6 Progress in the Verification of Reprocessing Input
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Analysis for Nuclear Material Safeguards L.
KOCH
Commission of the European Communities, Joint Research Centre, Karlsruhe Establishment, European Institute for Transuranium Elements, Karlsruhe, West Germany Ε.
MAINKA
Institut für Radiochemie, Kernforschungszentrum Karlsruhe, Postfach 22 66, D-7500 Karlsruhe 1, West Germany
The reprocessing input analysis is a key measurement in the nuclear fuel cycle not only from the safeguard point of view. The fuel can be directly analysed for the f i r s t time since i t s fabrication. A material balance between initial, fissioned and remaining material is possible with high accuracy. In addition, the portion of the fuel converted into special nuclear material e.g. plutonium is measured before it i s purified for recycling. Three possible methods for an input analysis are in use, of which the f i r s t one is applied usually by the plant operators, therefore the two latter ones can be used as a redundant measure (1,2,3). The method of choice for most plants is the volume concen tration method by which the volume of the dissolved fuel and the concentration of uranium and plutonium in it are measured. The Pu/U-method needs only analysis of the ratio of these two elements in the spent fuel but requires information about the burn-up and the initial amount of the fuel. A recently developed isotope correlation technique uses correlations between an isotopic ratio (which can be easi ly and with high accuracy measured) and the uranium or plu tonium quantity. To obtain the input of the actinides the initial amount of the fuel has also to be known. The following describes the progress made recently in Karlsruhe to verify the reprocessing input by automatic direct analysis, or by balancing pre- and post- irradiation amounts of fuel or by the isotope correlation technique. AUTOMATES FOR DIRECT ANALYSIS The automatic x-ray fluorescence spectrometer described earlier (4,5,6) has been improved: An instrument with a seven-channel analyser has been installed in the reprocessing f a c i l i t y , WAK, where i t is manually operated under test. The automatic sample preparation stage has been completely redesigned. A more com pact sampling device has been fabricated which is controlled by a microprocessor. This part of the automat is now being ex0-8412-0449-7/78/47-079-073$05.00/0 © 1978 A m e r i c a n C h e m i c a l Society
74
NUCLEAR
SAFEGUARDS
ANALYSIS
t e n s i v e l y t e s t e d c o l d under r o u t i n e c o n d i t i o n s . A l a b o r a t o r y f o r automatic i s o t o p e d i l u t i o n a n a l y s i s , AIDA, i s i n r o u t i n e use f o r a n a l y s i n g samples taken by the EURATOM safeguard i n s p e c t o r s . T h i s l a b o r a t o r y comprises the f o l l o w i n g automates: - ion-exchange to c o n d i t i o n uranium and plutonium f o r the sub sequent isotope a n a l y s i s ( F i g . 1), - a balance to weigh the sample and s p i k e s o l u t i o n f o r the i s o tope d i l u t i o n , - an α-spectrometer to determine Pu-238 and t r a n s p l u t o n i t e abundances, - an automatic mass-spectrometer a i d e d by a high-vacuum l o c k f o r continuous sample feeding ( F i g . 2) . The c o n d i t i o n i n g of the r e p r o c e s s i n g input s o l u t i o n sample i s done by s o r p t i o n o f the n i t r a t o complexes o f U and Pu on an anion-exchanger and subsequent e l u t i o n with d i l u t e n i t r i c a c i d (7) . The automat holds up to s i x columns each of which can be programmed i n d i v i d u a l l y f o r the charging o f two eluents and f o r y i e l d i n g up to four f r a c t i o n s w i t h v a r i a b l e volumes (8) . The a d d i t i o n of known amounts o f the spikes to a known a l i quot of the sample s o l u t i o n i s achieved by means of an automatic balance which d i r e c t l y transmits the weights v i a a PDP 11/10 to a IBM-370 computer f o r the a n a l y s i s e v a l u a t i o n ( F i g . 3) (9). A l l operations of the ma s s- spec t r orne t e r necessary to ana l y s e the i s o t o p i c abundance of uranium and plutonium are con t r o l l e d by a dedicated computer. Continuous l o a d i n g of the samp l e s i s achieved by a three-chamber high-vacuum l o c k which speeds up the measurement by preheating the samples before they enter the i o n source of the instrument. From a thorough systematic a n a l y s i s of a l l operations used i n manual o p e r a t i o n mass spec trometry, elaborate software has been w r i t t e n f o r a dedicated process computer. S t a r t i n g from i n s e r t i o n o f the samples i n t o the l o c k , t h e computer c o n t r o l s a l l steps such as baking out the samples, heating up i n the ion source, f o c u s s i n g and r e f o c u s s i n g the instrument, scanning a t a p r e - s e l e c t e d i o n c u r r e n t with p o s s i b l e subsequent measurement o f uranium, plutonium and neodymium from a s i n g l e sample and r e d u c i n g the mass spectra to atom r a t i o s , averaged over ten scans (9.10,11). DATA PROCESSING The handling of the data from r o u t i n e r e p r o c e s s i n g a n a l y s i s , generated f o r a s i n g l e a n a l y s i s over a p e r i o d o f s e v e r a l days, j u s t i f i e s o n - l i n e data processing. The c o n f i d e n t i a l i t y and data s e c u r i t y r e q u i r e d by safeguards make i t mandatory. The system employed i n AIDA g i v e s none of the o p e r a t o r s d i r e c t access e i t h e r to the c h a r a c t e r i s t i c s of the sample o r t o the r e s u l t . For each a n a l y s i s the i d e n t i t y and c h a r a c t e r i s t i c s of the sample are f i l e d i n a s p e c i f i c matrix o f the computer, which p e r i o d i c a l l y c o l l e c t s information a v a i l a b l e a t the automates. The data are sorted out according t o the a n a l y s i s i n d e n t i t y and f i l e d i n t o the corresponding matrix. As soon as one matrix has
K O C H AND M A I N K A
Figure 1.
Input
Analysis
Automatic device for six parallel U and Pu separations for subsequent MS analysis
Figure 2. Automatic MS and a high-vacuum lock for continuous sample feeding
76
NUCLEAR
SAFEGUARDS
ANALYSIS
been completed the programme i s s e l e c t e d according to the type of data and the e v a l u a t i o n o f the a n a l y s i s s t a r t s (9). The a-spectrometer and balance are on l i n e t o a PDP-11 which reduces the source data and transmits them t o the IBM-370. The measurements of the mass spectrometer are converted to mass r a t i o s by the process computer and are then t r a n s f e r r e d v i a the PDP-11 to the IBM ( F i g . 4) (1_2) . ISOTOPE CORRELATION TECHNIQUE The r e s u l t s are f i l e d i n a DATABANK together with e a r l i e r ( h i s t o r i c a l ) data where they can be checked by u s i n g the r e c e n t l y developed i s o t o p e c o r r e l a t i o n technique. From a s e t o f h i s t o r i c a l data o f s i m i l a r o r i g i n , a p p r o p r i a t e c o r r e l a t i o n s are s e l e c t e d f o r different applications. The c o n s i s t e n c y of the new dataset i s checked to see i f the a n a l y s i s o f one of the i s o t o p e s i s f a u l t y . By comparing d i f f e r e n t c o r r e l a t i o n s a p o s s i b l e e r r o r during the course o f the a n a l y s i s can be spotted. The burn-up determination needed f o r the Pu/U method can be done e i t h e r by the c o s t l y Nd-148 a n a l y s i s (also by u s i n g AIDA) or by employing c o r r e l a t i o n s between e.g. plutonium i s o t o p e r a t i o s versus the burn-up (Tab. 1) (13,14,15,16). A more advanced a p p l i c a t i o n of the i s o t o p e c o r r e l a t i o n t e c h nique i s the p r e d i c t i o n of the f i s s i l e m a t e r i a l content d i r e c t l y from i s o t o p e c o r r e l a t i o n s . For t h i s purpose, c o r r e l a t i o n s are under study between the i s o t o p i c r a t i o w i t h i n an a c t i n i d e or f i s s i o n product and the f i s s i l e isotope content r e l a t e d to the i n i t i a l metal atoms o f the u n i r r a d i a t e d f u e l (IMA). From such a c o r r e l a t i o n the Pu-content could be deduced: Pu = Pu IMA · U with U the i n i t i a l amount o f f u e l and the Pu IMA c o r r e l a t i o n , Pu IMA = a · Pu i s o t o p e r a t i o + b (Table 1 ) . CONCLUSIONS The v a l u e of the automatic x-ray f l u o r e s c e n c e spectrometery l i e s i n i t s p o t e n t i a l f o r producing q u i c k l y a measurement of the chemical c o n c e n t r a t i o n of f i s s i l e m a t e r i a l , which i s needed during i n v e n t o r y t a k i n g i n the v a r i o u s hold-up v e s s e l s . At present, t e s t s are on the way to improve the accuracy by means of a m u l t i channel analyser (18). The developement of AIDA can be regarded as being completed. F u r t h e r automation would o n l y be j u s t i f i e d by l a r g e r sample throughputs i n order to reduce the a n a l y s i s c o s t . From the present experience i t can be concluded t h a t AIDA has increased the sample throughputs by f i v e times compared t o t h a t from the e a r l i e r manual o p e r a t i o n . The accuracy (1/7) i s not a f f e c t e d by the automation; on the c o n t r a r y , the automatic procedure r e j e c t s samples showing an odd behaviour i n the mass spectrometer,thus e l i m i n a t i n g p o t e n t i a l wrongly prepared m a t e r i a l . A comparison between the three above mentioned methods shows t h a t the volume c o n c e n t r a t i o n procedure r e q u i r e s the h i g h e s t number of measurements. However no a d d i t i o n a l i n f o r m a t i o n o f the f u e l h i s t o r y i s r e q u i r e d (Tab. 2). For the second procedure the volume and d e n s i t y measurement as w e l l as
KOCH
AND
MAINKA
Input
Analysis
Figure 3. Automatic balance for aliquotation used in isotope dilution analysis
Figure
4.
Scheme of on-line data handling between automates, process computers, and an IBM-370
m
F
Τ
m
Τ
F
14.3 (Pu-242/240)
=
- 0.436
- 4.11
- 5.98 E-4
Pu-242 = 1.89 E-3 (Pu-242/240)
2.84 (Xe-132/131)
- 9.29 E-3
Pu-242 = 5.24 E-4 (Xe-132/131)
=
+ 4.48 E-4
78
29
51
11
51
34
- 3.61 E-4
Pu-240 = 7.80 E-3 (Pu-242/240)
Pu-240 19
η
Pu-240 = 5.65 E-3 (Pu-240/239)
b
_ 2.97 E-3
+
.97
.98
.99
.99
.98
.98
.99
R
8.0
5.8
6.7
6.6
3.9
3.2
5.5
error %
all
all
PWR
PWR
GARIGLIANO
OBRIGHEIM
GARIGLIANO
OBRIGHEIM
TRINO VERCELLESE
reactor
s = error of prediction; R = correlation coefficient)
= a · (isotope r a t i o )
numbers o f p o i n t s ;
Isotope c o r r e l a t i o n s t o p r e d i c t burn-up (F ), Pu-240 IMA or Pu-242 IMA. 2 2 1 2 (Error: s = σ (1 + / η ) ; σ = sums o f squared d e v i a t i o n s / ( n - 2 ) ; η =
2.00 E-3 (Xe-132/131)
y
Table I :
6.
KOCH
A N D MAINKA
Input
Analysis
79
Table H: Comparison o f p o t e n t i a l e r r o r sources (+) f o r each o f the methods.
ERROR SOURCES
MEASUREMENTS
j
- ω & U
3
METHOD
Ρ)
H
η
3 Β en en
ρ·
Χ « W f t H- S
Η· C
13 ο ο ^ Η 3
Ο Hi
0
0
ht) 25 Χ P i CD Η)
Ί) Η ^
e o n
Volume/concentration
+ + +
ADDITIONAL INFORMATION
OTHERS
> ο a » 3 fD ο Η, Ω 3 W π) ks
^ Η. Η·
Οϊ Ό
fD Hi Hi (D Ο ft
Η.
Ω
M
Ο fD Η· Ο CO 3 3 fD vQ ft & So PU Hi CO
+ + + +
148 Pu/U r a t i o
(
+ +
+ + +
+ + + +
+ +
+ +
+ + + +
Nd)
(Corr) Isotope C o r r e l a t i o n s (U,Pu) (Xe,Kr)
+ + + +
+ + + +
80
NUCLEAR SAFEGUARDS ANALYSIS
the aliquoting of the sample i s eliminated, but instead a burnup measurement i s needed, which can be done by isotope corre lations on actinide isotopic ratios thus avoiding the normally applied, costly Nd-148 analysis. Information on the i n i t i a l amount of uranium i s needed. The number of potential error sour ces i s reduced compared to the f i r s t method. For the third pro cedure only a simple isotope analysis i s required. However the need for additional information on the fuel i s increased. Be sides the i n i t i a l amount of uranium, h i s t o r i c a l data from which isotope correlations can be deduced have to be provided. The po tential error source of cross contamination during sampling i n side the reprocessing plant i s eliminated by using the fission gas correlations, since a cross contamination from samples taken from the exhaust gasses i s unlikely. 1
2 3
4 5
6 7 8 9 10
11 12 13
Koch L., Bresesti M. Inst. of Nuclear Material Management, New Orleans, USA; Journal of the Institute of Nuclear Mat. Manage ment, (1975) V o l . IV, No. III, P. 49 Koch L., Cottone G. Reaktortagung des dtsch. Atomforums, Karls ruhe, (1973) Tagungsberichte S. 287 Koch L., Ahrens H.J., Baeckmann A . v . , Cricchio Α . , De Meester R., Romkowski Μ., van der Stijl E., Wilhelmi M. Intern. Atomic Energy Agency: Int. Symposium on Safeguarding of Nuclear Ma t e r i a l , Wien; Proceedings of the Symposium (1975) Baeckmann A . v . , Koch L., Berg R. 70. Meeting of Americ. Chem. Soc. Chicago (1975) Baeckmann A . v . , Küchle M . , Weitkamp C., Avenhaus R., Baumung K . , Beyrich W., Böhnel Κ., Klunker J., Mainka Ε., Matussek P . , Michaelis W., Neuber J., Wertenbach Η . , Wilhelmi Μ., Woda Η . , H i l l e F., Linder W., Schneider V.W., S t o l l W., Koch L., Eberle R., Stegmann D . , Zeller W., Krinninger Η . , Mausbeck Η . , Ruppert E. Intern. Atomica Agency, Genf (1971) Proceedings of 4. Confe rence "Peaceful uses of Atomic Energy" A/Conf. 49/A/809 Baeckmann A.v., Koch L., Neuber J., Wilhelmi M. Intern. Atomic Energy Agency, Wien (1972) Proceedings SM-149/42 Koch L., Radiochim. Acta (1969) 12, 160 Bol D . , Brandalise Β . , Bier Α . , De Rossi M . , Koch L . EUR-5141 (1974) Brandalise Β., Cottone G . , Cricchio Α . , Gerin F., Koch L . EUR5669 (1977) Koch L., Wilhelmi Μ., Brandalise B., Rijkeboer C., Romkowski M. Proc. of 7. Int. Mass Spectrometer Conf., Florence (1976) V o l . 7 Wilhelmi Μ., Brandalise Β., Koch L., Rijkeboer C . , Romkowski M. EUR 5504 d (1977) Koch L . V Convegno d i Spettrometria d i Massa, Catania (1977) Annali de Chimica to be published Ernstberger R . , Koch L., Wellum R. ESARDA Symp. on Isotopic Correlation and i t s Application to the Nuclear Fuel Cycle, Stresa, Italy, May 9-11 (1978)
6.
14 15 16 17 18
KOCH AND MAINKA
Input Analysis
Wellum R., De Meester R., Kammerichs Κ., Koch L . i b i d . Brandalise B . , Koch L., Rijkeboer C . , Romkowski D. i b i d . Schoof S., Steinert Η., Koch L . i b i d . Beyrich W., Drosselmeyer E . KFK-1905 (1975) Neuber I . , Flach S., Braun R., Stöckle D. in KFK-2465 P.3-8 (1977)
RECEIVED JUNE 12,
1978.
