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Per-10 Basic Information Relating to Uranium

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Per-10 Basic Information Relating to Uranium PER-10 1 BASIC INFORMATION RELATING TO URANIUM-ENRICHMENT CALCULATIONS AND FUEL REQUIREMENTS FOR NUCLEAR POWER REACTORS by K.T. Brown m 3 ATOMIC ENERGY BOARD Pelindaba PRETORIA Republic of South Africa February 1977 :::: : =:::""""""::::::;::: i:::""""""" :::::::::i:::::::::::::::H:::""»"""::::::::::::::::: BASIC INFORMATION RELATING TO URANIUM-ENRICHMENT CALCULATIONS AND FUEL REQUIREMENTS FOR NUCLEAR POWER REACTORS hy K.T. Brown POSTAL ADDRESS: Atomic Energy Board Private Bag X256 PRETORIA 0001 PELINDABA Fi-ln liai v 1977 ISBN U 86Ü6U 654 9 Pago Page SAMEVATTING 2 ABSTRACT 2 3. REACTOR FUEL REQUIREMENTS 5 1. INTRODUCTION 3 3.1 Reactor Types 5 2. URANIUM ENRICHMENT 3 3.1.1 Pressurised-water roactor 5 2.1 Definitions 3 3.1.2 Boiling-water reactor 5 2.1.1 Natural uranium 3 3.1.3 CANDU-PHW 6 2.1.2 Fissile 3 3.1.4 High-temperature gas-cooled reactor 6 2.1.3 Fertile 3 2.1.5 Liquid-metal-cooled fast breeder reactor ... .6 2.1.4 Enrichment 3 3.2 Nuclear Fuel Cycles 6 2.1.5 Product 3 3.3 Typical Fuel Requirements 6 2.1.6 Feed 3 3.3.1 Pressurised-wator reactor 7 2.1.7 Tails, or waste 3 3.3.2 Boiling-water reactor 8 2.1.8 Cascade 3 3.3.3 CANDU-PHW 9 2.1.9 Separative work 4 3.3.4 High-temperature gas-cooled reactor 9 2.1.10 Separative-work unit 4 3.3.5 Liquid-metal-cooled fast breeder reactor ... 10 2.2 Enrichment Parameters 4 3.3.6 Comparative data 10 2.3 Optimum Tails Assay 5 4. REFERENCES 10 2.4 Non-Natural Feed 5 5. APPENDIX 11 LIST OF TABLES Page Page TABLE 1 Natural feed (F) required to produce unit mass of product as a function of product TABLE 11 Model BWR : net uranium and enrichment and tails assay 18 enrichment requirements 27 TABLE 2 Separative work required lu fjiitjduce unit TABLE 12 Model CANDU-PHW : net uranium mass of product as a function ö product enrichment and tails Ossisy for requirements 28 natural-uranium feed 19 TABLE 13 Model HTGR : net uranium and enrichment requirements 28 TABLE 3 Optimum tails assay for natural-uranium feed 20 TABLE 14 Power-reactor characteristics for representative 1 000 MW (electrical) TABLE 4 1,0% feed (F) required to produce unit units 29 mass of product as a function of product enrichment and tails assay 21 LIST OF FIGURES FIGURE 1 Separative work and natural-uranium TABLE 5 Separative work required to produce unit feed required to produce unit mass of mass of product as a function of product product at various enrichments 13 enrichment and tails assay for feed at 1,0% 235U 22 FIGURE 2 Optimum tails assay as a function of the ratio of natural-uranium-feed to TABLE 6 Optimum tails assay for feed of 1,0% separative-work costs 14 235U 23 FIGURES Separative work and 1,0% assay feed TABLE 7 0,4 % feed (F) required to produce unit required to produce unit mass of product mass of product as a function of product at various enrichments 15 enrichment and tails assay 24 FIGURE 4 Separative work and 0,4% assay feed TABLE 8 Separative work required to produce unit required to produce unit mass of product of mass of product as a function of at various enrichments 16 product enrichment and tails assay for feed at 0,4 % 235U 25 FIGURE 5 Optimum tails assay as a function of the ratio of uranium-feed to separative-work TABLE 9 Optimum tails assay for feed of 0,4 % costs for feeds of 1,0%, 0,711% and 235U 26 0,4 % mass assay 17 TABLE 10 Model PWR : net uranium and FIGURE 6 Nuclear fuel flows for the most common enrichment requirements 27 reactor types 17 SAMEVATTING ABSTRACT Kwantitatiewe inligting word verstrek om nie-spesialiste op Quantitative information is provided to enable die kerngebied in staat te stel om toevoer- en non-specialists in the nuclear field to calculate feed and skeidingswerkvereistps wat by die verryking van uraan separative-work requirements involved in the enrichment of betrokke is, te bepaal. Verteenwoordigende uraan- en uranium. Representative uranium and separative-work skeidingswerkverbruikstempo's vir verskeie algemene consumption rates for various common nuclear power kernkragreaktore, word ook aangedui. reactors are also presented. PER-10-3 1. INTRODUCTION fissile isotope in nature is 235(j( although others (such as 239pu and 233ij) can be manufactured artificially from This report is intended to provide fertile material. (i) quantitative information concerning the enrichment of uranium; and 2.1.3 Fertile (ii), representative fuel requirements for three current Fertile material can be transformed into fissile material by ^ types of commercial nuclear power reactors, as well the absorption of neutrons and (in most cases) subsequent i as for two advanced types of potential interest. transformation by radioactive decay. The most important 238u Thfij report is aimed at persons and organisations not fertile isotopes in nature are (which yields 239pu) directly involved in nuclear energy programmes and and 232-rh (which yields 233ij). assumes that the reader has little background in such fields. 2.1.4 Enrichment t As ^ar as uranium enrichment is concerned, the information In the context of relative isotopic proportions, enrichment is limited to the relationships amongst quantities and assays means to increase the relative proportion — or assay — of a of feed, waste and product uranium in an ideal enrichment particular isotope above that of the natural or other process, together with associated quantities of separative available feed material. Enrichment of uranium in the 235(j work. Economic factors are brought into account only isotope can be accomplished by various processes, such as superficially, in order to calculate the optimum waste (or gaseous diffusion, centrifugation, aerodynamics and laser tails') assays under particular price conditions. Neither separation. The opposite of 'enrichment' is 'depletion'. In significant technical descriptions of enrichment processes the absence of a reference point, 'enriched' uranium has a nor other economic data concerning the different processes mass assay higher than 0,711 %. are included. 2.1.5 Product The section concerning reactor fuel requirements mentions The product of a uranium enrichment plant is enriched in relevant aspects of nuclear fuel cycles, but the presentation the isotope 235u. The product assay is usually relatively is (nade as simple as possible. The fuel quantities facilitate low (up to about 4 % by mass for most commercial approximate calculations of uranium and enrichment reactors), but can also be well in excess of 90 % from demands associated with nuclear power programmes, but suitable plants. no such application is attempted in the report. 2.1.6 Feed The feed to a uranium enrichment plant is usually natural 2. URANIUM ENRICHMENT uranium, but depleted uranium or uranium with more than 0,711 % by mass of 235u may also be used as feed. The 2.1 Definitions uranium contained in spent fuel elements from natural-uranium reactors is depleted to below 0,711% 2.1.1 Natural uranium 235u, while that from enriched-uranium reactors usually Uranium, as it occurs in nature, consists of three isotopes. (but not necessarily) has higher assays than the natural These isotopes, together with other uranium isotopes that assay. can be manufactured by artificial means, have identical chemical properties. The three isotopes in natural uranium 2.1.7 Tails or waste have the following proportions by mass: Because the product of an enrichment plant is enriched in 235u, the tails stream must contain a lower 235y assay 234u 0,000 06 (0,006 %) than the feed. There are limits to the degree to which the 235u 0,007 11 (0,711 %) tails assay can be reduced, as will be seen below. The term 238u 0,992 83 (99,283 %) 'tails' (from an enrichment plant) is not to be confused with 'tailings' (from an extraction plant). The proportions by numbers of atoms are slightly different: 2.1.8 Cascade 234(j 0,000 06 (0,006 %) An enrichment plant generally consists of many stages, each 235(j 0,007 20 (0,720 %) of which accomplishes a small amount of separation of the 238u 0,992 74 (99,274 %) isotopes. The stages arc built up into a cascade, with interconnecting piping to channel the enriched and The 234(j appears in such small quantities that its presence depleted streams from each stage to other appropriate can be ignored for practical purposes. upstream and downstream stages. An 'ideal' cascade is one in which there are no departures (as a result of mixing 2.1.2 Fissile losses, for example) from ideal theory. Although no real A fissile isotope is one which can be fissioned by the plant meets the ideal, it is common (American) practice to addition of a zero-energy neutron, and fissile isotopes are base all calculations on ideal theory except in the case of essential to self-sustaining fission chain reactions. The only very high product enrichment (> 94 %). PER-10-4 2.1.9 Separative work The separative work done by a stage or by a cascade is the increase in value of the effluent materials (enriched and F = 1 (0,03 - 0,00251/(0,00711 - 0,0025) depleted) with respect to the value of the feed material. = 5,965 kg. The term 'value' used here is a mathematical function which reflects the value of a unit mass of uranium in termValues s of F for various product and tails assays with of its assay, and must not be confused with price or cost.natural-uraniu m feed are given in Table 1 and are also The derivation and significance of 'value' and 'separative shown in Figure 1.
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