Day 2 :
Keynote: Dismantling case study of the reactor block at the VVR-S nuclear research reactor Magurele, Bucharest
Time : 10:10- 10:40
Ioan Iorga is working from 2002 in several big projects like ROM 04029, BOA 3J0021 or EMERSYS. He is Senior Researcher in the decommissioning team from the NIPNE-HH institute in Romania. Under his coordination, the dismantling of radionuclide effluents pipes between the reactor and the treatment plant was successfully completed. He has published more than 8 papers in reputed journals presenting his work. He is one of main author of the VVR-S Decommissioning Plan. He is from 2013 class of PhD students at Faculty of Physics, University of Bucharest with thesis on “Studies to Assess Nuclear and Radiological Installation Prior to Decommissioning”.
The VVR-S nuclear research reactor owned by Horia Hubulei-National Institute of Physics and Nuclear Engineering (IFIN-HH), has functioned between 1957 and 1997 at a nominal thermal power of 2 MW, using low-enriched nuclear fuel (10%) type EK-10 and highly enriched fuel (36%) type S-36. The VVR-S research reactor served as the basis for experimental research and radioisotope production. On average, the installation functioned 5 days per week at full or variable power. The total thermal energy produced until 1997 was 9.59 GWd. Between 2015-2016 different activities for dismantling the reactor block of the research reactor was carried out. To avoid high exposure at this high risk activity, it was taken into account the maximum hazard event probability from different part of the reactor block including internal parts. The maximum gamma dose was on the high activated automatic control rod at 3 Sv/h because of the stainless steel composition of the lower part and the positioning in the middle of the reactor core. The gamma dose rate varied from 285 mSv/h until 3 Sv/h and goes down again at 1.5 Sv/h. In the same manner, we did not forget about the beta gamma contamination that was very high; the maximum value was around 31.25 k over the background in the cps (count per second) values. We expected Sr-Y as fission product. We developed a case study where we systematized the steps in dismantling activities on the reactor block respecting the Alara principle.
- Nuclear Engineering & Nuclear Physics
Dr. Wei Xiao has completed his PhD at the age of 31 years from University of California, Berkeley. He is a senior scientist and a team leader of nuclear materials simulation group at State Nuclear Power Research Institute, China.
Silicon carbide (SiC) is a promising cladding material in light water reactor. The fuel cladding is an important safety barrier in fission nuclear reactors, as it restrains most of the radioactive fission products within its volume. The ability to keep radioactive fission products within the cladding material determines whether SiC can be used as a safe cladding material. Iodine atom diffusion in SiC is calculated with first-principles calculation and nudged elastic band method (NEB) and compared with that in Zr. Without considering vacancy effect, the diffusion rate of iodine in SiC is slower than that in Zr. Consider the vacancy from the neutron irradiation, divacancy can speed up iodine impurity diffusion in SiC. Even larger vacancies slow down iodine diffusion in SiC. Meanwhile, vacancies slow down the diffusion of iodine atom in Zr.
Alexander Papash has his expertise in accelerator physics. He has more than 30 years of research and engineering experience in design and operation with scientific and commercial accelerator facilities worldwide, including investigations of non-linear effects and ion kinetics in ultra-low energy storage rings, beam dynamics studies in electron synchrotrons and cyclotrons. He proposed consistent explanation of high beam losses rates, fast growth of momentum spread and beam size in an ultra-low energy rings. Computer simulations of non-linear effects in an electrostatic ion storage rings have been performed and beam tracking in 3D relaxation electric fields were done. Ion kinetics and long term beam dynamics including transition and equilibrium conditions in ultra-low energy rings have been investigated and benchmarked against experimental data. Some predictions on future experiment results are made. He is a Scientist currently working at Karlsruhe Institute of Technology, Germany.
Electrostatic storage rings operate at very low energies in the keV range and have proven to be invaluable tools for atomic and molecular physics. Because of the mass independence of electric rigidity, these machines are able to store a wide range of different particles, from light ions to heavy singly charged bio-molecules, opening up unique research opportunities. However, earlier measurements have shown strong limitations on beam intensity, fast growth of beam size and decay of ion current, reduced lifetime of ion beam. The nature of these effects has not been fully understood. Also a large variety of experiments in future generation ultra-low energy storage and decelerator facilities including in-ring collision studies with a reaction microscope require a clear understanding of the physical processes involved into the operation of such rings. Nonlinear and long-term beam dynamics studies in ultra-low energy storage rings are presented on the examples of a number of existing and planned electrostatic storage ring facilities. The results from simulations were benchmarked against experimental data of beam losses in the ELISA storage ring. It was shown that decay of beam intensity is mainly caused by ion losses on ring aperture due to multiple scattering on residual gas. Beam is lost on electrostatic elements and collimators due to small ring acceptance. Rate of beam losses increases at high intensities because of the intra-beam scattering effect adds to vacuum losses. Detailed investigations into ion kinetics, under consideration of effects from electron cooling and multiple scattering of the beam on a supersonic gas jet target, were carried out and yielded a consistent explanation of the physical effects in a whole class of ultra-low energy storage rings. The lifetime, equilibrium momentum spread, and equilibrium lateral spread during collisions with the target are estimated. Based on computer simulations, the conditions for stable ring operation with an extremely low-emittance beam are predicted. Finally, results from studies into the interaction of ultra-low energy ions with a gas jet target are summarized.
Professor in the Department of Physics, NUS, Singapore
Professor van Kan obtained his PhD in Physics (University of Amsterdam) in 1996. In 2007 he received the Institute of Physics Singapore, Omicron Nanotechnology Award. Currently, he is Professor in the Department of Physics, NUS, Singapore. In his research he employs fast light ions for lithography and analysis. In his research group new methods are developed for next generation 3D nano-lithography with an emphasis on ion beam focusing and ion source development. He also uses nanoimprint lithography for single DNA molecules studies in nanofluidic lab on chip devices. His work has resulted in 146 scientific publications and 17 research grants.
Microscopy and miniaturization have been an integral part of scientific progress. Since MeV protons mainly interact with substrate electrons and the fact that proton induced secondary electrons just get enough energy to break bonds, a proton beam will follow a straight path through tissue or resist material. Proton microscopy has therefore several unique advantages over other forms of microscopy. The current downside is the poor source performance, about a million times less brighter compared to electron beam sources. The success of a next generation proton microscope depends on two main components: a stable high brightness source of MeV protons and a high quality focusing lens system. We have demonstrated 9.3 x 32 nm2 proton beam focus and have written 19 nm wide (100 nm tall) lines in HSQ resist. To address the limited brightness we are developing a new ion source based on electron impact ionization. Recent tests with “on chip ion sources” have shown potential to improve the ion beam brightness by a million times. This will allow us to develop a table top proton microscope capable of delivering sub 10 nm beam spot size for MeV protons. This new source will therefore enable:
· Sub 10 nm 3D nanofabrication without “proximity effects”.
· Sub 10 nm whole cell imaging, opening up new pathways to investigate the uptake of nanoparticles in drugs delivery.
· Since 0.5 MeV protons will cause double stand breaks in DNA, this new system will provide an insight to improve cancer treatment in radiobiology using 200 MeV protons.
Scientific Researcher of IFIN-HH, at the Reactor Decommissioning Department
Carmen Tuca has completed her Master's studies in Theoretical Physics and Mathematics at University of Craiova, Faculty of Physics. Now she is a PhD student in Nuclear Physics at University of Bucharest, Faculty of Physics. She is Scientific Researcher of IFIN-HH, at the Reactor Decommissioning Department, responsible for environmental, occupational health and safety problems. She has published more than 15 papers in scientific journals.
The paper describes the radiological impact on the workers who perform the decontamination of a hot cell from the VVR-S nuclear research reactor (NR), used for production of radioisotopes during the operation of the NR. The assessment of dose equivalent takes into account the used manual procedure to make the floor decontamination, due to the fact that the handling devices are broken. Due to the contamination of the cell’s floor, three methods were used to determine the high radiation areas: (i) Ambient dose equivalent measurements performed with portable digital survey meter with a gamma dose rate probe placed less 1 cm above the surface; (ii) thermoluminescent dosimeters placed directly on surface; (iii) From each high radiation area, (about 100 cm2 square surface) were taken samples and measured by gamma spectrometry to determine the radionuclides and corresponding activity used to calculate the equivalent dose rate at the point where the operator was placed (about 70 cm from the measurement point). Six hot points having the same order of magnitude for activity were identified and a seventh one with an activity with three order of magnitude higher was identified. Although the measurement conditions were difficult, the results were in a satisfactory agreement, validating the measurement. The dose rate assessment is for the worker who performs direct measurements of the ambient dose equivalent and for that one who performs the decontamination of the contaminated area. The calculation hypotheses: (i) Sampling yield for activity measurement is 10%; (ii) the activity is concentrated in the highest activity point, having a total activity equal with the sum of all hot points. For the worker who measures contamination, the external penetrant dose equivalent is less than 0.13 mSv for 5 minutes (3.78 mSv/h). For the worker who performs the decontamination (placed at about 45 cm from the contaminated area): i) The external irradiation is 0.34 mSv (operation at about 12 minutes) and dose rate is 1.717 mSv/h; ii) the internal committed effective dose, E(50) received by worker due to air inhalation is about 2.40 µSv based on the assumption that in the hot cell is spread just 10-4 of the total activity and the worker wears a mask having a filter with a retention efficiency at 99%.
Completed his PhD in University of Tsukuba
Tetsuaki Moriguchi has completed his PhD at the age of 29 years from University of Tsukuba. His interests are density distributions and radii of unstable nuclei located far from stability line on the nuclear chart.
We have performed reaction cross section (sR) measurements to deduce the matter density distribution of 14Be. We deduced the matter density distribution of 14Be from the measured sR of 14Be with both proton and carbon targets at around 41 and 76 MeV/nucleon and previously measured sR at relativistic energies. 14Be (Z=4, N=10) nucleus is thought to be the two-neutron halo nucleus consisting a core nucleus 12Be plus the two valence neutrons. Our observation supports this picture. Furthermore, the resultant density distribution is found to have dominant configuration of the s-wave with partial mixture of the d- or p-wave. In our analysis, 39% mixing of the p-wave is suggested. We also compared the deduced root-mean-square matter radius with the theoretical calculations. The detail of the comparison will be presented.
Professor at Nizhny Novgorod State university, Russia
Albina Orlova is working in the field of new inorganic materials used in nuclear chemistry for radwaste immobilization of dangerous isotopes, for actinide transmutation, as well for construction materials. She uses the structure properties and physico-chemical principles for elaboration of new ceramics with mineral-like crystal forms.
Safety improvement in management of radwaste is an actual problem on the final stage of the nuclear fuel cycle. There are 450 operating nuclear reactors in the world, and 67 more are being built. In the guidelines for the management of highly radioactive waste, developed by IAEA for countries-participants, a special place is given to ceramic materials based on inorganic compounds of oxide and salt character. Ceramics are recommended with a variety of structural forms, about 30 crystal modifications. Nature similarity as a key principle of technological advances of the 21st century, including of course the materials sciences, is used by us as the base for development of mineral-like materials for nuclear technology. The report presents our data on the structural-chemical modeling of various phases of different complexity of chemical compositions with the structures of minerals kosnarite, langbeinite, monazite, whitlokite, chlorapatite, pollucite, fluorite, garnet; their synthesis in the form of nano-powders and almost non-porous ceramics and also the results of stability studies. The prepared compounds were characterized by XRD, DSC, IR methods and were tested under heating, radiation and in aqueous systems. It was confirmed the formation of com-pounds with the proposed structures. The temperature regions of their existence were established. The results of leaching and irradiation with accelerated Хе-ions are presented. To improve stability and therefore enhance the ecological safety barrier in the storage and disposal of radwaste, we apply Spark Plasma Sintering (SPS) method to synthesize the ceramics. This technology provides a ceramic sintering within 3 to 12 minutes, with a density close to theoretical value. Small duration of sintering of nuclear materials is a significant factor in reducing the risk of release of radio-nuclides to environment.