Nuclear Safeguards Analysis - ACS Publications - American Chemical

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Safeguards N e e d s in t h e M e a s u r e m e n t A r e a : t h e R e a l m of

Measurements

Downloaded by 82.232.97.170 on May 31, 2018 | https://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0079.ch001

GLENN HAMMOND Office of Safeguards and Security, U.S. Department of Energy (DOE), Washington, DC 20545 CLEMENS AUERBACH Department of Nuclear Energy, Brookhaven National Laboratory, Upton, NY 11973 The ACS meeting and its program on "Nondestructive and Analytical Chemical Techniques for Nuclear Safeguards" provides a timely forum for permitting all of us from the various measurement areas in the nuclear field to participate and contribute to the v i t a l safeguards challenges. We wish to jointly share some of our ideas on measurements for safeguards, their evolution, and highlights and objectives of the emerging measurement advances. DOE's safeguards program relates to a l l its nuclear materials and f a c i l i t i e s , but concentrates on the more readily usable forms of f i s s i l e or special nuclear material (SNM) - plutonium, uranium enriched in 235 and 233 . I t supports the development of safeguards concepts for new power reactor designs and related fuel cycle f a c i l i t i e s . The general objective of the nation's safeguards program is to prevent successful malevolent acts involving special nuclear material and f a c i l i t i e s . The term "safeguards" then is used in a broad sense to include physical protection and materials control measures to deter and detect theft and to provide a monitoring and accountability capability for SNM flow streams, transactions and inventories. In addition, DOE considers U. S. national security to dictate that nuclear materials and f a c i l i t i e s wherever they appear in the world, should be protected against malevolent action as well as safeguarded internationally against nuclear proliferation. Reliable materials control and accountability include the need for (1) timely characterization of the material to determine the intensity of protection needed and quantitative determination of what, where and how much material is being protected (or requires protection) ; (2) rapid detection and localization of a loss and backup to physical protection; (3) effective means for investigation and, i f necessary, to i n i t i a t e actions for recovery, and (4) frequent testing for credible confirmatory assessment that the protection and control systems are working properly and have not been U

U

This chapter not subject to U.S. copyright. Published 1978 American Chemical Society Hakkila; Nuclear Safeguards Analysis ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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circumvented. The continuous monitoring of m a t e r i a l to meet these needs w i l l , i n a d d i t i o n , help meet plant r e q u i r e ments f o r process and q u a l i t y c o n t r o l , materials management, c r i t i c a l i t y c o n t r o l and h e a l t h and s a f e t y . To give you a p i c t u r e of the important r o l e that measure ments play i n safeguards and the development necessary f o r s u c c e s s f u l implementation, we would l i k e to f i r s t review b r i e f l y the h i s t o r y of nuclear m a t e r i a l s measurements; second, the r a t i o n a l e f o r r e l i a b l e measurement i n m a t e r i a l s c o n t r o l and a c c o u n t a b i l i t y ; t h i r d , types of measurements of nuclear m a t e r i a l s i n c l u d i n g t r a d i t i o n a l chemical and i s o t o p i c analyses, and the newer non-destructive techniques; f o u r t h , a n a t i o n a l nuclear standards and measurement assurance program; and f i n a l l y , the challenges we see i n accomplishing the various tasks i n v o l v e d . BACKGROUND AND

EVOLUTION

The c o n t r o l and measurements of nuclear m a t e r i a l s are not new. The nuclear m a t e r i a l s produced at Oak Ridge and Hanford i n the e a r l y 1940's were guarded c a r e f u l l y because of t h e i r extremely l i m i t e d q u a n t i t i e s and very s e n s i t i v e p o t e n t i a l m i l i t a r y a p p l i c a t i o n . The years just preceding World War II were marked by a dramatic e v o l u t i o n of a n a l y t i c a l chemistry of nuclear m a t e r i a l s as a science, drawing f r e e l y on developments i n p h y s i c a l chemistry and other r e l a t e d d i s ciplines. Since U. S. s c i e n t i s t s were i n the f o r e f r o n t of some of these developments, the Manhattan Project was able, j u s t as i n a number of other areas, to p r o f i t not only from the new advances but a l s o from d i r e c t c o l l a b o r a t i o n with the key s c i e n t i s t s r e s p o n s i b l e f o r them. With the a i d of i n d i v i d u a l s l i k e Ν. H. Furman of Princeton U n i v e r s i t y , C. F. Metz of the then newly e s t a b l i s h e d Los Alamos S c i e n t i f i c Laboratory and many others, the a n a l y t i c a l procedures d e v e l oped i n those days went f a r beyond s e r v i n g t h e i r immediate purpose. In c o n j u n c t i o n with new developments i n r a d i o chemistry, microchemistry and separation techniques, these procedures set a trend f o r a n a l y t i c a l techniques which has not been surpassed since, and indeed gave major impetus to the major advances i n a c t i n i d e chemistry. In s i m i l a r f a s h i o n , mass spectrometric techniques f o r measuring the i s o t o p i c composition of uranium were developed i n response to the demands of the Manhattan P r o j e c t , to a point where they could e v e n t u a l l y be adopted by the c i v i l i a n nuclear i n d u s t r y without much fundamental change. During the e a r l y years, the r e l a t i v e l y small p h y s i c a l i n v e n t o r i e s were d i f f i c u l t - t o - m e a s u r e however, using a v a i l able manual techniques which were tedious and time-consuming. Methods and techniques f o r chemical and i s o t o p i c analyses were s t i l l being developed f o r the new m a t e r i a l s . There

Hakkila; Nuclear Safeguards Analysis ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


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was v i r t u a l l y no instrumentation to reduce a n a l y s t s time, few standard reference m a t e r i a l s or standard methodology, and few l a b o r a t o r i e s for intercomparison of r e s u l t s . In f a c t , i n many cases, the a n a l y s i s was performed by the anal y s t who had just developed the method, and s t a f f who were f a m i l i a r with s t a t i s t i c a l methodology were not always a v a i l able to compare and review r e s u l t s . S h o r t l y a f t e r the war, the Atomic Energy Act placed r e s p o n s i b i l i t y for t h i s new energy source i n the hands of a c i v i l i a n agency. The nuclear m a t e r i a l processes and operations were s t i l l being developed and lacked e f f i c i e n c y . The m a t e r i a l was expensive to produce, and emphasis was placed on f i n a n c i a l r e s p o n s i b i l i t y for c o n t r o l . In subsequent years, p r i o r i t i e s — t e c h n i c a l , economic, and p o l i t i c a l — r e l a t e d to nuclear energy changed. L e g i s l a t i o n , the 1954 r e v i s i o n of the Atomic Energy Act and the P r i v a t e Ownership Act of 1964 ( P u b l i c Law 88-489) permitted expansion of the use of nuclear energy and r e l a t e d m a t e r i a l s Two years l a t e r i n 1966, f e d e r a l r e g u l a t i o n s were adopted which placed a s p e c i f i c o b l i g a t i o n on the domestic p r i v a t e i n d u s t r i a l sector to safeguard SNM. When i n t e r n a t i o n a l t e r r o r i s m e s c a l a t e d i n the e a r l y 1970's, nuclear m a t e r i a l s and r e l a t e d f a c i l i t i e s , at home and abroad, were recognized as p o s s i b l e targets for t e r r o r i s t purposes because of the p o t e n t i a l f o r extensive malevolent use and the growing a n t i nuclear i n t e r e s t s . The concept of balanced and i n t e g r a t e d systems was recognized as a means to improve e f f e c t i v e n e s s of safeguards. These developments led t o , among other t h i n g s , e v o l u t i o n a r y changes i n chemical and i s o t o p i c measurement methods along the l i n e s of i n c r e a s i n g r e l i a b i l i t y and speed u s i n g standards and automation. The AEC and i t s successor organi z a t i o n s (ERDA, NRC, DOE) have c o n s i s t e n t l y played a major r o l e i n supporting these a c t i v i t i e s , with the r e s u l t that measurement techniques at the U. S. Government-owned l a b o r a t o r i e s have become unique i n terms of s i z e , v e r s a t i l i t y and s o p h i s t i c a t i o n . I n t e r n a t i o n a l safeguards, as c a r r i e d out by the I n t e r n a t i o n a l Atomic Energy Agency (IAEA), places r e l i a n c e on m a t e r i a l s measurements i n a c c o u n t a b i l i t y systems. Signif cance i s attached to q u a n t i t i e s of nuclear m a t e r i a l s that could be used by a country as part of a nuclear e x p l o s i v e device. DOE, i n cooperation with other U. S. Government agencies, i n c l u d i n g the State Department, the Arms C o n t r o l and Disarmament Agency (ACDA), and the Nuclear Regulatory Commission (NRC) provides both safeguards experts and equipment to a s s i s t the IAEA. Implementation includes d i r e c t i n g a technology base towards answering t e c h n i c a l questions posed by U. S. n o n - p r o l i f e r a t i o n i n i t i a t i v e s and by U. S. p a r t i c i p a t i o n i n the I n t e r n a t i o n a l Nuclear Fuel Cycle


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E v a l u a t i o n (INFCE) program being conducted by the IAEA. Today, n a t i o n a l and i n t e r n a t i o n a l safeguards concerns are being addressed i n the development of concepts and supporting measurement technology for safeguard systems f o r spent f u e l storage, uranium enrichment, chemical reprocessing or coprocessing and p r o l i f e r a t i o n - r e s i s t a n t a l t e r n a t i v e f u e l c y c l e s . These e f f o r t s include major support to a n a t i o n a l N o n p r o l i f e r a t i o n A l t e r n a t i v e Systems Assessment Program (NASAP). Today, f u e l c y c l e a l t e r n a t i v e requires a comprehensive study and e v a l u a t i o n of measurement methods and instruments for the range of m a t e r i a l forms and compositions which are c h a r a c t e r i s t i c of the r e l a t e d processes. Accuracy, p r e c i s i o n and o p e r a t i o n a l features are required for o n - l i n e and a t - l i n e instrumentation to optimize m a t e r i a l s management, c o n t r o l and accounting systems. RATIONALE FOR

AN EFFECTIVE SAFEGUARDS MEASUREMENT SYSTEM

Measurements and measurement q u a l i t y assurance programs are v i t a l to m a t e r i a l s c o n t r o l and a c c o u n t a b i l t y safeguards systems. M a t e r i a l balance accounting i s drawn around a plant and several major portions of the plant processes by adding a l l measured r e c e i p t s to the i n i t i a l measured inventory and s u b t r a c t i n g a l l measured removals from the f i n a l measured inventory. Measurements e s t a b l i s h the q u a n t i t i e s of nuclear m a t e r i a l i n each c u s t o d i a l area and a f a c i l i t y as a whole as one of a number of safeguards subsystems c o n t r i b u t i n g to the d e s i r e d c a p a b i l i t y to l o c a l i z e losses and i n generating and assessing safeguard alarms. Of course, appropriate checks and balances are required to detect mistakes and protect the m a t e r i a l accounting system from fradulent source data; and a s t r i c t measurement q u a l i t y assurance program i s necessary to ensure the accurate c a l i b r a t i o n of the measurement systems and the r e p r o d u c i b i l i t y of the measurements. As part of the safeguards system, nuclear f a c i l i t i e s are required to e s t a b l i s h and r e p o r t , on a regular b a s i s , m a t e r i a l balances based on these measured values. Regul a t i o n s to t h i s e f f e c t have been promulgated by DOE and NRC. These r e g u l a t i o n s center on the concept of inventory d i f f e r e n c e s (ID), p r e v i o u s l y known as M a t e r i a l Unaccounted For (MUF), and defined by the expression ID = BI + A where BI A EI

-EI

-R

beginning inventory a d d i t i o n s to inventory p h y s i c a l inventory ending inventory

since the

last


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removals from inventory since the l a s t p h y s i c a l inventory.

If a l l uncertainties, biases, t r a n s c r i p t i o n errors, process holdups, unmeasured l o s s e s , e t c . are properly accounted f o r , then i n the absence of t h e f t or d i v e r s i o n ID should be zero. The r e g u l a t i o n s s t i p u l a t e that ID s exceeding predetermined l i m i t s of e r r o r (LEID) s h a l l be viewed as the r e s u l t of p o s s i b l e t h e f t or d i v e r s i o n of nuclear m a t e r i a l and appropriate a c t i o n taken. L i m i t s on how large the measurement u n c e r t a i n t y may be, based e i t h e r on a f i x e d amount or on a r a t i o of throughput, are determined by s t a t i s t i c a l means. The s t a t i s t i c a l means and appropriate mathem a t i c a l modeling techniques have r e c e n t l y received a d d i t i o n a l i n t e r e s t s by DOE and some of i t s c o n t r a c t o r s . The goal i s to develop s t a t i s t i c a l e r r o r propagation methodology which w i l l permit e v a l u a t i o n of appropriate LEID s from f a c i l i t y measurement c o n t r o l data. The goal includes a graded approach whereby the LEID values w i l l r e f l e c t the s t r a t e g i c s i g n i f i cance of a given nuclear m a t e r i a l stream (flow or i n v e n t o r y ) . Much has been w r i t t e n on the use of mathematical s t a t i s t i c s i n e v a l u a t i n g the complex problems associated with safeguards systems. We note i n p a r t i c u l a r the work by John Jaech, " S t a t i s t i c a l Methods i n Nuclear M a t e r i a l C o n t r o l " Q ).


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The realm of measurements for safeguards includes a v a r i e t y of techniques r e q u i r e d for c h a r a c t e r i z i n g and determining nuclear m a t e r i a l q u a n t i t i e s i n feed, process, product and waste streams; f o r standards and measurement c o n t r o l s , performance e v a l u a t i o n and system o p t i m i z a t i o n ; and f o r independent v e r i f i c a t i o n by a safeguards i n s p e c t o r ate . An e f f e c t i v e safeguards measurement system must combine the elements of v e r s a t i l i t y , r e l i a b i l i t y and t i m e l i n e s s . Streams to be measured include m a t e r i a l s ranging from essent i a l l y pure uranium and plutonium compounds, which are r e l a t i v e l y easy to sample and d i s s o l v e , to heterogeneous and i n t r a c t a b l e s o l i d waste generated i n the course of processing operations. This may include such d i v e r s e items as used c a s t i n g c r u c i b l e s , contaminated paper, rags, rubber gloves, f l o o r and hood sweepings, e t c . Each stream must be measured with an accuracy and p r e c i s i o n commensurate to the c o n t r i b u t i o n which the stream makes to the o v e r a l l nuclear m a t e r i a l balance. The guiding p r i n c i p l e i s the establishment of a f u l l y measured m a t e r i a l balance w i t h i n predetermined l i m i t s of e r r o r . To s a t i s f y these wide-ranging and sometimes c o n f l i c t i n g demands, a systematic and j u d i c i o u s choice must be made



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between methods which may be considered i n three i n t e r r e l a t e d areas: (1) bulk measurements which are d i r e c t e d to t o t a l volume and flow r a t e , gross and net weights, and t o t a l piece count; (2) sampling which i s d i r e c t e d to obt a i n i n g a r e p r e s e n t a t i v e and t r a c t a b l e p o r t i o n of a t o t a l batch under c o n s i d e r a t i o n ; and (3) a n a l y t i c a l determinations which are d i r e c t e d to s p e c i f i c c h a r a c t e r i s t i c s (chemical, p h y s i c a l , nuclear) of the m a t e r i a l under c o n s i d e r a t i o n . A n a l y t i c a l measurements then may be categorized broadly i n t o chemical and nondestructive methods. Chemical methods, i n the present context, are based on sampling followed by laboratory measurements of e i t h e r c o n c e n t r a t i o n or i s o t o p i c composition of SNM. Combined with appropriate bulk measurements these methods y i e l d the t o t a l quantity of SNM i n a given flow stream or inventory stratum. Nondestructive a n a l y s i s (NDA) i s based on the nuclear p r o p e r t i e s of uranium and plutonium; these p r o p e r t i e s are used to measure the SNM content of m a t e r i a l which cannot be sampled i n r e p r e s e n t a t i v e fashion or which does not e a s i l y y i e l d to d i s solution . It i s now recognized that a t r u l y e f f e c t i v e safeguards measurement system must make concerted use of both chemical and nondestructive methods. A c c o r d i n g l y , the thrust of recent DOE-sponsored research and development has been towards p o t e n t i a l s o l u t i o n s which incorporate the most d e s i r a b l e aspects of both approaches. Work at Los Alamos S c i e n t i f i c Laboratory, Lawrence Livermore Laboratory, New Brunswick Laboratory (now l o c a t e d at Argonne, I l l i n o i s ) and at other l a b o r a t o r i e s and f a c i l i t i e s , i s d i r e c t e d at making chemical methods both more t i m e l y by way of automation, and more responsive to non-homogeneous or otherwise i n t r a c t able m a t e r i a l s , even to the extent of i n c o r p o r a t i n g some aspects of NDA methodology. At the same time, advances i n e l e c t r o n i c s and detector c a p a b i l i t y combine to make p o s s i b l e i n c r e a s i n g l y s o p h i s t i c a t e d NDA approaches, i n terms of both v e r s a t i l i t y and accuracy. A s i g n i f i c a n t aspect of these developments i s the c l o s e c o l l a b o r a t i o n between DOE cont r a c t o r l a b o r a t o r i e s and f a c i l i t i e s abroad, notably i n the Federal Republic of Germany and other members of the European community and the I n t e r n a t i o n a l Atomic Energy Agency (IAEA). Some of these developments w i l l be covered i n d e t a i l by other p a r t i c i p a n t s i n t h i s Symposium. Other than a few exceptions, chemical methods i n use today are based i n essence on developments which took place during the Manhattan Project and have not changed s i g n i f i c a n t l y i n terms of the general p r i n c i p l e s i n v o l v e d . In 1963, the AEC with the a s s i s t a n c e of an Advisory Committee f o r Standard Reference M a t e r i a l s and Methods of Measurement reviewed, evaluated, and published "Selected Measurement Methods for Plutonium and Uranium i n the Nuclear



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Fuel C y c l e " (j2). The p u b l i c a t i o n was r e v i s e d i n 1972 to recognize i n t e r v e n i n g improvements (3). These wet a n a l y t i c a l methods are i n existence at nuclear f a c i l i t i e s to measure uranium and plutonium i n a v a r i e t y of m a t e r i a l s — metal, a l l o y s , s a l t s and oxides. Much of DOE's work r e l a t e d to the improvement and automation of a n a l y t i c l methods to reduce u n c e r t a i n t i e s i n i n v e n t o r i e s or m a t e r i a l s balance c o n t r o l i s being c a r r i e d out at the New Brunswick Laboratory (NBL) and the Lawrence Livermore Laboratory (LLL); and at the Los Alamos S c i e n t i f i c Laboratory (LASL) r e l a t e d to fast d i s s o l u t i o n methods f o r r e f r a c t o r y nuclear m a t e r i a l s , and the t e s t i n g of an inexpensive mass spectrometer f o r i n - p l a n t i n s p e c t i o n use. The Davies-Gray method which i s used f o r determining uranium has been the subject of extensive development work both at NBL and LLL. The o r i g i n a l method i s based on the r e d u c t i o n of U(VI) to U(IV) with F e ( l l ) i n H^PO^ solution, followed by o x i d a t i o n of excess F e ( l l ) with HNO^ i n the presence of a Mo(Vl) c a t a l y s t and t i t r a t i o n with I^C^Oy to a c o l o r i m e t r i c ( v i s u a l ) end p o i n t . The method was improved and r e f i n e d at NBL by the a d d i t i o n of V(IV) to the s o l u t i o n to markedly speed up the attainment of e q u i l i b r i u m , which allowed the use of potentiometic end-point d e t e c t i o n . These e f f o r t s have r e s u l t e d i n a f u l l y automatic uranium t i t r a t i o n system, developed by LLL and d e l i v e r e d to the new NBL s i t e at Argonne N a t i o n a l Laboratory (ANL) i n 1976. This system i s being tested c u r r e n t l y f o r n o n - i r r a d i a t e d uranium, i n c l u d i n g uranium a l l o y s and scrap. Some 44 samples can be analyzed i n an 8 hour day with a r e l a t i v e standard d e v i a t i o n of about 0.1%, using 20-150 mg samples. Complete f a u l t and malfunction d e t e c t i o n hardware and software are used to permit unattended operation. An a t t r a c t i v e feature of t h i s system i s that i t a u t o m a t i c a l l y shuts down should data not match standard uranium values. A n a l y t i c a l r e s u l t s are c a l c u l a t e d and p r i n t e d on a hard copy minicomputer. The A n a l y t i c a l Chemistry Group at LASL has been r e s p o n s i ble f o r a large number of important developments i n the s a f e guards measurement area. One of the more i n t e r e s t i n g ones concerns an o v e r a l l a n a l y t i c a l system f o r scrap and other h a r d - t o - d i s s o l v e m a t e r i a l . The system i s depicted schemati c a l l y i n Figure 1, which demonstrates how an o v e r a l l e r r o r of l e s s than 1.5% may be a t t a i n e d even though about 10% of the sample cannot be d i s s o l v e d . A high pressure d i s s o l u t i o n technique i s employed, and subsequent automated chemical a n a l y s i s i s performed by a spectrophotometer system which was developed at LASL and has since been r e f i n e d . The instrument incorporates a solvent e x t r a c t i o n system and dual f i l t e r s which enable s e q u e n t i a l a n a l y s i s of U and Pu i n the same s o l u t i o n . The instrument can accommodate samples i n the m i l l i g r a m to submilligram range.


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D i s s o l u t ion


>90%

dissolved

Automated Chemical A n a l y s i s RSD* + 1 %

Nuclear Safeguards Analysis - ACS Publications - American Chemical

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