Calculating neutron dosimeter activation in VVER-440 surveillance chains with Serpent

Tuomas Viitanen, Jaakko Leppänen

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

Abstract

The structural integrity of reactor pressure vessels (RPVs) can be studied by preparing test specimens from the RPV material, irradiating the specimens in the surveillance position or positions at the reactor periphery and measuring the material properties of the irradiated samples. To match the measurements of the test specimens to the state of the reactor pressure vessel at a certain moment of time, the neutron exposure of the irradiated test specimens as well as the reactor pressure vessel need to be determined. The exposure, more precisely the neutron fluence, is usually calculated using either deterministic or Monte Carlo calculation codes. Accuracy of the computational estimates can be increased by means of neutron dosimetry, i.e. by normalizing or adjusting the computational results to match the measured activation of neutron dosimeters. For this reason, also the surveillance specimens of Loviisa-1 and Loviisa-2 VVER-440 units are always irradiated together with several neutron dosimeters: The axial profile in the neutron fluence is monitored using Fe/Ni dosimeter discs, in addition to which the fluence spectrum is measured using separate wire dosimeters. In the current work, the measured activities from neutron dosimeters irradiated in the surveillance position of Loviisa-1 unit are used to validate Monte Carlo reactor physics code Serpent for calculations at the reactor periphery, for example surveillance position or RPV. The neutron source in the Serpent calculation is generated based on a full-core power distribution from simulator code HEXBU-3D, and Serpent is only used to calculate the neutron transport from the source points in the reactor core to detector locations. Since the neutron flux decreases by orders of magnitude between the reactor core and the locations of interest, the convergence of the Monte Carlo transport solution needs to be accelerated using new weight-window based variance reduction techniques of Serpent 2.1.27.
Original languageEnglish
Title of host publication26th Symposium of AER on VVER Reactor Physics and Reactor Safety
Subtitle of host publicationBook of Abstracts
Pages181-188
Publication statusPublished - 2016
MoE publication typeB3 Non-refereed article in conference proceedings
Event26th Symposium of AER on VVER Reactor Physics and Reactor Safety - Helsinki, Finland
Duration: 10 Oct 201614 Oct 2016

Conference

Conference26th Symposium of AER on VVER Reactor Physics and Reactor Safety
CountryFinland
CityHelsinki
Period10/10/1614/10/16

Fingerprint

surveillance
dosimeters
pressure vessels
activation
reactors
neutrons
reactor cores
fluence
reactor physics
normalizing
neutron sources
flux (rate)
integrity
point sources
simulators
adjusting
wire
moments
detectors
estimates

Keywords

  • neutron dosimeter activation
  • VVER-440
  • WWER-440
  • Serpent
  • Loviisa
  • Monte Carlo
  • variance reduction technique

Cite this

Viitanen, T., & Leppänen, J. (2016). Calculating neutron dosimeter activation in VVER-440 surveillance chains with Serpent. In 26th Symposium of AER on VVER Reactor Physics and Reactor Safety : Book of Abstracts (pp. 181-188)
Viitanen, Tuomas ; Leppänen, Jaakko. / Calculating neutron dosimeter activation in VVER-440 surveillance chains with Serpent. 26th Symposium of AER on VVER Reactor Physics and Reactor Safety : Book of Abstracts. 2016. pp. 181-188
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Viitanen, T & Leppänen, J 2016, Calculating neutron dosimeter activation in VVER-440 surveillance chains with Serpent. in 26th Symposium of AER on VVER Reactor Physics and Reactor Safety : Book of Abstracts. pp. 181-188, 26th Symposium of AER on VVER Reactor Physics and Reactor Safety, Helsinki, Finland, 10/10/16.

Calculating neutron dosimeter activation in VVER-440 surveillance chains with Serpent. / Viitanen, Tuomas; Leppänen, Jaakko.

26th Symposium of AER on VVER Reactor Physics and Reactor Safety : Book of Abstracts. 2016. p. 181-188.

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

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T1 - Calculating neutron dosimeter activation in VVER-440 surveillance chains with Serpent

AU - Viitanen, Tuomas

AU - Leppänen, Jaakko

PY - 2016

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N2 - The structural integrity of reactor pressure vessels (RPVs) can be studied by preparing test specimens from the RPV material, irradiating the specimens in the surveillance position or positions at the reactor periphery and measuring the material properties of the irradiated samples. To match the measurements of the test specimens to the state of the reactor pressure vessel at a certain moment of time, the neutron exposure of the irradiated test specimens as well as the reactor pressure vessel need to be determined. The exposure, more precisely the neutron fluence, is usually calculated using either deterministic or Monte Carlo calculation codes. Accuracy of the computational estimates can be increased by means of neutron dosimetry, i.e. by normalizing or adjusting the computational results to match the measured activation of neutron dosimeters. For this reason, also the surveillance specimens of Loviisa-1 and Loviisa-2 VVER-440 units are always irradiated together with several neutron dosimeters: The axial profile in the neutron fluence is monitored using Fe/Ni dosimeter discs, in addition to which the fluence spectrum is measured using separate wire dosimeters. In the current work, the measured activities from neutron dosimeters irradiated in the surveillance position of Loviisa-1 unit are used to validate Monte Carlo reactor physics code Serpent for calculations at the reactor periphery, for example surveillance position or RPV. The neutron source in the Serpent calculation is generated based on a full-core power distribution from simulator code HEXBU-3D, and Serpent is only used to calculate the neutron transport from the source points in the reactor core to detector locations. Since the neutron flux decreases by orders of magnitude between the reactor core and the locations of interest, the convergence of the Monte Carlo transport solution needs to be accelerated using new weight-window based variance reduction techniques of Serpent 2.1.27.

AB - The structural integrity of reactor pressure vessels (RPVs) can be studied by preparing test specimens from the RPV material, irradiating the specimens in the surveillance position or positions at the reactor periphery and measuring the material properties of the irradiated samples. To match the measurements of the test specimens to the state of the reactor pressure vessel at a certain moment of time, the neutron exposure of the irradiated test specimens as well as the reactor pressure vessel need to be determined. The exposure, more precisely the neutron fluence, is usually calculated using either deterministic or Monte Carlo calculation codes. Accuracy of the computational estimates can be increased by means of neutron dosimetry, i.e. by normalizing or adjusting the computational results to match the measured activation of neutron dosimeters. For this reason, also the surveillance specimens of Loviisa-1 and Loviisa-2 VVER-440 units are always irradiated together with several neutron dosimeters: The axial profile in the neutron fluence is monitored using Fe/Ni dosimeter discs, in addition to which the fluence spectrum is measured using separate wire dosimeters. In the current work, the measured activities from neutron dosimeters irradiated in the surveillance position of Loviisa-1 unit are used to validate Monte Carlo reactor physics code Serpent for calculations at the reactor periphery, for example surveillance position or RPV. The neutron source in the Serpent calculation is generated based on a full-core power distribution from simulator code HEXBU-3D, and Serpent is only used to calculate the neutron transport from the source points in the reactor core to detector locations. Since the neutron flux decreases by orders of magnitude between the reactor core and the locations of interest, the convergence of the Monte Carlo transport solution needs to be accelerated using new weight-window based variance reduction techniques of Serpent 2.1.27.

KW - neutron dosimeter activation

KW - VVER-440

KW - WWER-440

KW - Serpent

KW - Loviisa

KW - Monte Carlo

KW - variance reduction technique

M3 - Conference article in proceedings

SN - 978-963-7351-26-6

SP - 181

EP - 188

BT - 26th Symposium of AER on VVER Reactor Physics and Reactor Safety

ER -

Viitanen T, Leppänen J. Calculating neutron dosimeter activation in VVER-440 surveillance chains with Serpent. In 26th Symposium of AER on VVER Reactor Physics and Reactor Safety : Book of Abstracts. 2016. p. 181-188