Information Notice No. 81-26, Part 3, Supplement No. 1: Clarification of Placement of Personnel Monitoring Devices for External Radiation

                                               SSINS No.: 6835             
                                               IN 81-26, Part 3, Sup. No. 1 

                               UNITED STATES 
                           WASHINGTON, D.C. 20555 
                               July 19, 1982 

Information Notice No. 81-26, PART 3, SUPPLEMENT NO. 1: CLARIFICATION OF 


All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP), research and test reactors, fuel facilities, and 
Priority I material licensees. 


This information notice is a supplement to Information Notice No. 81-26, Part
3: Placement of Personnel Monitoring Devices for External Radiation 
Exposure, issued in August 1981. Guidance provided in August 1981 concerning 
dosimeter placement for determining whole body doses in situations where the 
principal source of radiation is from underfoot was overly conservative. 


The earlier guidance was, 

     "If the principal source of radiation is from underfoot, the 
     appropriate location for the dosimeter might be on the lower leg just 
     above the ankle, since the long bones of the lower leg contain active 
     blood-forming marrow." 

As defined in 10 CFR 20.101(b)(3), "'dose to the whole body' shall be deemed
to include any dose to the whole body, gonads, active blood-forming organs, 
head and trunk, or lens of eye." 

According to the International Commission on Radiological Protection (ICRP) 
publication No. 23, "Report of the Task Group on Reference Man," an adult's 
long bones of the lower leg contain essentially no blood-forming red bone 
marrow. Red marrow has been replaced by yellow marrow after the 18th year; 
yellow marrow performs no blood-forming function and is mainly fatty tissue.
ICRP-23 shows for the reference man's femur (thigh bone) a steeply declining
red marrow content until the early to middle twenties when no red marrow is 
evident in the femur shaft. However, in discussing red and yellow marrow 
distributions, ICRP-23 states, " must be pointed out that there is much
variation, and exceptions should not be regarded as unusual." In the woman, 
...the red marrow may occupy up to one-half to two-thirds of the shaft of 
the femur. . . . " 

Another factor is the body's ability to physically replace the yellow with 
active, red marrow in periods of stress, such as anoxemia, blood loss, 
anemia, etc. The time frame for the red for yellow marrow replacement was 
not known when ICRP-23 was published. 


                                               IN 81-26, Part 3, Sup. No. 1 
                                               July 19, 1982               
                                               Page 2 of 2                 


To monitor an adult for whole body doses when the principal source of 
radiation is from underfoot, a reasonable placement for a whole body 
dosimeter would be just above the knee. Any further generalization for whole
body dosimeter placement could be non-conservative, considering reported 
variability because of age, race, sex, and state of general health. Note 
that extremity monitoring requirements may dictate the placement of 
additional dosimeters in the feet and ankle area. 

No written response to this information is required. If you need additional 
information regarding this matter, please contact the Regional Administrator
of the appropriate NRC Regional Office. 

                                   Edward L. Jordan, Director 
                                   Division of Engineering and 
                                     Quality Assurance 

Technical Contact:  J. E. Wigginton

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