore, you can now decide whether delayed neutrons are created during fission. > > That's how it would look in practice: > \`settings.create\_delayed\_neutrons = False\` > > I hope someone finds this useful, and I am looking forward to your feedback.