Accident Testing of High Temperature Reactor Fuel Elements with the KüFA Device

The High Temperature Reactor (HTR) is characterised by an advanced design with passive safety features. Fuel elements are constituted by a graphite matrix containing sub-mm-sized fuel particles with TRi-ISOtropic (TRISO) coating, designed to provide high fission product retention. During a loss of coolant accident scenario in a HTR the maximum temperature is foreseen to be in the range of 1600-1650 °C, remaining well below the melting point of the fuel. The Cold Finger Apparatus (KüFA) is used to observe the combined effects of Depressurization and LOss of Forced Circulation (DLOFC) accident scenarios on HTR fuel. Originally designed at the ForschungsZentrum Jülich (FZJ), an adapted KüFA operates on irradiated fuel in hot cell at JRC-ITU. A fuel pebble is heated in He atmosphere for several hundred hours, mimicking accident temperatures up to 1800°C and realistic temperature transients. Nongaseous volatile fission products released from the fuel condense on a water cooled stainless steel plate dubbed "Cold Finger". Exchanging plates frequently during the experiment and analysing plate deposits by means of HPGe gamma spectroscopy allows a reconstruction of the fission product release as a function of time and temperature. In order to achieve a good quantification of the release, a careful calibration of the setup is mandatory. An especially tailored collimator was designed to perform plate scanning with high spatial resolution, thus yielding information about the fission product distribution on the condensation plates. The analysis of condensation plates from recent KüFA tests shows that fission product release quantification is possible at high and low activity levels. Chemical dissolution has been performed for some condensation plates in order to assess beta nuclides of interest such as 90Sr and possibly 129I using an Inductively Coupled Plasma – Mass Spectrometer (ICP-MS) and to cross check the HPGe gamma spectroscopy measurements. First results show consistency for the obtained Cs data.

SEEGER Oliver;  LAURIE Mathias;  BOTTOMLEY Paul;  FERREIRA TEIXEIRA Antonio;  VAN WINCKEL Stefaan;  RONDINELLA Vincenzo;  ALLELEIN H.J.; 

2016-03-04

IEEE

JRC84795

978-1-4799-1046-5,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC84795,   

10.1109/ANIMMA.2013.6728004,