Quantcast Neutron Shielding - doe-std-1128-98_ch10187

 

Click here to make tpub.com your Home Page

Page Title: Neutron Shielding
Back | Up | Next

Click here for thousands of PDF manuals

Google


Web
www.tpub.com

Home

   
Information Categories
.... Administration
Advancement
Aerographer
Automotive
Aviation
Construction
Diving
Draftsman
Engineering
Electronics
Food and Cooking
Logistics
Math
Medical
Music
Nuclear Fundamentals
Photography
Religion
   
   

 

Share on Google+Share on FacebookShare on LinkedInShare on TwitterShare on DiggShare on Stumble Upon
Back
Distance - doe-std-1128-98_ch10186
Up
DOE Standard Guide of Good Practices for Occupational Radiological Protection In Plutonium Facilities
Next
Table 6.11. Photon Dose Rates at 2 Meters from Cylinders of Plutonium Containing 1 kg of Plutonium at 5 Years After Chemical Separation - doe-std-1128-98_ch10188


DOE-STD-1128-98
Table 6.11 gives examples of how effective various gamma shielding
materials are in reducing the dose rates from low-exposure (6% 240Pu)
and high-exposure (19% 240Pu) sources. The sources consist of cylinders
containing 1 kg of plutonium oxide; the dose rates are given at a distance
of 2 m from the source. This example is typical of the shielding
effectiveness for cans of plutonium containing kilogram quantities of
plutonium oxide, as might be found in storage vaults.
In contrast, Figure 6.6 shows the reduction in photon dose rates from a
small sample of plutonium oxide power weighing about 100 grams. The
dose rates were measured at a distance of 3 cm from the surface of the
plutonium, which was contained in polyvinyl chloride plastic bags (a
total thickness of 33 mil or 0.85 mm) for radiation measurements. The
isotopic composition of the plutonium was similar to that given in Table
6.12.
Photon radiation is a significant source of exposure, especially during
D&D activities, when most of the plutonium has already been removed.
Much of the photon exposure problem originates from thin dust layers, as
described in the preceding paragraphs. High photon doses often originate
from "streaming" through glove ports from dust layers on gloves. But
there also can be appreciable neutron dose rates, even in supposedly
"empty" glove boxes, from plutonium hold-up, especially in fluorinator
glove boxes where there is a high neutron emission rate from alpha-
neutron reactions. Wearing lead-loaded aprons can reduce dose rates by a
factor of 2 in plutonium fuel manufacturing. High-exposure plutonium
(>10% 240Pu) should be handled in glove boxes with lead-loaded
Neoprene gloves although some loss of mobility and dexterity may
result. The photons from plutonium are easily shielded by several
millimeters of lead or iron, but it requires almost 15 cm (6 in.) of
polyethylene or hydrogenous moderator to reduce neutron doses by a
factor of 10. Simplistically stated, the gamma dose rate is a function of
surface area, while neutron dose rate is a function of the mass of the
plutonium and its chemical form.
6.4.3.2 Neutron Shielding
The neutron radiations from plutonium are much more difficult to shield
than the photon radiations. As a rule of thumb, it requires about 15 cm of
hydrogenous shielding to reduce the neutron dose rate by an order of
6-35


Privacy Statement - Press Release - Copyright Information. - Contact Us

Integrated Publishing, Inc.