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Bruno Bärs

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Born 1935 in Finland. Doctor of Technology from Helsinki University of Technology (Presently Aalto University) 1971. Worked as Senior Research Scientist in Nuclear reactor noise, neutron dosimetry for nuclear power plants, nuclear reactor physics and technology. 11 STEX (Short Term Expert) missions for IAEA to different countries in the world. About 90 scientific publications in international and national journals and about 50 confidential research reports to nuclear power companies.

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Papers by Bruno Bärs

Experience from and research activities at the Otaniemi TRIGA reactor

5. European conference of TRIGA users Portoroz, 1978

Experiences from the TRIGA reactor in Finland Abstract

5. Euroean comference of TRIGA users Portoroz 1978, 1978

Experience from the Finnish 250 kW TRIGA reactor is reported. The maximum fuel elongation duri... more Experience from the Finnish 250 kW TRIGA reactor is reported. The maximum fuel elongation during 16 years operation is about 2.4 mm (B-ring) . No fuel damages have occurred (U-ZrH1.0, Al-clad). The instrumentation has partly been renewed and a possible renewal of the whole instrumentation is under consideration. The communication with other TRIGA laboratories reveals similar trends to upgrade or to completely replace elder instrumentation. In order to test a theoretical model, to obtain experience and parameters for optimization and for possible use of the mean square (or Campbell's technique) for reactor power measurements, a series of measurements were carried out. The present fission and compensated ionization chambers in the FiR-1 reactor were used. The influence of compensation voltage, filter frequency, reactor power etc.were investigated. The preliminary results and findings are reported. The occupational (whole body) dose-commitment to about 100 workers in the laboratory has been about 20 man.rem/year (includes about 60 per cent from background radiation). The average additional dose (above background) has been in the range 4...10 mrem/working month x person during the last years. The largest occupational whole body dose ever measured is 1.35 rem/ year and the largest dose for the thyroid 1.9 rem/event and about 5 rem from several events during a one year period. Small contaminations of I131, Po 210 (α: from Bi210), Sb122 and Sb124 have been detected and have required decontamination of some working areas, some irradiation facilities etc. The yearly radiation dose from Ar41 release (≤30 Ci/1300 h oper time) and to a person in the neighbourhood of the reactor was semi-empirically estimated to be at most about 100 μrem/year (dose commitment < 1 man.rem/year). The maximum thyroid dose from the largest I131 release (2 mCi/year) was estimated to about 100 μrem/year. (author)

MEASUREMENT OF Ar41 RELEASE FROM A TRIGA REACTOR

VTT Rea Summary report 2:19 1 page, 1977

MEASUREMENT OF Ar"! RELEASE FROM A TRIGA REACTOR

Summary report VTT 1 page 2:19, 1977

ON THE VARIETY AND HIERARCHY OF DATA EXTRACTION METHODS IN NUCLEAR REACTOR NOISE ANALYSIS

Nuclear Instruments and Methods, 1972

A review and systematic approach to the data extraction problem in nuclear reactor noise analysis... more A review and systematic approach to the data extraction problem in nuclear reactor noise analysis is presented. A large number of signal representations and data extraction methods are obtained by using expansions of the fundamental joint probability and related quantities into sets of observable quantities and by using natural classification criteria specifying the experimental conditions. Most previously used and suggested techniques are members 0f this set. A large number of alternate or modified techniques can be suggested some of which may be of practical interest. The hierarchy of representation given in this work also indicates that the application of information theory to noise problems may be a useful and powerful approach.

COMPARISON OF SOME GAMMA DETECTORS AND ENVIRONMENTAL MEASUREMENT OF SMALL Ar41 RELEASES FROM A TRIGA REACTOR

VTT Reactor laboratory Report 37, 1977

GM-detectors, liquid- and NaI(Tl)-scintillation detectors and semiconductor detectors were compar... more GM-detectors, liquid- and NaI(Tl)-scintillation detectors and semiconductor detectors were compared in order to measure small airborne Ar41 activity concentrations. A 12,5 cm x 12,5cm NaI(Tl)-scintillation detector was used to semiempirically estimate the the radiation exposure arising from airborne Ar41 release passing 5 meters (estimated) above the detector at a distance of 130 meters from a 250 kW Triga-reactor under downwind conditions. The height of the release point was 19m. The exposure was found to be 0.45 µR/h at an Ar41 release rate of 18 mCi/h (670 MBq/h) under downwind conditions and at wind speed of3 m/s. The mean annual exposure rate from 1300 hours reactor operation is of the order of 40...100 µR/y (+100 -50%) at this test point and at a release rate of 2.5...6 µCi/s. The maximum exposure at the ground level is at a distance of about 200 meters (ca 10 x height of chimney) and is of the order of 100 µR/y. At close distances from the point of release a line source model can be used to for the approximate estimation of the exposure.

COMPARISON OF SOME GAMMA DETECTORS AND ENVIRONMENTAL MEASUREMENT OF SMALL AR41 RELEASES FROM A TRIGA REACTOR

Technical research center of Finland VTT, 1977

GM-detectors, liquid- and NaI(Tl)-scintillation detectors and semiconductor detectors were compar... more GM-detectors, liquid- and NaI(Tl)-scintillation detectors and semiconductor detectors were compared in order to measure small airborne Ar41 activity concentrations. A 12,5 cm x 12,5cm NaI(Tl)-scintillation detector was used to semiempirically estimate the the radiation exposure arising from airborne Ar41 release passing 5 meters (estimated) above the detector at a distance of 130 meters from a 250 kW Triga-reactor under downwind conditions. The height of the release point was 19m. The exposure was found to be 0.45 µR/h at an Ar41 release rate of 18 mCi/h (670 MBq/h) under downwind conditions and at wind speed of3 m/s. The mean annual exposure rate from 1300 hours reactor operation is of the order of 40...100 µR/y (+100 -50%) at this test point and at a release rate of 2.5...6 µCi/s. The maximum exposure at the ground level is at a distance of about 200 meters (ca 10 x height of chimney) and is of the order of 100 µR/y. At close distances from the point of release a line source model can be used to for the approximate estimation of the exposure.

COMPARISON OF SOME GAMMA DETECTORS AND ENVIRONMENTAL MEASUREMENT OF SMALL 41Ar RELEASES FROM A TRIGA REACTOR

Nuclear Instruments and Methods 150 p.595, 1978

GM-detectors, liquid-(NE 110) and Nal(Tl)-scintillation detectors and semiconductor detectors wer... more GM-detectors, liquid-(NE 110) and Nal(Tl)-scintillation detectors and semiconductor detectors were compared in order to measure small airborne 241Ar activity concentrations. A dia 12.7 cm x h 12.7 cm Nal(Tl)-scint.. detector was used to semiempirically estimate the radiation exposure arising from airborne 41Ar release passing 5 m (estimated) above the detector at a distance of 130 m from a 250 kW Triga reactor. The height of the release point was 19 m. The exposure was found to be 0.45 uR/h at an 41Ar release rate of 18 mCi/h (670 MBq/h) under downwind conditions and at the most prevalent wind speed of 3 m/s.

Control rod calibrations in the FiR 1 reactor by the rod drop methods

Tech Univ of Helsinki Dept of Tech Physics Report 45 1967, 1967

Control röd calibrations on the TRIGA Mark II reactor FiR-1 utilizing rod-drop methods are report... more Control röd calibrations on the TRIGA Mark II reactor FiR-1 utilizing rod-drop methods are reported. Three known rod-drop methods are compared with each other. The method which considers the effects of prompt neutrons was found to be accurate, simple, reliable and rapid. The effect of the long dropping times are reduced by a simple extrapolation technique. The restrictions arising from the quasistationary condition in the theory are avoided by introducing a correction. Theory and experiments for several successive rod-drops are also presented. The rod-drop methods are compared with some other methods for reactivity measurements.

Om kärnreaktorers stokastiska kinetik ( in Swedish) 1965

Licentiat work Technical University of Helsinki, 1965

Noise Measurements in a Subcritical Facility Based on Photon Detection

Experiences with Nb Dosimeters for Neutron Flux Measurements

Stochastic Fluctuations in the Power Pulses of Triga Reactors

On the influence and use of gamma radiat

Acta Polytechnica Scandinavica. Physic including nucleonics series Ph 79, 1971

The influence and use of gamma radiation in reactor noise measurements is studied, based on a spa... more The influence and use of gamma radiation in reactor noise measurements is studied, based on a space-and energy-independent reactor and detector model. The approach is based on the forward Kolmogorov equation and is carried out in a consistent and unified way. The influence of the correlated and non-correlated photon radiation and

Variance or AC Technique in Nuclear Reactor Power Measurements

Kenenergie 26, 2 63-68, 1983

The theoretical foundations for the variance, AC or Campbell technique are given and reveal a nov... more The theoretical foundations for the variance, AC or Campbell technique are given and reveal a novel possibility to further suppress the influence of the background radiation. Some methods for the neutron flux measurements are compared. Variance measurements with a fission detector in the Finnish TRIGA type research reactor are reported and they verify the main features of the stochastic detector model.

Variance and higher order signal moments in neutron flux measurements

Nuclear Instruments and Methods in Physics Research 275(2) , 1989

Explicit expressions are derived for the second (also called variance or Campbell signal) and hig... more Explicit expressions are derived for the second (also called variance or Campbell signal) and higher order central moments of signals from a neutron detector in a nuclear fission reactor. The signal is treated as a compound distribution, which is composed of detection rates of different types of events with fluctuating pulse amplitudes and with arbitrary pulse shapes. The technique with probability generating functions (pgf) is applied. The present results provide an extended theoretical basis for the utilization of different signal moments for flux monitoring in nuclear fission reactors.

Use of Higher Order Signal Moments and High Speed Digital Sampling Technique for Neutron Flux Measurements

IEEE Transactions on Nuclear Energy 40 no 4 p 832-839, 1993

The second (conventional variance or Campbell signal), the third, and the modified fourth order c... more The second (conventional variance or Campbell signal), the third, and the modified fourth order central signal moments associated with the amplified and filtered currents from two electrodes of an ex-core neutron sensitive fission detector were measured versus the reactor power of the 1-MW TRIGA reactor in Mexico City. Two channels of a high-speed (400-MHz) multiplexing data sampler and an analog-to-digital converter with 12-b resolution and 1-Mword buffer memory were used. The data were further retrieved into a PC, and estimates for autocorrelation and cross-correlation moments up to the fifth order, coherence, skewness, excess, etc., quantities were calculated offline. Five-mode operation of the detector was achieved, including conventional counting rates and currents in agreement with theory and the authors' previous results with analog techniques. The signals are proportional to the neutron flux and reactor power in some flux ranges. The suppression of background noise is improved and the lower limit of the measurement range is extended as the order of moment is increased, in agreement with theory

Use of niobium for accurate relative fast neutron fluence measurements at the pressure vessel in a VVER-440 NPP.

Proc. of the 5th ASTM-Euratom Symposium on Reactor Dosimetry, 1984

Experimental estimation of neutron doses for the surveillance chain 5K with Japanese and French steel specimens and check of the the neutron spectrum applied in the Loviisa 1 nuclear power plant, Technical Research Centre of Finland, Summary of report 1991 IAEA coordinated res programme (1992).

IAEA coordinated research programme Optimizing of reactor pressure vessel surveillance programmes and their analysis, 1991

Information theoretical aspects of power spectrum measurements in nuclear reactors

TKK-F-A102 Technical University of Helsinki, Department of Technical Physics, 1970

Experience from and research activities at the Otaniemi TRIGA reactor

5. European conference of TRIGA users Portoroz, 1978

Experiences from the TRIGA reactor in Finland Abstract

5. Euroean comference of TRIGA users Portoroz 1978, 1978

Experience from the Finnish 250 kW TRIGA reactor is reported. The maximum fuel elongation duri... more Experience from the Finnish 250 kW TRIGA reactor is reported. The maximum fuel elongation during 16 years operation is about 2.4 mm (B-ring) . No fuel damages have occurred (U-ZrH1.0, Al-clad). The instrumentation has partly been renewed and a possible renewal of the whole instrumentation is under consideration. The communication with other TRIGA laboratories reveals similar trends to upgrade or to completely replace elder instrumentation. In order to test a theoretical model, to obtain experience and parameters for optimization and for possible use of the mean square (or Campbell's technique) for reactor power measurements, a series of measurements were carried out. The present fission and compensated ionization chambers in the FiR-1 reactor were used. The influence of compensation voltage, filter frequency, reactor power etc.were investigated. The preliminary results and findings are reported. The occupational (whole body) dose-commitment to about 100 workers in the laboratory has been about 20 man.rem/year (includes about 60 per cent from background radiation). The average additional dose (above background) has been in the range 4...10 mrem/working month x person during the last years. The largest occupational whole body dose ever measured is 1.35 rem/ year and the largest dose for the thyroid 1.9 rem/event and about 5 rem from several events during a one year period. Small contaminations of I131, Po 210 (α: from Bi210), Sb122 and Sb124 have been detected and have required decontamination of some working areas, some irradiation facilities etc. The yearly radiation dose from Ar41 release (≤30 Ci/1300 h oper time) and to a person in the neighbourhood of the reactor was semi-empirically estimated to be at most about 100 μrem/year (dose commitment < 1 man.rem/year). The maximum thyroid dose from the largest I131 release (2 mCi/year) was estimated to about 100 μrem/year. (author)

MEASUREMENT OF Ar41 RELEASE FROM A TRIGA REACTOR

VTT Rea Summary report 2:19 1 page, 1977

MEASUREMENT OF Ar"! RELEASE FROM A TRIGA REACTOR

Summary report VTT 1 page 2:19, 1977

ON THE VARIETY AND HIERARCHY OF DATA EXTRACTION METHODS IN NUCLEAR REACTOR NOISE ANALYSIS

Nuclear Instruments and Methods, 1972

A review and systematic approach to the data extraction problem in nuclear reactor noise analysis... more A review and systematic approach to the data extraction problem in nuclear reactor noise analysis is presented. A large number of signal representations and data extraction methods are obtained by using expansions of the fundamental joint probability and related quantities into sets of observable quantities and by using natural classification criteria specifying the experimental conditions. Most previously used and suggested techniques are members 0f this set. A large number of alternate or modified techniques can be suggested some of which may be of practical interest. The hierarchy of representation given in this work also indicates that the application of information theory to noise problems may be a useful and powerful approach.

COMPARISON OF SOME GAMMA DETECTORS AND ENVIRONMENTAL MEASUREMENT OF SMALL Ar41 RELEASES FROM A TRIGA REACTOR

VTT Reactor laboratory Report 37, 1977

GM-detectors, liquid- and NaI(Tl)-scintillation detectors and semiconductor detectors were compar... more GM-detectors, liquid- and NaI(Tl)-scintillation detectors and semiconductor detectors were compared in order to measure small airborne Ar41 activity concentrations. A 12,5 cm x 12,5cm NaI(Tl)-scintillation detector was used to semiempirically estimate the the radiation exposure arising from airborne Ar41 release passing 5 meters (estimated) above the detector at a distance of 130 meters from a 250 kW Triga-reactor under downwind conditions. The height of the release point was 19m. The exposure was found to be 0.45 µR/h at an Ar41 release rate of 18 mCi/h (670 MBq/h) under downwind conditions and at wind speed of3 m/s. The mean annual exposure rate from 1300 hours reactor operation is of the order of 40...100 µR/y (+100 -50%) at this test point and at a release rate of 2.5...6 µCi/s. The maximum exposure at the ground level is at a distance of about 200 meters (ca 10 x height of chimney) and is of the order of 100 µR/y. At close distances from the point of release a line source model can be used to for the approximate estimation of the exposure.

COMPARISON OF SOME GAMMA DETECTORS AND ENVIRONMENTAL MEASUREMENT OF SMALL AR41 RELEASES FROM A TRIGA REACTOR

Technical research center of Finland VTT, 1977

GM-detectors, liquid- and NaI(Tl)-scintillation detectors and semiconductor detectors were compar... more GM-detectors, liquid- and NaI(Tl)-scintillation detectors and semiconductor detectors were compared in order to measure small airborne Ar41 activity concentrations. A 12,5 cm x 12,5cm NaI(Tl)-scintillation detector was used to semiempirically estimate the the radiation exposure arising from airborne Ar41 release passing 5 meters (estimated) above the detector at a distance of 130 meters from a 250 kW Triga-reactor under downwind conditions. The height of the release point was 19m. The exposure was found to be 0.45 µR/h at an Ar41 release rate of 18 mCi/h (670 MBq/h) under downwind conditions and at wind speed of3 m/s. The mean annual exposure rate from 1300 hours reactor operation is of the order of 40...100 µR/y (+100 -50%) at this test point and at a release rate of 2.5...6 µCi/s. The maximum exposure at the ground level is at a distance of about 200 meters (ca 10 x height of chimney) and is of the order of 100 µR/y. At close distances from the point of release a line source model can be used to for the approximate estimation of the exposure.

COMPARISON OF SOME GAMMA DETECTORS AND ENVIRONMENTAL MEASUREMENT OF SMALL 41Ar RELEASES FROM A TRIGA REACTOR

Nuclear Instruments and Methods 150 p.595, 1978

GM-detectors, liquid-(NE 110) and Nal(Tl)-scintillation detectors and semiconductor detectors wer... more GM-detectors, liquid-(NE 110) and Nal(Tl)-scintillation detectors and semiconductor detectors were compared in order to measure small airborne 241Ar activity concentrations. A dia 12.7 cm x h 12.7 cm Nal(Tl)-scint.. detector was used to semiempirically estimate the radiation exposure arising from airborne 41Ar release passing 5 m (estimated) above the detector at a distance of 130 m from a 250 kW Triga reactor. The height of the release point was 19 m. The exposure was found to be 0.45 uR/h at an 41Ar release rate of 18 mCi/h (670 MBq/h) under downwind conditions and at the most prevalent wind speed of 3 m/s.

Control rod calibrations in the FiR 1 reactor by the rod drop methods

Tech Univ of Helsinki Dept of Tech Physics Report 45 1967, 1967

Control röd calibrations on the TRIGA Mark II reactor FiR-1 utilizing rod-drop methods are report... more Control röd calibrations on the TRIGA Mark II reactor FiR-1 utilizing rod-drop methods are reported. Three known rod-drop methods are compared with each other. The method which considers the effects of prompt neutrons was found to be accurate, simple, reliable and rapid. The effect of the long dropping times are reduced by a simple extrapolation technique. The restrictions arising from the quasistationary condition in the theory are avoided by introducing a correction. Theory and experiments for several successive rod-drops are also presented. The rod-drop methods are compared with some other methods for reactivity measurements.

Om kärnreaktorers stokastiska kinetik ( in Swedish) 1965

Licentiat work Technical University of Helsinki, 1965

Noise Measurements in a Subcritical Facility Based on Photon Detection

Experiences with Nb Dosimeters for Neutron Flux Measurements

Stochastic Fluctuations in the Power Pulses of Triga Reactors

On the influence and use of gamma radiat

Acta Polytechnica Scandinavica. Physic including nucleonics series Ph 79, 1971

The influence and use of gamma radiation in reactor noise measurements is studied, based on a spa... more The influence and use of gamma radiation in reactor noise measurements is studied, based on a space-and energy-independent reactor and detector model. The approach is based on the forward Kolmogorov equation and is carried out in a consistent and unified way. The influence of the correlated and non-correlated photon radiation and

Variance or AC Technique in Nuclear Reactor Power Measurements

Kenenergie 26, 2 63-68, 1983

The theoretical foundations for the variance, AC or Campbell technique are given and reveal a nov... more The theoretical foundations for the variance, AC or Campbell technique are given and reveal a novel possibility to further suppress the influence of the background radiation. Some methods for the neutron flux measurements are compared. Variance measurements with a fission detector in the Finnish TRIGA type research reactor are reported and they verify the main features of the stochastic detector model.

Variance and higher order signal moments in neutron flux measurements

Nuclear Instruments and Methods in Physics Research 275(2) , 1989

Explicit expressions are derived for the second (also called variance or Campbell signal) and hig... more Explicit expressions are derived for the second (also called variance or Campbell signal) and higher order central moments of signals from a neutron detector in a nuclear fission reactor. The signal is treated as a compound distribution, which is composed of detection rates of different types of events with fluctuating pulse amplitudes and with arbitrary pulse shapes. The technique with probability generating functions (pgf) is applied. The present results provide an extended theoretical basis for the utilization of different signal moments for flux monitoring in nuclear fission reactors.

Use of Higher Order Signal Moments and High Speed Digital Sampling Technique for Neutron Flux Measurements

IEEE Transactions on Nuclear Energy 40 no 4 p 832-839, 1993

The second (conventional variance or Campbell signal), the third, and the modified fourth order c... more The second (conventional variance or Campbell signal), the third, and the modified fourth order central signal moments associated with the amplified and filtered currents from two electrodes of an ex-core neutron sensitive fission detector were measured versus the reactor power of the 1-MW TRIGA reactor in Mexico City. Two channels of a high-speed (400-MHz) multiplexing data sampler and an analog-to-digital converter with 12-b resolution and 1-Mword buffer memory were used. The data were further retrieved into a PC, and estimates for autocorrelation and cross-correlation moments up to the fifth order, coherence, skewness, excess, etc., quantities were calculated offline. Five-mode operation of the detector was achieved, including conventional counting rates and currents in agreement with theory and the authors' previous results with analog techniques. The signals are proportional to the neutron flux and reactor power in some flux ranges. The suppression of background noise is improved and the lower limit of the measurement range is extended as the order of moment is increased, in agreement with theory

Use of niobium for accurate relative fast neutron fluence measurements at the pressure vessel in a VVER-440 NPP.

Proc. of the 5th ASTM-Euratom Symposium on Reactor Dosimetry, 1984

Experimental estimation of neutron doses for the surveillance chain 5K with Japanese and French steel specimens and check of the the neutron spectrum applied in the Loviisa 1 nuclear power plant, Technical Research Centre of Finland, Summary of report 1991 IAEA coordinated res programme (1992).

IAEA coordinated research programme Optimizing of reactor pressure vessel surveillance programmes and their analysis, 1991

Information theoretical aspects of power spectrum measurements in nuclear reactors

TKK-F-A102 Technical University of Helsinki, Department of Technical Physics, 1970

Experience from and research activities at the Otaniemi TRIGA reactor 40030691.pdf

European TRIGA Users Conference, 1977

A digital reactivity meter for nuclear fission reactors