U.S. Nuclear Regulatory Commission

Averaging of Radiation Levels Over the Detector Probe Area

HPPOS-013 PDR-9111210108

Title: Averaging of Radiation Levels Over the Detector

Probe Area

See the letter from L. V. Gossick to J. J. Munro (Tech/Ops,

Radiation Products Division) concerning PRM-20-9 and dated

March 23, 1979. The letter states that averaging of

radiation levels over the cross-sectional area of a probe

of reasonable size is acceptable for demonstrating

compliance with the requirements of 10 CFR 20.205 (c) (2).

This health physics position also applies to "new" 10 CFR

20.1906 (d) (2).

PRM-20-9 was a petition submitted to NRR requesting

amendment of 10 CFR Part 20.205 (c) (2) regarding surface

radiation level limits of packages for transport. It was

requested that 10 CFR Part 20.205 (c) (2) be amended so

that radiation levels found five centimeters from the

external surface of the package in excess of 100

millirem/hour or three feet from the package in excess of

10 millirem/hour would require the immediate notification

of the Director of the appropriate NRC Regional Office and

the final delivering carrier. In determining the radiation

levels, the measurements were to be averaged over a

cross-sectional area of ten square centimeters with no

linear dimension being greater than five centimeters.

As written, 10 CFR 20.205 (c) (2) required a licensee who

received a package of radioactive material in excess of

Type A quantity to monitor the external radiation levels

both at the surface and at three feet from the surface of

the package. If the radiation levels exceeded 200

millirems per hour at the surface or 10 millirems per hour

three feet from the surface, the licensee was to

immediately report to the Director of the appropriate NRC

Regional Office and to the final delivering carrier.

In denying the petition, the NRC stated that the proposed

changes to 10 CFR Part 20.205 (c) (2) would result in

increased costs to the licensee without a corresponding

benefit in improved public health or safety. In fact, the

proposed changes would result in higher collective hand

doses being delivered to package handlers.

In its ruling, the NRC stated that radiation levels

averaged over a cross-sectional area of a probe of

reasonable size is acceptable for demonstrating compliance

with the requirements specified in 10 CFR 20.205 (c) (2)

[or 10 CFR 20.1906 (d) (2)]. "A probe of reasonable size"

was defined as: (1) the sensitive volume of the probe being

small compared to the volume of the package being measured,

and (2) the largest linear dimension of the sensitive

volume of the probe being no greater than the smallest

dimension of the package. Geiger-Mueller tubes may be used

for both small and large packages but ionization chambers

should be used only for large packages. Averaging is not

acceptable for demonstrating cracks, pinholes, uncontrolled

voids, or other defects prior to the first use of any

packaging for the shipment of licensed materials as

required by 10 CFR 71.53.

Regulatory references: 10 CFR 20.201, 10 CFR 20.205, 10

CFR 20.1501, 10 CFR 20.1906, 10 CFR 71.53

Subject codes: 7.1, 12.17

Applicability: All