close proximity are not completely independent.
The degree of dependence
with distance between samples is required information for kriging.
The
design and results of this study are discussed by Doctor and Gilbert
(1978).
Our capability for using kriging techniques was greatly enhanced in 1977
by arranging to access the BLUEPACK kriging program available on the
Nevada Operations Office computer in Las Vegas via a high-speed computer
terminal operated by Boeing Computer Services in Richland, Washington.
This will allow us to handle efficiently the rather large amounts of
data commonly required for kriging. Thus far, our major use of BLUEPACK
has been by Dr. Delfiner in the analysis of the Area 13 (Project 57)
data (Delfiner and Gilbert, 1978).
ESTIMATING PLUTONIUM INVENTORY AND SPATIAL DISTRIBUTION AT NUCLEAR SITES
Design Aspects
We have used the experience gained at safety-shot sites to try new
sampling designs at nuclear test sites for estimating Pu inventory and
spatial distribution.
Perhaps a fundamental change in our approach is
to design field sampling plans for the primary purpose of estimating
spatial distribution as opposed to inventory.
If a field sampling plan
allows for the efficient estimation of spatial distribution, then inventory estimates can also be estimated from the data.
However, the reverse
is not necessarily true.
That is, a sampling plan for inventory may not
be efficient for estimating spatial distribution.
The basic field design approach is set out in sampling protocols developed during 1977 by NAEG scientists for nuclear site studies.
These are
discussed by Essington (1978).
A basic design change from safety-shot
sites is to no longer insist that sample locations be chosen at random.
Instead, field instrument readings (beta + gamma, alpha, and FIDLER) as
well as soil and vegetation samples are collected on systematic grids
over the study site.
Sampling is done in two phases.
During Phase l,
the grid spacing is rather wide (usually 400 feet). Data at these
locations are augmented by instrument readings every 20 feet taken along
eight radials at 45° intervals commencing at ground zero and continuing
out as far as 2,000 feet. This grid and transect information is used to
design Phase 2 sampling where soil, vegetation, and/or instrument measurements suitable to the particular features of the study site in question
are obtained.
Phase 2 designs are expected to use grids of different
mesh sizes, the finer grid spacing being used near ground zero areas or
in other regions where concentration levels appear to change rapidly on
the basis of information gathered during Phase 1.
The grid data should
be suitable for estimating both Pu spatial distribution and inventory
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