TARGET ARRANGEMENT FOR SPALLATIONSNEUTRONENQUELLEN.

The invention refers to a target arrangement for SpaIlationsneutronenquellen, with kontinuierlieh the target materials at the point of impact of the proton beam vorbeigeftihrt wird.

With the jtingsten development of the acceleration technology ffir high ProtonenstrSme (within the mA range) it became grundsiitzIieh m6glich to use a Spallation (nuclear evaporation) of heavy elements by protons high-energy (about 1 GeV) to the building of neutron sources which are equivalent in its thermal neutron flux a Hoehflussreaktor or this still tibertreffen. See more gegentiber to a reactor grundsiitzliche advantages, like for example the renouncement of fissile material, devoted substantially reduced production of radioactive noble gases and a substantially smaller Geflihrdungspotential ftir the environment, there his critical Anordnnng existiert.

Such Spallations neutron sources could replace in the future Forsehungsreaktoren to a large extent and win also as preliminary stage ftir electrical Brtitanlagen a high meaning, if the problem of the Wiinneabfuhr can become satisfying from the target gel6st. The high W irmedichten yon for instance MW/1, which cause a heating rate of the material yon 104 k/s and more, resulting in a Spallationstarget, ready substantial Schwierigkeiten.

Leistungsfiihige Spallationsquellen were not built so far yet. As preliminary stages pulsed neutron sources which can be regarded use wassergektihlte station/Irish target arrangements with Leistungsdiehten yon unite kW/l in the time-borrowed means (J.M. Carpenter, Nuc. Inst. Met. 145 91-112).

After a project proposal yon 1966 (Bartholomew G.A. and Tunnicliffe P.R. < < The AECL Stndy for to intense neutron generator, Chalk River, AECL-2600) soil the proton beam vertikaI in a str0mendes target from fltissigem lead Wismnt eutectic to be shot in, which with high speed (about 5 m/s) into the target and Wiirmetau containing cycle is umgepumpt. A large quantity of fltissigen radioactive metal (some tons) measured in circulation to be held. This concept was held so far ffir the only miSgliehe password of the problem. A such plant has however the following disadvantages:

- The proton beam yon 1 GeV energy and milliamperes currentstrong unite must, in order to avoid a station/their bullethole windows (after short time the zerst6rt wtirde) into vertical Richtnng to be nmgelenkt. This is with difficulty realizable and at high expenditure verbunden.

- The Fltissigmetallkreislaufist dependent on the use of the Pb-Bi-eutectic. Thus the long-lived, fltichtige and poisonous mercury isotope 194-Hg becomes and the particularly unpleasant by neutron capture in bismuth with the Spallation, because C - active and fltichtige polonium produces. Both could with employment yon high-melting heavy metals, like W or Ta, avoided werden.

- To the production particularly high Neutronenfltisse is it under Umst inden wtinsehenswert to use the materials Th or U-238 fissile by fast Neutrohen. This kSnnen because of their high fusion point likewise groove in solid state uses werden.

- The Flfissigmetallkreislauf is technically very complex, with high costs verbnnden nnd because of the large gespeieherten W irmemenge in case of a Bruehs of the strongly loaded pipings gef ihdich.

- A Rtickhaltung of the reaction products is not in the Fltissigkeit gew ihrleistet.

Task of the invention is it to develop a Targetanordhung which hrleistet a high measure of Flexibilitiit in the choice of the target material gew and is used with that the target as Festk6rper, whereby the reaction products are to-tick-held large. The gegentiber Flfissigmetallkreislauf smaller technical expenditure and an arrangement, the one horizontal bullethole of the proton beam furthermore is aimed at erlaubt.

To the Li$sung of this task invention in accordance with isse target arrangement is the kind initially specified in wesentlichert dadnrch characterized that the target material at the extent rofierenden, infien gektihlten Rades arranged ist.

Preferably the Innenktihlung of the Rades takes place via Zuand Abftihrung of the Ktihlmittels, which is preferably formed dutch water, more tiber the wave of the Rades, in particular more tiber the wave part present above the Rades (under simultaneous Ktihlung of the Wellenlager). The wheel interior becomes by a umhtillenden coat against the surrounding vacuum within the range of the accelerator channel abgeschirmt.

This aussere coat works the proton beam and within the range of its generally cylindrical Flfiche as entrance window far consists from there in this range in particular of a metal with small mass number, like A1, Zr or Ti.

This window becomes of that fibre the wheel shaft zutretenden Ktihlmittel, which intersperses the target material planned at the wheel extent, directly gektihlt.

Windows and target material are in particular replaceable conceived. The generally ringfiSrmige actual target can compound from individual Ringsegmenten sein.

The whole wheel l iaft in the Volnmen, which stands with the volume of the proton tunnel in connection. Since the pressure will presumably be appropriate for the Drnck erfordeflichen in the proton tunnel in the range of the Rads around some orders of magnitude more tiber, some throttle points are to be planned, between those differentially pumped kann.

Ffir the structure of the target material and the Kfihlkan ile contained in it to leave see a multiplicity yon to M6gliehkeiten finding, which will have to be judged inter of a set of aspects, like mechanical and thermal load, exchangeability, s Ktihlmittelstr6mung and other more. The simplest case of a full ring is flowed around, that only outside by the Ktihlmittel, is realizable in principle, ffihrt abet because of the large Wttrmeleitungsstreeken of etwa3 cm with 6 cm a high target to temperatures IO around 800 °C in the target inside. These are wfinschenswert even with high-melting target materials nieht, because of the developing mechanical stresses. It will be to plan from there a divided arrangement, also from the point of view of the disassembly in a meaning a cell favourably ist.

Gemtiss of a preferential Ausftihrungsform of the invention the target material yon evolventenf6rmigen Ktihlmittelkan ilen pulled through, ftir the Ktihlmittelzufuhr opposite to the Rotationsriehtung of the Rades gekrtimmt are and into the gap between windows and target material moons. The Rfickffihrung of the Kfihlmittels knows more tiber opposite gekrtimmte, evolventenf6rmige Ktihlkan le in the target material to take place or abet likings the umhtillenden Mantelfliiche.

For this purpose the actual ringf6rmige target can with gekrtimmten, in particular evolventenf6rmigen slots provide or alas segments be compound, zwisehen those entspreehende Kantile ffeigelassen is. The segments kSnnen ffir a simple assembly on the wheel provided with a foot its. The arrangement of the target material with in particular evolventenf6rrnig gekrtimmten slots or Kan len has the advantage that within the dazwisehenliegenden target material always a gleieher W irmeweg ffir the derivative of the Wtirrne produced by the penetrating proton beam available ist.

As particularly zweekmtissig at present (the W rmeabfuhrbedingungen adapted) segment width yon an about 1 to 2 cm is regarded. The Kane arranged between them has about a width yon 1 to 2 RAM. This composition of the target from gekrtimmten, in particular involute NFS RMI towards segments or (between slots formed) < < Pseudo Segmenten> > it has in the fibrigen advantage that fibre the total thickness of the target material handing KOhlkanttle is planned kSnnen, without the proton beam in the process of the wheel movement on praktiseh target material-free Bereiehe trifft.

In order bending the segments upward by the centrifugal energy to verrneiden, k6nnten ffir high numbers of revolutions flat steel bar chenhaft Bleehe on Oberund lower surface of the segments connected with these werden.

Preferably the wheel is horizontal arranged, and its target material planned at the periphery moved see so perpendicular to a proton beam hitting in generally horizontal Riehtung. The Raddurehmesser is appropriate for insbes5 separates with approximately 2.5 M. with Rotationsgesehwindigkeiten in the area of approximately 1 cycles per second can one reach in such a way that the Whrme is rapidly herausgeffihrt dureh materials handling from their developing zone genfigend, so that only one heating takes place from gr6ssenordnungsm issig 100 K. With a proton energy yon about 1 GeV betr igt for example daftir would require-borrow approximately 2 m/s per MW of the energy converted in the target to Umfangsgesehwindigkeit. The target material, which in the fibrigen dureh a Ktihlmittel - like in particular with water - is gektihlt, attained w it-end the remaining circulation his output temperature zurfiek.

Sew-following the invention is described on the basis of Ausffihrungsbeispielen with reference to the angeffigten designs details, it shows sehematiseh:

Fig. la and lb the structure of target and Fig. 2a to 2C its arrangement in a Spallationsneutronenquelle.

In accordance with eat figure la the erfindungsgemiisse target arrangement essentially by a umhtilltes wheel 1 on a wheel shaft 2 one forms, fibre the Ktihlmittel in the way outlined in figure lb to the wheel-center disk and to the target ring zubeziehungsweise yon there abgeftihrt wird.

The iussere coat of the Rades forms the proton beam 4.<br to its generally zylindrisehen flat steel bars iehe em windows 3 ffir/> This window can be welded or angesehraubt, whereby the variant shown in the top of the figure la permits a relieved window change. The target material is distributed likings the wheel extent and in particular yon nutenf6rmigen Ktihlkan ilen interspersed, how it is suggested in the longing CCIT A-A yon to figure la, or by gekrtimmte segments in an educated manner, like it more in detail shown in figure lb wird.

Gemiiss figure lb target material of Kan, compound from segments 5 the ', len 6 interspersed, which are preferably formed between the segments. The tiber opposite Ktihlkan le zutretende KfihlmitteI gekrttmmten for the rotation direction of the Rades arrived, dureh centrifugal force effect untersttitzt, into which gap 7 between target and window 3, which are gektihlt in this way intensively. The Rtiekffihrung of the Kfihlmittels effected either Kan ile within the target, gekrtimmte through opposite, or however likings the wheel coat. In the lower part of the figure lb the Ktihlmittelverlanf is within the wheel-center disk angedeutet.

This can exhibit, as in figure la is suggested, (yon Kfihlmittelzufuhrkan ilen interspersed) a carrying structure or be to a large extent hollow, whereby the respective Ausffihrungsform itsforderungen yon the existing Stabilit is determined. Yon segments with different Krtimmungsriehtung it has the flat steel bars ichenhafte connection shown in figure lb the advantage that bending the segments upward is prevented to a large extent. Furthermore the Schiehtaufbau shown offers the M6gliehkeit, a heterogeneous target to plan, there the middle segments from the material of the Spallationstargets and the iusseren from a neutron-multiplying medium (to the BeispieI fuel element) manufactured its k6nnten. If fissile material should be used, k6nnte the center section from U-238 (or, because of the easier workability, better W rmeleitung and the absence yon Phasen0bergtingen:

from thorium) to be geferfigt, and which iusseren () segments k6nnten with one about 1-2 mm thick Sehieht from 20% enriched uranium are occupied, in which the zurtickstr6menden thermisehen neutrons is almost vSllig absorbed and used for splitting. Aueh in this case kiSnnten the usseren segments from fuel element manufactured its to use over the n-2n-Prozesse with energies above 2 MEV and for the fission neutrons a certain reflector effect too erzielen.

The arrangement of such a target with perpendicular standing wheel axle in a Spallationsneutronenquelle is outlined in the figures 2a to 2C, those the substantial structure of such a source (2a) with the allocation yon target material and proton beam and/or jet pipes in supervision (2b) as well as the arrangement of the turning target and its storage in the moderator tank (2e) zeigen.

How one sees, the proton beam enters dureh the Periphefie of the Rades. The neutrons set free in the target enter arranged moderator (for example D20) at Oberund lower surface of the target from and in one don, where they are thermalisiert. The jet pipes are then in one level each above and below the Targetrads angeordnet.

In detail figure 2a shows the turning target I with wasserfiihrender wave 2 as well as the drive stator 8 and drive rotor 9,10 and 11 is the matter and a firm Wellenlager.

Upper Drehdurchftihrungen 12 takes place to water-and - the expiration 13. With 14 the camp block is characteristic. The screen covers an upper mobile screen 15, a lower mobile Abscbirmung 16 as well as a screen 17 in Targeth6he. A vacuum-tight Schleusentor 18 knows fibre more nether not represented rails shifted werden.

In the moderator tank 19 are the jet pipes 20 as well as lo a Rtissel 21 of the very low-temperature irradiation plant angeordnet.

A trick potting 22 ' erm6glicht a variation of the irradiation position during very low-temperature irradiation. In the upper range are the upper screen 23 of the moderator tank 19, a removable plug 24 as well as an evacuating line 25 for production yon Hoehvakuum. A Hoehvakuumleitung 25 ' is likewise at the proton tunnel 26 vorgesehen.

27 is a jet pipe for bringing in a cold Neutronenquelle.

To water-and - expiration 13 is transferred in the designs by 90° dargestellt.

Gegeniiber a Fli ssigmetalltarget after the state of the art shows that invention in accordance with the isse, inside gekiihlte turning target following advantages:

- Absolute Flexibility in the choice of the Targetmaterials.

This permits either:

the use of the nuclear fission to the Neutronenvervielfaehung (U or Th as target material) or:

avoidance yon transuranic element production dutch employment 0 yon Pb or Bi, which auszeiehnen themselves by low absorption cross section f IR thermal neutrons, whereby however the production of the flat steel bars ichtigen Sehwermetalle Hg and Po is taken in purchase, or:

the employment v0n Ta or W as target materials, with which neither are formed for transuranic element or Hg and Po, however the somewhat smaller neutron flux expect leave/> - Avoidance of a Flfissigmetallkreislaufs and the associated technical expenditure and Gef hrdungspotentials.

- Avoidance of the necessity for a vertical proton bullethole, whose praktisehe feasibility fiir StrSme unite yon mA in question are posed, at least however a raise-borrowed teehnisehen and cost darstellt.

For instance j of the wheel radius takes the target material arranged at the extent of the Rades. It is, more nether erl utert, in form yon gekrfimmten target segments or dummy segments was preferably planned like further above, what has more gegentiber a target ring from full material the following advantages:

- Reduction of the thermal tensions, - optimization of the Kiahlmittelstr0mung, - Vergr6sserung of the Kiihlflfiche, - minimization of the way fiir W rmeleitung, - leiehtere assembly and in particular disassembly in the activated Zustand.

The thickness of the segments is to be laid out for the application entspreehend. In particular the target points to one < < Schichtanfbau > from Zuund Abfiihrungssegmenten anf, as it is suggested in the lower part yon to figure Ib. The Kr mmung the segments in the AbstrSmbereich is opposite thereby to in the Zustr6mbereieh. The drive takes place for example dureh a Scheibenlfiufer Motor.

Except the variants shown of the turning target with Innenkiihlung - in particular through spalff Srmige channel - amplifiers are ndlich different Ausf it-form with zweckm ssig distributed drillings (f IR the K ihlmitteltransport) in the target ring realizable or also an arrangement yon target material in form yon balls (if necessary with two differentiate-borrowed Durehmessern), which become of the Ktihlmittel umstr6mt. The target ring can be formed aueh by (station - res) Fliissigmetall, be gekiihlt dureh the kiihlmitteldurchstr6mte of pipes kann.

That managing besehriebene enfindungsgem isse turning target f r Spallationsquellen offers gegent more ber firm targets, which already are in use or in the building, extraordinary advantages. In particular be void the very complex FHissigmetallktihlung.<br held with stationery the target to the Bew iltigung the raise-borrowed Wiirmediehte ffir necessarily/> ; 2 sheets designs v-It, ltJ i, 2 Blfitter No. 1 " 3 B i/I SECTION A-A/J FIG. la I I i i FIG.lb