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A study on Loviisa NPP (VVER-440) dose rate measurement's ability to detect small primary-to-secondary coolant leaks A. Ketolainen ISOE European Symposium on Occupational exposure management at nuclear facilities Turku, Finland, June 2008 Fortum Antti Ketolainen
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Table of contents Introduction SEKUN computer code
Dose rate measurements Results Conclusions Fortum Antti Ketolainen
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Introduction At Loviisa NPP coolant leaks will be detected on the basis of different parameters Low liquid level of pressurizer or high liquid level of steam generator can indicate primary-to-secondary coolant leaks Different kinds of coolant leak incidents and accidents has specified operating procedures which will be executed when certain operating limits will be exceeded Primary-to-secondary coolant leak will raise activity at the secondary circuit Small primary-to-secondary coolant leaks can be distinguished from the other coolant accident -transients by the information of the dose rate measurements Fortum Antti Ketolainen
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SEKUN computer code 1989 documented FORTRAN code (H. Wallin's licentiate thesis: "Computer-based calculation model for radiation doses caused by reactor accidents") developed to calculate radiation doses and activity releases to the power plant's environment at primary-to-secondary coolant leak transients Primary circuit: 1 calculation node Secondary circuit: 5 calculation nodes 2 steam generators, 4 nodes (steam and liquid sides) damaged steam generator with supposed coolant leak one steam generator for all other steam generators 1 node for feed water in the tank and condenser Fortum Antti Ketolainen
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SEKUN node model Fortum Antti Ketolainen
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SEKUN Input data = f(time) Thermohydraulic rates (APROS)
Nuclide specific activity concentrations of the primary and secondary coolants Dose rate measurements were programmed to the code during the project The SEKUN calculates activity concentrations for every node Monitored dose rates in the primary and the secondary circuits are estimated on the bases of the calculated activities Fortum Antti Ketolainen
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Dose rate measurements
Secondary coolant's radiation dose measurement in blowdown systems of steam generators (RY) 1,25"x1" NaI-scintillator,energy window: 0,15 - 2,2 MeV Radiation dose measurement of the secondary circuits steam side (RA): RA-911 NaI-scintillation detectors, 0,2 - 2,2 MeV (noble gas) Also dose rate measurement for higher gamma energies (RAxxR921) (not included in this presentation) Fortum Antti Ketolainen
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Dose rate measurements
Interpretation of the secondary coolant's measuring results requires information about specific activities in the primary circuit Primary coolant's radiation dose measurement (TV04) 1"x0,5" NaI-scintillator, 0,15 - 2,2 MeV measuring range: *1010 kBq/m3 Fortum Antti Ketolainen
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The basic idea of the study
Thermohydraulic simulations: APROS 5.04 Activity calculations: SEKUN 2 kg/h is the maximum allowed leak (power plant's specifications) before the actual leak was used as a starting hypothesis Fortum Antti Ketolainen
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Calculation Different operational conditions and primary-to-secondary coolant leaks were modelled with APROS 5.04 simulation software Fortum Antti Ketolainen
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Results 0,5 kg/s leakage in power operation
Primary (TV04) and secondary (RY) coolant's radiation dose measurements Fortum Antti Ketolainen
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Results 0,5 kg/s leakage in power operation
Radiation dose measurements at the secondary circuit steam side (RA-911) Fortum Antti Ketolainen
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Results 0,5 kg/s leakage in hot standby
Primary (TV04) and secondary (RY) coolant's radiation dose measurements Fortum Antti Ketolainen
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Results 0,5 kg/s leakage in hot standby
Radiation dose measurements at the secondary circuit steam side (RA-911) Fortum Antti Ketolainen
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Conclusions Secondary coolant's radiation dose measurement (RY) in power operation Fortum Antti Ketolainen
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Conclusions Secondary coolant's radiation dose measurement (RY) in hot standby Fortum Antti Ketolainen
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Conclusions Radiation dose measurements at the secondary circuit steam side (RA-911) in power operation Fortum Antti Ketolainen
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Conclusions Radiation dose measurements at the secondary circuit steam side (RA-911) in hot standby Fortum Antti Ketolainen
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Conclusions > 0,5 kg/s primary-to-secondary coolant leaks can be identified with dose rate measurements Information of the primary circuit's activity is also required for identification of primary-to-secondary leak Activity concentrations which have been identification limits for primary-to-secondary coolant leaks were correct Better protection from the background radiation for RA meters would make easier the identification of leak Fortum Antti Ketolainen
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Thank You!!! Antti Ketolainen Design engineer FNS Ltd.
Fortum Antti Ketolainen
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