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CNGS operation and environmental issues

F. Malacrida, T. Schmittler, P. Vojtyla, H. Vincke

H. Vincke et al. NBI 2012, CERN2

Outline

Environmental issues Tritium issue and mitigation

Dose to public due to water and air releases from CNGS

Operational (radiation protection) issues Exchange of two vacuum Be windows

Traceability system for radioactive equipment at CERN

H. Vincke et al. NBI 2012, CERN3

Tritium level in CNGS sumpsTNM42:

• H-3 activity : ~370 Bq/l, almost dry, water inflow negligible

TNM41:• H-3 activity : ~500 kBq/l, 1-2 l/h water inflow,

ph-value of 12, no automatic release, filled into containers

TSG4:• H-3 activity : ~2.3 MBq/l, up to 20 l/h water inflow

in access mode, ~ 2-4 l/h in beam mode, no automatic release, filled into containers, ph-value of 7-8 (neutral)

TCV4:• H-3 activity end of 2008: 16 kBq/l stopped automatic release, contains

hydrocarbons oil separator, up to 30l/h water inflow, access was required frequently (~every 14 days), water filled into containers, end of 2009 H-3 activity 45kBq/l 1 Bq = 27 pCiAllowed release if H-3 activity < 6kBq/l (1% of Swiss exemption

limit for HTO)

H. Vincke et al. NBI 2012, CERN4

….. improve tightness in the ventilation unit and ventilation pipes and doors

Even sealing water drainage system and sumps from air flow coming from the target chamber

Tritium mitigation

Big effort to assure that the target chamber remains in an under pressure wrt other areas.

Avoid propagation of tritiated air into other areas and in particular being in contact with water

Re-circulating air in TCC4 and TSG4 with an intentional small air leak during operation

H. Vincke et al. NBI 2012, CERN

Two new sumps in CNGS

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2 new small sumps since 2010 (1m3)

TSG4

20-30 l/hr

TAG41

PGCN

2 l/hr

1-2 l/hr

Goes into containers

TCV4

3-20 l/hr

Release path:LHC point 8 , River Le Nant, Lake Geneva

H. Vincke et al. NBI 2012, CERN6

Beginning of 2010:Due to the additional sumps:PGCN sump water (H-3 activity ~ 1kBq/l) could be released automatically.

However, the levels of TAG 41 sump water was still too high (>6kBq/l) for an automatic release.

(temporary) storage of CNGS containerEnd of 2010: We changed the CNGS ventilation scheme:Access gallery was put in over pressure (compared to CNGS TCC4 and TCV4 chamber).

We stopped completely the air leak mode (500m3/h); i.e. no more 500m3/h of air from target chamber into the access gallery. H-3 level in TAG41 < 6 kBq/l automatic release allowed.

Instead of 150 containers/year ... only ~40. No need to empty the sump during operation

H. Vincke et al. NBI 2012, CERN7

Evaporation and Impact Study

ENCON evaporator in ISR3 at CERN

In 2011 we started to move the containers to the CERN waste center where a evaporator was installed.So far, 55 m3 of tritiated water (H3 activity <6kBq/l) has been evaporated.

Impact study:

Determination of the maximum quantity of evaporated water limited by the effective dose to the members of the reference population groupAssumptions:

Dose quota: 1 mSv/year (optimization above 10 mSv/y, taking into account the other sources of exposure of the reference population group)

Quota = (10-6 Sv/y) / (1.93 10-20 Sv/Bq) = 5.2 1013 Bq/y ~50 TBq/year

Currently stored : total activity H-3 =

0.1 TBq corresponding to 2 nSv to the public.

H. Vincke et al. NBI 2012, CERN8

Geographical situation

CNGS Target chamber

SPS Point 4CNGS air release point

Le Nant

LHC Point 8CNGS water release point

H. Vincke et al. NBI 2012, CERN9

Environment – Regulatory aspectsCERN Safety Code F Rev. – Radiation Protection (2006)

Effective dose limit for members of the public: 0.3 mSv/y;

Partitioning: 0.1 mSv/y direct exposure to ionizing radiation; 0.2 mSv/y exposure due to releases of radioactive

substances to air and water; ALARA: Justification & Optimization:

De minimis dose: <10 µSv/y a facility is deemed to be justified and optimized;

Attention! 10 µSv/y must not be confused with a dose limit. It is rather a dose constraint or a dose objective.

1 mSv = 100 mrem

H. Vincke et al. NBI 2012, CERN10

Some numbers on H-3• CERN rain water several Bq/l

• CERN detection limit 1.6 Bq/l

• Limite d’exemption LE (Switzerland) 600 kBq (HTO) .. Ingestion of 1 kg HTO with 600 kBq leads to a dose (E50) of 10 uSv.

• Sewage water (Switzerland):• 6kBq/l (weekly average) and 60 MBq (total per month)

• Liquid waste (Switzerland):• 600 kBq/l and 60 MBq (total)

• Environmental impact: Swiss immission limits as a reference; LE/50 i.e. 12 kBq/L HTO on a monthly average.

• EU drinking water limit 1000 Bq/l …100 Bq/l under discussion

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01/01/2010 01/01/2011 01/01/2012 01/01/20130

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152012: 2.9E+19 potQ: 0.24 GBqE: 3.2 nSv

2011: 4.8E+19 potQ: 0.34 GBqE: 4.7 nSv

Average beam intensity Monthly tritium concentration in water released from the LHC site PA8 (Bq/L)

Ave

rage

bea

m in

tens

ity (p

ot/s

/ 10

12)

M

onth

ly tr

itium

con

cent

ratio

n (B

q/L)

2010: 4.0E+19 potQ: 0.65 GBqE: 9.0 nSv

Target chamber isolated

Water release

H. Vincke et al. NBI 2012, CERN12

Air emissions The closed HVAC system of the target chamber

removes most of the aerosol-bound radioactivity; The filtration is completed by HEPA filters at the

outlet; Consequences:

Only short-lived radioactive gases (mostly 41Ar) are released at levels worth to consider;

Also HT and HTO pass through but their radiological impact on members of the public is negligible;

However, we did not expect such releases also from the transfer tunnel TI-8!

Lesson learned: In complex tunnel systems, the actual air-flow may be difficult to predict.

1301/01/2010 01/01/2011 01/01/2012 01/01/20130.0

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Average beam intensity Monthly releases of short-lived radioactive gases (mostly 41Ar)

2012: 2.9E+19 potQ: 1.4 TBqE: 0.52 µSv

2011: 4.8E+19 potQ: 1.6 TBqE: 0.57 µSv

Ave

rage

bea

m in

tens

ity (p

ot/s

/ 10

12)

Sh

ort-l

ived

radi

oact

ive

gase

s (TB

q)

2010: 4.0E+19 potQ: 0.84 TBqE: 0.31 µSv

Air release

H. Vincke et al. NBI 2012, CERN14

Replacement of Be windowBe-window (0.25mm thick, diameter 70mm on 114mm flange) just in front of the target had to be exchanged twice:

Window 1: March 2011 (after 14.34E19 pot): Dose rate (on 12. April 2012): 2000 / 250 uSv/h (contact /10cm)Window 2: April 2012 (after 4.9E19 pot): Dose rate (on 12. April 2012): 1500 / 200 uSv/h (contact /10cm)

Collective dose of exchange of window in 2012: 364 uSv

H. Vincke et al. NBI 2012, CERN15

Traceability of radioactive equipment at CERN (TREC)

Hardware Buffer zones, workshops etc. are

equipped with a PC & 2D barcode reader

Generic, unique, unambiguous traceability labels;

Software Available for handheld devices

like iPads or iPhones. Uses database of existing

equipment and locations at CERN Functionality to create electronic

data handling transport request by TREC

E-mail notification to inform when the measurements are completed.

H. Vincke et al. NBI 2012, CERN16

Lessons learnedFor high intensity fixed-target facilities:

Stray radiation can be minimized by locating the target station deep underground

Ground water activation is ‘easy’ to handle when the facility is located under the ground water table

The impact of releases of radioactive substances to the atmosphere can be reduced by recycling HVAC systems and long delay times before release (long tunnels). Filter removes most of the aerosol-bound radioactivity

In complex tunnel systems, the actual air flow is difficult to predict

Tritium is difficult to ‘contain’, it is very mobile.

Difficult to get rid of tritiated water.

Contamination of water present underground with tritium is a serious challenge but it is rather a PR issue than a RP problem (at CERN).

H. Vincke et al. NBI 2012, CERN17Courtesy of Greenpeace

The full commented version can be obtained on requestfrom Pavol Vojtyla. E-mail Pavol.Vojtyla@cern.ch

One of the “highlights”

… something to read of your flight back ?