NL’CLEAR ENERGY FOR DESALINATION*

The rapidI) Increasing dcmJnJ$ for frcah wafer ha\c IcJ to intcnslticd cffor~s fo dc\elop the dcsali- nation of ahnc \rawr \\htch umquel) mcrc~scs the supply. Dcsalinarlon on II lrrrgr scale will require an cnormou~ amount elf cnrrg?. It IC in thts rcgxci that nuclc-ar cncrgj oikrs considcrablc potenttal for the future of dcwluwrwx Thrrc arc tsonomic nd~anta~~_ in combtntng dcrillhnation with CICS- tncai pouer prrxiuctwn in n du&purpose u;iwr anJ pxxor\cr piant. The ratio of \rarcr-to-powx ou!put for optzmzrcd Juzl-purprt,e nuclear plants is usualI> m rhc range of 45-13 Ittres*hWh. JcpatJmg on the I>WZ of reactor. De\clopmcnts in nuclear rextom. culminatmg in the forcscrable future m xcry large fast br~xxlcrs. arc‘ c~pcxxrd to reduce >tcam coa to S-12 US cents per million Lc.11. Thr corrcrspondlng coot of dc~lt~ci \\ater, aHo\\mg for re-optimization of the da&nation plant. woulJ be &out 3 CS cenf4 per m*.

There is a growing conccrrl about the adequacy of fresh water suppiics to meet the demands which are rapidly expanding as a result of increasing population, rising king standards, progrrssi\e industrialization and intensive irrigation. The fresh \\ater supp1.v in iakes. rkers clnd underground represents on@ a very smail amount of the World water supply. Furthermore. there is a very uneven distribution of the limited high quality water suppiies in relation to demand. Thus. \thile many areas have at present no particular problem of water supply, in some populous areas water

must be transported for considerable distances and in others serious shortages of xtcster are bc_cinnin$ to appear.

Less than l/I2 of the earth’s Iand surface is cultivated today because the remainder is mostly too cold. dry, x\et or steep. If the arid and semi-arid regions, which consti- tute about two-thirds of the total land surface of the world, arc to be developed, ad- ditional ways of supplying water must be found.

To mLwt this situation, considerable etTorts are being made to develop natural supplies more intensi\eIy. to reduce specific consumption by industry and agriculture and to develop the desalination of saiine water which uniquely increases the supply of fresh water.

The desalination of saline water offers considerable promise in the future as an alternative supply of \\ater. To be practicable on 3 large scale its cost must be reduced.

* Paper presented at the Second European Symposium on Fresh Water from the sc3, May 9-12, 1967, Athens, Greea. European Federation of Chemial Engineering.

89 Desalination. 2 (1967) 89-98

90 D. B. RRKE AND D. S. BRICGS

A reduction in cost can be envisaged mainly by reducing the cost of energy to the desalination process. This will result in a reduction not only in the energy cost com- ponent of the water cost but also. through reoptimization, in the capital cost compon- ent. It is with respect to reduced encr_q cost that nuciear energy offers consider- able potent%: f;or the future of desalination. It is also expected that dcsalina- tion process improvements and modification \cill wrmit a reduction in specific energy consumption and a reduction in capita! imestment.

ESERGY REQWREWISTS

All the processes for desalting uatcr use energy. whether thermal, electrical or mecha- nical. Thermal ener_q is utilized in the multi-stage flash distillation process. which is one of the most praeticahlr for large-scale application in the near future. Only this process is considered in this paper.

A modern plant using this process requires ;f thcrmsl enertz input of at ieast 250,000 Btu per m3 of water desalted. Thus the desalination of saline abater on a large scale will require an enormous amount of energy.

Also. assuming energ_v at 30 cents per million Btu, the energy cost component of the water cost would be 71 cents per m”. Hence, a substantial reduction in the cost of desalted water could be realized if an inexpensive source of ener_w were av$lrtble.

The maximum evaporator brine temperature in a multi-flash distillation plant is at present limited by economic means of scale control to about I20 C (about 25O’F). On the other hand, the generating costs of electric pot&et plants are louest when the steam is produced at higher temperatures. Because of these two facts. there are economic advantages in combining the production of water with the production of po\ver.

Such a dual-purpose plant rather than a power-only one gives two advantages to nuclear as compared with fossil-fuclled plants,

(a) the unit cost of reactors fails more rapidly with increasing size than does that of fossil-fuelled plants.

(b) for economic production of desalted water such installations should operate at very high load factor which favours a power plant with low fuel costs.

For lowest desalted water cos& dual-purpose operation imposes 3 limit on the ratio of the water-to-power output. This is because the steam is produced initially at higher temperature and pressure than can be utilized for heating in the desalting plant and the “excess” energy is used for power production. With standard back-

pressure tubines there is a range in this ratio of water to power over which the incrcm- ental water cost is nearly constant, the upper value of this range depending on the reactor type. For high-temperature reactors producing superheated steam, this value is around 0.3 md (US] MWe (17 1itresjkWh). For reactors producing saturated steam it is about 0.8 (126).

DesaIinarrion, 2 (1967) 89-98

XU~LEAR ICSERGY TOR DESAL~NA rioN 91

An interesting esample ofa study for a dual-purpose nuclear plant involving agricul- tural uses for the water has been made for the Borg-El-Arab Project. United Arab

Republic (I). Consideration is beinS given to constructing a dual-purpose nuclear

reactor producing 150 rMtVe (net) and _ _ 3OooO mj.‘d of desalted water. The study

includes the establishment of a 1,000 ha experimental agriculture project (2).

Tfie team (I) involved in the study concluded from a preliminary economic analysis

that use of high cost desalted water (see Table I) to supplement the limited conven- tional sources is economically feasible at current prices for the special circumstances of olive production. Additional information, as would be obtained if the pilot project

were constructed. is ncccssary in order to dctcrminc possible crops and cropping

patterns to permit water production throughout the year. Also from the pilot project

the economic quantity of desalted hater, taking into account yield, salt tolerance

and application methods. would be detcrmincd.

Steam cost (U.S. Cents blt3tu) encqp

Fuel costs (U.S. mills. kWh)

Electric poucr cost (U.S. mills k\Vhl

Rnntral Proth-titm Cosf of Desafd H’arzr (U.S. mtfars .I 10’) Diwc-r rusts

17.0 19.5 18.8 21.3

I.!xl 2.30 1.90 2.30

5.31 5.71 6.47 6.87

Steam energy

Electric power

Chemiais

Operatton and maintenance laOour

Stores and msintenance materiztl

Idirect cosfs

232.0 166.0 257.0 190.0 61.6 67.4 76.5 81.2

49.5 49.5 49.5 49.5

123.0 123.0 123.0 123.0

30.0 30.0 30.0 30.0

Fixed charges 420.0 4’0.0 600.0 600.0 Tube reptacemrnt 90.0 90.0 90.0 90.0

Total annual cost 1007.1 1045.9 t 126.0 1163.7

Water cost U.S. cents:m3 16.1 16.9 19.5 20.3

DEVELOPMESTS l?ri NJCLEAR REACTORS

By the end of 1966, nuclear power plants in operation had a total capacity of nearly 9,000 MWe. These plants have performed well and have provided a firm basis for

Desalination. 2 (1967) 89-98

92 D. R. BRiCE ASD n. 5. BRIGGS

developmer?ts and the costing of further plants of similar types. The de\elopmentj in existing systems. particufarly incrcnscs in size and more compact designs. have ted to very great rtzductions in thr c&al cost per kW instaIkd. The capital costs for some recent contracts hn\c been equivalent to about StO kW thermal for the nu~krtt

steam gwcrzting system which could sup& n desalting piant and this figure may go down to S15,‘k:W therma? \\ith further improrcments. Fig. I sho\\s the trends in

the capital costs of nuclear plant3 of various tlxzs \+ith increasing size and aswcirtted improvements in design. The capital costs hwc not been normatizcd and xfer to the conditions and assumptions used in the countries of origin; therefore. no comparison betHew reactor types should be m;%de.

The reduction in unit capital cost has been a big factor in bringing the ovetd

generating costs for nuclear powr plants below those for contrntionnl plants, at feast in large sizes. This achievement hrts resulted in a dramatic inzrea% in the ordcr- in_r of nuclear stations such that by 1970 the total inrtalfed nuclear capacity %siiI be about 25,000 MS/e und by 1975 the figure ma> welt approach 1oO.fKK) MN’c

As ;?. consequence there uiil be a large increase in the throughput of nuclesr fuel which is expected to give Ggnificant reductions in the fuel costs, E&ides the cost of

uranium and its enrichment. the principal cost components of nuclertr fuel qcle for enrichtd rertcfors are fabrication and reprocessing. The fuel fabrication costsapplicabic in 1980 are ryxcted fo be 30 to 10 Ti b&o\\ those for the carI? 1970’s. With regard to reprocasing. at present nn industrial rcproccssing ptant t\ith a nominat throughput

xx

(Note: These costs refer to the conditians and auumptions wed in the wuntries of origin and do not, therefore, stTord a bzsts for compsrison betwxn reactor t)ws).

of or& ton of uranium per day leads to reprocessing charges of S5O:kg, When the size is increased to 5 tons of uranium per day throughput. the reprocessing charge can drop to one-half, and for 3 pktnt of 10 tons of urtinium per day throughput it may be Iess than one-third.

Dedinarim, 2 (1967) 89-99

hiCLEAR tSERGY FOR CESALINATION 93

It is estimated that the above-mentioned improvements in the capital cost per kW therm& and in the fuel fabrication and reprocessing costs could lead to steam costs of about 70 US cents per million kcal (about 18 cents per miIlion Btu) by the

mid 1970’s. Although the existing water and gas-cooled reactors can compctc successfully with

conventional steam boilers and will continue to improle their economic\, they still have certain limitations, including rather poor fuel utilization. If the projected nuclear capacity were to consist entirely of light-water and enriched gas-cooled reactors. then the currently assured low-cost uranium reserves of 500,000 to ~,~ tons would be committed by the late 1980’s when the installed nuclear capacity is expected to be owr SO0 million kH’. The use of such reactors for any large-scale dcsaltmg ap- plications would increase the pressure on low-cost uranium resen’es. It is obvious that the= is rcrtl incentive and need for developing advanced types of reactors of- fering better fuel utilization and even lower costs of steam for production of ciectricity and water.

In this connection. t\&o general approaches art: being followed: development of advanced converter reactors and breeder reactors.

The advanced converters include heavy-water-moderatrd, high-temperature gas-

cooled and liquid-fuel systemi. These systems all have good fuel utilization charact- eristics and either use or could use thorium as a fertile material. Estimates show that advanced conwxters of the high-temerature ps-cooled and heavy-water organic- cooled types, developed in the late 1970’s could, in units of 3000 to 4000 MIV thermal, achieve steam costs of 48-60 cents pc’r million kcal (:j).

The successful development of breeder reactors would free mankind for a very long time from concern about fuel resources for the production of power and process steam. The thermal breeder reactors could evolve from advanced thorium converters, mentioned above. The fast breeders could be based upon the fast reactor prototypes currently under construction. These include the 1000 MH’ thermal BN-350 in the Soviet Union to \+hich it is planned to couplea 120.000m3/d desalting plant and the 6430 MW thermal Dounreay prototype in the United Kingdom. The projections made in the United Kingdom, the Soviet Union, and the USA indicate that commer- cial breeder rectors could be in operation by the late !970’~ or early 19SWs. A 4,000 MW thermal breeder reactor in operation by the early 19803 costing S25/kW the- rmal, may yield steam costs of 24-40 cents per million kcal (6-10 cents per million Btu).. Further developments may reduce the steam costs to S-12 cents per million km1 for very large bxeders in the 1990’s (4).

Summmarizing the situation regarding nuclear plants, it is apparent that current types of reactors in large sizes are already capable of producing steam on a com- petitive basis with fossil fuels. It is aoticipated that future reactor systems will yield steam at much lower costs. How will this availability of very inexpensive heat

influence the cost of desalted water? It is obvious that even if steam could be produced at a negligible cost. the

production of electricity or water would still require considerable expense because

Desufination. 2 (1967) 89-98

93 D. B. RRICE AND D. S. BRKGS

of the high capital costs invoked in electricity generating equ~pmeut, desaiter. and auxiliaries. In a dual-purpose nuclear desalting plant, designed to produce

4t3&00(?-600,G? mJ[d of desalted water and based on current or near-future technolol5y, the steam cost component isestimated to be about one-third of the total uatet cost, Drastic reductions in steam costs would require redesigning and reoptimizing of desalting plants on the basis of different parameters leading towards fewer stages and lower performance ratios. The combined effect of this reoptimization would result In foyer unit capirrtf costs for desalination plants. Thus the aseifability of very cheap nucicar hear could not only cut down the cost of the ener_q component but make dcsahers cheaper to build and thereby lead to tven tawr water costs.

CO!3 OF WATER

Ten yzars ago. the cost of desalted water was at kaslt 100 US cents per m3. For some ofthc larger plants (4.m6.ooO m3:ii). built within the Iast feu years, the cost is about 25 cents pet m3. The COG of desalted Hater from very Iarge desalination plants with opacities of the order of 4QWMI m”id, operated in conjunction with po~cr genera- tion, has been estimated to be about 6 cents per m3. Some past, present and clear- t‘uture costs of desafting sea Uater are @iten in Table If.

Prim? iype Period

Shipboard and small commcrctaf 200 19-G-50 100-l 30

Comrncrciat 2,ooa-s.ooo 19-w So_8c,

Advanced commctia~ 4-m M6a-46 25-55

A&awed tixhnology +a00 1967-70 21-24

Single and dual-purpose rnrcfmcdiate sire 2~*aoo-cr;o,ooo 1968-70 16-B

Sin@ and dual-purpox farg capacity zlwKGao,aoo 1972-7s T-13

Hearings before the Subcommittee on Irrigation and Re&mrltion of the Committee on If%- terior and lnwbxr Affairs, House of Reprcxntatkes, Eighty-Ninth Congress, Second Session USA, Serial No. 89-31. dated 18 February 1966.

The current research and development programmes for auctear power reactors will continue to produce improved reactors with progressively fewer s&xx-an costs, as indicated in the preceding section. However improvements in heat SOURXS alone will

~~s~inu;i#~, 2 (1%7) 89438

SUCf.E_.R ESERGY FC3R DESALINATION 95

not be suficicnt to yield water costs below about 3 US cents pet m3 (4). If the cost of desalted water is to bc brought below this figure, considerable efforts must also by made touards improving de4ting technology.

The circumstnnlrs of uater requirements for municipal and industrial purposes are

such that no strict limit can be placed on the price that can be afforded. For mun-

i&xl purposes;, the ncccssity of fresh wttcr for man’s healthy existcncc is the domin- ant factor while, for industrial products. of Ggniticant increase in the cost of water

genentllv leads to only a small increaw in the total product cost. For these reasons, _ >c\eral large nuclc;lr desalination schcmcs itrc already under consideration for areas where thcrc is shortage of natural sup&s.

An cirimate of the price that successful conventional agriculture in arid regions could afford to pay for irrigation wter is shown in Table III \\here a profit of US SIOO,‘ha to the farmer is assumed. The tnblc sho\\s that, for those conditions and assumption%;, the akcrrtge price for water would ha\c to hc about 0.5 US cents per m3.

P’hile it il; not possible to gi\c oicr-all figures that are valid for all crops under ail climatic and economic conditions, the rough order of magnitude is that a cost of 3 US cents per m3 is about the highest price that an be paid for irrigation water.

TABLE 111

CQSl OF IRRIGAXIOS WATER

Crop Yield per Total P&it .-fntuunt .-lmounr Pus&de hccrare inrome per hn awilabk irri.qaf. price

per ha in L’.S.S for wuter in per m3 in ti.S.S waler’ nr-‘!hdt in U.S. cents

Whertr

Cotton

115

280b

3.5 tons

%i”,:

1200 kg of seeds

Maize

Alfalfa hay

I60

165

5 tons

10 tons (nit dry)

24.5 110 20 UJQo 0.40

450 170 70 12,Ow 0.58

300 l-20 40 7,500 0.53

300 135 3s 10,000 0.35

” lnctuding adequate fertilization expenses. * inciuding picking costs. c Assuming U.S. S lOO;ha profit. d hscd on present irrigation practice for application of the amount cf water specified.

Desalination, 2 ( 1967) 89-98

96 D. B. BRICE AND D. S. BRIGGS

Water costing 3 US cents per m3 could be used only for speciality fruits and vegeta- bles within easy access of large urban centrts. Certainly for large irrigation cntcr- priscs, it is essential that irrigation water cost less than I US cent per n?. The above- mentioned figures should be considered as the price that could be paid by farmers for water delivered at their headgates. Taking into account the operational cost of irrigation systems and some unavoidable losses, under most circumstances about OS to 1.5 US cents per m3 could be considered as the range of price that agriculture could afford to pay for irrigation w;itcr.

In practice it seems therefore that, except in very specific cases. it uiII not be possible to consider the economic use of desalted water for irrigation as long as its production costs without subsidy is more than about 1.5 US cents per mJ. As the application of water for irrigation is presently practired, it is only when this cost can be reduced to the order of 0.5 US cents per m3 that the use of desalted water for irrigation will develop on a very large state. However, new seed strains, the use of pesticides to control insects and plant diseases, the application of fertihzers to ensure adequate supply of plant nutrient elements and other advances in agriculture can appreciably reduce the amount of water required per unit of crop produced.

USE OF WATER X!SD POWER

Since the ratio cf water-to-power output for a dual-purpose nuclear desalination plant is limited at present by technical considerations to about 45-125 litres,‘kWh, it is of interest to consider actual ratios of water-to-power use per capita.

Over-all ratios vary enomtously, reaching several thousands of litres/kWh for some developing countries. If, however, water for agriculture is excluded. on the grounds that the cost of desalted water will remain too high for this use for some time, the range is much less. Although, in many deveIoping countries. the resulting ratio still ex- ceeds 125 litre!kWh, in more developed countries it is generally 1ess-e.g. the average for Europe is about 85 litrcs/kWh.

It should be borne in mind also that power use is increasing more rapidly than water use-e.g_ by over 3 y,< per annum in France (5,s). If this trend continues, as is likely for a considerable time, ratiosof water-to-power use will fall by a factor of two in about 20 years and by a factor of five in about 50 years. Thus, while the water-to- power ratio of dual-purpose plants may be restrictive at present in some applications, it is unlikely to prove a severe limitation in general.

ROLE OF THE IAEA

The question of availability of reasonabIe cost water for social, industrial and agri- cultural deveiopment in different parts of the world deserves foremost consideration. The development of -water resources is already rceiving top priority, and wherever indigenous supplies are inadequate or expensive, desalination may offer an economic solution for meeting needs. The development of nuclear desalting technology will

Desalination, 2 (1%7) 89-98

XUCLEAR ESFRGY FOR DESALINATION 97

requircagreot deal of co-operation among nations, in which the international orgoniza- tions could play a useful role.

Although nuclear desalting technology is at a stage that may be comparable with that of nuclear power a decade or so ago, the promise that if offers has aroused great interest in developing countries and it is most desirable that there should be means for a continuing exchange of information on the latest developments and a source of authoritative advice to Governments intcrestcd in exploiting this technolo_q.

The Agency is providing the former chiefly by meam of panels in which experts from interested countries-developing and advanced-meet once or twice a year to review progress.

Since there are generally economic advantages in combining the production of electric power and water in the same dual-purpose plant, the Agency has been giving special attention to this matter and convened a panel on the subject in November 1966. The Panel studied especialty the reactors that are suitabfe for single-or dual- purpose desalting applications, and the means of varying the ratio of production of water to production of power SO as to satisfy different local conditions and needs.

Advice and assistance to Member Stat+ is provided by missions such as those sent during the year to Chile and Peru in which experts from the United Nations Se- cretariat took part.

TO enable the Agency’s Secretariat to provide the authoritative advice needed by Member States it must itself ktzp in close touch with developments. It has been able to do so by taking some part in the Israeli and United Arab Republic studies, and the joint Agency/‘Mesico,‘United States study described below, and by participating

in a new study which is being carried out jointly by Greece and the United States on various possibilities for supplying wafer and power to the Athens 2rca (including a dual-purpose nuclear plant).

A project of particular interest to the Agency is the joint Agency/Mexico/United States study on the technical and economic practicability of constructing a dual- purpose plant to supply wafer and ekctricity to the border states in both countries near the head of the GuIf of California. The study is detaiied and far-reaching and includes surveys of hydrological and soil conditions, seismological and geological surveys of possible plant sites, arrangements for the best use of reactors and water plants, problems of transporting and distributing the wafer produced, and of using the power produced. It is expected to be completed in about one year and will provide the Secretariat with valuable experience for helping with similar detailed studies in other parts of the world.

coNcLusIoE;s

1. Dual-purpose nuclear desalination plants show considerable promise as a means of augmenting natural supplies of fresh water.

2. With present technology, such plants merit close consideration where there is a shortage of water for municipal and industrial purposes and where relatively large-sized plants are suitable.

lkahation, 2 (1Y67) 89-98

1.

2

3.

4

5.

6.