Posting of Accelerator EnclosuresVashek Vylet and Keith Welch

DOE Accelerator WorkshopSLAC, August 17 – 19, 2010

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Introduction

• In a recent audit (DOE/Site Office) Jlab was found in violation of 10 CFR 835 for not posting “Very High Radiation Area” sign at entrance to accelerator enclosure. This decision is to be further clarified by DOE.

• Situation relevant to other labs that do not post radiological areas to reflect “Beam On” condition

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Radiation Area - 10 CFR 835

• Radiation area (RA) means any area, accessible to individuals, in which radiation levels could result in an individual receiving an equivalent dose to the whole body in excess of 0.005 rem (0.05 mSv) in 1 hour at 30 centimeters from the source or from any surface that the radiation penetrates.

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Similarly, …

• High radiation area (HRA) > 0.1 rem in 1 hour at 30 cm

• Rest of wording same, including “accessible to individuals”.

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And …

• Very high radiation area (VHRA) means any area accessible to individuals in which radiation levels could result in an individual receiving an absorbed dose in excess of 500 rads (5 grays) in one hour at 1 meter from a radiation source or from any surface that the radiation penetrates.

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Posting

• DO WE NEED TO POST ACCELERATOR ENCLOSURES FOR “BEAM ON” CONDITIONS?

• Posting requirement of RA, HRA or VHRA rests on the condition of accessibility. 10 CFR 835 does not elaborate on the meaning of “accessible”

• Guidance documents (G 420.2-1 and G 441.1-1C) in apparent disagreement

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G 420.2-1 – Guidance to Acc. Order

• “An exclusion area is an area that is locked and interlocked to prevent personnel access while the beam is on. A fully enclosed and interlocked area is considered inaccessible.”

• Jlab and number of other DOE labs use this interpretation and do not post for “Beam ON” conditions

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G 441.1-1C – for use with 10 CFR 835• “Radiological areas and radioactive material areas

are defined based upon area accessibility. An area is considered to be accessible to individuals when it contains entrance or access points of sufficient size to permit human entry, i.e., such that any portion of the body may be exposed to the radiological hazard. “

• “Areas with entrance or access points consisting of locked doors or other controls and interlocks (including those specified under 10 CFR 835.502), should be considered accessible to individuals.”

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G 441.1-1C – for use with 10 CFR 835• HOWEVER: Language in Guide indicates that it is intended

for “Small (low voltage, less than or equal to 10 MeV) accelerators used for radiography, ion implantation, …”

• “Although the basic radiological control program requirements discussed in this Guide are generally applicable to the large multi-purpose research accelerators, the complexities associated with these facilities may require additional consideration beyond the scope of this Guide. Additional* requirements for those RGDs with particle energies exceeding 10 MeV are provided in DOE O 420.2B, Safety of Accelerator Facilities.”

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Guide is not a requirement …

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Which interpretation?

• Argument for G 420.2-1: Suitable & adapted to large, complex accelerator facilities

• It seems that G 420.2-1 resulted from collaboration of DOE with contractor community (Workshop in 2004 – presentation by DeVaughn Nelson).

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What should prevail?

• One should evaluate the cost & benefit of “Beam On” condition posting

• Costs: • $$ in material and personnel time (many k$ at Jlab)• Psychological: may unnecessarily scare some workers

and/or contribute to “signage blindness”

• Benefits: None• Unlikely to measurably increase safety beyond level

provided by engineered controls• Unlikely to prevent life loss or injury

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Example from Jlab• Jlab’s FSAD contains detailed risk analysis of

great number of conceivable accident scenarios

• Posting (warning signs) are listed as Credited Controls only as generic “initial assumption”.

• Posting was not credited with reducing likelihood of severity of outcome in any event scenario.

• Jlab Acc. enclosures are locked and interlocked

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Jlab FEL: This sign was deployed before 10 CFR 835

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Hall A Hall B

Same as FEL, both these halls use the same pre-835 sign. Note the sign overload.

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Opinions from other labs

• “SLAC takes credit for the interlocks and interprets an operating accelerator housing where dose rates could reach Very High Radiation Area levels as not accessible.”

• Argonne: “I believe that the postings need only reflect the conditions that may be present when a person can actually enter the area."

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Opinions from other labs

• Fermilab: “For exclusion areas (i.e., interlocked areas with no personnel access allowed) we post them for the plausible beam-off condition. For primary beam enclosures this usually means they are high radiation areas.”

• Excerpt from Fermilab RPP: “Because radiation levels can vary significantly with the operation of the accelerators and the impracticability of reposting every time the beam is turned on or off, accelerator/beamline enclosures are posted for the radiological conditions present when the beam is off. Physical controls, which render access impossible during operation, are imposed for those areas in which radiation levels could pose a significant danger to personnel."

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Opinions from other labs

• ORNL: “In keeping with the DOE Accelerator Order and the requirements of 10CFR835 ORNL recognizes the interlocks as preventing an individual from getting access to the operating conditions on the "wrong" side of the door.”

• SNS/ORNL: “We do not consider locked and interlocked areas to be accessible. The access ways to these areas are posted according to the radiation levels that would be expected inside the doors should the machine be dropped out of beam permit.”

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Conclusion

• Jlab favors using accessibility interpretation from Accelerator Order Guide G 420.2-1

• This workshop is an appropriate forum for discussing benefits and impact of the options at hand