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European Laboratory for Particle Physics |
In the cleaning up operation that followed Radiation Protection Group (RP Group) was heavily involved. The radioactivity had mostly been kept contained in the confinement built around the dismantling site such that neither air nor floor contamination inside the North hall and nearby barely exceeded the Guideline values in CERN's Radiation Safety Manual for a simple Controlled radiation area. No radioactivity was detectable in the environment as it was confirmed by measurements the Host State Authorities performed when called upon. The cleaning up operation inside the North hall normalized the situation such that after one day only the very near zone and the interior of the confinement remained to be dealt with. Eventually the already disassembled DU plates were safely packed into boxes whilst that what remained of the detector stack was transferred back into the calorimeter vessel. Past experience with the dismantling of uranium calorimeters had in most cases shown a considerable surface deterioration of DU plates such that large amounts of triuranium octoxide (U3O8) came off during the disassembly. Outside experts investigating the cause of the uranium fire gave as a possible explanation that this time, contrary to the past experience, part of the powder that had been fallen off had been possibly composed of reduced forms of uranium oxides that can undergo further oxidation and hence ignite spontaneously.
In the fact finding report following the incident the competence of CERN's fire brigade as well as that of RP Group coping with the situation was acknowledged but a couple of queries arose particularly concerning the role of the Technical Inspection and Safety Division TIS in such dismantling operations. Whilst the inspecting (controlling) tasks of TIS are obvious, the Division and clearly RP Group also perform some executive duties in their normal work. The discussions are still on, however, it was decided that the Division that had caused the issue in bringing the uranium on to the site must bear the burden of the follow up. Hence EP and not the Strategic Material Controller shall organize the repatriation of the DU to the States.
In 1999 RP Group had even more heavily been involved than in previous years in work linked to the fact that both LEP (Large Electron Positron Collider) and LHC (Large Hadron Collider) are considered in France as Basic Nuclear Installations (INB). During the usual annual visit of the INB inspectors the results of radiation protection measurements for LEP operating at 98 GeV were presented and at the end of the year a series of measurements was performed around the LEP machine running at 100 GeV. Otherwise the Group predominantly participated in the writing of three official reports that are important to get the necessary authorizations for:
- operating LEP at energies above 100 GeV per beam,
- the dismantling of LEP and
- the construction and operation of the LHC.
The report "Avenant au Rapport définitif de Sûreté et aux Règles d'Exploitation du LEP: Augmentation de l'énergie du LEP à 105GeV" was delivered to INB in March and concentrated on the radiological consequences when driving LEP beam energies beyond 100 GeV. The salient point is whether the high-energy tail of the synchrotron radiation (SR) spectrum induces radioactivity in the machine components. It was found that only at 105 GeV, the highest energy investigated, some marginal levels of activity would be created but only in the part of the LEP vacuum chamber that is directly hit by SR.
The "Rapport préliminaire de Sûreté du LHC" was finished by October and contains a full description of the radiological issues for the large hadron collider including a detailed scheme of installation of radiation monitoring systems around the machine, in experimental areas as well as in the environment.
Finally the "Rapport de Sûreté pour le démantèlement du LEP" was sent to Paris in December. It contains the separation of LEP areas into nuclear and conventional zones according to the requirements for the dismantling of an INB. This zonage was based on a careful intercomparison of results of measured induced radioactivity in typical LEP materials placed around the two internal dumps of the machine with those of Monte Carlo calculations performed in the same geometry. In using these results it could be shown that most of the machine components are located within conventional i.e. non-radioactive areas of LEP. Later in the year the INB authorities demanded that in addition to the machine the dismantling of the experiments should be included in the report. Activities in the framework of INB will continue in the future as the new Convention between the Département de Sûreté Nucléaire (DSIN) in France and CERN will not only include the LHC but bring its injector SPS up to the target regions into the périmètre INB.
Many more new projects and improvement of existing installations were dealt with in 1999:
- Design studies were done for the operation of the Antiproton Decelerator (AD) with antiprotons and a reinforcement of the shielding was proposed.
- The Antiproton Trapping experiment (ATRAP) needed special attention due to the combined radiation of the antiproton beam and the use of a 5.5 GBq source of 22Na within the experiment.
- The research programs of the CERN Linear Collider (CLIC) and the CLIC Test Facility (CTF3) continue and required studies of an improved shielding layout.
- A feasibility study of a high intensity neutrino experiment at the PS was performed.
- The Time of Flight (TOF) project was presented at the Radiation Protection Committee (RPC) and approved. During the design phase important changes in the beam layout required a continuous and careful follow up.
- The shielding for the new Common Muon and Proton Apparatus for Structure and Spectroscopy experiment (COMPASS) in the Experimental Hall North 2 (EHN2) was completed. The radiation monitor system inside the hall was rebuilt whilst a new site station for the measurement of stray radiation was installed at the CERN fence nearby.
- The Long Base Line Neutrino Experiment sending CERN Neutrinos to Gran Sasso (CNGS) was continuously followed up as ideas about the beam lay out and the target region changed considerably in the course of the year. Following the approval of the installation by the CERN Council at the end of the year will require that the earlier studies made on the radiological impact of this installation on the environment are transformed into parts of the environmental impact report.
Although the preliminary Safety Report for the LHC had been submitted to INB in 1998, the Monte Carlo calculations for a more detailed and updated description of the radiation parameters of the collider continued. The topics of induced radioactivity, radiation doses to equipment and the influence of the LHC operation on the environment were covered. Calculations on the radioactivity produced in the event of a total beam loss in the LHC in a general sense and more detailed in the betatron-scraping region at point 7 and around point 8 were made. The production of radioactive isotopes in rock (molasse) in which the LEP/LHC tunnel is imbedded was studied for the expected beam losses. For a deeper understanding of the situation, a collaboration was started with the Ecole d'ingénieurs de Genève on the identification of natural radionuclides in molasse. This study is necessary in view of establishing the zero-base situation before the operation of the LHC starts. Estimation of doses to components close to the low-beta insertions at LHC point 2, A Large Ion Collider Experiment (ALICE), were performed and the shielding requirements for the access shafts to the LHC injection lines were looked into. Calculations on the radiological impact of radioactivity in gaseous form that may escape from the access pit of the future LHC were performed identifying the critical group of the population living nearby these pits and using the latest version of the diffusion model published by the Hauptabteilung für Sicherheit in Kernanlagen (HSK) in Switzerland.
The preparation for the LHC continued also in other fields and saw the following activities where RP Group was heavily involved:
- The de-classification of most of the West hall as a controlled radiation area in view of using it as an assembly hall for the ATLAS experiment,
- The dismantling of the SD18 building built on top of the SM18 pit and located over the positron injection region where after adding more top shielding it was assured that construction work in the area can be performed without creating a controlled radiation area and
- Preparatory work for the dismantling of the T1 target and the displacement of the H3 beam at the SPS in view of making space for the LHC injection region.
One of the tasks of RP, the dealing with radioactive material and waste, went into high gear in 1999. The Group elaborated the basis of a call for tender for a study concerning the pathways of radioactive material at CERN starting at the source e. g. radioactive machine parts taken out of the accelerator tunnel up to the possible elimination of these items as radioactive waste. In fact, this study anticipated the INB request that arrived in the second half of the year for an étude déchet the Organization must deliver. The RP proposal actually is contained in an annex of a report describing in detail the present state of radioactive material and waste at CERN. On the more practical side, the increasing amount of waste coming in for treatment and intermediate storage gave rise to a design study and cost estimate for an additional long term storage building in the radioactive waste treatment center located inside the PS ring.
Elimination of radioactive waste in general and from the accelerator environment in particular requires quantitative knowledge of the radionuclide inventory for the materials involved. To this end a collaboration with the Paul-Scherrer-Institut (PSI) was started for determining radionuclides in solid material that are difficult to measure like 3H. For a faster analysis of low concentrations of induced radioactivity a low level background laboratory equipped with a Ge diode with 60% efficiency was taken into operation mainly dedicated to the measurements of very low level radioactive (TFA) material from the LEP dismantling. A second Ge set-up and its corresponding lead shielding were optimized to measure the bags of radioactive waste to be sent to the PSI for elimination. A local network was installed to control the three Ge detectors, the NaI detector and the alpha spectrometer of the site section.
A new storage system for used ISOLDE targets was built in a side tunnel of the former Intersecting Storage Rings (ISR). This new system ensures a reduction in exposure to the persons involved in storage activities. In addition, it offers the possibility to take the targets out easily for future dismantling and sorting of the materials after sufficient cooling.
In collaboration with the Physikalisch Technische Bundesanstalt (PTB) the identification and measurement of alpha emitting radionuclides in the Isotope Separator on Line installation (ISOLDE) was investigated. This is in view of possible gaseous emissions from uranium or thorium production targets. The collaboration will continue.
The system monitors for the detection of radiation at the CERN gates was further improved by installing a double detector at the Main entrance. Some of the monitors on the Meyrin site had been influenced by the accelerator operation giving spurious alarms. Thanks to the efforts of the Technical Support Section of TIS-TE Group an elegant electronic solution was developed that permits to operate the monitors with an even higher sensitivity than before.
In personal dosimetry the working procedures (and habits) compatible with the new Quality Manual were firmly established. Another Manual is prepared for the calibration service and the accreditation of the latter with the Swiss Accreditation Service was started. The full procedure should be finished in 2000. In this context the writing of new and the updating of old Radiation Protection Procedures (PRP) as a precursor to future quality assurance documents continued throughout the year.
Two new developments in the field of personal dosimetry became known in the course of the year: Legal dosimetry in France now requires two dosimeters to be worn in parallel in controlled radiation areas: passive and operational (active) dosimeters where the performance of the latter should be upgraded to the same level as that of passive dosimeters. RP already had started in the past to replace the quartz fiber dosimeters by electronic devices. Although these dosimeters permit electronic readout fulfilling one of the French requirements for operational monitoring introducing the system will mean additional work of recording and follow up. The second news was that the NTA emulsion used in personal monitoring would no longer be available in 2001. This opens a new discussion on the future of personal dosimetry at CERN being further animated by the fact that the gamma film which had shown very good performance in the past has failed - although only marginally in 1999 - the Swiss performance test in two consecutive years.
On the more technical side, a new TLD reader was acquired and run in. The neutron film darkroom was completely refurbished and equipped with an automatic film processing system.
Discussions that are as old as the existence of CERN about medical fitness certificates for visiting scientists working in controlled radiation areas were taken up again in 1999 in collaboration with the Organization's Medical Service and the Association of CERN users (ACCU). It seems that in the long run only the access control through mechanical means based on personal access rights will give the desired traceability for the authorization of people into different areas. This will be the basic concept for the LHC underground experimental areas being classified INB. During the year an access control system for the ISOLDE experimental hall was proposed and will serve as a pilot project for future installations.
Following an idea that was born during the time of the CRII-Rad attack on the Organization and on the request of the Swiss Authorities a Radiation Protection Review Panel (RPRP) composed of five members of five CERN member states was launched to look into all aspects of radiation protection at CERN. The RPRP met once in autumn of 1999 and will continue its work in the new year.
Furthermore as an aftermath of the CRII-Rad affair and with respect to the environment a contract was signed between the Institut F. -A. Forel in Versoix, the ECOTOX Laboratory in Geneva, the Office Féderal de la Santé physique (OFSP) in Bern and CERN on a thorough investigation of the radiological situation in the river Nant d'Avril. As a first step the planned measurement station was set up in autumn.
The CERN-European Union (EU) Reference Radiation Facility (CERF) saw two runs of nearly two weeks each in 1999. CERF is very popular among physicists working in dosimetry hence beam time was running short with thirty different teams using the facility. The annual EU collaboration meeting was held at CERN in June.
As in the past members of the Group participated in working groups, committees and projects like the Neutrino Factory Working Group, the Electron Laboratory For Europe (ELFE), the Neutrinos at the Main Injector (NuMI) project in the States, the Arbeitskreis für Dosimetrie (AKD), the ISO Technical Committee 85 on radiation protection and the Swiss group of experts on dosimetry.
Every year when composing the summary of RP activities at CERN I am astonished how much my Group has been able to achieve. At the end of my mandate as group leader and on the occasion of my last Annual Report I would like to thank all my collaborators for supporting me and for their work for the Organization where in their efforts they frequently went beyond the call of duty. I have enjoyed my years at CERN working hard myself always trying to motivate my staff. In spite of some regrets everybody will have after 32 years of service I am proud of having guided the Radiation Protection Group during nine years to the satisfaction of the CERN personnel and Management as well as the Host State Authorities. As good news for the future I would like to mention that two young engineers Isabelle Brunner and Pierre Carbonnez joined RP Group during the year and will certainly help to keep up the quality of RP work. With regret we said Good-bye to Denise David who left CERN and the Group after 40 years of devoted service for a well-deserved retirement.
I consider the house that I leave behind as being in a good state and during the time that I am still at CERN I will help to make the transition for my successor Dr. Hans Menzel as smoothly as possible. The challenges he will face are not less than those I encountered in the past as the Group has to continue to document the quality assurance of its services, dig deeper into the problem of radioactive materials and waste and attack the question of operational dosimetry both passive and active. I wish Hans all the best for the future. May he get as much satisfaction in the job as I had the privilege to find myself.