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, 25-27 June 2008 Fortum Antti Ketolainen 25.6.2008

Table of contents Introduction SEKUN computer code Dose rate measurements Results Conclusions Fortum Antti Ketolainen 25.6.2008

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 25.6.2008

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 25.6.2008

SEKUN node model Fortum Antti Ketolainen 25.6.2008

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 25.6.2008

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 25.6.2008

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: 100 000 - 1*1010 kBq/m3 Fortum Antti Ketolainen 25.6.2008

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 25.6.2008

Calculation Different operational conditions and primary-to-secondary coolant leaks were modelled with APROS 5.04 simulation software Fortum Antti Ketolainen 25.6.2008

Results 0,5 kg/s leakage in power operation Primary (TV04) and secondary (RY) coolant's radiation dose measurements Fortum Antti Ketolainen 25.6.2008

Results 0,5 kg/s leakage in power operation Radiation dose measurements at the secondary circuit steam side (RA-911) Fortum Antti Ketolainen 25.6.2008

Results 0,5 kg/s leakage in hot standby Primary (TV04) and secondary (RY) coolant's radiation dose measurements Fortum Antti Ketolainen 25.6.2008

Results 0,5 kg/s leakage in hot standby Radiation dose measurements at the secondary circuit steam side (RA-911) Fortum Antti Ketolainen 25.6.2008

Conclusions Secondary coolant's radiation dose measurement (RY) in power operation Fortum Antti Ketolainen 25.6.2008

Conclusions Secondary coolant's radiation dose measurement (RY) in hot standby Fortum Antti Ketolainen 25.6.2008

Conclusions Radiation dose measurements at the secondary circuit steam side (RA-911) in power operation Fortum Antti Ketolainen 25.6.2008

Conclusions Radiation dose measurements at the secondary circuit steam side (RA-911) in hot standby Fortum Antti Ketolainen 25.6.2008

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 25.6.2008

Thank You!!! Antti Ketolainen Design engineer FNS Ltd. anttiv.ketolainen@fortum.com +358 40 751 8956 Fortum Antti Ketolainen 25.6.2008