Belgian Nuclear Research Centre Research Articles

Practices of incident reporting in a nuclear research center: A question of solidarity

Incident reporting is usually considered as an effective means to improve the safety of “at risk” socio-technical systems (e.g. nuclear plants, large industrial facilities, hospitals), as it allows implicated actors to learn from past incidents. Safety could thus be enhanced via the use of an institutionalized Incident Reporting System (IRS), enabling organizations to improve the quality of actions and reactions in case of a deviation from normality, or to prevent such deviations from happening in the first place. Yet, there is a lack of inductive analyses of actual, on-site uses of IRS. In this paper, we address this gap, using the results of 28 semi-structured interviews conducted with agents from the Belgian Nuclear Research Center (SCK·CEN). The study relies on a vulnerability-oriented Science and Technology Studies (STS) approach. Our results show that practices of incident reporting are more varied than the institutionalized ones. Indeed, actual reporting practices are to be related to specific expressions of solidarity between colleagues within a negotiated drift – a pragmatic interpretation of the reporting procedure. These results are discussed in a vulnerability-oriented perspective. Overall, the paper displays a grounded analysis of incident reporting practices which may contribute to a better understanding of how safety is co-constructed by workers, and provides opportunities for further research and concrete path of actions for practitioners.

Estimate of the reactivity of the VENUS-F subcritical configuration using a Monte Carlo MSM method

The GUINEVERE project was launched in 2006 in order to study the feasibility of transmutation in Accelerator Driven subcritical Systems (ADS). This facility, hosted at the Belgian Nuclear Research Center SCK·CEN, couples the fast subcritical lead reactor VENUS-F with an external neutron source provided by the GENEPI-3C accelerator.In order to test on-line subcriticality monitoring techniques, an independent measurement of the reactivity of VENUS-F was achieved using the Modified Source Multiplication Method (MSM). The unknown reactivity of the subcritical configuration of interest was determined by comparing detector count rates driven by an external neutron source in this configuration with those obtained in a slightly subcritical configuration whose reactivity was determined by rod drop experiments. To account for spatial effects, MSM correction factors were calculated for all the detectors using the Monte Carlo neutron transport code MCNP. The corrected reactivity values of all the detectors were found to be consistent. This led to a final estimate of −5.28±0.13$ for the reactivity of VENUS-F.The MSM factors calculated with MCNP were found to be insensitive to the assumptions made for modeling the reactor and the detectors. Thus the MSM method appears to be a robust technique for measuring large subcriticality values with good accuracy.

Description of modular devices for the measurement of external dosimetry in radiation protection.

In 2002 the Group of Radiation Dosimetry and Calibration of the Belgian Nuclear Research Centre (SCK•CEN) has developed an experimental device based on the optically stimulated luminescence (OSL) working with Al2O3:C detectors (TLD-500 and Luxel) stimulated with an argon laser. A set of devices made from different modules have been developed to permit external dosimetry measurements with thermoluminescence (TL) and OSL techniques under different conditions. This study describes these measurement devices that can be made with these modules and some of the characteristics of the different systems. These devices present several advantages in terms of measurement possibilities: a small number of modules allow the use of different detection materials (Al2O3:C, BeO, quartz electronic components and tiles) and different measurement methods (TL, CW-OSL and pulsed OSL). Some applications are commented.

Carbon ion irradiation of the human prostate cancer cell line PC3: A whole genome microarray study

Hadrontherapy is a form of external radiation therapy, which uses beams of charged particles such as carbon ions. Compared to conventional radiotherapy with photons, the main advantage of carbon ion therapy is the precise dose localization along with an increased biological effectiveness. The first results obtained from prostate cancer patients treated with carbon ion therapy showed good local tumor control and survival rates. In view of this advanced treatment modality we investigated the effects of irradiation with different beam qualities on gene expression changes in the PC3 prostate adenocarcinoma cell line. For this purpose, PC3 cells were irradiated with various doses (0.0, 0.5 and 2.0 Gy) of carbon ions (LET=33.7 keV/μm) at the beam of the Grand Accélérateur National d’Ions Lourds (Caen, France). Comparative experiments with X-rays were performed at the Belgian Nuclear Research Centre. Genome-wide gene expression was analyzed using microarrays. Our results show a downregulation in many genes involved in cell cycle and cell organization processes after 2.0 Gy irradiation. This effect was more pronounced after carbon ion irradiation compared with X-rays. Furthermore, we found a significant downregulation of many genes related to cell motility. Several of these changes were confirmed using qPCR. In addition, recurrence-free survival analysis of prostate cancer patients based on one of these motility genes (FN1) revealed that patients with low expression levels had a prolonged recurrence-free survival time, indicating that this gene may be a potential prognostic biomarker for prostate cancer. Understanding how different radiation qualities affect the cellular behavior of prostate cancer cells is important to improve the clinical outcome of cancer radiation therapy.

The differences in perception of radiological risks: lay people versus new and experienced employees in the nuclear sector

This paper studies the differences in perception of two radiological risks – an accident at a nuclear installation and medical X-rays – between four different groups: the general population without (1) and with experience related to radiological risks (2), new employees (3) and professionally exposed people (4) in the nuclear sector. More precisely, this study determines if differences in risk perception can be explained by the level of experiences with ionizing radiation, the knowledge level about radiological risks, the confidence in authorities, the attitude towards nuclear energy, the trust in a management of nuclear installations, gender and age. The data are gathered using computer assisted personal interviews based on the SCK-CEN Barometer of the Belgian Nuclear Research Centre. The relations between risk perception and the independent variables are tested with linear regression analysis. The risk perception of both risks differs significantly between the four population groups. The professionally exposed people and the new employees in the nuclear sector have a significant higher risk perception for medical X-rays compared to the risk for an accident at a nuclear installation. For the general population without experience, it was just the opposite. The general population with experience does not have a significant difference in risk perception between the two radiological risks. Level of experiences with ionizing radiation is determined as an important variable; people have a lower perception of radiological risks when they have higher experiences with risk.

VALIDATION OF A MONTE CARLO MODEL OF THE FORK DETECTOR WITH A CALIBRATED NEUTRON SOURCE

The investigation of experimental methods for safeguarding spent fuel elements is one of the research areas at the Belgian Nuclear Research Centre SCK•CEN. A version of the so-called Fork Detector has been designed at SCK•CEN and is in use at the Belgian Nuclear Power Plant of Doel for burnup determination purposes. The Fork Detector relies on passive neutron and gamma measurements for the assessment of the burnup and safeguards verification activities. In order to better evaluate and understand the method and in view to extend its capabilities, an effort to model the Fork detector was made with the code MCNPX. A validation of the model was done in the past using spent fuel measurement data. This paper reports about the measurements carried out at the Laboratory for Nuclear Calibrations (LNK) of SCK•CEN with a 252Cf source calibrated according to ISO 8529 standards. The experimental data are presented and compared with simulations. In the simulations, not only was the detector modeled but also the measurement room was taken into account based on the available design information. The results of this comparison exercise are also presented in this paper.

Nuclear-physics applications of MYRRHA

The Belgian Nuclear Research Centre SCKCEN is currently working on the design of the MYRRHA research reactor, able to operate in both critical and sub-critical mode as an Accelerator-Driven System (ADS). When operated as an ADS, the MYRRHA reactor core will be coupled to an external neutron source, which is generated by a 600- MeV, 2- to 4-mA proton beam impinging on a lead-bismuth spallation target. By using a small fraction (up to 5%) of the MYRRHA proton beam, intensities of 100-200 A can be sent to a separate facility called ISOL@MYRRHA. Given the high proton energy, most isotopes known on the chart of nuclides can be produced. The production in the hot-target is followed by selective ionization and extraction of atoms in a Radioactive Ion Beam (RIB). Following mass-purification, high-intensity RIBs will be delivered for a large variety of experimental programmes requiring long measurement times. By its experimental programme, the ISOL@MYRRHA facility will be complementary to running and planned Isotope Separator On-Line (ISOL) facilities in Europe and abroad.

Review of the natC(n, γ) cross section and criticality calculations of the graphite moderated reactor BR1

A review of the experimental data for natC(n,γ) and 12C(n,γ) was made to identify the origin of the natC capture cross sections included in evaluated data libraries and to clarify differences observed in neutronic calculations for graphite moderated reactors using different libraries. The performance of the JEFF-3.1.2 and ENDF/B-VII.1 libraries was verified by comparing results of criticality calculations with experimental results obtained for the BR1 reactor. This reactor is an air-cooled reactor with graphite as moderator and is located at the Belgian Nuclear Research Centre SCK•CEN in Mol (Belgium). The results of this study confirm conclusions drawn from neutronic calculations of the High Temperature Engineering Test Reactor (HTTR) in Japan. Furthermore, both BR1 and HTTR calculations support the capture cross section of 12C at thermal energy which is recommended by Firestone and Révay. Additional criticality calculations were carried out in order to illustrate that the natC thermal capture cross section is important for systems with a large amount of graphite. The present study shows that only the evaluation carried out for JENDL-4.0 reflects the current status of the experimental data.

The Use of μCT and ESEM in the Study of the Osmosis-Induced Water Uptake by Eurobitum Bituminized Radioactive Waste

Laboratory water uptake tests are performed at the Belgian Nuclear Research Centre SCK•CEN to obtain insight into the hydromechanical behavior of Eurobitum bituminized radioactive waste under geological disposal conditions. Small nonradioactive and radioactive Eurobitum samples are hydrated in restricted swelling conditions (i.e., nearly constant volume conditions and constant stress conditions). Microfocus X-ray computer tomography (μCT) proves to be a very suitable technique to follow up the ingress of water in the samples. μCT analyses demonstrate that, under the studied hydration conditions, the water uptake by Eurobitum samples is a diffusion controlled process. A characterization of the partially leached samples with environmental scanning electron microscopy (ESEM) shows that the hydration of salt crystals and the subsequent dilution of the salt solution result in an increase in pore size that is limited to a few tens of μm in restricted swelling conditions. The μCT and ESEM analyses allow improvement in the understanding of water uptake by Eurobitum in restricted swelling conditions. In this article we discuss the μCT and ESEM analyses of nonradioactive Eurobitum samples that were hydrated for 2 to 4 years at a constant stress of 1, 22, 33, and 44 bar or in nearly constant volume conditions.

Osmosis-induced water uptake by Eurobitum bituminized radioactive waste and pressure development in constant volume conditions

The chemo-hydro-mechanical (CHM) interaction between swelling Eurobitum radioactive bituminized waste (BW) and Boom Clay is investigated to assess the feasibility of geological disposal for the long-term management of this waste. These so-called compatibility studies include laboratory water uptake tests at the Belgian Nuclear Research Center SCK•CEN, and the development of a coupled CHM formulation for Eurobitum by the International Center for Numerical Methods and Engineering (CIMNE, Polytechnical University of Cataluña, Spain).In the water uptake tests, the osmosis-induced swelling, pressure increase and NaNO3 leaching of small cylindrical BW samples (diameter 38mm, height 10mm) is studied under constant total stress conditions and nearly constant volume conditions; the actual geological disposal conditions should be intermediate between these extremes. Two nearly constant volume tests were stopped after 1036 and 1555days to characterize the morphology of the hydrated BW samples and to visualize the hydrated part with microfocus X-ray Computer Tomography (μCT) and Environmental Scanning Electron Microscopy (ESEM). In parallel, a coupled CHM formulation is developed that describes chemically and hydraulically coupled flow processes in porous materials with salt crystals, and that incorporates a porosity dependent membrane efficiency, permeability and diffusivity.When Eurobitum BW is hydrated in (nearly) constant volume conditions, the osmosis-induced water uptake results in an increasing pressure to values that can be (in theory) as high as 42.8MPa, being the osmotic pressure of a saturated NaNO3 solution. After about four years of hydration in nearly constant volume water uptake tests, pressures up to 20MPa are measured. During this hydration period only the outer layers with a thickness of 1–2mm were hydrated (as derived from μCT and ESEM analyses), and only about 10–20% of the initial NaNO3 content was released by the samples. In the studied test conditions, the rates of water uptake and NaNO3 leaching are low because of the low porosity, and thus low permeability, of the hydrated BW samples in combination with a highly efficient semi-permeable bitumen membrane. In contrast to the hydration in free swelling conditions, the increase in porosity is limited by the high pressures in the nearly constant volume tests. Furthermore, at the interface with the stainless steel filters, a low permeable re-compressed bitumen layer is formed, as observed on the ESEM images.The experimental results of pressure increase and NaNO3 leaching, as well as observations on μCT and ESEM images (e.g. compression of leached layers, high dissolved NaNO3 concentration in hydrated BW after about four years), were reproduced rather successfully by the coupled CHM formulation for Eurobitum BW. A long-term model prediction of the evolution of the osmosis-induced pressure in the nearly constant volume tests shows that the pressure would reach a maximal value of about 20MPa after about 5.5years, after which the pressure would start to decrease. After 10,000days (∼27years) the pressure would have decreased to a value of ∼2MPa.

The osmosis-induced swelling and NaNO3 leaching of radioactive and artificially aged Eurobitum bituminized waste

ABSTRACTThe behavior of Eurobitum bituminized radioactive waste under geological disposal conditions is studied in water uptake tests at the Belgian Nuclear Research Centre SCK•CEN to assess the feasibility of geological disposal for the long-term management of this waste. The hydro-mechanical behavior of this waste is affected by the continuous evolution of the rheological properties of bitumen due to radio-oxidation (i.e. ageing).The effect of the bitumen ageing degree on the kinetics of the water uptake, swelling and NaNO3 leaching is investigated in water uptake tests with ∼30 years old radioactive samples and inactive samples that were artificially aged. The first results of swelling and NaNO3 leaching of (i) radioactive samples that have been hydrated for more than 2 years at a constant total stress of 2.2 MPa, and (ii) a thermally aged sample that has been hydrated for ∼1.5 years under nearly zero effective stress conditions, revealed lower swelling and higher leach rates for these samples compared to non-aged samples. The effect of ageing on the osmotic efficiency of bitumen as a semi-permeable membrane is less pronounced when swelling of the samples is limited, and changes in time, probably because of the formation of low porosity layers, which seems to mask the difference in bitumen membrane efficiency of aged and non-aged bituminized waste.

External and Environmental Radiation Dosimetry with Optically Stimulated Luminescent Detection Device Developed at the SCK.CEN

The laboratory of Radiation Dosimetry and Calibration of the Belgian Nuclear Research Centre (SCK.CEN) is using thermoluminescence dosimetry for more than thirty years for routine measurements and for R&D investigations. In 2002, it has developed an experimental device based on the optically stimulated luminescence (OSL) technique. This device is working with AL2O3:C crystals stimulated by the green line (488 nm) emitted by a 150 mW argon laser. This paper describes this device, its characteristics, some applications in space dosimetry and the R&D works initiated in this field during the next few years.

Description of a portable devices developed at SCK•CEN for OSL and TL dosimetry

Abstract The Expert Group of Radiation Dosimetry and Calibration of the Belgian Nuclear Research Centre (SCK•CEN) uses thermoluminescence (TL) dosimetry for more than thirty years for routine measurements and for R&D purposes. In 2002, an experimental device based on the optically stimulated luminescence (OSL) was developed for research. It works with AL 2 O 3 :C detectors (TLD-500 & Luxel™) stimulated with a green line generated by a 150 mW Ar + laser. Since 2008, modular OSL devices have been developed using light emitting diodes (LED) and working with reflection or transmission mode. This paper describes these modules. The characteristics of the different systems are compared on experimental results: detections limits, linearity, sensitivity. The modular device presents advantages in terms of measurement possibilities with respect to the laser device: a small number of modules allows the use of different detection materials (AL 2 O 3 :C, BeO, quartz, electronic components) and different measurement methods (TL, CW-OSL and pulsed OSL). The modules are controlled by a personal computer and a microcontroller array. The whole set is able to measure a wide range of doses by changing the number of LEDs and is able to work in situ . The future trends are commented as well as some applications.

Design of a planar probe diagnostic system for plasmatron VISIONI and its application for the study of deuterium retention in W–Ta alloys

One of the issues still to be clarified with respect to the possible use of tungsten and tungsten alloys as first wall material in fusion reactors is the retention of hydrogen isotopes under fusion-relevant conditions, such as the presence of helium ash, neutron irradiation, thermal shock. The low flux, high temperature plasma simulator VISIONI, being currently constructed at the Belgian nuclear research center SCK·CEN, will have the unique ability to handle radioactive materials – neutron irradiated samples and tritium plasma. Currently it is being tested with non-irradiated samples and deuterium plasma. To monitor the plasma parameters near the investigated specimen, a planar probe system has been developed. It was demonstrated that the plasmatron is able to provide conditions relevant for the ITER first wall. Investigations of deuterium retention in W–Ta alloys have been performed, using thermodesorption spectroscopy. A hypothesis of the existence of three kinds of trapping sites for deuterium in W–Ta alloys, based on deuterium release studies, is suggested.

Acoustic Sensor for In-Pile Fuel Rod Fission Gas Release Measurement

Innovative in-pile instrumentation is crucial for advanced experimental programs in research reactors. In this field, we developed a specific acoustic sensor to improve the knowledge of fission gas release in Pressurized Water Reactor (PWR) fuel rods when irradiated in Material Testing Reactors (MTR). In order to perform experimental programs related to the study of the fission gas release kinetics, the CEA (French Nuclear Energy Commission) acquired the ability to equip a pre-irradiated PWR fuel rod with three sensors, allowing the simultaneous on-line measurements of the following parameters: 1) fuel temperature with a centreline thermocouple type C 2) internal pressure with a specific counter-pressure sensor, 3) fraction of fission gas released in the fuel rod with an innovative acoustic sensor. The third detector, which has been developed and is patent pending by CEA, SCK·CEN (Belgian Nuclear Research Center) and IES (French research laboratory of Montpellier II University and French National Research Center), is the subject of this paper. This original acoustic sensor has been designed to measure the molar mass and pressure of the gas contained in the fuel rod plenum. For in-pile instrumentation, the fraction of fission gas, such as Krypton and Xenon, in Helium, can be deduced on-line from this measurement. The principle of this non destructive and on-line acoustical sensor is the following: a piezoelectric transducer generates acoustic waves in a cavity connected to the fuel rod plenum. The acoustic waves are propagated and reflected in this cavity and then detected by the transducer. The data processing of the signal gives the velocity of the acoustic waves and their amplitude, which can be related respectively to the molar mass and to the pressure of the gas. The piezoelectric material of this sensor has been qualified in nuclear conditions (gamma and neutron radiations). The complete sensor has also been specifically designed to be implemented in MTR conditions. For this purpose some technical points have been studied in details: 1) fixing of the piezoelectric sample in a reliable way with a suitable signal transmission, 2) size of the gas cavity to avoid any perturbation of the acoustic waves, 3) miniaturization of the sensor because of narrow in-pile experimental devices, 4) appropriate cables to transmit high frequency signal under nuclear conditions.

Innovations for In-Pile Measurements in the Framework of the CEA-SCK•CEN Joint Instrumentation Laboratory

Optimizing the life cycle of nuclear systems under safety constraints requires high-performance experimental programs to reduce uncertainties on margins and limits. In addition to improvement in modeling and simulation, innovation in instrumentation is crucial for analytical and integral experiments conducted in research reactors. The quality of nuclear research programs relies obviously on an excellent knowledge of their experimental environment which constantly calls for better online determination of neutron and gamma flux. But the combination of continuously increasing scientific requirements and new experimental domains -brought for example by Generation IV programsnecessitates also major innovations for in-pile measurements of temperature, dimensions, pressure or chemical analysis in innovative mediums. At the same time, the recent arising of a European platform around the building of the Jules Horowitz Reactor offers new opportunities for research institutes and organizations to pool their resources in order to face these technical challenges. In this situation, CEA (French Nuclear Energy Commission) and SCK'CEN (Belgian Nuclear Research Centre) have combined their efforts and now share common developments through a Joint Instrumentation Laboratory. Significant progresses have thus been obtained recently in the field of in-pile measurements, on one hand by improvement of existing measurement methods, and on the other hand by introduction in research reactors of original measurement techniques. This paper highlights the state-of-the-art and the main requirements regarding in-pile measurements, particularly for the needs of current and future irradiation programs performed in material testing reactors. Some of the main on-going developments performed in the framework of the Joint Instrumentation Laboratory are also described, such as: - a unique fast neutron flux measurement system using fission chambers with 242Pu deposit and a specific online data processing, - an optical system designed to perform in-pile dimensional measurements of material samples under irradiation, - an acoustical instrumentation allowing the online characterization of fission gas release in Pressurized Water Reactor fuel rods. For each example, the obtained results, expected impacts and development status are detailed.

Testing three types of active personal neutron dosemeters for application in a nuclear research centre

The neutron personal dosimetry at the Belgian Nuclear Research Centre, SCK·CEN, is currently done using bubble detectors. Both a BD-PND and a BDT detector are worn by staff whenever exposure to neutrons is possible. This system has now been in operation for 10 years. However, in recent years some electronic neutron personal dosemeters have become commercially available. At SCK·CEN, we have performed a series of tests to evaluate whether the bubble detectors can be replaced by an electronic dosemeter for neutrons. We have tested three types of dosemeters: the EPDN2, the DMC-2000GN and the Saphydose-N.

Lessons Learned From Soft Computing Applications At SCK-CEN

By answering "what is soft computing?" we briefly examine four research projects of soft computing applications at the Belgian Nuclear Research Centre (SCK-CEN) from the practical point of view. We draw lessons learned from the examined projects including reactor control, cost estimation, energy policy, and nuclear safeguards. We conclude that soft computing techniques are new computer information processing methods that are complementary to all traditional approaches for real-problem solving and that present great challenges in practice.

Microstructural analysis of MTR fuel plates damaged by a coolant flow blockage

In 1975, as a result of a blockage of the coolant inlet flow, two plates of a fuel element of the BR2 reactor of the Belgian Nuclear Research Centre (SCK•CEN) were partially melted. The fuel element consisted of Al-clad plates with 90% 235U enriched UAl x fuel dispersed in an Al matrix. The element had accumulated a burn up of 21% 235U before it was removed from the reactor. Recently, the damaged fuel plates were sent to the hot laboratory for detailed PIE. Microstructural changes and associated temperature markers were used to identify several stages in the progression to fuel melting. It was found that the temperature in the center of the fuel plate had increased above 900–950 °C before the reactor was scrammed. In view of the limited availability of such datasets, the results of this microstructural analysis provide valuable input in the analysis of accident scenarios for research reactors.

Introduction to a special Festschrift issue celebrating the microbiology of Cupriavidus metallidurans strain CH34

Although this series of ten reports focuses on themicrobiology of a single bacterium namely the beta-proteobacterium Cupriavidus metallidurans CH34,this volume is of general interest for several reasons.Firstly, this unusual multiple toxic metal ion-resistantbacterium has been a model for how microbes handlesuch toxic metal (loids) from the time of its firstisolation (Mergeay et al. 1978, 1985). Moreover, itcontinues to be a useful model, as seen in this series ofreportsaswellasinanysearchoftheliterature,usedforan expanding range of interests from metal responsephysiology (Nies et al. 1990, 1989; Nies 2000; Rouxet al. 2001; Sendra et al. 2006) and basic moleculargenetics (Lejeune et al. 1983), to genomics (theorganism is unusual in having two chromosomes plustwo large plasmids; Mergeay et al. 2003), microbialecology (Vander Auwera, this series), to applicationsinenvironmentalbiotechnology(Diels,thisseries)andeven in space research (Leys, this series).As an introductory aside, but a necessary explana-tion here, strain CH34 is complicated in that it has hadat least five official names, starting as a Pseudomonasstrain (Mergeay et al. 1978), then Alcaligeneseutrophus (Lejeune et al. 1983), then Ralstonia eutro-pha, then Ralstonia sp., then Ralstonia metallidurans,to Wautersia metallidurans and finally (we hope)Cupriavidusmetallidurans,including twochangesinasingle year (Vandamme and Coenye 2004), as thetaxonomy of related bacteria evolved. Interestedreaders (if one wants useful and comprehensiveliterature) are advised to also search by ‘‘CH34’’ andnot only by genus and species names. The letters CHrefer to Christian Houba, at that time (in 1976), astudent from the Universite´ of Lie`ge, who first isolatedmetal-resistant bacteria in a region in Belgium wellknown for its metallurgical industry historical past aswell as for metal-accumulating plants.The current reports are from a small FestschriftSymposium on work with strain CH34 that was heldat the SCK CEN (the Belgian Nuclear ResearchCentre of Mol) in April 2008. The science reported,included herein and much more that did not result inmanuscripts, was a wonderful endorsement of theimportance of this fascinating microbe, the benefits ofa research program continuing over decades, and thefellowship and collegiality of the small internationalgroup of CH34 workers. We hope this continues.References