Andrea Querol

Indoor radon measurements in the city of Valencia

The indoor radon risk in Valencia (Spain) was studied more than twenty years ago in two surveys using different methodologies and leading to contradictory results. We report here on new indoor radon measurements with the charcoal canister technique, which confirm the low average level of indoor radon in the city, with a geometrical mean of 24 Bq/m(3) and an arithmetic mean of 27 Bq/m(3).

Break Size Effects on CET Response in an Upper Head SBLOCA Transient

In the transients produced during Small Break Loss-Of-Coolant Accidents (SBLOCA), the maximum Peak Cladding Temperature (PCT) in the core could suffer rapid excursions which might strongly affect the core integrity. Most Pressurized Water Reactors (PWR) have Core Exit Thermocouples (CETs) to detect core overheating by considering that superheated steam flows in the upward direction when core uncovery occurs during SBLOCAs. Operators may start Accident Management (AM) actions to mitigate such accident conditions when the CET temperature exceeds a certain value. However, in a Vessel Upper Head SBLOCA, a significant delay in time and temperature rise of CETs from core heat-up can be produced.This work is developed in the frame of OECD/NEA ROSA Project Test 6-1 (SB-PV-9 in JAEA) handled in the Large Scale Test Facility (LSTF) of the Japan Atomic Energy Agency (JAEA). Test 6-1 simulated a PWR pressure vessel Upper-Head SBLOCA with a break size equivalent to 1.9% of the cold leg break under the assumption of total failure of High Pressure Injection System (HPIS).The paper shows several analyses about the geometry variables (size, location, flow paths and Upper Head nodalization) which can influence on the pressure vessel Upper Head SBLOCA model performed using the thermal-hydraulic code TRACE5.© 2012 ASME

X-ray simulation with the Monte Carlo code PENELOPE. Application to Quality Control

A realistic knowledge of the energy spectrum is very important in Quality Control (QC) of X-ray tubes in order to reduce dose to patients. However, due to the implicit difficulties to measure the X-ray spectrum accurately, it is not normally obtained in routine QC. Instead, some parameters are measured and/or calculated. PENELOPE and MCNP5 codes, based on the Monte Carlo method, can be used as complementary tools to verify parameters measured in QC. These codes allow estimating Bremsstrahlung and characteristic lines from the anode taking into account specific characteristics of equipment. They have been applied to simulate an X-ray spectrum. Results are compared with theoretical IPEM 78 spectrum. A sensitivity analysis has been developed to estimate the influence on simulated spectra of important parameters used in simulation codes. With this analysis it has been obtained that the FORCE factor is the most important parameter in PENELOPE simulations. FORCE factor, which is a variance reduction method, improves the simulation but produces hard increases of computer time. The value of FORCE should be optimized so that a good agreement of simulated and theoretical spectra is reached, but with a reduction of computer time. Quality parameters such as Half Value Layer (HVL) can be obtained with the PENELOPE model developed, but FORCE takes such a high value that computer time is hardly increased. On the other hand, depth dose assessment can be achieved with acceptable results for small values of FORCE.

Uncertainty analysis in the simulation of X-ray spectra in the diagnostic range using the MCNP5 code

An accurate knowledge of the photonic spectra emitted by X-ray tubes in radiodiagnostics is essential to better estimate the imparted dose to patients and to improve the image quality obtained with these devices. In this work, several X-ray spectra have been simulated using the MCNP5 code to simulate X-ray production in a commercial device. To validate the Monte Carlo results, simulated spectra have been compared to those extracted from the IPEM 78 database. The uncertainty associated to some geometrical features of the tube and its effect on the simulated spectra has been analyzed using the Noether-Wilks formula. This analysis has been focused on the thickness of collimators, filters, shielding and barrel shutter. Furthermore, results show that the uncertainty due to geometrical parameters (0.98% in terms of Root Mean Squared) is higher than the statistical uncertainty associated to the MCNP5 calculations.

Application of Tikhonov and MTSVD methods to unfold experimental X-ray spectra in the radiodiagnostic energy range

A thorough knowledge of the primary spectrum is very important for Quality Control (QC) of X-ray tubes. A methodology to assess primary spectrum using a Compton spectrometer has been simulated with the MCNP5 code based on the Monte Carlo (MC) method. The Pulse Height Distribution (PHD) recorded in the detector is related with the primary X-ray spectrum by means of a Response matrix. Tikhonov and Modified Truncated Singular Values Decomposition (MTSVD) unfolding methods have been applied to the Response matrix to assess the primary spectrum. Both methods are tested comparing unfolded results with theoretical spectra from IPEM-78 catalogue.

Assessment of quality control parameters for an X-ray tube using the monte carlo method and unfolding techniques

Quality Control (QC) parameters for an X-ray tube such as Half Value Layer (HVL), homogeneity factor and mean photon energy, can be obtained from the primary beam spectrum. A direct Monte Carlo (MC) simulation has been used to obtain this spectrum. Indirect spectrometry procedures such as Compton scattering have been also experimentally utilized since direct spectrometry causes a pile-up effect in detectors. As well the Compton spectrometry has been simulated with the MC method. In both cases unfolding techniques shall be applied to obtain the primary spectrum. Two unfolding methods (TSVD and Spectro-X) have been analyzed. Results are compared each other and with reference values taken from IPEM Report 78 catalogue. Direct MC simulation is a good approximation to obtain the primary spectrum and hence the QC parameters. TSVD is a better unfolding method for the scattered spectrum than the Spectro-X code. An improvement of the methodology to obtain QC parameters is important in Biomedical Engineering (BME) applications due to the wide use of X-ray tubes.

Analysis of the Core Exit Temperature and the Peak Cladding Temperature During a SBLOCA: Application to a Scaled-Up Model

The authors are grateful to the Management Board of the OECD-NEA ROSA Project; thus, this work contains findings produced within this project. This work is partially supported by the Grant-in-Aid for Scientific Research of the Spanish Ministerio de Educacion (Grant number: AP2009-2600), the Spanish Ministerio de Ciencia e Innovacion under Projects ENE2011-22823 and ENE2012-34585, and the Generalitat Valenciana under Projects PROMETEOII/2014/008 and ACOMP/2013/237.

Scaling Application of a Hot Leg SBLOCA Scenario to a Nuclear Power Plant

Several experimental facilities, such as the Large Scale Test Facility (LSTF) of the Japan Atomic Energy Agency (JAEA), have been built to reproduce some accidental scenarios because full-scale testing is usually impossible to perform.One of the objectives of these Integral Test Facilities (ITFs) is to obtain measured data to be compared to simulations in order to test the capability of the thermalhydraulic codes to reproduce experimental conditions.The applicability of these experimental results to a full-size power plant system depends on the scaling criteria adopted.The present paper is focused on the simulation and the scaling of the Test 1-2 in the frame of the OECD/NEA ROSA Project to a Nuclear Power Plant (NPP). This test simulates a hot leg 1% Small Break Loss-Of-Coolant Accident (SBLOCA) in a Pressurized Water Reactor (PWR) under the actuation of High Pressure Injection (HPI) system and Accumulator Injection System (AIS).A scaled-up NPP TRACE5 input has been developed from a LSTF TRACE5 model validated by authors in previous works. The scaled-up model has been developed conserving the power-to-volume scaling ratios of LSTF components, initial and boundary conditions. Lengths and diameters of hot legs have been scaled from LSTF model trying to conserve Froude number.A comparison between both TRACE5 models (LSTF and scaled-up NPP) is performed (system pressures, discharged inventory and collapsed liquid levels). Special TRACE5 models such as Choked flow model and OFFTAKE model have been tested. A 3D VESSEL component has been tested in comparison to 1D TEE component to simulate the hot leg where the SBLOCA is located and varying the break orientation (downwards and upwards). Finally, a sensitivity analysis has been made to determine the effect of the break size in the SBLOCA range.Copyright

Unfolding X-ray spectra using a flat panel detector

It is difficult to measure the energy spectrum of X-ray tubes due to the pile up effect produced by the high fluence of photons. Using attenuating materials, appropriate detector devices and the Monte Carlo method, primary X-ray spectrum of these devices can be estimated. In this work, a flat panel detector with a PMMA wedge has been used to obtain a dose curve corresponding to certain working conditions of a radiodiagnostic X-ray tube. The relation between the dose curve recorded by the flat panel and the primary X-ray spectrum is defined by a response function. Normally this function can be approximated by a matrix, which can be obtained by means of the Monte Carlo method. Knowing the measured dose curve and the response matrix, the primary X-ray spectrum can be unfolded. However, there are some problems that strongly affect the applicability of this method: i.e. technical features of the flat panel and inherent characteristics of the involved radiation physics (ill-posed problem). Both aspects are analyzed in this work, concluding that the proposed method can be applied with an acceptable accuracy for spectra without characteristic lines, for instance, tungsten anode in the 50-70 kVp range.

Uncertainty analysis in X-ray spectra simulation: Effect of geometric tube features: (Anode angle and filter thickness)

Knowledge of the primary X-ray spectrum in the radiodiagnostic energy range is essential for evaluating dose image quality and absorbed dose to patients. In this work, the X-ray production of a commercial device has been simulated using the Monte Carlo (MC) code, MCNP5. Simulated spectra have been compared with theoretical ones extracted from IPEM 78 database to perform an uncertainty analysis of the model. The uncertainty in the MCNP5 model is due to the combination of statistical, physics and input uncertainties. This work has been focused on the analysis of uncertainty associated to some geometrical features of the tube and its effect on the simulated spectra using the Noether-Wilks formula. The geometrical features considered are anode angle and thickness of collimators, shielding, beryllium and aluminium filters. The uncertainty in the MCNP5 simulation results due to the input parameter uncertainties was found to be more significant than the statistical uncertainty component.