Measurements campaign carried out during an evacuation of irradiated fuel assemblies of a nuclear power plant
European IRPA congress, Florence, 8-11 October 2002
T. LAHAYE*, P. HARTMANN**, P. ALEXANDRE*, T. BOLOGNESE-MILSZTAJN*, D. BUCHDAHL***, D. CUTARELLA*, Y. GUIBBAUD**, C. ITIÉ*, S. MÉNARD*, H. MULLER*, J.L. POCHAT*, C. TEXIER* and L.VAN-RYCKEGHEM*
In recent years, the following main factors have contributed to increase the doses of the workers exposed to neutrons:
- the use of fuel with mixed oxides of uranium and plutonium (MOX) in 900 MWe reactors;
- the increase of the combustion rates (> 35000 MWj / t);
- the intensification of the contamination controls of transport casks;
- the application of the new recommendation of the ICRP 60.
To take into account these factors, the French Institute for Radiological Protection and Nuclear Safety, IRSN (Institut de Radioprotection et de Sûreté Nucléaire) led a research programme in the field of neutron dosimetry. Within the framework of the process initiated by the French national electricity produces, EDF (Electricité de France) for the radioprotection optimisation of the workers, IRSN carried out a campaign of measurements during the evacuation of a fuel transport cask at the EDF power plant Dampierre-en-Burly (4 x 900 MWe) in July 2000. During this campaign, IRSN carried out a large program of measurements including the following actions:
- tests of the prototype validation of an individual electronic neutron dosimeter (Saphydose-n) now on the market;
- characterization of neutron radiation fields at different workplaces. Measurements are realised with spectrometry Bonner Sphere System (BSS) at 17 locations around the transport cask (the groundwork) pit of the fuel building and on the transport truck;
- response study of individual bubble neutron dosimeter and of several industrial neutron ratemeters (Harwell, Berthold, Cramal 21);
- determination of photon dose rates starting from the average readings of several industrial ratemeters (Scintomat, Befic, Babyline).
The main results of the measurement campaign are:
- ratemeter responses are dispersed when compared to the reference value (based on spectrometry);
- response of the neutron electronic dosimeter prototype “Saphydose-n” complying with the reference system;
- over response of the bubble neutron dosimeter when compared to the reference value;
- this work shows that bubble neutron dosimetrers over estimate the dose rate in such working conditions. Previous European work concluded that their responses are very dependant on the conditions in the workplace.
*Institut de Radioprotection et de Sûreté Nucléaire, Département de Protection de la santé de l’Homme et de Dosimétrie, Service de DOSimétrie, Laboratoire d’études et de Recherches en Dosimétrie Externe, B.P.17, 92265 Fontenay aux Roses
**Electricité de France, Division Production Nucléaire, Site de Cap Ampère,1 place Pleyel, 93282 Saint-Denis
***Electricité de France, Division R & D, Département OPP, 6 quai Watier, 78401 Chatou