T2K radiation shield and waste Aug Yuichi Oyama (KEK) Revised on Oct

In the past NBI workshops……. Radiation shielding of Proton Beamline, Target Station, Decay Volume, Beam Dump/Muon Pit and access tunnels were discussed in NBI See ● Design of cooling water system as well as ventilation system of air/Helium were reported in NBI See ● ● In this talk, I would like to concentrate on real operation and problems related to the cooling water systems, and problem related to radioactivity from Air/Helium. I do not talk about radiation shield.

Radio-activation of cooling water ● Radioisotopes are produced from Oxygen in H 2 O. Neutrons from the beam with energy larger than ~20MeV break the O nuclei O 8 Several kinds of isotopes with Z ≦ 8 and N ≦ 8 are made as spallation products. ● Nominal cross sections are ~30mb. They are 3 H, 7 Be, 11 C, 13 N, 15 O, 14 O, 16 N, 14 C. ● Production rate of the radioisotope is obtained from  (neutron flux) x  (cross section) x V(volume of water).

E(MeV)lifetime comments 3H3H yIn this talk 7 Be0.478 (10%)53.3dIn this talk 11 C0.511x220m 13 N0.511x210m 15 O0.511x22m 14 O2.370s 16 N67s 14 C ydecay rate is negligible Isotopes generated in cooling water In addition, 22 Na, produced from Al of magnetic horn and resolved in the cooling water, is serious radioactive source. Disposal of 3 H and 7 Be is the main problem in the cooling water exchange. Negligible after a few hours because of their short lifetime ● ●

Cooling water systems in T2K neutrino beam line ● BD cooling water system TS cooling water system （ DV downstream and BD ） （ TS and DV upstream ） Horn cooling water system We have three independent cooling water systems ● Total water in the system are 2.7m 3 for Horn, 5.6m 3 for TS and 3.1m 3 for BD. ● Water in horn cooling water system were exchanged every month. Water in other systems were exchanged after 6 months of beam operation.

Neutrino beam in this year and in near future *20 days beam and 10 days maintenance for 1 month. *Continues 6 month operation per year *Beam power : 750kW ● Our tentative goal within a couple of years is: ● We have finished 6 months of < 60kW beam operation between Jan-Jun ● Between 6 runs in Jan-Jun 2010, maximum p.o.t. was 12.2x10 18 in May, which corresponds to about 1/22 of 750kW x 20days Run. ● Based on our experience in Jan-Jun 2010 Runs, realistic cooling water exchange scenario is considered.

Ion exchangers 3 horns 5m 3 Buffer tank at B2 (4m 3 effective) To Ocean 24m 3 Dilution tank 1 24m 3 Dilution tank 2 TS underground area (We cannot access during neutrino beam period) NU2 (ground level) (We can access even during neutrino beam period) Monthly maintenance for Horn cooling water 10~15m 3 Buffer tank at NU2 Ion exchangers Horn tank 0.9m 3 total 2.7m 3 Under design 160liter/min H 2 SO 4 NaOH 1)Beam (~20days) 2)Remove 7 Be (2~4days) 3)Measurement of 7 Be and move to the buffer tank (1day) 4)To dilution tank. After dilution, 3 H/ 7 Be measurement (~2days) 5)Dispose water. Go to 4) if more water

3 H in horn cooling water in Jan-Jun 2010 Run Run Period (2010) Pot (x10 18 ) Bq/cc (Bq/cc) /10 18 pot GBqdilutions 2901/23-02/ /22-03/ /18-03/ /13-05/ /09-06/ /07-06/ future750kW x 20d ● If the capacity of the dilution tank and maximum concentration by regulation (60Bq/cc) is taken into account, maximum 3 H in one dilution-disposal process is 1.44GBq. 3 H cannot be removed by ion-exchanger. Dilution is only the ● way for disposal. We need multiple dilution process soon.

Total 3 H from neutrino beam line Expected 3 H production after 6 months (750kW, 120days) operation. ● ● The radio-active water can be disposed if the concentration of 3 H is less than 60Bq/cc. Total water (m 3 ) Concentration (Bq/cc) Total 3 H (GBq) (1)Horn (2)TS (3)BD Total495 Larger dilution tank and quick dilution procedure are needed. 360GBq of 3 H needs 8300m 3 water. Numbers are scaled from data in Feb.2010 Run. (Note that the total water of official swimming pool is 2500m 3 ) If we use present dilution tank (24m 3 ), we repeat the dilution work ~350 times.

Run Period (2010) Pot (x10 18 ) Bq/cc (Bq/cc) /10 18 pot Ion.Ex. Period Bq/cc after Ion.Ex. After /Before GBq after Ion.Ex. 2901/23-02/ /22-03/ d4.32.2% /18-03/ d5.51.8% /13-05/ d130.9% /09-06/ d401.9% /07-06/ d372.1%0.081 future750kW x 20d ~50~0.1%~0.1 From a regulation, remaining 7 Be in the drain water should be less than 0.1GBq per month. In the 750kW x 20days operation, 99.9% removal is required. ● 7 Be in horn cooling water in Jan-Jun 2010 Run At present, 7 Be removal efficiency is 97% for 2days, 98% for 3days and 99% for 4days. ●

Total 7 Be from neutrino beam line Expected 7 Be production after 6 months (750kW, 120days) operation. ● Total water (m 3 ) Concentration (Bq/cc) Total 3 H (GBq) (1)Horn (2)TS (3)BD Total906 Numbers are scaled from data in Feb.2010 Run. ● Unlike 3 H, 7 Be from TS and BD are smaller than 7 Be from Horn by one order of magnitude. Most of 7 Be in TS and BD are thought to be trapped in the pipe of the water circulation system. ● Necessity of ~99.9% 7 Be removal by ion-exchanger is unchanged. Dissolution of such 7 Be into water must be watched out.

● ● 22 Na are produced from Aluminum of horn. No 22 Na in TS and BD cooling water system. Life time of 22 Na (  1/2 =2.6y) is much longer than 7 Be (  1/2 =53.3d) 22 Na in the ion exchanger are serious radiation source because ● E  from 22 Na is 1.27MeV MeV x 2. These energies are larger than  -rays from 7 Be (0.477MeV). ○ Total water (m 3 ) Concentration (Bq/cc) Total 3 H (GBq) (1)Horn (1 month)0.072 Total Na from neutrino beam line Expected 22 Na production after 6 months (750kW, 120days) operation. ● Numbers are scaled from data in Mar.2010 Run. Most of 22 Na are captured by ion-exchanger together with 7 Be. ○

Ion-Exchangers ● By accumulating 7 Be and 22 Na, ion-exchangers become strong source of radiation dose (~50mSv/h). Shielding around the ion-exchanger is needed. At present, 7 Be removal efficiency is 97% for 2days, 98% for 3days and 99% for 4days. This must be improved. ● Resins of the ion-exchangers are mostly occupied by iron ion resolved from the pipe of the water circulation system. So, the lifetime of the ion-exchanger does not depend on beam power. In K2K, we need only 1~2 ion- exchangers per 5 years. ● If the radiation dose from 7 Be/ 22 Na, and lifetime of the ion-exchanger are taken into account, one year use and 2~3 years cooling before disposal is realistic scenario. We need space for ~4 ion-exchangers. ●

Ion-exchangers of horn cooling water system and its shielding 5.0  Sv/h 240  Sv/h 60mm iron shield (Measurements in March 2010)

Unit :  Sv/h AB 7 Be 22 Na 7 Be 22 Na After 1 month beam After 6 months beam After 2 years cooling After 3 years cooling Expected radiation dose around the ion exchanger for Horn cooling water system B A ● 6 months of 750kW beam is assumed, and contribution from 7 Be and 22 Na are calculated. ● Although radiation dose from 7 Be is dominant just after the beam, that from 22 Na become larger after 2 years cooling. ● The iron shielding reduce the dose from 7 Be by 98%, but the dose from 22 Na by 96%. The shielding is less effective for 22 Na.

Accumulation of metal and RI in the Resin Blank Resin Metal ion of strong coupling RI of weak coupling ( 7 Be, 22 Na) RI of weak coupling gradually pushed out to downstream by metal ions of strong coupling. If all resin are occupied by metal ions, RI overflow from the ion exchanger. ● water 100  Sv/h (90cm) 40  Sv/h 240  Sv/h (75cm) 130  Sv/h (60cm) 35  Sv/h (50cm) 5.5  Sv/h (0cm) water By measuring the peak position of the radiation dose, we can expect the lifetime of the ion exchangers. From the Mar measurement, the lifetime seems to be longer than 6 months. (Note that the lifetime does not depend on the beam power.) ● ● We must keep watching the peak of the radiation dose to know the life of the ion exchanger.

How to remove 7 Be by the ion-exchanger more effectively ● 7 Be are sometimes adsorbed on metal-oxide colloids and become electrically neutral. Their adsorptivity on cation-exchange resins become low. In fact, 60% of 7 Be are adsorbed on metal- oxide colloids if the pH of the cooling water is 6.0. ● If the cooling water become acid, the metal-oxide colloids return to soluble metal ions, and 7 Be also return to ions. Therefore, it is recommended to change the water to acid for effective removal of 7 Be by the ion-exchanger. Suggestion by Prof. Bessho (KEK Radiation Science Center) Colloid ion Particle

Does the disposal scenario designed before the experiment work well? ● Production rate of 3 H/ 7 Be calculated from  x  x V is correct. For example, total 3 H production in 750kW x 120 days is calculated to be 381GBq, where extrapolation from Feb. measurement is 360GBq. However, total water volume was changed at the last stage of the design, and disposal scenario was not updated. ● We need at least 2~3 days for one dilution-dispose procedure. We need long time for a official radioactivity measurements and for getting bureaucratic permission. ● We need long time for removal of 7 Be by ion-exchangers. No! It takes 4 days for 99% removal, but our requirement is 99.9%. ● Total volume of the dilution tank is 50m 3, but effective volume is only 24m 3 ! Very large safety margin. ● 20% of safety margin is strongly recommended for the concentration limit of 3 H (60Bq/cc).

Ion exchangers 3 horns 5m 3 Buffer tank at B2 (4m 3 effective) To Ocean 24m 3 Dilution tank 1 24m 3 Dilution tank 2 TS underground area (We cannot access during neutrino beam period) NU2 (ground level) (We can access even during neutrino beam period) After the installation of new buffer tank 10~15m 3 Buffer tank at NU2 Ion exchangers Horn tank 0.9m 3 total 2.7m 3 Under design 160liter/min By adding the new buffer tank: 1)We can repeat the dilution process even in beam period. 2)We can use ion-exchangers for longer time under the pH control. H 2 SO 4 NaOH

Radio-activation of Air and He After the March Run (3.89 x p.o.t.), 3 H from He in Helium vessel and Decay Volume was measured. It was 12.0mBq/cc and the expectation from  x  x V is 14.2mBq/cc. The agreement is excellent ! ● ● Unlike cooling water case, the volume of the Helium vessel and Decay volume did not changed at the last stage of the design. So, does everything go well? ● We had a couple of problems so far….. - Leak of Radioactive air from TS and BD - 3 H from Helium vessel problem See next 2 slides NO!

Leak of Radioactive Air from TS and BD Radioactive air was leaked from TS and BD. Radioactivity in the ground level exceeded the limit from the regulation ( < 0.5mBq/cc). ● ● - Air-tightening for cable hole, door …… (TS,BD) - New air-tightened Dumpers (TS,BD) - Cover whole surface of concrete blocks (TS) In TS, radioactivity of 0.5mBq/cc at 30kW was improved to /- 0.09mBq/cc at 40kW. This air-tightening is satisfactory up to 325kW operation. ● In BD, radioactivity of 0.25mBq/cc was improved to /- 0.05mBq/cc at 40kW. This air-tightening is satisfactory up to 3000kW operation. ● Still 90mBq/cc of 41 Ar exist under the sheet. Thicker sheet is preferred. ●

When the top of the Helium vessel is opened for maintenance works, 3 H in the Helium vessel are diffused in the TS building even after the ventilation of the radioactive He was completed. ● At present, we open the Helium vessel for 3 days per week. In order to reduce drain water, the temperature of the TS building is set to 24 o C, which is higher than usual by 4 o C. ● Drain water from air conditioner (2~3m 3 per day) in the TS building are radio-activated. 16Bq/cc (Helium Vessel closed) -> 96Bq/cc (Helium Vessel opened) Note that radioactive water can be disposed if 3 H concentration is less than 60Bq/cc. 96Bq/cc in water corresponds to 3mBq/cc in air (2  in body) and legal limit is 500mBq/cc in air to enter the area Hidden 3 H from Helium Vessel problem ● ●

Summary Only dilution is the way to dispose 3 H. Large dilution tank as well as quick dilution process are necessary. ● 7 Be must be removed by ion exchanger. ● Quick removal with 99.9% efficiency is required. Control of pH of the water is under consideration. ● 7 Be and 22 Na accumulated in the ion-exchanger is a serious source of strong radiation dose. The ion-exchanger should be disposed after 1 year use and 2 or 3 years cooling. ● For longer circulation in ion-exchanger system under pH control, and for multiple dilution process, a new buffer tank with ion-exchangers is under design. Cooling Water Air and Helium So far, We had two problems. However, they are not fatal. ●

Old

Total 3 H from neutrino beam line Expected 3 H production after 6 months (750kW, 120days) operation. ● ● The radio-active water can be disposed if the concentration of 3 H is less than 60Bq/cc. Total water (m 3 ) Concentration (Bq/cc) Total 3 H (GBq) (1)Horn (2)TS (3)BD Total360 Larger dilution tank and quick dilution procedure are needed. 360GBq of 3 H needs 6000m 3 water. Numbers are scaled from data in Feb.2010 Run. (Note that the total water of official swimming pool is 2500m 3 ) If we use present dilution tank (24m 3 ), we repeat the dilution work ~250 times.

Total 7 Be from neutrino beam line Expected 7 Be production after 6 months (750kW, 120days) operation. ● Total water (m 3 ) Concentration (Bq/cc) Total 3 H (GBq) (1)Horn (2)TS (3)BD Total834 Numbers are scaled from data in Feb.2010 Run. ● Unlike 3 H, 7 Be from TS and BD are smaller than 7 Be from Horn by one order of magnitude. Most of 7 Be in TS and BD are thought to be trapped in the pipe of the water circulation system. ● Necessity of ~99.9% 7 Be removal by ion-exchanger is unchanged. Dissolution of such 7 Be into water must be watched out.

Supplements

3H3H 7 Be datacalculationdatacalculation (1)Horn (2)TS (3)BD Total Unit : GBq 750kWx120d Data and Calculation of 3 H/ 7 Be production ● Production rate of 3 H/ 7 Be calculated from  x  x V is correct.

New buffer tank under design Old system 2 ion-exchangers 10~15m 3 buffer tank H 2 SO 4 NaOH Iron shield

Radioactivity in Exhaust Air (TS/NU3) TS R#31: 30kW ⇒ Current level : 40kW –New air-tightened MVDs (SP ・ Machine room) –Cover whole surfaces of concrete blocks –0.5 / 0.08 (0.17) x 40kW x 30d/20d = 375 (175) kW 90mBq/cc (Ar41) under the sheet ⇒ stronger sheet is preferred NU3 R#32: 0.25mBq/cc ⇒ Current level : 40kW –Air-tightening ・ New MVDs for machine room –0.5 / 0.01 (0.06) x 40kW x 30d/20d = 3,000 (500) kW

3 H from Helium vessel problem When the top of the Helium vessel is opened for maintenance works, 3 H in the Helium vessel are diffused in the TS building. ● At present, we open the Helium vessel for 3 days per week, and the temperature of the TS building is set to 24degree, which is higher than usual by 4 degree. ● Drain water from air conditioner in the TS building are radio-activated. 16Bq/cc (Helium Vessel closed) -> 96Bq/cc (Helium Vessel opened) Note that radioactive water can be disposed if 3 H conc. is less than 60Bq/cc. 96Bq/cc in water corresponds to 3mBq/cc in air (2  in body) and legal limit is 500mBq/cc in air to enter the area

End