Neutron measurements around a TN85-type storage cask with high-active waste

Several types of casks have been deposited in the German interim storage facility for spent fuel assemblies and vitrified high-active waste (HAW) at Gorleben since 1995, most of them of the CASTOR (R) type. In 2008 a delivery of 11 TN85-type casks arrived. They belong to the Transnuclear/Areva cask family and, compared to the flasks of the German (GNS) CASTOR (R) type, they differ in the neutron shielding design. Generally, radiation exposure of personnel during transportation and storage of casks containing spent fuel and vitrified waste is caused by mixed photon/neutron fields. Frequently, especially at casks for vitrified waste from reprocessing, neutrons are the major component of radiation exposure. Spectrometric and dosimetric investigations were made around a cask of the TN85-type. Neutron fluence spectra and reference values of the ambient dose equivalent H*(10) were measured by means of a Bonner sphere spectrometer (BSS) at several locations on the cask surface and in its environment. Moreover, commercial area dosemeters, LB6411 neutron monitors and conventional AD 6-type photon dosemeters were used. In addition, the responses of two electronic personal dosemeters for mixed fields (EPD-N2, DMC 2000GN) and a TLD albedo dosemeter were investigated. The neutron spectra obtained from the BSS are presented and compared with former measurements at CASTOR (R) type casks. The relative responses of the LB6411 survey meter and the individual dosemeters are discussed. The LB6411 monitor indicates H*(10) around the TN85 cask with tolerable measuring uncertainties. The personal dosemeters provide acceptable results for photons but overestimate the neutron dose considerably. (c) 2010 Elsevier Ltd. All rights reserved.