KEK Radiation Related Topics neutrino beam construction subgroup Yuichi Oyama (KEK) and target monitor subgroup for

Contents (1) Proton beamline (2) Target Station (3) Decay Volume (4) Beam dump / Muon pit (5) Cooling water (6) Air/Helium beam period maintenance after beam stop

Arc Section 1W/m line loss Final Focusing 0.25kW point loss Preparation Section 0.75kW point loss Radiations in the Proton Beamline Following energy loss are assumed from our experience. ● Regulations H < 0.25  Sv/h at surface boundary of the concrete ● Soil Concrete H < 5mSv/h (line loss) and of the Soil H < 11mSv/h (point loss) at

Example : Shielding around the tunnel The thickness of the shielding is calculated by the Moyer’s formula and MARS simulation. ● Arc section Final Focusing section 0.25  Sv/h 1.2  Sv/h 0.05mSv/h 2.5m air 5.6m soil 2.3m concrete5.0m air 6.2m soil 2.5m concrete 11mSv/h

Example : Radiation in the Access Tunnel For more complicated geometry, MARS simulation is employed. ● The graphical view of the calculation shows that the ‘kink’ of the access tunnel effectively reduce the radiation. ● H ～ 0.5  Sv/h

３３ｍ Iron Shielding Helium Container Surface building service pit ２２ｍ Iron Shielding 40tonne crane Target, 1st Horn Beam Window 2nd Horn3rd Horn Final Focusing section Decay Volume Concrete Beam Window １１ｍ ground level Buffle Schematic view of the Target Station storage of radioactive materials Underground machine room Concrete

H < of the concrete Iron2.2m 20cm Concrete wall Iron1.5m Concrete 3.6m Conc 1m Radiation during the beam operation （２）（２） （３）（３） （１）（１） H < 0.25  of the control area fence Regulations Concrete 4.5m H < 12.5  of surface building Threemust be satisfied.

Calculation of shielding thickness by MARS Instead of 3D real geometry, virtual cylindrical geometry is used to improve statistics. ● Calculation with 3D real geometry are in progress for the final confirmation. ●

Example: floor of the surface building z r Target station With 4.5m of concrete above the service pit, radiation at floor of the surface building satisfy H <12.5  Sv/h

Determination of the control area boundary by MCNP Surface building 0.25  Sv/h Top view We need 10m between the surface building and the fence ● Neutron sources are defined on the floor, and the dose above the floor is adjusted to be 12.5  Sv/h. ● 12.5  Sv/h

低温設備 Target Station 2nd machine room Control area (class-2) Radiation Control Area Control area (class-1)

Residual Dose after beam stop ~0.1  Sv/h Service PitMachine room After beam stop and ventilation, we must access this area After 1 year operation and 1 day cooling with 0.75MW, the residual dose at the top of the iron shielding is We can enter and work in the service pit.

Exchange of the target and/or horn storage of radioactive materials Target station : top view Target station : Cross-sectional view ● ● Open the top of the beamline shielding Broken target/horn is highly radioactivated, and must be kept in the storage of radioactive materials for several years. The shielding also must be kept in the storage during the exchange ●

Residual dose of the Target/Horn ● Residual dose of 3cm  x 90cm Carbon Graphite target (in a Al container) and 1 st magnetic horn is calculated. + DCHAIN-SP + 7 Be life 50GeV 0.75MW proton Target Horn (1)(Sv/h)(2)(Sv/h)(1)(Sv/h) 1 day month year year8.3x x year year x QAD-CGGP2 (1)NMTC/JAM(nmtclib95) + cross section(9mb) (2)Hadron fluence(MARS) After 1 year operation ● Horn must be kept in the storage for more than 10 years.

Aluminum 0.2m Concrete 1m Iron 2.2m 22  Sv/h 0.56Sv/h 0.65Sv/h 0.1  Sv/h Residual dose of the Shielding ● ● Residual dose of the shielding calculated by MARS (1 year operation, 1 day cooling, 0.75MW) ● Further calculation is needed after the “scenario” is fixed. Use of Al surface reduce the radiation about one order of magnitude.

Open the shielding 3m Requirement for the boundary during the maintenance 0.25  Sv/h MCNP is used.  -ray source are ● defined on the Al tunnel surface. 0.75MW 1-year operation, 1-day cooling Radiation from residual dose in the tunnel is satisfactory small. ● 0.4Sv/h

Calculation of Decay Volume Shielding As the target station, virtual cylindrical geometry is used in the MARS calculation. ● m downstream of target station He Concrete 5.5m 5mSv/h log(H(mSv/particle)) Concrete thickness (m) 5.0 ～ 5.9m of concrete and additional ～ 6m of soil are needed to satisfy concrete and soil surface condition ●

Radiation behind the Beam Dump ● At the muon pit, muons from  →  must be measured with energy threshold of 2 ～ 5GeV to study neutrino property. ● Copper 1.5m + Iron 1.5m + concrete 0.5m satisfy this requirement. The threshold for the muons is E th ～ 4.5GeV ● The residual dose in the muon pit(30days beam, 1 day cooling, 0.75MW) is 0.2  Sv/h. ● We can enter the muon pit after the beam stop.

To 2nd machine building Management of Cooling Water ● Radioactive primary cooling water is circulated only in the underground control area during the beam period. ● Regulation : Radioactive water can be exhausted to outside (ocean) if radioactivity is less than 15Bq/cc. Target/Horn cooling Heat exchange Primary cooling water system Secondary cooling water system Third cooling water system

Disposal Scenario of Radioactive Water ● After 20days operation, the all radioactive water is transferred to a DP tank in the disposal system. The cooling system for the decay volume is used for this purpose (to save money). ● After measurement of radioactivity in the dilution tank, the water can be disposed. It takes 1 or 2 days for the measurement. Heat exchange Decay Volume TS underground machine room Beam Dump machine room Primary cooling water from Target/Horn Primary cooling water from Beam Dump Fresh water Dilution tank DP tank Disposal line They are mixed with fresh water in the dilution tank. ●

component Water in the beam- line (liter) Water in the system (liter) Neutron fluence (/cm 2 /p) Total 3 H (GBq) 15Bq/cc equiv. Vol. (m 3 ) Norm. Cond. Mag Target11008x Horn x x x366x3 Target Station x Decay Volume x Beam Dump x MW, 20days operation Summary of cooling water and their ● We need a capacity of ～ 600m 3 to dispose all together. If we make 60m 3 dilution tank, we must repeat the dilutions 10 times. radio-activation ● We must also consider a possibility to confine the primary cooling water in the radiation control area forever.

Ventilation of Air and Helium ● ● Air in the low radioactivity area (e.g. surface building) is always ventilated even during the beam period. Regulation : Radioactive gas (air/Helium) can be ventilated to environment if radioactivity is less than 5mBq/cc. High radioactivity area (e.g. underground control area) is closed in the beam period. ● After the beam stop, high radioactive air/Helium must be mixed with fresh air and ventilated gradually if the radioactivity exceed 5mBq/cc.

component volume (m 3 ) Neutron fluence (/p/cm 2 ) Radio- activatio n(Bq/cc) 5mBq/cc equiv. Vol. (m 3 ) Ven tilati on Ventilatio n time(h) Surface building   A1 Service pit230 5   B0.03 U.g. machine room330 5   B0.04 radioactive storage780 5   B0.1 Iron cooling (out)?38 1   B0.005 Iron cooling (cent)?33 1   B?0.004 Iron cooling (in)?28 2  C5.6 TS Helium (air)135 2  (80)86400C10.8(270) DV Helium (air)  (20)256000C32(800) 0.75MW, 20days operation Summary of Air/Helium and their radio-activation  air =30mb,  He =1.2mb, Ventilation : 8000m 3 /h, < 5mBq/cc A : Ventilate during beam period; B : Ventilate directly after beam stop C : Ventilate by mixing with fresh air after beam stop