Standard Test Method for Non-Destructive Assay of Nuclear Material in Waste by Passive and Active Neutron Counting Using a Differential Die-Away System
|Publication Date:||1 February 2009|
|ICS Code (Fissile materials and nuclear fuel technology):||27.120.30|
This test method covers a system that performs nondestructive
assay (NDA) of uranium or plutonium, or both, using the active,
differential die-away technique (DDT), and passive neutron
coincidence counting. Results from the active and passive
measurements are combined to determine the total amount of fissile
In the active mode, the system measures fissile isotopes such as 235U and 239Pu. The neutrons from a pulsed, 14-MeV neutron generator are thermalized to induce fission in the assay item. Between generator pulses, the system detects prompt-fission neutrons emitted from the fissile material. The number of detected neutrons between pulses is proportional to the mass of fissile material. This method is called the differential die-away technique.
In the passive mode, the system detects timecoincident neutrons
emitted from spontaneously fissioning isotopes. The primary
isotopes measured are 238Pu, 240Pu, and
242Pu; however, the system may be adapted for use on
The active mode is used to assay fissile material in the following ranges.
For uranium-only bearing items, the DDT can measure the 235U content in the range from about 0.02 to over 100 g. Small mass uranium-bearing items are typically measured using the active mode and only large mass items are measured in passive mode.
For plutonium-only bearing items, the DDT method measures the 239Pu content in the range between about 0.01 and 20 g.
The passive mode is capable of assaying spontaneouslyfission
This test method requires knowledge of the relative abundances of the plutonium or uranium isotopes to determine the total plutonium or uranium mass.
This test method will give biased results when the waste form does not meet the calibration specifications and the measurement assumptions presented in this test method regarding the requirements for a homogeneous matrix, uniform source distribution, and the absence of nuclear material lumps, to the extent that they effect the measurement.
The complete active and passive assay of a 208 L drum is nominally 10 min or less but either mode can be extended to meet data quality objectives.
Some improvements to this test method have been reported (1, 2, 3, 4).2 Discussions of these improvements are not included in this test method although improvements continue to occur.
The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 8.
2 The boldface numbers given in parentheses refer to a list of references at the end of the text.