Regulatory Guide 5.18

Limit of Error Concepts and Principles of Calculation in Nuclear Materials Control

ML003739959
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Issue date:	01/31/1974
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RG-5.18
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January 1974 U.S. ATOMIC ENERGY COMMISSION

REGULATORY GUIDE

DIRECTORATE OF REGULATORY STANDARDS

REGULATORY GUIDE 5.18 LIMIT OF ERROR CONCEPTS AND PRINCIPLES

OF CALCULATION IN NUCLEAR MATERIALS CONTROL

A. INTRODUCTION

values of the measurements, and the effect of the shift can therefore be thought of as a bias. When the shift is Section 70.51 of Part 70 of Title 10 of the Code of itself a random variable characterized by a mean and Federal Regulations requires certain AEC licensees variance, various statistical procedures can be employed authorized to possess special nuclear material to to distinguish the random components due to systematic calculate statistical limits of error as part of their effects from those due to "purely random" effects.

material control and accounting procedures for use in When scrutinizing a particular measurement procedure, assuring that special nuclear material in their possession It is imperative to differentiate between systematic is accounted for. This guide Identifies concepts, effects which behave like biases and those which are principles, and referenced methods that are acceptable created by random phenomena. In particular, biases do to the Regulatory staff for calculating such limits of not "propagate" in the same way as do random error. variables.

B. DISCUSSION

Subcommittee N15-3 of the American National Standards Institute (ANSI) Standards Committee NIS,

Statistical controls are required as an integral part of Methods of Nuclear Materials Control, has developed a special nuclear materials control and accounting systems standard for calculating limits of error. This standard is to assure that licensees of fuel processing and fuel designated ANSI N15.16, "Limit of Error Concepts and fabrication facilities effectively account for the special Principles of Calculation in Nuclear Materials Control."

nuclear material they possess and localize losses when The limit of error is defined in 10 CFR Part 70 as the they occur. A primary statistical Indicator of control is uncertainty component used in *constructing a 95%

the quantity of material unaccounted for, which is the confidence interval associated with a quantity after any observed difference between the amount of material that recognized bias has been eliminated or its effect should be on hand (book inventory) and the amount of accounted for. Regulatory Guide 5.3, "Statistical material determined as physically on hand (ending Terminology and Notation for Nuclear Materials inventory). Another indicator is an observed Management," dated February 2,1973, states that limit shipper-receiver difference, which results from of error is construed as the uncertainty component used comparing two independent determinations of to construct a 95% confidence interval and states, in transferred material. Essential to a comprehensive addition, that the uncertainty component should include evaluation of the significance of these Indicators are systematic as well as random error

s. The new ANSI

statistical techniques using associated limits of error for standard N15.16, however, defines limit of error as twice testing whether detected Imbalances may be attributable the standard deviation of the estimator. This is not to measurement error, biases other than those due to consistent with 10 CFR Part 70 and Regulatory Guide measurement, possible diversions, or other factors. 5.3 since it does not always result in 95% confidence intervals.

In the treatment of measurement data, the concept of a systematic error is Important. A systematic error is

C. REGULATORY POSITION

said to have occurred when all members of a subset of the measured values are shifted in the same direction and The concepts, principles, and referenced methods by the same amount. This shift changes the expected for calculating limits of error contained in the final draft USAEC REGULATORY GUIDES Cophs of pJldW sul.d wAy be ebtakud by request histing die dM910si d~md V

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0. Genral

of ANSI N15.16, "Limit of Error Concepts and 1. The calculated limits of error defined in Section 3.2 Principles of Calculation in Nuclear Materials of the standard should be based on 95% confidence Control," 1 are generally acceptable to the Regulatory intervals for the estimator, which must consider the K

staff for use in nuclear material control and accounting effective degrees of freedom associated with the procedures, subject to the following: estimated variance.

2. Section 4.6 of the standard should be interpreted to mean that mistakes and blunders arising from the Copies may be obtained from the Institute of Nuclear recording, processing, or reporting of measurement data, Materials Management, SOS King Ave., Columbis, Ohio 43201, whenever they are appropriately identified, should be Attn: Mr. It. L. Toy. excluded from the input to a limit of error calculation.

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