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Some radiological issues in the n-TOF facility

Some radiological issues in the n-TOF facility. insufficient shielding of TT2a activation of rock and air close to the target use of unsealed alpha sources in detectors. Shielding of TT2a. access by door 201 (mechanical lock) houses n-TOF target water regeneration plant

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Some radiological issues in the n-TOF facility

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  1. Some radiological issues in the n-TOF facility insufficient shielding of TT2a activation of rock and air close to the target use of unsealed alpha sources in detectors

  2. Shielding of TT2a • access by door 201 (mechanical lock) • houses n-TOF target water regeneration plant • Plan: accessible during beam transfer PS -> SPS and PS -> AD • Accidental exposition of 2 persons, Hp(10) =0.5 mSv • Consequence: beam interlocked with radiation monitor (autumn 2001)

  3. TT2A TT2 PS- n-TOF - interface

  4. Simulations:beam loss in TT2 • H. Vincke and M. Silari (TIS-RP): • real loss scenario of last autumn could be reproduced • other loss scenarios yield higher dose • worst case: more than 200 mSv in one single supercycle (16.8 s) • recommendation to close area while beam is transferred from PS

  5. Simulated loss scenarios dipole failure - beam grazing vacuum chamber loss directly into wall

  6. Activation close to target • p-beam from PS hits target in angle of 100 • no proper beam dump • secondary hadron cascade escapes • activates rock and air • (creates background in n-TOF experimental area) • no ventilation of target area • have to assume that all activated air reaches environment undiluted • creates measurable environmental radioactivity

  7. Results on activation • A. Muller (TIS-RP): • at nominal intensity • 7Be: 1000 Bq/m3 • 24Na: 300 Bq/m3 • assuming 4 air exchanges per day, release of • 7Be: 240 MBq/month • 24Na: 90 MBq/month • no filtered ventilation,no monitoring: • have to assume that all is released into environment, exceeds all other releases from CERN installations

  8. Arrangement of additional shielding • Aim: reduce activation by reducing track-length of secondaries in air. • A. Ferrari, V. Vlachoudis (SL-ECT): • Monte Carlo Simulation of air activation: correct within a factor of two (this is very good!) • 14 m of additional concrete shielding arranged along n-TOF tube. • effect: reduce activation by about factor of 7 – 10 (calculated) • TIS-RP will conduct immission measurements at fence once n-TOF has started

  9. n-TOF detectors • n-TOF uses unsealed alpha emitters as detectors for fission or capture • Problems: • very low authorisation limits LA • manipulation to be done in specific work sectors (not n-TOF experimental area) • work sectors A not available at CERN • closed detector still a hazard (thin entrance windows)

  10. Examples of alpha-detectors • Proposal INTC/P145

  11. Proposed technical procedure (I) • Ship assembled, closed detectors in protective cases to CERN • ISOLDE target handling building (179) • Put personal protective equipement on • Inspect integrity of detector • If o.k., ship in protective case to n-TOF • with PPE, mount in n-TOF tube. • Reverse for dismounting

  12. Proposed technical procedure (II) • Delivery of open alphas sources to CERN • transfer in glove box (bat 179) – type B • mounting in detector • ship in protective case to n-TOF • with PPE, mount in n-TOF tube. • Reverse for dismounting • limited to reasonable amount of activity(will try 15 000 LA)

  13. Administrative procedure • Submit technical procedures to OFSP, • Get advice from OFSP • Integrate in Procedure • resubmit … • Eventually, receive authorisation from OFSP • INTC will give beam time conditionally to final authorisation from OFSP

  14. Summary • n-TOF – an example of how not to plan and construct a “cheap” experiment • re-use of old tunnels proves problematic – a clear message to SPL, CLIC, and other potential projects • unfiltered, unmonitored air activation and authorisation of unsealed alpha sources may put the success of the whole experiment in question • Time and money spent now could have been saved with better, more thorough preparation • There are no easy economies when safety is an issue – a message to LHC and CNGS

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