Razvoj programa za proračun kritičnosti Monte Carlo metodom

undergraduate thesis

• Title (english): Program development for criticality calculations using Monte Carlo method
• Author: Fran Lubina
• Mentor: Mario Matijević (mentor)
• Committee member: Mario Matijević (predsjednik povjerenstva)
• Committee member: Krešimir Trontl (član povjerenstva)
• Committee member: Siniša Šadek (član povjerenstva)
• Granter: University of Zagreb; Faculty of Electrical Engineering and Computing; Zagreb
• Defense date and country: 2024-09-13, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Computing

Abstract

Tema ovog rada jest razvoj C++ programskog rješenja za proraˇcun kritiˇcnosti fisijskih
nuklearnih sistema Monte Carlo metodom. Ulazna datoteka korisnika sadrži sve
potrebne informacije za definiranje simulacijskog modela te je njezin format baziran
na formalnoj gramatici koja posjeduje leksiˇcka i sintaksna pravila. Za izgradnju parsera
ulazne datoteke korišteni su alati Lex i Yacc, toˇcnije njihove GNU nadogradnje
Flex i Bison. Flex kao ulaz prima datoteku koja sadrži regularne izraze koji definiraju
leksiˇcke jedinke te generira leksiˇcki analizator u jeziku C++. Bison kao ulaz prima datoteku
s produkcijama formalne gramatike uz pripadnu semantiˇcku akciju za pojedino
pravilo te generira semantiˇcki analizator u jeziku C++. Geometrija modela konstruira
se kombinatornom geometrijom (Booleovom algebrom) nad skupom primitivnih
tijela tj. analitiˇckih površina kako bi korisnik definirao volumene ispunjene materijalima
(udarnim presjecima) od interesa. Osim geometrije modela, ulazna datoteka
sadrži i razne kontrolne parametre kao što su broj neaktivnih i aktivnih ciklusa neutrona,
poˇcetnu svojstvenu vrijednost efektivnog faktora multiplikacije neutrona (keff)
te poˇcetnu prostornu raspodjelu fisijskih neutrona. A priori poznati broj neaktivnih ciklusa
neutrona ne ulazi u statistiˇcki proraˇcun keff, ve´c služi za konvergenciju fisijskog
izvora neutrona prema fundamentalnom prostornom obliku (engl. eigenmode). Kao
pokazatelj te konvergencije fisijskog izvora koristi se metrika NCDS (engl. Nine Center
Distances Sum). Tek nakon postizanja fundamentalnog fisijskog oblika, program
aktivira pra´cenje sluˇcajne šetnje neutrona u tzv. aktivnim generacijama (ciklusima). U
slucˇaju fisije, oslobod¯eni neutroni se spremaju u tzv. fisijsku banku te se koriste kao
izvor ˇcestica u idu´coj generaciji. Program u konaˇcnici daje statistiˇcku procjenu faktora
keff i njegove standardne devijacije. Za procjenu keff kombiniraju se tri analitiˇcka
procjenitelja koji prate apsorpciju, fisiju i duljinu prevaljenog puta neutrona.

Abstract (english)

The subject of this thesis is the develoment of a C++ software solution for criticality
simulations of fissile assemblies using the Monte Carlo method. The input file
contains sufficient data to define the simulation model. The program warrants the development
of a suitable formal grammar to describe the input file complete with lexical
and syntax rules. To generate the input parser Lex and Yacc, more precisely, their respective
GNU extentions were used; namely Flex and Bison. Flex takes an input file
with regular definitions of the lexical tokens and generates a lexical analyzer in C++.
Bison takes, as its input, a file containing the productions of the formal grammar as
well as their corresponding semantic actions. Bison generates a syntax analyzer in
C++. The model geometry is constructed by using combinatorial geometry (Boolean
algebra) on a set of primitive shapes i.e. analytic surfaces to yield closed 3D shapes
with finite volumes filled with materials (nuclear cross sections) of interest. Along
with geometric definitions, the input file also contains several control parameters, such
as the number of active and inactive cycles, the initial effective neutron multiplication
factor eigenvalue (keff) and the initial spatial distribution of neutrons. The a priori
defined number of inactive cycles does not go into the final statistical estimate of the
multiplication factor, instead they are used for the sole purpose of achieving the source
eigenmode. The NCDS (Nine Center Distances Sum) metric is used as the source
convergence indicator. Only after the source eigenmode has been achieved does the
program begin tracking the particle random walks, these cycles are known as the active
cycles. When a fission event occurs the resulting neutrons are store in a dedicated
data structure, the fission bank. The final program output is a statistical estimate of the
effective neutron multiplitcation factor and its standard deviation. Three estimators are
combined to yield the final keff value, based on: absorption, scattering and traversed
path length.

• Keywords: Monte Carlo; kritiˇcnost; svojstvena vrijednost; transport neutrona; simulacija
• Keywords (english): Monte Carlo; criticality; eigenvalue; neutron transport; simulation
• Language: croatian
• URN:NBN: urn:nbn:hr:168:153290
• Study programme: Title: Computing; Study programme type: university; Study level: undergraduate; Academic / professional title: sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka računarstva (sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka računarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Closed access
• Created on: 2024-10-12 21:22:26