Volume 66, Issue 4

The Code with – the capability of – Internal Assessment of Uncertainty (CIAU) is a tool proposed by the Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione (DIMNP) of the University of Pisa. Other Institutions including the nuclear regulatory body from Brazil, “Comissäo Nacional de Energia Nuclear”, contributed to the development of the tool. The CIAU aims at providing the currently available Relap5/Mod3.2 system code with the integrated capability of performing not only relevant transient calculations but also the related estimates of uncertainty bands. The Uncertainty Methodology based on Accuracy Extrapolation (UMAE) is used to characterize the uncertainty in the prediction of system code calculations for light water reactors and is ‘internally’ coupled with the above system code. Following an overview of the CIAU development, the present paper deals with the independent qualification of the tool. The qualification test is performed by estimating the uncertainty bands that should envelope the prediction of the LOBI test Al-93 (small break loss of coolant accident). The current limitation of the ‘error’ database, implemented into the CIAU prevented a final demonstration of the qualification. However, all the steps for the qualification process are demonstrated.

For the selection and design of measures to scope with the hydrogen which will be produced in the course of a severe accident in LWRs a simple postulate – e. g. 75 % zircaloy oxidation of all fuel rod claddings – is not appropriate. In our opinion, realistic (best estimate) analyses with indication of the uncertainties are substantially more suitable. However, the problem thereby lies in the determination of these uncertainties. The current work presents a method, which determines the uncertainty band for the in-vessel hydrogen production calculated with the MELCOR program using a mathematical-statistic method (SUSA). For the exercise a “Total loss of the alternating current supply” for the planned European Pressurised Water Reactor (EPR) has been chosen as a representative scenario. Besides the actual uncertainties of the computational program concerned with such an analysis also the sensitive parameters can be identified.

The start up physics studies SPS of the Second Egyptian Research Reactor is presented in this work. The SPS consists of the approach to criticality, the power and flux distribution of the first critical core, criticality, power and flux distribution of the working core. The working core is the beryllium-reflected core with cobalt loaded for irradiation. Some of the neutronic parameters are determined, these parameters are the power peaking factor, power distribution, the excess reactivity for both the water and beryllium reflector cores, the core excess reactivity with the cobalt loaded, the reactivity worth of the cobalt irradiation box. Flux distribution for one fast, three eipthermal and one thermal energy group are also determined. All the above neutronic parameters are calculated by using the lattice cell code WIMSD4 and the two dimensional diffusion code DIXY2.

The recently developed module PIJM for computing first-flight collision matrices in cluster geometry for the WIMS code, using an improved numerical technique in the in-plane integrations of the Bickley functions which considers each system region individually, has been extended to treat lattice cells with square outer boundaries. Comparisons with the standard square PIJ routine are presented for a test case, showing significant discrepancies among the results.

The main goal of this work is to develop quantitatively reliable tools that can be used to identify the origin of a nuclear event, e. g. discriminate between a nuclear explosion and an accidental reactor release. A model has been developed, which takes into account the wide range of conditions and parameters, which may exist in connection with nuclear events. Using the model, specific isotope activity ratios are defined, promising to be effective in event characterization, while reducing the influence of various nuclear scenarios to a minimum. Besides, an attempt was made to quantify the concept of “short irradiation reactor” and to set its limits, as related to an event characterization method.

The Rossendorf Beamline at the European Synchrotron Radiation Facility is equipped with a unique radiochemistry experimental station. This dedicated station has been designed to perform environmentally relevant experiments on radionuclides, in particular actinides, using synchrotron based X-ray absorption fine structure spectroscopy. The technical concepts and the layout of this experimental station, where radioactive solids and liquids with activities of up to 185 MBq can be studied, are presented. The radiological safety of experimenters, equipment, and of the environment are ensured by the specially developed radiochemistry safety system. The multibarrier concept, the ventilation and air monitoring systems, the radiological protection system, and special software components for recording and visualisation of the safety status are described in detail.

In order to guarantee a high level of accuracy in all areas concerned with radon and radon decay products measurement the BfS has established a quality assurance management system. A set of calibration chambers and containers was installed in the laboratories which were subsequently accredited as a German Calibration Service (DKD) Calibration Laboratory for the units of radon and the potential alpha energy concentration of its short-lived decay products. It is traced back to the national standard established at the Physikalisch-Technische Bundesanstalt (PTB), which is at the same time the national institute for science and technology, and the highest technical authority for metrology in Germany. The equipment makes possible scientific investigations as well as calibrations for the measuring quantity “concentration of Rn-222 in air” in the range between 50 Bq/m 3 and 100 kBq/m 3 and also for the measuring quantity “potential alpha-energy concentration” (PAEC) in the range between 2 MeV/cm 3 (3.2 E-7 J/m 3 ) and 4000 MeV/cm 3 1 (*6 .4 E-4 J/m 3 ).

Many requirements for the quality assurance of the licensee and the independent measuring centre can be derived from the Directive for the “Surveillance of emission and immission of mining work” (REI Mining). However, these should be viewed within the context of “Instructions of measurement related to the surveillance of radioactivity in the environment and to the registration of radioactive emissions from nuclear installations” (MA). Further, it would be advisable to compare the REI Mining requirements to both the Directive for the “Surveillance of emission and immission from nuclear installations” (REI) as well as to the “General administration order to the integrated measuring and information system of the precautionary Radiation Protection Act” (AVV-IMIS). In this article, the various requirements are compared, their common and different aspects are discussed, and possible conclusions for the licensee, the independent measuring centre and the authority of supervision and licencing are presented.

The Forschungszentrum Rossendorf (FZR) e. V is constructing a new large-scale test facility, TOPFLOW, for thermalhydraulic single effect tests. The acronym stands for Transient Two Phase Flow Test Facility. It will mainly be used for the investigation of generic and applied steady state and transient two phase flow phenomena and the development and validation of models of Computational Fluid Dynamic (CFD) Codes.

The ATHLET code has been improved and validated for the safety analysis of high flux research reactors against experimental data of the Thermalhydraulic Test Loop of Oak Ridge National Laboratory (ORNL). Therefore, an extensive series of “stiff mode” experiments were recalculated. The comparison between experiments and ATHLET posttest calculations shows that the extended code simulates accurately the thermalhydraulic conditions and the flow instabilities in a wide range of inlet velocity, heat and mass flux.