[en] The reactor RA is a heavy-water channel-type research reactor. Regarding the accountability of nuclear material, the specific features of reactor RA are: The segmental form of fuel elements; numerous fuel elements in the reactor core and numerous elements to be reloaded annually; and the flexibility and complexity of the in-core fuel management. Consequently, there are many fuel elements in the spent fuel storage with an incoherent and rather complex irradiation history. To account for the nuclear material in the irradiated fuel elements, under the given circumstances, some ''fast'' procedure for the fuel burnup evaluation should be used. In this respect, the fuel work integration procedure, based on the power distribution evaluation, has been investigated. The radial power distribution is measurable by the channel coolant flow-rate and the inlet/outlet temperature difference. The axial distribution is calculated by the two-group homogeneous diffusion approach. The gamma spectrometry method is used to verify the ''power distribution procedure''. The intercomparison is made on 17 fuel elements from two fuel channels with different in-core history. The differences between obtained results were within the experimental error associated with both methods. This indicates that the ''power distribution method'' is a useful tool for routine application on the irradiated fuel of the RA reactor. However, to correlate it successfully further measurements by gamma spectrometry should be done. (author)

[en] The International Atomic Energy Agency (IAEA) has the unique responsibility and authority for obtaining safeguards information under the terms of its agreements. Safeguards information in this paper refers to accountancy data, design information and quantitative inspection data. When discussing a computerized information system for processing safeguards data one must distinguish between a facility, a State, and an international information system. All data fed into the international system and all output from the system are treated with the utmost confidence. The computerized data are encrypted and the printed reports controlled. As the amount of data increased and the user requirements became more complex, the Department of Safeguards realized in 1976 that the current operating system eventually would not be able to meet the demands. A team was established to determine the long-term needs of IAEA Safeguards and to implement a system to satisfy those needs. (author)

[en] The performance of some existing titrimetric methods for plutonium estimation is reviewed in the context of plutonium accountancy in nitric acid solutions of irradiated mixed plutonium-uranium oxide fast reactor fuels. A novel titrimetic procedure is described in which plutonium is oxidized to plutonium VI by cerium IV in nitric acid solution, the excess oxidant destroyed chemically, and plutonium VI reduced by a measured excess of iron II which is back-titrated with potassium dichromate. The procedure is suitable for use in both glove-boxes and remote-handling facilities. The precision and accuracy of the procedure are described, both for pure plutonium solutions, and for plutonium in the presence of simulated fission products representing highly burned-up fuels. (author)

[en] The report describes the experience gained by the Central and Northern Europe Section of the Agency's Department of Safeguards in safeguarding the on-load reactor at Bohunice A-1 Nuclear Power Plant, Czechoslovakia. Measures to re-establish the inventory in the case of failure of surveillance devices are indicated. The correlation between the different fission product yields and burnup values have been established. (author)

[en] Current Agency criteria and practices are presented for safeguards at mixed-oxide fuel fabrication facilities. The paper includes a description of typical process activities and the types of materials normally encountered. Credible diversion possibilities and related concealment activities are discussed and Agency criteria for such facilities are reviewed. Requirements and the approach being pursued to counter protracted and abrupt diversion strategies are presented, with a discussion of specific verification requirements necessary to satisfy the short detection time criteria. (author)

[en] A thermal ionization mass-spectrometry system with automatic data evaluation is described. The experimental procedure for determining the isotopic composition of uranium and plutonium is given. The experimental results obtained with standard materials, uranium as well as plutonium, are discussed. The stability of the system in terms of bias correction factor is described as a function of time. The influence of some experimental parameters on this stability is shown. (author)

[en] The irradiated fuel bundle counters for CANDU 600-MW reactors provide the IAEA with a secure and independent means of estimating the inventory of the spent-fuel storage bay at each inspection. Their function is straightforward - to count the bundles entering the storage area through the normal transfer ports. However, location, reliability, security and operating requirements make them highly ''intelligent'' instruments which have required a major development programme. Moreover, the bundle counters incorporate principles which apply to many unattended safeguards instruments. For example, concealing the operating status from potential diverters eases reliability specifications, continuous self-checking gives the inspector confidence in the readout, independence from continuous station services improves tamper-resistance, and the detailed data display provides tamper indication and a high level of credibility. Each irradiated fuel-bundle counter uses four Geiger counters to detect the passage of fuel bundles as they pass sequentially through the field-of-view. A microprocessor analyses the sequence of the Geiger counter signals and determines the number and direction of bundles transferred. The readout for IAEA inspectors includes both a tally and a printed log. The printer is also used to alert the inspector to abnormal fuel movements, tampering, Geiger counter failures and contamination of the fuel transfer mechanism. (author)

[en] Direct, non-destructive measurement on irradiated fuel of the gamma activity associated with the radioactive decay of fission products provides important data on the state of the fuel and its irradiation history, i.e. power distribution, physical state of the pins and assemblies, and burnup. For the past six years regular measurements have been made on the assemblies from the PWR reactor at the Ardennes nuclear power plant by means of prototype equipment (constructed and used by the French Atomic Energy Commission (CEA)) which is immersed in the fuel cooling pond. Concurrently, Framatome has designed and constructed devices for examining irradiated water-reactor fuel which are based, apart from gamma spectrometry, on such inspection methods as visual observation, measurement of dimensions and analysis of possible deformation. The two organizations have pooled their efforts and are continuing the development work in order to gain from experience already acquired and to supplement it with laboratory tests, thereby improving the measurement technique and broadening its range of application. The present development of the technique is geared first to systematically monitoring the operation of the reactors and, second, to identifying irradiated assemblies by measurement of the burnup and cooling time. (author)

[en] One of the basic problems in designing nuclear materials control systems is to handle and store the information necessary for plant operation and safeguards purposes. The method presented in this paper describes all kinds of nuclear material having different characteristics with a uniform and efficient data scheme. It is used to build up the data base of the nuclear materials control system for the Karlsruhe Nuclear Research Centre. (author)

[en] Surveillance and containment, which are indispensable supporting measures for material accountability, do not provide those charged with safeguarding an installation with the assurance beyond the shadow of a doubt that all the input and output uranium will in fact be measured. Those who are concerned with developing non-intrusive techniques for safeguarding uranium enrichment plants under the Nuclear Non-Proliferation Treaty have perceived the possibility that data on the minor uranium isotope concentrations in an enrichment cascade withdrawal and feed streams may provide a means either to corroborate or to contradict the material accountability results. A basic theoretical study has been conducted to determine whether complete isotopic measurements on enrichment cascade streams may be useful for safeguards purposes. The results of the calculations made to determine the behaviour of the minor uranium isotopes (²³⁴U and ²³⁶U) in separation cascades, and the results of three plant tests made to substantiate the validity of the calculations, are reviewed briefly. Based on the fact that the ²³⁴U and ²³⁶U concentrations relative to that of ²³⁵U in cascade withdrawal streams reflect the cascade flow-sheet, the authors conclude that the use of the minor isotope concentration measurements (MIST) in cascade withdrawal streams is a potentially valuable adjunct to material accounting for safeguarding a ²³⁵U enrichment cascade. A characteristic of MIST, which qualifies it particularly for safeguards application under the NPT, is the fact that its use is entirely non-intrusive with regard to process technology and proprietary information. The usefulness of MIST and how it may be applied are discussed briefly. (author)