Measured Gamma Dose Rates cont'd

DOE-STD-1128-98

There are only a few codes specifically designed for plutonium dose

calculations in the ORNL code center(1); they include the following:

-- PUSHLD - Calculation of Gamma Radiation Dose Rates from

Three- Dimensional Plutonium Sources and Shield Geometries at

Various Distances, HEDL-TME 73-89, Hanford Engineering

Development Laboratory (Strode, 1974).

-- BMC-MG - A Multigroup Monte Carlo Kernel Integration Neutron

and Gamma-Ray Shielding Code System for Plutonium, BNWL-

1855, Pacific Northwest Laboratory (Zimmerman, 1975).

-- PURSE - A Plutonium Radiation Source Code, PNCT 852-78-13,

Japan Power Reactor and Nuclear Fuel Development Corp., Tokai-

Mura, Japan.

The PUSHLD computer code has the advantage that the calculated

results were experimentally verified to make certain that the low-energy

build-up factors were correct. There are undoubtedly several other codes

that could give accurate dose rates from plutonium, particularly if a

radioactive decay code is used to calculate the amount of progeny as a

function of time. For example, the Los Alamos code MCNP (Briesmeier,

1986) would provide accurate neutron and photon doses if the decay

progeny were included in the calculations. Unfortunately, all of these

codes were developed years ago to operate on mainframe computers, and

simple "user-friendly" versions are not available for personal computers.

There are some empirical equations that can be used to calculate dose

rate through simple shields, such as Neoprene, when plutonium is

directly handled in a glove box. Because of the dominance of low-energy

X-rays, the surface dose rates from plutonium sources can be quite high.

Roesch and Faust have derived a formula for predicting the surface dose

rate from plutonium through a 100-mg/cm2 shield:

Ds(rad/h) = 171 f238 + 0.51 f239 + 2.4 f240 + 8.7 f241

(6.2)

+ 0.15 f242 (0.074 f241)t

where Ds

= the surface dose rate of plutonium metal or oxide, rad/h

(1) RISC, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6362, Telephone (423) 574-6176.

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