TRIGA Burnup CalculationsUsing SERPENT

Anže Pungerčič, Dušan Ćalić, Luka Snoj(anze.pungercic@ijs.si)

Jožef Stean Institute, Reactor Physics Department, Slovenia

8th International Serpent User Group MeetingEspoo, Finland, May 29 – June 1, 2018

Outline

• Introduction

• Complete operational history analysis• Steady-State operation

• Pulse mode operation (Pulse experimental database)

• Serpent model and burnup methodology• STRIGA computer tool

• Results of burnup analysis

• Plans for the future

Introduction• TRIGA Mark II research reactor at the „Jožef Stefan“

Institute started operation in 1966.

• Reconstruction in 1991 enabled pulse mode operation.

• Initiated activities to analyse complete operationalhistory of the JSI TRIGA research reactor:

• Steady-State operation

• Pulse mode operation

JSI TRIGA side view

Reactor core• Fuel type: Cylindrical fuel elements

• Fresh fuel composition: U mixed with ZrH

• 91 Positions

• Six concentric rings

• 4 Control rods

• JSI TRIGA utilization (398 JSI TRIGA related articles1966-2018).

• 15 articles regarding burnup calculation (only usingdeterministic TRIGLAV)

• Large discrepancies (> 500 pcm ) for calculations withburned fuel

• Experimental validation of reactor simulation codeswith excess reactivity measurements.

Burnup analysis vital for:

• Optimization of fuel management

• Decommissioning of the research reactor

Motivation

Operational history analysis• Every operation made with the JSI TRIGA reactor

documented in reactor logbooks.

50 logbooks

20 000 pages

Steady-State: Extracted information• Operational parameters

• Reactor power (changes)

• Operation time

• Core configuration changes (fuel element positions)

• Weekly excess reactivity measurements

Pulse experimental database

• Fuel isotopic composition (Future)• Provides the needed information to simulate or analyse each

pulse separately.

• Publicly available at http://trigapulse.ijs.si

Insertedreactivity

Power andtemperature

signals

Pmax, Etot, FWHM, Tmax

Control rod calibration and

position

Serpent model andburnup methodology

- STRIGA program package

Serpent TRIGA model validated on core configuration No. 132 (benchmark) and compared to MCNP

D. Ćalić, G. Žerovnik, A. Trkov, L. Snoj “Validation of the Serpent 2 code on TRIGA Mark II benchmark experiments” Applied Radiation and Isotopes, 107 (2016) 165-170.

Control rods withfuel followersused after 1991.

Multiple universes:• Reactor core• Each fuel el. position

Makes fueltracking andshuffling easier

STRIGA: Computer tool for TRIGA researchreactors

•Development•Fortran 77

•Purpose•Monte Carlo calculation for TRIGA research reactor•Burnup calculations•Typical steady state calculations

•Goal•Increase the accuracy of TRIGA benchmark usingburned fuel

Cycle 1

Dimension and material data

Serpent input filesTRIGLAV input

files

STRIGA procedure 1/3

• Triglav.inp

• elem.inp

STRIGA

TRIGA.dim TRIGA.lib

materials.inp

3D pins.inp

triga.i

Serpent burnupcalculations

burnup.inp

Serpent output file forcycle 1

STRIGA procedure 2/3

SLIB = utility code that converts Serpentoutput file to ISO library format for

TRIGA reactor

triga.i_dep.mTRIGA.iso

Fuel isotopic library with atomicnumber densities and burnup for

each fuel element

Cycle 2

Dimension, material data and isotopic composition of burned fuel

Serpent input files

TRIGLAV inputfiles

STRIGA procedure 3/3

• Triglav.inp

• elem.inp

STRIGA

TRIGA.dim TRIGA.lib

materials.inp

3D pins.inp

triga.i

Serpent burnupcalculations

TRIGA.iso

burnup.inp

•History after 1991 simulated in 2000 CPU hours(σ𝒌𝒆𝒇𝒇 ≈ 𝟏𝟓 𝒑𝒄𝒎)

•Complete history in ≈ 10000 CPU hours

Results of TRIGA burnup analysis

Different fuel element types.

Goal: Analyse the effects of differentfuel element types.• Fuel element properties:

• Aluminium-LEU

o Low enriched uranium (20 %)

o Without Zr rod

o Aluminium cladding

o 8.5 wt% uranium

• FLIP-HEU (Absorber erbium)

o High enriched uranium (70 %)

o Stainless Steel cladding

o 8.5 wt% uranium

• SS-LEU 8.5 wt% U

o Stainless Steel cladding

• SS-LEU 12 wt% U

Fuel region

Absorbers

SerpentModel

Graphite

Uppercladding

Bottomcladding

Isotope profile:• Each fuel el. divided

into:o 100 axial

o 10 radial

o 30 tangentialregions.

TRIGLAV (in-house developed 2D diffusion approximationcode)

Reduction of excess reactivity Cycle No. 69 Cycle No. 218

Measured 𝑝𝑐𝑚 𝑘𝑔𝑈

𝑀𝑊𝑑-94.4 ± 12.8 -292.4 ± 67.3

Calculated with TRIGLAV 𝑝𝑐𝑚 𝑘𝑔𝑈

𝑀𝑊𝑑-78.4 ± 3.9 -216.0 ±10.8

Core 69 Core 218

Serpent and TRIGLAV comparison

Individual isotopes effect on excess reactivity

• Operational history of the JSI TRIGA research reactoranalysed.

• Constructed a publicly available pulse experimental database (http://trigapulse.ijs.si)

• The validated Serpent TRIGA model used for completehistory simulation with the help of the STRIGA computer tool.

• Noticeable differences between different types ofTRIGA fuel elements

• Good agreement between in-house developedTRIGLAV and Serpent for burnup changes in excessreactivity.

Summary

Future work (discussion)• Uncertainties in final fuel el. burnup and its isotopic

composition.

• Effect of the choice in reactor power P and time t on that power.

Thank you for attention!