IJSThe J. Stefan Institute home page is located at http://www.ijs.si/

Andrej Trkov's Home Page

Head of Reactor Physics Department

Institute Jozef Stefan
Reactor Physics Department  F- 8
Jamova cesta 39
Si-1000 Ljubljana

Contact information :

phone (at work)  +386 (1) 5885-324
fax  +386 (1) 5885-377
e-mail address andrej.trkov@ijs.si
home page http://www.rcp.ijs.si/~andrej/


Principal Research Activities

Nuclear Data - Evaluation, Verification, Processing, Validation

CORD2 - PWR Reactor Core Design Package

GNOMER - Core Power Distribution with Thermohydraulic Feedbacks

DMR043 - Digital Reactivity Meter

LOADF - Power Reactor Core Monitoring

WLUP - WIMS-D Library Update Project


Other Interests





Nuclear Data

An important part of my research activities are devoted to nuclear data. Early work involved the implementation of the FEDGROUP-C code for generating multigroup constants for deterministic neutron transport calculations. Later, emphasis was shifted to the NJOY code system (developed at Los Alamos National Laboratory). I contributed to the WIMSR module for generating constants in the WIMS-D Library Format and numerous other small patches.

The success of a reliable nuclear data file depends on file verification and validation. For this purpose the ENDVER package was developed, which allows comparison of the contents of evaluated nuclear data files with the experimental data in the EXFOR database. The data retrieval engine was my contribution to the ENDVER package (available from the IAEA), which complements the database management and the Graphics User Interface prepared by Viktor Zerkin. Together these components are part of the ENDF data retrieval interface at the IAEA and the NNDC.

Data processing is the first step in data validation, which is nowadays a standard step in the nuclear data evaluation process. Most commonly this is done by preparing a library for a Monte Carlo transport code like MCNP and simulating integral benchmarks such as compiled in the ICSBEP and SINBAD compilations.

All of the above requires thourough knowledge of the ENDF format, which is used worldwide for storage and exchange of nuclear data. I am the co-editor of the ENDF-6 Formats Manual.

With the experience outlined above I can contribute to the development of the EMPIRE code system for nuclear model calculations, which is one of the major codes for nuclear data evaluation. My main responsibility is data file assembly, and formatting.

Model caclculations need to be combined with experimental data to improve the performance of the evaluated data and to constrain the uncertainties. To this end I worked with D.W. Muir, the author of the GANDR System to use GANDR for nuclear data evaluation work.

The main achievement in the field of nuclear data is the inclusion of several evaluations (thorium, protoactinium, isotopes of tungsten, manganese) into the ENDF/B-VII.1 evaluated nuclear data library. The work was done through broad international collaboration under the IAEA.

CORD2 - PWR Reactor Core Design Package

One of my main areas of interest (and the ultimate goal of other activities) are Reactor Core Design Calculations, with empahsis on the Pressurised Water Reactors (PWR). An integrated package CORD-2 was developed, which consists of calculational modules, a number of data libraries that describe the core and the fuel and a set of library maintenance and utility codes.

In the package, utilities are available for automatic preparation of inputs for the well known, WIMS-D lattice code from AEA, Winfrith. The non-commercial versions of the code are available from the NEA Data Bank.

GNOMER - Core Power Distribution with Thermohydraulic Feedbacks

The main workhorse of the CORD-2 package is the GNOMER Green's function nodal neutron diffusion code, which is used for fuel assembly cross section homogeniztion, as well as for the whole core power distribution calculation in 3D cartesian geometry, including thermohydraulic feedbacks.

DMR043 - Digital Reactivity Meter

In pressurised water power reactor after refuelling it is required to carry out a series of tests to verify that reactor core reactivity parameters are within the limits of the technical specifications.

Reactor core reactivity at constant core configuration can in principle be determined by measuring the doubling time of the neutron flux. This method is limited to small, positive reactivity values. It is too time consuming for practical applications in power reactors.

A better way of measuring reactivity is by solving the inverse point kinetics equations, using the neutron flux signal from the neutron detectors as input. Early reactivity computers were analogue devices. Their main disadvantage is that they can not model all features of the neutron point kinetics equations and that they need very careful calibration to work correctly. More modern digital devices are more robust, accurate and easy to use.

In the early 80's the first digital reactivity computer DMR042 was designed at the "Jozef Stefan" institute by Glumac and Vidmar. It was based on a microcomputer and used successfully at the Krsko NPP during startup tests before cycles 2, 3, 4 and 5. In the meantime a new digital reactivity DMR043 was designed, based on a PC computer and utilising better numerical algorithms and allowing the full non-homogeneous form of the point kinetics equations to be modelled. It has been used at the Krsko NPP ever since (the Krsko plant is now in its 16-th cycle of operation).

As an offspin of the high performance reactivity computer, a new method for measuring control rod worth was designed. It was tested during the startup tests in cycle 6 and used as the primary control rod worth measuring technique since cycle 7 in 1987. Its main advantage is the short measuring time. All it takes is the time for the measured control rod to be fully inserted into the core and to bring the reactor back to the original power leve. The savings in time (and money) are quite substantial, considering that one day of full power operation is worth between 0.5 and 1 million US dollars. For illustration, the startup tests before cycle 16 took just about 12 hours to complete!

The Krsko NPP is not the only plant in which the new control rod worth measuring technique is used. A publication by Westinghouse appeared a few years ago, outlining the "Dynamic Rod Worth" measuring technique. This is an idependent development, but reference is made to some of our earlier work. This method is now offered commercially by Westinghouse.

For the DMR-043 I contributed the software and several design features, which make the device easy to use. I also made a major contribution to the new control rod worth measuring technique, particularly the error analysis and the implementation of the correction factors, which provide sufficient accuracy of the method for practical purposes.

LOADF - Power Reactor Core Monitoring

Certain  reactor core parameters are not available to the reactor operator because they are difficult (or impossible) to measure. They can be provided by calculations, running on-line and simulating the operation of the reactor. This is the main purpose of the LOADF package.

The LOADF package runs on the process computer of the Krsko NPP. It contains GNOMER as the main calculational module. It solves the 3D neutron diffusion equation in cartesian geometry assuming core octant symmetry. It reads the necessary parameters from the Process Information System database. The calculated parameters are also stored in this database to be available to the operators as necessary. The main parameters displayed at present are the Xenon and Iodine distributions, axial power distribution, shutdown margin and various reactivity parameters.

The main design problems were related to the reliability of the information in the database and the relatively modest computational capacity of the process computer, which is about 10 times slower than a 200 MHz Pentium PC.

The LOADF package was delivered to Krsko NPP in April 1999. The performance up to date is quite satisfactory.

WLUP - WIMS-D Library Update Project

The multigroup constants library is one of the weakest points of the non-commercial WIMS-D series of codes. The "WIMS-D Library Update Project" (WLUP) is under way with the International Atomic Energy Agency (IAEA). It is a Co-ordinated Research Project (CRP) with participants from several laboratories. At present, updated libraries are available for testing purposes. A number of benchmarks for library validation are also provided. Several utility codes can be downloaded, including the library maintenace utility code WILLIE ,which allows data intercomparison, deletion of materials, insertion of new data, conversion between binary and ASCII format and other tasks.

Within the scope of the WIMS-D Library Update Project (WLUP), the NJOY code was made operational to generate data for the WIMS-D library. A number of updates were proposed, which are compatible with  NJOY99 .

Other activities


This is something I discovered in recent years. Much of the credit goes to the trainer Urban Praprotnik with his positive attitude and a few hints to improve my technique, which made running painless and really enjoyable relaxation. I managed the Vienna Marathon in 2011 in less than four hours. Due to circumstances I did not make the full running trip from Ljubljana to the seaside, but I made two halves (in 2010 and 2012). Maybe next year...


It is very enjoyable but hard to describe. You just have to see for yourself what it is like on "The sunny side of the Alps".


This is the usual way of going to work in summer (about 12.5 km one way), but WHERE IS SUMMER THIS YEAR???


Mainly this is a long and distant past, but very pleasant to remember. Here are James, Andrej, Rob and Dave in Shadowfax
and here is the result of our sweat.

There is some tradition in the family: my son Mitja is rowing for Ljubljanica.

(This home page is under construction)

Andrej Trkov, Created 21-May-99, updated 2011.