n_TOF Technical Reportn_TOF Technical Report

INTC, CERN 21 May 2007

P. Cennini AB-ATBn_TOF Technical Coordinator

• Status of the old Target Removal Status of the old Target Removal • New target designNew target design• Infrastructure upgrade Infrastructure upgrade

Target HandlingTarget Handling

• 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 passing through the Shaft by using the Hoist System.This operation is done passing 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 RemovalOld Target Removal

• Shielding removal in the Access PitShielding removal in the Access Pit : : donedone• Radioactivity measurement in the Access PitRadioactivity measurement in the Access Pit: : donedone• Simulations of the Target ActivationSimulations of the Target Activation: : donedone• Risk Analysis for he Target RemovalRisk Analysis for he Target Removal: : done done (EDMS 771843)(EDMS 771843)

• Procedure for the Target RemovalProcedure for the Target Removal: : done done (EDMS 774982)(EDMS 774982)

• Crane upgradeCrane upgrade:: under discussionunder discussion• Un-sticking test:Un-sticking test: done . done .• Proposal for the Target removal by using the existing Proposal for the Target removal by using the existing Hoist system:Hoist system: waiting for approval waiting for approval (EDMS 774982)(EDMS 774982)

• Any further action on the target is conditioned by the Any further action on the target is conditioned by the purchase of a new Host Systempurchase of a new Host System(10 to 12 months delay and ~350 kCHF budget)(10 to 12 months delay and ~350 kCHF budget)

Old Target Removal:Old Target Removal: What need to be doneWhat need to be done

• Problem: Problem: The Hoist SystemThe Hoist SystemThe existing system is not agreed for the handling of a radioactive loadThe existing system is not agreed for the handling of a radioactive load

• Solutions:Solutions:

• Installation of a new CraneInstallation of a new CraneThis solution has been already investigated. This solution has been already investigated. (Cost 350 kCHF, delivery time 4 to 6 months for the purchasing procedures and 5 to 6 (Cost 350 kCHF, delivery time 4 to 6 months for the purchasing procedures and 5 to 6 months for construction and installation)months for construction and installation)

• Modification of the existing CraneModification of the existing CraneThe feasibility of a solution requiring a mechanical design validated by SC-The feasibility of a solution requiring a mechanical design validated by SC-GS in the framework of GS in the framework of Code D1-7.2Code D1-7.2, has been investigated , has been investigated (EDMS 787079).(EDMS 787079).

• Definition of an exceptional procedure for the target recoveryDefinition of an exceptional procedure for the target recovery in in case of stacking of the existing Hoist System (Risk Analysis)case of stacking of the existing Hoist System (Risk Analysis)

• Independently on the adopted solution, Independently on the adopted solution, the infrastructure and the the infrastructure and the procedure for the Target recovering in case of stacking of the Hoist System procedure for the Target recovering in case of stacking of the Hoist System must be found.must be found.

The New Target:The New Target:Design OptionsDesign Options

• Considering:Considering: The The activationactivation of the shielding around the Target Area. of the shielding around the Target Area. The The timetime needed to remove and reinstall the shielding (6 months). needed to remove and reinstall the shielding (6 months). The “cost” of the received dose to do this operation The “cost” of the received dose to do this operation (ALARA).(ALARA). The The “Gained Experience”“Gained Experience” with the old Target with the old Target

• Two lines have been investigated:Two lines have been investigated:1.1. Cladded lead TargetCladded lead Target cooled with the existing cooling system cooled with the existing cooling system

2.2. New designNew design (tungsten, tantalum, air cooling, …) (tungsten, tantalum, air cooling, …)

• The The Cladded Lead TargetCladded Lead Target is solution studied up to now is solution studied up to nowhttp://pceet075.cern.ch/Meetings/TB2006/ The Mini-Pool SolutionThe Mini-Pool Solution

The design study for other solutions is pending the decision on budget The design study for other solutions is pending the decision on budget and resources allocationsand resources allocations

The New Target:The New Target:Design SpecificationsDesign Specifications

Neutron Flux: Neutron Flux: unchangedunchanged Target materialTarget material: : leadlead Target cladding:Target cladding: aluminum alloy, stainless steal or zircalloy.aluminum alloy, stainless steal or zircalloy. Target cooling:Target cooling: water (existing system)water (existing system) Target dimension:Target dimension: ~ 100 liters, ~1.3 tons (cylindrical shape)~ 100 liters, ~1.3 tons (cylindrical shape) Moderation:Moderation: water / heavy water / borated water (exchangeable)water / heavy water / borated water (exchangeable) Useful n-beam diameter at the exit of the target:Useful n-beam diameter at the exit of the target: 40 cm40 cm Orthogonal flight-path:Orthogonal flight-path: foreseenforeseen 2.2 MeV 2.2 MeV flash: flash: optimized (10 %), by replacing the Moderator.optimized (10 %), by replacing the Moderator. Decommissioning: Decommissioning: this aspect is part of the new design.this aspect is part of the new design.

• Due to a very Due to a very low activationlow activation, , transparency to neutrons transparency to neutrons (allowing the (allowing the use of thick walls)use of thick walls) and metallurgical compatibility with the lead and metallurgical compatibility with the lead and and the existing poolthe existing pool, the use of an aluminum alloy for the cladding and the , the use of an aluminum alloy for the cladding and the support structure should be privileged .support structure should be privileged .

The New Target:The New Target:GeometryGeometry

p beam

Lead

Cooling WaterModerator ContainerH2O or D2O

Cladding

Existing Cooling Basin (aluminum)

The New Target:The New Target:Flux SimulationsFlux Simulations

Old Target H2O

New Target H2O

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:The New Target:Simulations, Energy DepositionSimulations, Energy Deposition

The New Target:The New Target:Simulations, Thermal StudySimulations, Thermal Study

Transient elasto-plastic study in progress

The New Target:The New Target: What need to be doneWhat need to be done

Visual Inspection of the old Target and sample analysis to Visual Inspection of the old Target and sample analysis to verify the verify the feasibility of the design optionsfeasibility of the design options..

Learn from the gained experience on the old Target after 5 years of run Learn from the gained experience on the old Target after 5 years of run (~ 6 x10(~ 6 x101919 protons on target) protons on target)..

Visual Inspection of the Cooling basin and the connection piping to the Heat Visual Inspection of the Cooling basin and the connection piping to the Heat Exchanger to Exchanger to verify theverify the possibility to use the existing Cooling Systempossibility to use the existing Cooling System. In . In case of serious contamination, the cleaning of the system should be case of serious contamination, the cleaning of the system should be envisaged.envisaged.

The two actions require the availability of a HOIST SYSTEMThe two actions require the availability of a HOIST SYSTEM

Finalize the Design Study. Several Finalize the Design Study. Several solutions are investigatedsolutions are investigated and, if needed, and, if needed, some specifications could be reconsidered like the implementation of the some specifications could be reconsidered like the implementation of the moderator exchange.moderator exchange.

Conclude the Conclude the Simulations Simulations (neutron flux, energy deposition) for the final (neutron flux, energy deposition) for the final DesignDesign

Write-up of the Write-up of the Safety FileSafety File (peer review) (peer review) Activation and Dose-rate Simulations in view of the Activation and Dose-rate Simulations in view of the Permanent DisposalPermanent Disposal..

Ventilation of the Target Area:Ventilation of the Target Area:Ventilation ParametersVentilation Parameters

Ventilation of the Target Area:Ventilation of the Target Area:Simulations ParametersSimulations Parameters

• Isotope production yield:Isotope production yield: simulated with FLUKA (39 isotopes considered)• Target material:Target material: Lead Lead (dimensions of the old Target)• Target Shielding: Target Shielding: unchangedunchanged• Irradiation time:Irradiation time: 6 months/year• Proton intensity:Proton intensity: 55x 7 7x10101212 p/supercycle p/supercycle• Protons on target:Protons on target: 3.2xx1019 p (previous runs 1.3x1019 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- Continuous Laminar Flow- Enclosed volume with recirculation and Flush Before Access- Enclosed volume with recirculation and Flush Before Access

Ventilation of the Target Area:Ventilation of the Target Area:Simulation ResultsSimulation Results

The Estimated Dose for the Critical Group produced by The Estimated Dose for the Critical Group produced by nn_TOF during a yearly run of 180 days at the maximum _TOF during a yearly run of 180 days at the maximum allowable proton intensity is:allowable proton intensity is:

• Continuous Laminar Flow :Continuous Laminar Flow : ~ 1µSv ~ 1µSv (~0.25 nSv/h)(~0.25 nSv/h) ****

• Flush Before Access:Flush Before Access: ~~ 0.01 µSv/flush0.01 µSv/flush

**** Dominated by Dominated by 77Be, Be, 32,3332,33P and P and 4141Ar.Ar.

Ventilation of the Target Area:Ventilation of the Target Area: FeasibilityFeasibility

• Location of the ventilation Location of the ventilation machinery: ISR-I8machinery: ISR-I8

• Location of the Radiation Location of the Radiation Measurement Station: ISR-I8Measurement Station: ISR-I8

• Release of the air: top of the Release of the air: top of the ISR hill (at sufficient altitude)ISR hill (at sufficient altitude)

Main CharacteristicsMain Characteristics

• Permanent air circulation in Permanent air circulation in the Target Areathe Target Area

• Continuous filtering (efficient Continuous filtering (efficient capture of capture of 77Be and Be and 32,3332,33P)P)

• Monitoring of the released air Monitoring of the released air

Ventilation of the Target Area: Ventilation of the Target Area: What need to be doneWhat need to be done

The The release to the Public release to the Public close to the detection level of close to the detection level of nn_TOF, _TOF, is reachableis reachable (probably not distinguishable from the variations of the (probably not distinguishable from the variations of the natural background)natural background)..

Optimization could be studied, Optimization could be studied, economic and social factors economic and social factors being taken in account (reduced full scenario).being taken in account (reduced full scenario).

The solution adopted will be in The solution adopted will be in conformity with the global conformity with the global Agreement between CERN and the Host StatesAgreement between CERN and the Host States. .