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Cs-137 event



I noticed this event description in the NRC daily events report.  It

involved a rigger inadvertently handling a 1.3 Ci Cs-137 source for 10

sec.  From my HP-101 course:



specific gamma ray constant = 0.33 R-m2/Ci-h   (from Cember, 3rd

edition, page 187)



assumptions:  extremity dose (fingertips) at 1 cm

                     whole body dose at 1 ft

                     source encapsulation completely attenuates betas



The resulting calculations show an extremity dose of ~ 12 R and a whole

body dose of 13 mR for the 10 second exposure, ignoring the approach and

withdrawal doses.



I can't figure out how the licensee reported an extremity dose of 20

mR.  I also don't understand why they used a whole body distance of 2.5

feet.  The distance from the fingertips (with fingers curled to hold the

source) to just above the elbow is approximately 1 foot; definitely less

than 2.5 feet.



I'd be grateful if someone with first hand knowledge of the event could

explain this.



The opinions expressed are strictly mine.

It's not about dose, it's about trust.

Curies forever.



Bill Lipton

liptonw@dteenergy.com



General Information or Other Event Number: 40445

Rep Org: CALIFORNIA RADIATION CONTROL PRGM

Licensee: SCHLUMBERGER TECHNOLOGY CORP

Region: 4

City: OILDALE State: CA

County:

License #: 0144-15

Agreement: Y

Docket:

NRC Notified By: ROBERT GREGER

HQ OPS Officer: JEFF ROTTON  Notification Date: 01/13/2004

Notification Time: 23:10 [ET]

Event Date: 01/10/2004

Event Time: 18:00 [PST]

Last Update Date: 01/13/2004

Emergency Class: NON EMERGENCY

10 CFR Section:

AGREEMENT STATE

 Person (Organization):

Jeffrey Clark (R4)

PATRICIA HOLAHAN (NMSS)





Event Text



AGREEMENT STATE REPORT INVOLVING PERSONNEL RADIATION EXPOSURE



On 01/12/04, the State of California received a report from Schlumberger

Technology of an incident that occurred about 1800 PST on 01/10/04. A

1.3 curie Cs-137 source fell off of its tool. A rig hand picked up the

source with his fingertips thinking it was the base of a lightbulb. A

Schlumberger crew member told the worker to leave it on the deck. The

source was recovered with the source handling tool, and returned it to

the shielded container.



Touching exposure was estimated to be 20 mrem with calculations based on

maximum touching time of 10 seconds. Whole body exposure was estimated

to be 2.9 mrem with calculation exposure based on beginning at 6 feet

from the source and closest distance at 2.5 feet for maximum of 2

minutes. The source has exposure characteristics of 2 mrem/hr at 200

inches (min) from shielded (dovetail) end, and 2 mrem/hr at 680 inches

(max) from the non-shielded end.





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