What need to be done to restart n_TOF (in 2007?) 4 Short description of the Facility 4 Old Target removal in the provisional Storage place (Service Gallery). 4 New Target Design and Construction 4 Ventilation of the Target Area 4 Target Repository for the new Target 4 Summary Presented by P. Cennini n_TOF Technical Coordinator ATC-ABOC Days, CERN January 2007

n_TOF Short Description ATC-ABOC Days, CERN January 2007 The main characteristics of the Facility are: Broad Neutron Energy eV to 250 MeV Broad Neutron Energy eV to 250 MeV High Integral Neutron Flux: 6.2  10 5 n/cm 2 /7  p (uncollimated) High Integral Neutron Flux: 6.2  10 5 n/cm 2 /7  p (uncollimated) Long flight path: m Long flight path: m Very good Energy Resolution:0.05 % at 1 keV 0.4 % at 1MeV, 2 % at 100 MeV. Very good Energy Resolution:0.05 % at 1 keV 0.4 % at 1MeV, 2 % at 100 MeV. n_TOF is a neutron source used for the measurement by Time Of Flight of neutron induced reactions n_TOF is a neutron source used for the measurement by Time Of Flight of neutron induced reactions The neutrons are produced by the impact (spallation) of a 20 GeV/c proton beam on a lead Target. The neutrons are produced by the impact (spallation) of a 20 GeV/c proton beam on a lead Target.

n_TOF Short Description ATC-ABOC Days, CERN January 2007

n_TOF Short Description: The neutron flux at the Measuring Station ATC-ABOC Days, CERN January 2007 Neutron Energy, log 10 (E) [eV] Neutron flux [dn / dlogE / cm 2 /pulse Pb r=40 cm l= 40 cm 5 cm H 2 O Moderation 1 eV 16 ms 100 MeV 1.6 µs

n_TOF Short Description: Energy Resolution & proton Beam ATC-ABOC Days, CERN January  proton 20 GeV/c RMS  7 ns Protons on Target: 3.5x10 13 p distributed in a SUPERCYCLE (16.8 s long) in DEDICATED MODE (7x10 12 p/bunch) or in PARASITIC MODE (4x10 12 p/bunch).

n_TOF Geographical Situation ATC-ABOC Days, CERN January 2007

Dimensions: 80  80  60 cm 3 Pure Lead: 4 t H 2 O moderator: 5 cm Al-window: 1.6 mm Al-container: 140 l The Lead Target ATC-ABOC Days, CERN January 2007

Target Handling ATC-ABOC Days, CERN January 2007 The Target must be moved from TT2-A to the Depository in the Service Gallery. The Target must be moved from TT2-A to the Depository in the Service Gallery. This operation is done through the Shaft by using the Hoist System. This operation is done through the Shaft by using the Hoist System. A system using several video cameras is used for the remote control. A system using several video cameras is used for the remote control.

Old Target Removal: Present Status. ATC-ABOC Days, CERN January 2007 Shielding in the Shaft: removed Shielding in the Shaft: removed Direct measurement of the dose rate: done (~15 mSv/h max) Direct measurement of the dose rate: done (~15 mSv/h max) Simulations of the Target activation and dose mapping: done Simulations of the Target activation and dose mapping: done (results in agreement with the measurement) Risk analysis for the removal (EDMS ) : done Risk analysis for the removal (EDMS ) : done Operating Procedure (EDMS ) : done Operating Procedure (EDMS ) : done Dose rate estimation for the Procedure (EDMS ) : done Dose rate estimation for the Procedure (EDMS ) : done

Old Target Removal: What need to be done ATC-ABOC Days, CERN January 2007 Problem: reliability of the Hoist System Problem: reliability of the Hoist System The probability of failure of the existing system is considered too high. Solutions: Solutions: Installation of a new Crane with improved reliability Installation of a new Crane with improved reliability This solution has been already investigated. An offer in the framework of the “Contrat de maintenance Equipement de Levage et de Transport” is available. (Cost 320 kCHF, delivery time 19 weeks) Modification of the existing Crane Modification of the existing Crane The feasibility of a solution requiring a mechanical design validated by SC-GS in the framework of Code D1-7.2, has been investigated (EDMS ). Independently on the adopted solution, the infrastructure and the procedure for the Target recovering in case of stacking of the Hoist System must be provided. Independently on the adopted solution, the infrastructure and the procedure for the Target recovering in case of stacking of the Hoist System must be provided. (According with informal discussions with SC-GS)

The New Target: Motivation & Design Options ATC-ABOC Days, CERN January 2007 Why a new Target for n_TOF? Why a new Target for n_TOF? To avoid the contact between the lead and the cooling water Considering: Considering: The activation of the shielding around the Target Area. The activation of the shielding around the Target Area. The time needed to remove and reinstall the shielding (6 months). The time needed to remove and reinstall the shielding (6 months). The “cost” of the received dose to do this operation (ALARA). The “cost” of the received dose to do this operation (ALARA). The short time schedule (expected n_TOF restart mid August 2007) The short time schedule (expected n_TOF restart mid August 2007) The “Gained Experience” with the old Target The “Gained Experience” with the old Target Two lines have been investigated: Two lines have been investigated: 1. Cladded lead Target cooled with the existing cooling system 2. New design (tungsten, tantalum, air cooling, …) The Cladded Lead Target solution is envisaged at the present time.The Cladded Lead Target solution is envisaged at the present time. The access to the Target area is done via the shaft without the need to remove the shielding in TT2-AThe access to the Target area is done via the shaft without the need to remove the shielding in TT2-A

The New Target: Design Specifications ATC-ABOC Days, CERN January 2007  Neutron Flux: unchanged  Target material: lead  Target cladding: aluminum alloy, stainless steal or zircalloy.  Target cooling: water (existing system)  Target dimension: ~ 100 liters, ~1.3 tons (cylindrical shape)  Moderation: water / heavy water / borated water (exchangeable)  Useful n-beam diameter at the exit of the target: 40 cm  Orthogonal flight-path: foreseen  2.2 MeV  flash: optimized (10 %), by replacing the Moderator.  Decommissioning: this aspect is taken in account. Due to a very low activation, transparency to neutrons (allowing the use of thick walls) and metallurgical compatibility with the lead, the use of an aluminum alloy for the cladding and the support structure should be privileged.Due to a very low activation, transparency to neutrons (allowing the use of thick walls) and metallurgical compatibility with the lead, the use of an aluminum alloy for the cladding and the support structure should be privileged.

The New Target: Flux Simulations, Geometry ATC-ABOC Days, CERN January 2007 H2OH2OOld Target H 2 OD2OD2O p Case studied

The New Target: Flux Simulations ATC-ABOC Days, CERN January 2007 Old Target H 2 O New Target H 2 O Ratio New/Old Considering the advantages of a smaller Target dimension, (decommissioning, handling) the flux reduction is acceptable Moderator thickness 5 cm ~4.4 tons of lead ~1.3 tons of lead

The New Target: Geometry ATC-ABOC Days, CERN January 2007 p beam Lead Cooling Water Moderator Container H 2 O or D 2 O Cladding Existing Cooling Basin (aluminum)

The New Target: Simulations, Energy Deposition ATC-ABOC Days, CERN January 2007

The New Target: Simulations, Thermal Study Transient elasto-plastic study in progress ATC-ABOC Days, CERN January 2007

The New Target: What need to be done ATC-ABOC Days, CERN January 2007  Visual Inspection of the old Target and sample analysis to verify the feasibility of the design options. Learn from the gained experience on the old Target after 5 years of run (~ 6 x10 19 protons on target).  Visual Inspection of the Cooling basin and the connection piping to the Heat Exchanger to verify the possibility to use the existing Cooling System. In case of serious contamination, the cleaning of the system should be envisaged. The two actions require the availability of a HOIST SYSTEM  Finalize the Design Study. Several solutions are investigated and, if needed, some specifications could be reconsidered like the implementation of the moderator exchange.  Conclude the Simulations (neutron flux, energy deposition) for the final Design  Write-up of the Safety File (peer review)  Activation and Dose-rate Simulations in view of the Permanent Disposal.

Ventilation of the Target Area: Ventilation Parameters ATC-ABOC Days, CERN January 2007

Ventilation of the Target Area: Simulations Parameters ATC-ABOC Days, CERN January 2007 Isotope production yield:Isotope production yield: simulated with FLUKA (39 isotopes considered) Target material: LeadTarget material: Lead (dimensions of the old Target) Target Shielding: unchangedTarget Shielding: unchanged Irradiation time:Irradiation time: 6 months/year Proton intensity: p/supercycleProton intensity: 5x 7x10 12 p/supercycle Protons on target:xProtons on target: 3.2x10 19 p (previous runs 1.3x10 19 p) Dose to the publicDose 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 of the Target Area: Simulation Results ATC-ABOC Days, CERN January 2007 The Estimated Dose for the Critical Group produced by n_TOF during a yearly run of 180 days at the maximum allowable proton intensity is: The Estimated Dose for the Critical Group produced by n_TOF during a yearly run of 180 days at the maximum allowable proton intensity is: Continuous Laminar Flow : ~ 1µSv (~0.25 nSv/h) **Continuous Laminar Flow : ~ 1µSv (~0.25 nSv/h) ** Flush Before Access: ~ 0.01 µSv/flushFlush Before Access: ~ 0.01 µSv/flush ** Dominated by 7 Be, 32,33 P and 41 Ar.

Ventilation of the Target Area: Layout for the minimum Release Scenario ATC-ABOC Days, CERN January 2007 RP Monitor

Ventilation of the Target Area: Feasibility ATC-ABOC Days, CERN January 2007 Location of the ventilation machinery: ISR-I8 Location of the ventilation machinery: ISR-I8 Location of the Radiation Measurement Station: ISR-I8 Location of the Radiation Measurement Station: ISR-I8 Release of the air: top of the ISR hill (at sufficient altitude) Release of the air: top of the ISR hill (at sufficient altitude) Main Characteristics Permanent air circulation in the Target Area Permanent air circulation in the Target Area Continuous filtering (efficient capture of 7 Be and 32,33 P) Continuous filtering (efficient capture of 7 Be and 32,33 P) Monitoring of the released air Monitoring of the released air

Ventilation of the Target Area: What need to be done ATC-ABOC Days, CERN January 2007  The release to the Public close to the detection level of n_TOF, is reachable (probably not distinguishable from the variations of the natural background). òOptimization could be studied, economic and social factors being taken in account (reduced full scenario). òThe solution adopted will be in conformity with the global Agreement between CERN and the Host States.

Repository for the New Target What need to be done ATC-ABOC Days, CERN January 2007 òAt the date there is only one place in The Service Gallery to store (temporarily) a Target. òThe place for an additional Storage Place for a radioactive device is available. òThe procedures for the final disposal of the old Target outside CERN are under discussion with the Swiss Authorities and PSI. òThe possibility to do this operation in 2007 or 2008 subsist, making available the existing place to store the new Target in the near future (if needed). Therefore òThe construction of the new Repository could be postponed

What need to be done to restart n_TOF Summary ATC-ABOC Days, CERN January 2007 TitleDescription GroupFTEkCHF Old Target RemovalNew Crane Purchase AB-ATB 320 Video Remote ControlAB-ATB Old Target RemovalModification Existing Crane AB-ATB SC-GSTS-IC New Target Design & Production AB-ATB Simulations (neutronics) AB-ATB 0.5 Target Area Ventilation Civil EngineeringTS-CE 40 (full scenario)Ventilation System DesignTS-CV Air Recirculation SystemTS-CV 35 Air Extraction SystemTS-CV 35 Environmental MonitoringSC-RP 90 New target Disposal (CERN)Repository ConstructionTS-CE 100 Experimental Area Alignment System AB-ATB TotalAB-ATB TotalAB-ATB (2.55) (630) (2.55) (630) Target Permanent DisposalInfrastructure DesignAB-ATB RadioprotectionSC-RP 0.2 SimulationsAB-ATB 0.2

What need to be done to restart n_TOF Summary ATC-ABOC Days, CERN January 2007 TitleDescription GroupFTEkCHF OperationRe-Installation n_TOF BeamAB-ATB 0.3 AT-VAC TS-IC TS-CV 0.05 TS-SU 0.05 RadioprotectionSC-RP 0.3 Total AB-ATB Total AB-ATB Option 1 -New Crane, New Target, New Target Repository, Ventilation, Old Target Definitive Disposal, Alignment System: FTEs AB-ATB 3.1, Budget 1100 kCHF Option 2 -Modification Old Crane, New target, Ventilation, Old Target Definitive Disposal: FTEs AB-ATB 2.95, Budget 650 kCHF Estimations presented to the ATC