Time stamped list mode data from gamma-ray spectroscopic measurements on 47 nuclear fuel assemblies performed at Clab, Sweden, September 2016 through March 2019

Using a high-purity Germanium gamma-ray energy spectroscopic detector system, time-stamped list-mode data sets were acquired during axial scanning of 19 boiling water reactor (BWR) and 28 pressurized water reactor (PWR) type of nuclear fuel assemblies. The data sets were collected during two measurements campaigns in September 2016 and March 2019 at the Central Interim Storage Facility for Spent Nuclear (Clab) in Sweden. A certified calibration source of 137Cs was positioned along the central line of sight between the measured fuel assembly and the detector. Data sets from measurements with only the calibration source and other background sources, i.e. without a nuclear fuel assembly present, are also included. The list-mode structure of the measured data allows for an axially-resolved as well as energy-spectral resolved intensity of nuclide-specific gamma lines emitted from the spent nuclear fuel. Data presented here can be used e.g. for validation of gamma-ray transport simulation tools or for development of methods to estimate parameters of the spent nuclear fuel based on data from gamma-ray spectroscopy.


a b s t r a c t
Using a high-purity Germanium gamma-ray energy spectroscopic detector system, time-stamped list-mode data sets were acquired during axial scanning of 19 boiling water reactor (BWR) and 28 pressurized water reactor (PWR) type of nuclear fuel assemblies. The data sets were collected during two measurements campaigns in September 2016 and March 2019 at the Central Interim Storage Facility for Spent Nuclear (Clab) in Sweden. A certified calibration source of 137 Cs was positioned along the central line of sight between the measured fuel assembly and the detector. Data sets from measurements with only the calibration source and other background sources, i.e. without a nuclear fuel assembly present, are also included. The list-mode structure of the measured data allows for an axiallyresolved as well as energy-spectral resolved intensity of nuclidespecific gamma lines emitted from the spent nuclear fuel. Data presented here can be used e.g. for validation of gamma-ray transport simulation tools or for development of methods to estimate parameters of the spent nuclear fuel based on data from gamma-ray spectroscopy. Table   Subject Nuclear Energy and Engineering Specific subject area High-level radioactive waste management Type of data Table  How data were acquired Measurements were performed using a high-purity Germanium (HPGe) detector of model GX4018 from Canberra Industries with a relative efficiency of 40%, equipped with cryostat model CP5-Plus-SL and preamplifier model 2002CSL. Time-stamped list-mode data were acquired from the detector using Lynx from Canberra Industries. All data were acquired while a certified 137 Cs calibration source was positioned along the line of sight of the detector. The 137 Cs calibration source number AH-6333 of type CDR8252 was certified by Eckert and Ziegler Nuclitec Gmbh, Germany, to have an activity of 3.73 MBq on 1 June 2016 at 12:00 UTC, with a three percent (two-sigma) relative uncertainty.

Data format
Raw Parameters for data collection Trapezoidal shaping of detector pulses from the detector was performed by the Lynx device using a rise time of 2.8 μs and a flat top of 0.6 μs.

Description of data collection
Data were collected by saving list-mode detector data during acquisitions. Two types of measurements were performed; Measurements with nuclear fuel assemblies present and background measurements without the fuel assemblies. Background measurements were performed in sequences of about 10 min acquisitions. The fuel assemblies were positioned in the water pool and axially moved during acquisition in front of a collimator built into the pool wall, rotated so that one of its four corners points towards the detector. The 137 Cs calibration source was positioned along the centre line of the collimator slit both during background and fuel measurements. The detector and associated electronics were located in a room adjacent to the pool.

Data source location
Institution Value of the Data • Open access to raw gamma spectroscopic data from measurements on spent nuclear fuel enable independent review of analysis performed in the context of high-level radioactive waste management. • Developers of methodologies for characterizing and safeguarding spent nuclear fuel and developers of gamma-ray transport simulation codes can benefit from getting access to this data. • The multi-variate structures in the data can be used to research properties of spent nuclear fuel and to design specialized experiments and/or measurement setups that are customized to specific situations e.g., to gain insight into what is required from a measurement system to be used in the context of transport, storage, encapsulation and disposal of spent nuclear fuel.

Data description
Measurement data is saved in a text format. All text files with measurement data are saved together in a gzip compressed tar archive, available from the linked repository. The text format is structured as a measurement header , followed by a sequence of one or more meta-batches . Each meta-batch is structured as a sequence of one or more event data batches . Each event data batch is structured as an event batch header , followed by one or more event data lines and an event batch footer . Table 1 shows an example of a data file together with a description of its structure. Table 1 Example of measurement data, displaying the structure of the measurement text file. Some lines were removed for brevity, indicated by "/…/". The measurement header contains three rows of information; 1) The acquisition start date and time in UTC. 2) The structure of the event data lines in the later event data batches.
3) The number of meta-event data batches.
The rest of the files contains one or more meta-batches where each meta-batch contains one or more event data batches. Each meta-batch begins with one row of information specifying how many event data batches it contains. All event data batches in the meta-batch follows after the first row of meta-batch information. Table 2 Parameters of measured fuel assemblies. The use of the terms "FuelType 1 , "Fuel Type 2 , …, indicate if the fuel assembly was constructed by the same or different commercial vendors. BU = Burnup, IE = Initial enrichment of 235 U (weight percent in U). Loading and discharge date refers to the dates when the fuel assembly was loaded and discharged from the reactor. The column "# Cycles" displays the number of irradiation cycles during reactor operation. ( * ) indicates that the information was unknown. ( * * ) indicates that the fuel assembly was reconstructed after discharge from the reactor. Fuel assemblies identified by BWRnn, PWRnn and BTnn are the same as those measured in references [1][2][3]  Each event data batch begins with a row of the information specifying the live time of the data acquisition system when the batch begins. Then follows the actual list mode data for all events in the event data batch. Each event data row contains two comma-separated integer values; The real time since the start of acquisition and pulse height of the event. The last row of each event data batch specify how many events that were contained in the batch, i.e. how many event data rows already printed before the last row of the event. Table 3 Information about all background data measurements. The note indicate that a certain width of lead and copper plates were positioned between the detector and the collimator in order to reduce low-energy background radiation hitting the detector. The filename column displays the name of the measurement file within the compressed data archive. All rows of meta-information are prefixed with a hashtag character ('#') to indicate that they are not event data rows.
Sequential background measurements are grouped into one text file with each group following the above structure. The background measurements' file name begins with "background" and contain the start time of the first acquisition contained in the file.
Data from each axial measurement scan of a fuel assembly is saved separately in a text file, structured as described above. The name of the file for fuel assembly measurements begins with the identification of fuel assembly, followed by the acquisition start date and time and ends with information on which corner of the assembly that was measured. Table 2 displays parameters of the measured fuel assemblies. Table 3 displays information about the background measurements performed. Table 4 displays information about all fuel assembly measurements performed, including acquisition start date and time for each measurement and an association to the fuel assemblies in Table 2 and background in Table 3 . Measurements of fuel assemblies used the same lead and copper attenuation plates as those used in the associated background measurement.

Experimental design, materials and methods
The measurement system used for performing the measurements is described in more detail in references [ 1 , 2 ]. In summary, the spent nuclear fuel is placed in a fixture in the pool allowing it to be scanned axially, and rotated along its axis, in front of a conical horizontal collimator slit situated in the pool wall in front of the detector. A certified calibration source of 137 Cs is placed in a fixed position on the central line of sight in the collimator slit at the edge of the collimator slit at its end pointing towards the pool, way from the detector.
The fuel assembly to be measured was rotated so that one of its four corners faced the collimator and detector and the fuel assembly was then scanned axially up and down in front of the detector. Data was acquired during a time period that began before the up-going fuel assembly was in the field-of-view of the collimator and lasted until it has passed the field-of-view on its way down, i.e. each measurement file for a scan contains data from a fuel assembly going up and then going down in front of the detector. Typically, such an up-down axial scan took about 10 min. This procedure was repeated for other corners of the fuel assembly. Note that the 137 Cs source was present also during these scans, thus requiring counts from the calibration source to be subtracted from the 137 Cs peak in the energy spectrum from the fuel assembly.
Background measurements were performed without the fuel placed in its fixture. These measurements allows for quantifying the count rate both from the 137 Cs source and from other background sources, e.g. naturally occurring radiation from the concrete walls of the measurement room in which the detector was placed. Such background data sets were acquired on several occasions between measurements on fuel assemblies. Table 4 Information about all nuclear fuel measurements. The background and nuclear fuel identification corresponds to the identification used in tables 3 and 2 , respectively. The corner number indicate which of the four corners of the fuel assembly that was facing the detector during the axial scan. The filename column displays the name of the measurement file within the compressed data archive.