Posting of Accelerator Enclosures
Vashek Vylet and Keith Welch
DOE Accelerator Workshop
SLAC, 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 …
10
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
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