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Projects / Programmes source: ARIS

Development of Computational Tools for the Determination of the Neutron Field in the Containment of a Pressurized Water Reactor

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Research activity

Code Science Field Subfield
2.03.02  Engineering sciences and technologies  Energy engineering  Fuels and energy conversion technology 

Code Science Field
T160  Technological sciences  Nuclear engineering and technology 

Code Science Field
2.02  Engineering and Technology  Electrical engineering, Electronic engineering, Information engineering 
Keywords
Fission reactor, stochastic neutron transport methods, variance reduction, neutron field in containment, detector response function
Evaluation (rules)
source: COBISS
Evaluation of bibliographic research performance indicators according to ARIS methodology
Citations Citations for bibliographic records in COBIB.SI that are linked to records in citation databases
source: WoS source: Scopus source: COBISS
Researchers (15)
no. Code Name and surname Research area Role Period No. of publications
1.  38278  PhD Klemen Ambrožič  Energy engineering  Researcher  2017 - 2020  112 
2.  36329  PhD Aljaž Čufar  Energy engineering  Junior researcher  2017 - 2018  651 
3.  39521  PhD Tanja Goričanec  Computer intensive methods and applications  Researcher  2017 - 2020  92 
4.  03943  PhD Ivan Aleksander Kodeli  Computer intensive methods and applications  Researcher  2017 - 2020  966 
5.  38202  PhD Bor Kos  Energy engineering  Junior researcher  2017 - 2020  671 
6.  04538  PhD Marjan Kromar  Energy engineering  Researcher  2017 - 2020  300 
7.  19167  PhD Igor Lengar  Materials science and technology  Researcher  2017 - 2020  1,200 
8.  36338  PhD Vid Merljak  Energy engineering  Researcher  2017 - 2020  38 
9.  32163  PhD Vladimir Radulović  Energy engineering  Researcher  2017 - 2020  244 
10.  07991  Slavko Slavič  Energy engineering  Technical associate  2017 - 2020  94 
11.  27819  PhD Luka Snoj  Energy engineering  Researcher  2017 - 2019  1,863 
12.  37483  PhD Žiga Štancar  Energy engineering  Junior researcher  2017 - 2020  366 
13.  08557  PhD Andrej Trkov  Energy engineering  Head  2017 - 2020  795 
14.  15742  Bojan Žefran    Technical associate  2017 - 2020  152 
15.  29546  PhD Gašper Žerovnik  Computer intensive methods and applications  Researcher  2017 - 2020  232 
Organisations (2)
no. Code Research organisation City Registration number No. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  90,742 
2.  2735  University of Maribor, Faculty of energy technology  Krško  5089638052  3,486 
Abstract
The proposed research project is based on the research and development of methods and models suitable for the accurate determination of the neutron field inside the reactor building of the pressurized water reactor for an arbitrary reactor statepoint. A high fidelity calculation platform with very detailed geometrical model (e.g. at least 5000 input lines of instructions) capable to produce in an acceptable running time a total flux statistical errors less than 1 %, especially in regions of interest, is proposed. Based on the good experience for calculation of the neutron transport in such complicated, heavily shielded problems and complex geometry, MCNP code, which is based on the stochastic Monte Carlo (MC) method using continuous energy neutron cross section library, will most likely be selected. The problem addressed is dependent on the successful variance-reduction implementation. ADVANTG software will be used to couple MC calculation with deterministic transport code producing a hybrid system. ADVANTG automates generation of the space- and energy-dependent mesh-based weight-window bounds and biased source distributions that are used in the MC code to accelerate calculations. Suitability of the hybrid calculation will be explored and if needed combined with some more rudimentary method such as source biasing and weight cut-off approach. The calculation system will be developed and tested on the NPP Krško case. The following tasks need to be completed: to investigate and develop suitable process to transform CAD files to MC input and to develop as accurate as reasonably possible NPP Krško reactor building geometrical model, to investigate and develop Monte Carlo acceleration methods capable to produce neutron distributions with minimal statistical uncertainty, to develop analytical tools capable to simulate every NPP Krško operating condition (statepoint), verification and validation of the calculation scheme based on the comparison with measurements and determination of uncertainties. With successful completion of the calculation platform several other problems, that require accurate neutron flux determination, can be studied. For example knowledge of the ex-core nuclear detector response function in transients is needed in the determination of the spatial correction function, which is used by the rod insertion technique implemented for the control rod measurements during the start-up tests after each plant outage. Improvements in the correction function estimation induce higher accuracy of the reactivity determination. It should be noted that the rod insertion method, developed at our department, was a world novelty at the time of publication. Further refinements could lead to another breakthrough in the measurement process. Accurate determination of the neutron dose rates inside the containment is important for planning and minimization of the workers exposure dose rate and consequently increase workers safety, Neutron sensitive equipment in the reactor building can be relocated to places with lower neutron exposure or properly shielded. Material degradations due to aging and radiation damages are the limiting factors for the nuclear power plants lifetime. In the recent initiative to extend LWRs lifetime from 60 to 80 years several new research programs on aging and degradation processes in NPPs were established. Among others, electrical cable aging, pressure vessel embrittlement and concrete aging are especially important. More accurate models could potentially identify hot spots, where additional shielding would be warranted. In addition, better neutron field characterization contributes to the better knowledge of the aging phenomena and helps to estimate aging effects more accurately. Better determination of the activated material is important also for the estimation of the decommissioning costs and for the determination of the source needed in photon (gamma) calculations.
Significance for science
As shown in section 12 acceleration of the Monte Carlo calculations by coupling with deterministic transport codes (e.g. hybrid codes) is still under the continuous development. There is still no universal variance reduction method that would yield best results in all circumstances. Behaviour of different acceleration methods in a real geometrically complex systems, such as reactor building of the nuclear power plant, is extremely valuable for further field development. If the proposed high fidelity approach should become an industry-standard, several obstacles need to be overcome:   How to rapidly create geometrical input from the CAD files that are usually available? Which acceleration method capable to produce neutron distributions with minimal statistical uncertainty should be chosen in available calculation time? How to develop analytical tools capable to adequately simulate any reactor statepoint?   Proposed project will tackle all these questions. Important aspect of the project is availability of the measured neutron dose rates that enable direct comparison of the calculations with measurements.   Since the developed calculation platform will enable accurate neutron distribution determination, several other processes could be examined:   Determination of the nuclear instrumentation response on dynamic reactor transients, which is valuable for the accuracy of the rod insertion technique used for the control rods reactivity measurement. Better neutron field characterization contributes to the better knowledge of the aging phenomena and helps to capture aging effects more accurately. More accurate radionuclide activity determination is essential for the proper gamma characterization.
Significance for the country
Realization of this research project will have positive implications for the safe and economic operation of the NPP Krško.  Industry (NPP Krško) interest and willingness to financially support the project shows project relevance. The proposed research will enable: accurate determination of neutron dose rates in the containment, important for planning and minimization of workers exposure dose rate and increase their safety, determination of nuclear instrumentation response in dynamic reactor transients, to determine correction factors for reactivity measurements (e.g. control rod worth measurement by the rod insertion method during start-up tests after plant outage), determination of neutron fluence on vital components inside reactor building (e.g. electrical cables, pressure vessel, concrete structure etc.), for better surveillance and planning of additional shielding to increase equipment longevity with improved  economy of plant operation, basis for the estimation of the radionuclide inventory and activity of irradiated structures, needed in decommissioning planning and gamma source determination in photon transport calculation, more accurate neutron energy spectrum on locations inside the containment, to improve the accuracy of measurements that depend on the assumptions about the neutron spectrum.   Proposed high fidelity calculation platform and gained knowledge could result in establishment of a spin-off company offering commercial services to utilities abroad. Improvements in the rod insertion method have direct commercial value, through shortening of the measurement time .    The research project will contribute to better knowledge and experience of the researchers in the field of nuclear and radiation safety and promote the education of young researchers. Jožef Stefan Institute is one of the few Slovenian institutions authorized to provide independent expert opinions required by law (see last reference in section 9.1). Importance local expertise for the safety of nuclear installations is recognized in our society: the Slovenian top legislation act »Ionising Radiation Protection and Nuclear Safety Act« (ZVISJV) in Article 134 (ensuring the qualifications of authorized experts and competent authorities) directs the state to »ensure resources for the financing of the development of studies and independent expert reviews and international expert cooperation in the field of protection against ionising radiation and nuclear safety«. Furthermore, the »Resolution On Nuclear and Radiation Safety in the Republic of Slovenia for the period 2013–2023« (ReNRS13–23) in Section 7.1 Research states that sustainable development of nuclear research needs stable financial support in terms of full time employment at least 15 researchers for radiation, nuclear and reactor physics. That number is significantly lower and projects as this proposal can improve the capabilities to support Slovenian Nuclear Safety Administration and increase the safety of nuclear installations.
Most important scientific results Interim report, final report
Most important socioeconomically and culturally relevant results Interim report, final report
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