Development of an incremental methodology for tracking the burnup-dependent isotopic vectors of fuel elements in the TRIGLAV program package for research reactors

Torres Garcia, Jesus Israel (author), Trkov, Andrej (mentor)

An incremental methodology has been developed to consider the isotopic changes of the fuel elements during their burnup process in the TRIGLAV code. Through the modification of the internal subroutines and the implementation of new and auxiliary programs, the incremental scheme tracks the exact isotopic concentrations of the pin-cells (fuel elements) as they undergo the depletion cycle by saving the specific material compositions of the unit-cells at every intermediate burnup step in master isotopic libraries. These updated libraries, carrying the isotopic vectors of the fuel as a function of burnup, serve as input data in the subsequent cross-section homogenization before undergoing the global diffusion calculation. The resulting burnup and isotopic distributions from this new methodology were compared with the data from the original -integral- scheme and from Serpent simulations through their relative differences. In every case the root-mean-squared deviations are less than 1%, so the model remains validated. Highest discrepancies arise from the TRIGLAV's treatment of the unit-cells that represent partially inserted Control Rods. The analysis showed that the resulting burnup levels for the individual pin-cells are mismatching because in the incremental scheme the cross-section homogenization is following more closely the number density changes of the unit-cells at each intermediate step of the depletion cycle, hence impacting their specific burnup increments (dBU). It has also been noted that the individual isotope densities for particular pin-cells have increasing differences when compared (up to 5%) depending on their position inside the core, and thus on their burnup process. Overall, the study explored the physical effects of the isotopic changes in a research reactor and the significance of tracking the burnup-dependent isotopic concentrations of the fuel elements.

• Language: English
• Keywords: Research reactor, fuel element burnup, TRIGLAV, isotopic vectors
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2025
• PID: 20.500.12556/RUL-169454
• COBISS.SI-ID: 238319619
• Publication date in RUL: 29.05.2025

Secondary language

• Language: Slovenian
• Title: Razvoj inkrementalne metodologije za sledenje od zgorevanja odvisnih izotopskih vektorjev gorivnih elementov v programu TRIGLAV za raziskovalne reaktorje

Abstract

Razvita je bila inkrementalna metodologija za sledenje izotopskim spremembam gorivnih elementov med njihovim procesom zgorevanja v programu TRIGLAV. S spremembo notranjih podprogramov in uvedbo novih ter pomožnih programov inkrementalna shema natančno sledi izotopskim koncentracijam gorivnih elementov (osnovne-celice) med ciklom zgorevanja goriva, pri čemer shranjuje specifično materialno sestavo osnovnih celic na vsakem vmesnem koraku zgorevanja v master izotopsko knjižnico. Te posodobljene knjižnice, ki vsebujejo izotopske vektorje goriva kot funkcijo zgorevanja, se uporabijo kot vhodni podatki pri nadaljnji homogenizaciji reakcijskih jedrskih presekov, preden se izvede globalni difuzijski izračun. Rezultati zgorevanja in izotopske porazdelitve iz te nove metodologije so bili primerjani s podatki iz izvirne integralne sheme ter s simulacijami s programom Serpent iz literature in z izračunom relativnih razlik. V vseh primerih so kvadratna povprečna odstopanja (RMS) manjša od 1%, kar potrjuje veljavnost modela. Največja odstopanja so povezana z obravnavo osnovnih celic, ki predstavljajo delno vstavljene kontrolne palice. Analiza je pokazala, da se dosežene ravni zgorevanja posameznih gorivnih elementov razlikujejo, ker inkrementalna shema bolj natančno sledi spremembam numerične gostote osnovnih celic na vsakem vmesnem koraku zgorevanja goriva, kar posledično vpliva na njihove specifične inkremente zgorevanja (dBU). Prav tako je bilo ugotovljeno, da imajo posamezne izotopske gostote pri določenih gorivnih elementih večje razlike (do 5%), odvisno od njihovega položaja v sredici reaktorja in s tem njihovega procesa zgorevanja. Na splošno je študija raziskala fizikalne učinke izotopskih sprememb v raziskovalnem reaktorju ter pomen sledenja izotopsko odvisnim koncentracijam gorivnih elementov med zgorevanjem.

• Keywords: TRIGLAV, raziskovalni reaktor, zgorevanje gorivnih elementov, izotopski vektorji