Long-term residual radioactivity in an intermediate-energy proton linac (original) (raw)
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EPJ Web of Conferences, 2017
The Paul Scherrer Institute (PSI) is the largest national research center in Switzerland. Its multidisciplinary research is dedicated to a wide field in natural science and technology as well as particle physics. The High Intensity Proton Accelerator Facility (HIPA) has been in operation at PSI since 1974. It includes an 870 keV Cockroft-Walton pre-accelerator, a 72 MeV injector cyclotron as well as a 590 MeV ring cyclotron. The experimental facilities, the meson production graphite targets, Target E and Target M, and the spallation target stations (SINQ and UCN) are used for material research and particle physics. In order to fulfill the request of the regulatory authorities and to be reported to the regulators, the expected radioactive waste and nuclide inventory after an anticipated final shutdown in the far future has to be estimated. In this contribution, calculations for the 20 m long beamline between Target E and the 590 MeV beam dump of HIPA are presented. The first step in the calculations was determining spectra and spatial particle distributions around the beamlines using the Monte-Carlo particle transport code MCNPX2.7.0 [1]. To perform the analysis of the MCNPX output and to determine the radionuclide inventory as well as the specific activity of the nuclides, an activation script [2] using the FISPACT10 code with the cross sections from the European Activation File (EAF2010) [3] was applied. The specific activity values were compared to the currently existing Swiss exemption limits (LE) [4] as well as to the Swiss liberation limits (LL) [5], becoming effective in the near future. The obtained results were used to estimate the total volume of the radioactive waste produced at HIPA and have to be reported to the Swiss regulatory authorities. The comparison of the performed calculations to measurements is discussed as well.
Health Physics, 2007
The LINAC-ADONE accelerator complex of the INFN-LNF Frascati National Laboratories, operating for 27 y prior to the commissioning of DA⌽NE, was dismantled in 1993. The scraps resulting from the decommissioning of LINAC-ADONE have been temporarily stored in the same Frascati laboratory, waiting for definitive disposal. Relying on recommendations of the IAEA, European Commission and Italian committees, an experimental characterization study of the LNF repository was performed. The main objective was a classification of the scraps on the basis of internationally recognized "clearance levels," which are 0.1 Bq g ؊1 for the isotopes of interest for this work. Secondly, a measurement of the materials suspected to be above 0.1 Bq g ؊1 was planned. Activation isotopes were expected from the aluminum, copper, steel, and iron of the LINAC and the ADONE ring sections. For screening purposes, the repository area has been divided into zones, where in-situ measurements with a portable HP-Ge detector have been performed. In addition, small samples have been cut from a representative number of pieces, and accurate laboratory measurements have been made with a low background HP-Ge spectrometer. The experimental results are in good agreement with other studies and show that a large part of the material is below the mentioned specific activity level.
Induced radioactivity in the target station and decay tunnel from a 4MW proton beam
An important aspect of a future CERN Neutrino Factory is the material activation arising from a 2.2 GeV, 4 MW proton beam striking a mercury target. A first estimation of the hadronic inelastic interactions and the production of residual nuclei in the target, the magnetic horn, the decay tunnel, the surrounding rock and a downstream dump has been performed by the Monte Carlo hadronic cascade code FLUKA. The aim is both to assess the dose equivalent rate to be expected during maintenance work and to evaluate the amount of residual radioactivity, which will have to be disposed of after the facility has ceased operation. This paper discusses the first results of such calculations.
Predicting Induced Radioactivity at High Energy Accelerators
1999
Radioactive nuclides are produced at high-energy electron accelerators by different kinds of particle interactions with accelerator components and shielding structures. Radioactivity can also be induced in air, cooling fluids, soil and groundwater. The physical reactions involved include spallations due to the hadronic component of electromagnetic showers, photonuclear reactions by intermediate energy photons and low-energy neutron capture. Although the amount of induced radioactivity is less important than that of proton accelerators by about two orders of magnitude, reliable methods to predict induced radioactivity distributions are essential in order to assess the environmental impact of a facility and to plan its decommissioning. Conventional techniques used so far are reviewed, and a new integrated approach is presented, based on an extension of methods used at proton accelerators and on the unique capability of the FLUKA Monte Carlo code to handle the whole joint electromagnetic and hadronic cascade, scoring residual nuclei produced by all relevant particles. The radiation aspects related to the operation of superconducting RF cavities are also addressed.
Residual radioactivity at the CERN 600MeV synchro-cyclotron
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2012
The 600 MeV synchro-cyclotron (SC) was the first accelerator that came into operation at CERN in 1957. It provided beams for CERN's first particle and nuclear physics experiments and operated for 33 years until it was shut down in 1990. In view of a planned partial decommissioning of the facility, a range of measurements were carried out to evaluate the levels of residual radioactivity in the accelerator and its surrounding after about 20 years of cooling time. Gamma spectrometry measurements were performed on 113 samples collected inside the three floors of the accelerator vault, on the cyclotron itself and on concrete samples taken from various parts of the building walls, up to a depth of 50 cm in the shield. About 40% of all samples contain traces of neutron-induced radionuclides, mainly 60 Co (in metals), 133 Ba, 137 Cs, 152 Eu and 154 Eu (in concrete). Values of specific activities range from 5 mBq/g to 781 Bq/g. The maximum activity induced in concrete was observed at the depth of 40 cm in the wall near the cyclotron extraction channel. The laboratory measurements were supplemented by in-situ gamma spectrometry performed with the ISOCS system. A complete dose rate survey was also performed yielding isodose maps of the three levels of the building. The isotope production and the residual radioactivity in the barite walls of the SC bunker were simulated with the FLUKA and JEREMY codes in use at CERN for predicting residual radioactivity in activated accelerator components, and the results compared with the gamma spectrometry data. A detailed comparison of calculated and measured specific activities shows generally good agreement, to within a factor 2 in most cases. These results serve as indirect validation of the capabilities of these codes to correctly predict residual radioactivity with only a very approximate knowledge of the irradiation profile and after a very long (20 years) cooling time. Overall the results provided in this paper may be of use for estimating residual radioactivity in proton accelerators of comparable energy and for benchmarking computer codes.
Radiological risk analysis of particle accelerators
Reliability Engineering & System Safety, 2008
Considering the growing use of high-current accelerators in medicine, industry and research, there is a need for evaluating the hazard potentials of new accelerator systems from the design stage itself. The present paper discusses the factors taken care of in a radiological safety analysis of accelerators. Possible hazards identified are beam loss, target rupture, faulty components and personnel being trapped in an active area. Human error is one of the major factors leading to accelerator hazard. How radiation dose to both occupational workers and general public is reduced and taken care of are discussed. r
Experimental study of radiation shielding requirement for a 3 MeV proton Linac
RRCAT is developing a low energy front end linear accelerator to serve as an injector to the high energy proton accelerator for the establishment of Spallation Neutron Source. The front end Linac consists of an ion source, Low Energy Beam Transport (LEBT) and Radio Frequency Quadrupole (RFQ) delivering pulsed Hion beam of 3 MeV energy and 30 mA current to be stopped in a beam dump. In order to make reasonable estimates of prompt neutron and gamma dose rates from thick targets that can be used as the beam dump, an experiment was conducted at the Folded Tandem Ion Accelerator, BARC. The measurements were carried out at 0 and 90 with respect to the proton beam bombarding different targets that can be used as core material of beam dumps. The source terms in these two directions are important from the shielding point of view. The neutron spectrum and the dose rates were measured using a conventional and a LET based neutron dose equivalent meter, while the gamma dose rates were measured using a pressurised ion chamber based dosimeter. The results indicate that the neutron dose rates from Cu and GLIDCOP were similar in nature, while it was significantly lower for the Ni target. The gamma dose rates also showed the same trend with similar values for Cu and GLIDCOP while being lower for Ni target. The results have been used in evaluation of radiation shielding design for the 3 MeV protons Linac at RRCAT.
Progress in Nuclear Science and Technology, 2014
Beam loss criterion such as 1 W/m for an uniformly distributed loss has been applied at high power proton or heavy ion accelerator. It has been accepted based on the exposure level due to radioactive accelerator components during a hands-on maintenance and is a very important factor in shielding analysis of such high power, high energy accelerators. Well-developed Monte Carlo codes and inventory codes, which have been used for an activity calculation, were confirmed by benchmarking of published experimental data. The modular style method (PHITS+DChain-SP) and all-in-one style method (Fluka) using Monte Carlo code were applied to verify the criterion. The beam loss at bulk target and one-point loss at beam pipe and a uniformly distributed loss were simulated. The dose distribution and the decay scheme were compared with the control level of a hands-on maintenance. It was proved that more considerations were required instead of taking 1 W/m simply as the beam loss criterion. Especially the energy dependency effect was discussed mainly.