Here are the edits that I made. There were some sentences that you highlighted as passive voice but which I feel are acceptable.
"Moltres is an open source coupled neutronics/thermal hydraulics simulation application for simulating MSRs."
"The MSFR model studied in this paper [3], is a reference design for a fast-spectrum MSR developed under ..."
"... its chosen start-up fuel composition is a eutectic mixture of ..."
Here are the edits that I made. There were some sentences that you highlighted as passive voice but which I feel are acceptable.
"Moltres is an open source coupled neutronics/thermal hydraulics simulation application for simulating MSRs." "The MSFR model studied in this paper [3], is a reference design for a fast-spectrum MSR developed under ..." "... its chosen start-up fuel composition is a eutectic mixture of ..."
abstract.pdf