Risk Analysis P. Cennini AB-ATB on behalf of the n_TOF Team  Procedure  Documents in preparation  Conclusions Second n_TOF External Panel Review, CERN, 14 February 2008

Procedures  According with the CERN Safety Policy a new Project or a significant Upgrade of an existing System, require the preparation of a Safety File.  The scope of this document is to guarantee that the Safety Rules applying at CERN are satisfied and that the adopted solutions are in line with the ALARA principle as far as the Radioprotection is concerned. A Safety File is divided in three documents: 1.Explanatory Part where the solution adopted are described 2.Demonstrative Part where the choices are justified 3.Operating Part where the operating procedures are described The Operating Part is “dynamic” and is continuously upgraded following the Acquired Experience during exploitation.

Procedures The Documents are classified in the EDMS and validated following a defined Approval Procedure

Procedures  In the Safety File the description is maintained concise.  In the document there are links to detailed descriptions, calculations or test.  Depending on the level of potential Danger, a Risk Analysis is organized to help in the choice of Options.

Documents in preparation: Ventilation System This document is of primary importance because is covering the risks of contamination for the Public. The solution adopted, based on the simulations reported in the next slides, is a continuous air recirculation in the Target Area without exchange with outside. The circulating air is filtered and the isotope content monitored. The access in the area is granted only with beam off (interlock) and after an appropriate delay. The air in the tunnel is expelled only if the radioactivity is below the exception limits. The Operating Procedure is a part of the Safety Document.

Ventilation System: Area lay-out Critical Group: Border Guards Target Experimental Area Decay Tube

Ventilation System: Simulation parameters Isotope production yield: simulated with FLUKA (39 isotopes considered) Isotope production yield: simulated with FLUKA (39 isotopes considered) Target material: Lead (dimensions of the old Target) Target material: Lead (dimensions of the old Target) Target Shielding: unchanged Target Shielding: unchanged Irradiation time: 6 months/year Irradiation time: 6 months/year Proton intensity: 5x 7x10 12 p/supercycle (2.4x10 12 p/s) Proton intensity: 5x 7x10 12 p/supercycle (2.4x10 12 p/s) Protons on target: 3.8x10 19 p (previous runs 1.6x10 19 p) Protons on target: 3.8x10 19 p (previous runs 1.6x10 19 p) Dose to the public Dose to the public - Definition of critical groups (border guards) - Calculation of dose conversion coefficients based on environmental models Investigated Solutions: Investigated Solutions: - Continuous Laminar Flow - Enclosed volume with Recirculation and Flush Before Access

Ventilation System: Release estimation The Estimated Dose for the Critical Group produced by n_TOF on the basis of a 180 days run at the maximum allowable proton intensity is: Continuous Laminar Flow : ~ 1µSv (~0.25 nSv/h) Flush Before Access: ~ 0.01 µSv/flush Since the goal for the whole CERN is to release <10 µSv/year, the Flush Before Access solution is adopted. For this item the Risk Analysis, part of the Safety File, is considered sufficient

Target Cooling System: Risk Analysis This item presents also the risks for the Public due to the possible release of contaminated water outside CERN. The risks for Personnel should be also carefully evaluated. Since the Target Cooling is a pressurized system, the possible spill of contaminated water must be evaluated. The risk reduction is done at the design level adopting the CODAP code used for the design of pressurized vessels and by implementing in any part of the system the “double containment” approach. For this item the Risk Analysis, part of the Safety File, is considered sufficient

Documents in preparation: Vacuum System This item presents risks for Personnel. The risks associated to the possible abrupt breaking of a window in a tube under vacuum is a common problem in the CERN Accelerators tunnels. The risks associated to the vacuum tube in the n_TOF neutron time of flight path should be evaluated due to the large volume under vacuum. The potentially dangerous part is constituted by three sectors ~ 60 m longs of Ø=80, 60, 40 cm (~ 60 m 3 ). On the Ø=80 side a window described in the next slide is closing the volume. On the Ø=40 side a Gate Valve (very robust construction) is closed in case of access to the Experimental Area (interlock)

Vacuum System: The neutron Window The neutron window, constructed machining a monolithic Al alloy block, has a reinforced structure assuring good mechanical performances. According with a study taking in account the fatigue endured in the past runs, the life time expectation under the new load conditions is estimated to: ~ 2x10 11 pulses of 7x10 12 protons (~ 10 5 years of run…….)

Risk Analysis: Vacuum System The possibility of an abrupt breaking of the neutron window (or valve) should be assessed and the consequences evaluated. For this item the Risk Analysis, part of the Safety File, could be validated by an external consultancy.

Documents in preparation: Old Target Disposal After the first discussion on the subject with PSI made last year before the target removal, the shipment to PSI is a realistic solution. The Safety File describing the shipping procedure based on the measured dose rate and FLUKA simulations will be prepared during The shipment could take place end 2008 or beginning In principle the target will be housed in a sealed container disposed together with the target. Finalisation of the shipment will be discussed with PSI. For this item the Risk Analysis, part of the Safety File, is considered sufficient

CONCLUSION The Safety File procedure is a good tool for the assessment of the measures taken to minimize the risks. The Safety File procedure is a good tool for the assessment of the measures taken to minimize the risks. The risk evaluation is done on the basis of a standard matrix. The risk evaluation is done on the basis of a standard matrix. In case of a recognized high risk level, an external consultancy remains an open option. In case of a recognized high risk level, an external consultancy remains an open option. Many aspects of the Safety have been already analyzed but the formal document are not yet ready. Many aspects of the Safety have been already analyzed but the formal document are not yet ready. The Risk Analysis will be done in parallel with design effort. The Risk Analysis will be done in parallel with design effort. Thank you for your attention Thank you for your attention