129:
667:, along with the use of burnable neutron poisons within the fuel pellets, is used to assist regulation of the core's long term reactivity, while the control rods are used for rapid reactor power changes (e.g. shutdown and start up). Operators of BWRs use the coolant flow through the core to control reactivity by varying the speed of the reactor recirculation pumps (an increase in coolant flow through the core improves the removal of steam bubbles, thus increasing the density of the coolant/
234:
31:
202:
to compensate for them, an automatic control system adjusts the control rods small amounts in or out, as-needed in some reactors. Each control rod influences some part of the reactor more than others; calculated adjustments to fuel distribution can be made to maintain similar reaction rates and temperatures in different parts of the core.
221:. Control rods are usually used in control rod assemblies (typically 20 rods for a commercial PWR assembly) and inserted into guide tubes within the fuel elements. Control rods often stand vertically within the core. In PWRs they are inserted from above, with the control rod drive mechanisms mounted on the reactor
588:
was undergoing evaluation for pressurized water control rods. Dysprosium titanate is a promising replacement for Ag-In-Cd alloys because it has a much higher melting point, does not tend to react with cladding materials, is easy to produce, does not produce radioactive waste, does not swell and does
201:
can be measured, and is roughly proportional to reaction rate and power level. To increase power output, some control rods are pulled out a small distance for a while. To decrease power output, some control rods are pushed in a small distance for a while. Several other factors affect the reactivity;
601:
reactors. A disadvantage is less titanium and oxide absorption, that other neutron absorbing elements do not react with the already high-melting point cladding materials and that just using the unseparated content with dysprosium inside of minerals like
Keiviit Yb inside chromium, SiC or c11B15N
687:, rather than direct mechanical linkage. This means that in the event of power failure, or if manually invoked due to failure of the lifting machinery, the control rods fall automatically, under gravity, all the way into the pile to stop the reaction. A notable exception to this
181:
increases exponentially over time. When reactivity is below 1, the rate of the reaction decreases exponentially over time. When all control rods are fully inserted, they keep reactivity barely above 0, which quickly slows a running reactor to a stop and keeps it stopped (in
514:
are frequently used. The wide absorption spectrum of boron also makes it suitable as a neutron shield. The mechanical properties of boron in its elementary form are unsuitable, and therefore alloys or compounds have to be used instead. Common choices are high-boron
376:
also limits lifespan of a control rod. They may be reduced by using an element such as hafnium, a "non-burnable poison" which captures multiple neutrons before losing effectiveness, or by not using neutron absorbers for trimming. For example, in
336:, and the required mechanical and lifespan properties. The rods may have the form of tubes filled with neutron-absorbing pellets or powder. The tubes can be made of stainless steel or other "neutron window" materials such as zirconium, chromium,
573:
for wear resistance, hardness, and machineability. Such alloys are designated as
Hafaloy, Hafaloy-M, Hafaloy-N, and Hafaloy-NM. The high cost and low availability of hafnium limit its use in civilian reactors, although it is used in some
643:, but with the opposite effect. This is not explainable by neutron reflection alone. An obvious explanation is resonance gamma rays increasing the fission and breeding ratio versus causing greater capture of uranium, and others over
691:
mode of operation is the BWR, which requires hydraulic insertion in the event of an emergency shut-down, using water from a special tank under high pressure. Quickly shutting down a reactor in this way is called
507:. It has good mechanical strength and can be easily fabricated. It must be encased in stainless steel to prevent corrosion in hot water. Although indium is less rare than silver, it is more expensive.
663:) added to the reactor coolant, allowing the complete extraction of the control rods during stationary power operation, ensuring an even power and flux distribution over the entire core. This
578:
reactors. Hafnium carbide can also be used as an insoluble material with a high melting point of 3890 °C and density higher than that of uranium dioxide for sinking, unmelted, through
631:. Since they all swell with boron, in practice other compounds are better, such as carbides, or compounds with two or more neutron-absorbing elements together. It is important that
116:. Each reactor design can use different control rod materials based on the energy spectrum of its neutrons. Control rods have been used in nuclear aircraft engines like
1235:
1186:
545:
has excellent properties for reactors using water for both moderation and cooling. It has good mechanical strength, can be easily fabricated, and is resistant to
186:). If all control rods are fully removed, reactivity is significantly above 1, and the reactor quickly runs hotter and hotter, until some other factor (such as
484:
around the vessel part especially in case of core catching reactors or if filled with sodium or lithium. Fission-produced xenon can be used after waiting for
187:
833:
limited to use only in research reactors due to increased swelling from helium and lithium due to neutron absorption of boron in the (n, alpha) reaction
392:
are excellent neutron absorbers and are more common than silver (reserves of about 500,000t). For example, ytterbium (reserves about one M tons) and
1306:
174:
190:) slows the reaction rate. Maintaining a constant power output requires keeping the long-term average neutron multiplication factor close to 1.
786:
B is responsible for the majority of the neutron absorption. Boron-containing materials can also be used as neutron shielding, to reduce the
1316:
619:
boride, which is already used in the colour industry. Less absorptive compounds of boron similar to titanium, but inexpensive, such as
488:
to precipitate, when practically no radioactivity is left. Cobalt-59 is also used as an absorber for winning of cobalt-60 for use as a
1239:
926:
510:
Boron is another common neutron absorber. Due to the different cross sections of B and B, materials containing boron enriched in B by
225:
head. In BWRs, due to the necessity of a steam dryer above the core, this design requires insertion of the control rods from beneath.
768:
gas can be injected into the primary coolant cycle. This is because nitrogen has a larger absorption cross-section for neutrons than
1277:
1018:
989:
1311:
897:
193:
A new reactor is assembled with its control rods fully inserted. Control rods are partially removed from the core to allow the
168:
539:
production or directly with an energy optimized melting centrifuge, using the heat of freshly separated boron for preheating.
396:, 400 times more common, with middle capturing values, can be found and used together without separation inside minerals like
1043:
644:
1144:
210:
1197:
761:
1073:
206:
183:
128:
500:
97:
480:-cooled reactors, but does not function in cases of pressure loss, or as a burning protection gas together with
579:
523:. The latter is used as a control rod material in both PWRs and BWRs. B/B separation is done commercially with
333:
608:
is another such material. It can be used alone or in a sintered mixture of hafnium and boron carbide powders.
881:
Competition between densification and microstructure development during spark plasma sintering of B4C–Eu2O3.
847:
214:
194:
178:
149:
499:
Silver-indium-cadmium alloys, generally 80% Ag, 15% In, and 5% Cd, are a common control rod material for
167:
The number of control rods inserted, and the distance to which they are inserted, strongly influence the
1259:(Technical report). Office of Scientific and Technical Information, United States Department of Energy.
93:
85:
1232:
Behavior of control rods during core degradation: pressurization of silver-indium-cadmium control rods
721:
476:
is also a strong neutron absorber as a gas, and can be used for controlling and (emergency) stopping
137:
746:
solutions of fissile material; the corrosion of the cadmium in the acid will then generate cadmium
648:
585:
511:
326:
101:
89:
787:
713:
389:
378:
314:
503:. The somewhat different energy absorption regions of the materials make the alloy an excellent
1273:
1260:
1243:
668:
318:
973:
972:
Bowsher, B. R.; Jenkins, R. A.; Nichols, A. L.; Rowe, N. A.; Simpson, J. a. H. (1986-01-01).
919:,a new mineral species from the Shatford Lake pegmatite group, southeastern Manitoba, Canada.
742:) or a cadmium compound has been added to the system. The cadmium can be added as a metal to
1257:
Silver-indium-cadmium control rod behavior and aerosol formation in severe reactor accidents
705:
605:
504:
332:
The material choice is influenced by the neutron energy in the reactor, their resistance to
322:
161:
54:
1274:"Experiments on silver-indium-cadmium control rod failure during severe accident sequences"
779:
As the neutron energy increases, the neutron cross section of most isotopes decreases. The
1301:
1123:
804:
611:
Many other compounds of rare-earth elements can be used, such as samarium with boron-like
369:
337:
233:
222:
141:
109:
105:
82:
42:
1022:
997:
30:
809:
757:
680:
524:
1295:
814:
799:
684:
664:
520:
362:
310:
153:
145:
117:
659:
Other means of controlling reactivity include (for PWR) a soluble neutron absorber (
959:
198:
113:
1051:
1098:
743:
496:
reflector and absorber side turned to stop by a spring in less than one second.
306:
913:
Harvey M. Buck, Mark A. Cooper, Petr Cerny, Joel D. Grice, Frank C. Hawthorne:
237:
The absorption cross section for B (top) and B (bottom) as a function of energy
660:
620:
570:
282:
274:
218:
602:
tubes deliver superior price and absorption without swelling and outgassing.
975:
Silver-indium-cadmium control rod behaviour during a severe reactor accident
952:, A new ytterbium silicate from amazonitic pegmatites of the Kola Peninsula.
688:
546:
489:
382:
298:
241:
Chemical elements with usefully high neutron capture cross-sections include
50:
17:
492:
source. Control rods can also be constructed as thick turnable rods with a
896:
Anthony
Monterrosa; Anagha Iyengar; Alan Huynh; Chanddeep Madaan (2012).
765:
636:
632:
616:
612:
562:
493:
397:
302:
270:
266:
34:
Control rod assembly for a pressurized water reactor, above fuel element
783:
747:
725:
640:
575:
566:
542:
485:
393:
373:
294:
286:
278:
262:
250:
78:
70:
62:
46:
1264:
1247:
884:
773:
769:
739:
736:
590:
554:
536:
477:
290:
258:
246:
242:
74:
66:
549:
in hot water. Hafnium can be alloyed with other elements, e.g. with
385:-moderated and -cooled reactors that use fuel and absorber pebbles.
1165:
868:
780:
732:
728:
693:
516:
481:
473:
254:
232:
157:
127:
58:
29:
764:, if the solid control rods fail to arrest the nuclear reaction,
709:
704:
Mismanagement or control rod failure have often been blamed for
598:
594:
558:
1124:"Infrarotabsorbierende Druckfarben - Dokument DE102008049595A1"
550:
593:. It was developed in Russia and is recommended by some for
81:
without themselves decaying. These elements have different
869:
ytterbium (n.gamma) data with
Japanese or Russian database
683:, control rods are attached to the lifting machinery by
978:(Technical report). UKAEA Atomic Energy Establishment.
27:
Device used to regulate the power of a nuclear reactor
651:, which has a half-life of approximately 26 minutes.
305:. Alloys or compounds may also be used, such as high-
197:
to start up and increase to the desired power level.
45:
to control the rate of fission of the nuclear fuel –
1187:"Enriched boric acid for pressurized water reactors"
938:
A. V. Voloshin, Ya. A. Pakhomovsky, F. N. Tyusheva:
329:, and boron carbide–europium hexaboride composite.
720:neutron absorbers have often been used to manage
960:Abstract in American Mineralogist, S. 1191
639:, have much the same high capture qualities as
1272:Steinbrueck, M.; Stegmaier, U. (May 6, 2010).
1236:Office of Scientific and Technical Information
776:; hence, the core then becomes less reactive.
1099:"Method for making neutron absorber material"
557:to increase tensile and creep strength, with
217:is two seconds for 90% reduction, limited by
132:1943 Reactor diagram using boron control rods
8:
635:, and probably also other elements such as
325:, gadolinium nitrate, gadolinium titanate,
927:Abstract in American Mineralogist, S. 1324
879:Sairam K, Vishwanadh B, Sonber JK, et al.
655:Additional means of reactivity regulation
898:"Boron Use and Control in PWRs and FHRs"
861:
826:
175:effective neutron multiplication factor
1044:"Hafnium alloys as neutron absorbers"
790:of material close to a reactor core.
209:time for modern reactors such as the
77:, that are capable of absorbing many
7:
731:. In several such accidents, either
173:of the reactor. When reactivity (as
724:which involve aqueous solutions of
569:for corrosion resistance, and with
253:. Other candidate elements include
156:output of the reactor, the rate of
136:Control rods are inserted into the
1240:United States Department of Energy
885:https://doi.org/10.1111/jace.15376
25:
1278:Karlsruhe Institute of Technology
1078:Everything-Science.com web forum
1230:Powers, D.A. (August 1, 1985).
700:Criticality accident prevention
309:, silver-indium-cadmium alloy,
188:temperature reactivity feedback
1307:Nuclear power plant components
883:J Am Ceram Soc. 2017;00:1–11.
679:In most reactor designs, as a
531:, but can also be done over BH
177:) is above 1, the rate of the
53:. Their compositions include
1:
1255:Petti, D.A. (March 1, 1987).
1166:"Sigma Periodic Table Browse"
1021:. Web.mit.edu. Archived from
925:1999, 37, S. 1303–1306 (
760:-cooled reactors such as the
164:output of the power station.
211:European Pressurized Reactor
1126:. Patent-de.com. 2008-09-30
1333:
1317:Pressurized water reactors
1168:. Nndc.bnl.gov. 2007-01-25
958:1983, 5-5, S. 94–99 (
501:pressurized water reactors
98:pressurized water reactors
140:and adjusted in order to
138:core of a nuclear reactor
381:or in possible new type
334:neutron-induced swelling
120:as a method of control.
88:for neutrons of various
1194:EaglePicher Corporation
647:conditions such as for
1312:Nuclear reactor safety
923:Canadian Mineralogist.
848:Advanced CANDU reactor
432:, or keiviite (Yb) (Yb
238:
215:Advanced CANDU reactor
195:nuclear chain reaction
179:nuclear chain reaction
150:nuclear chain reaction
133:
94:Boiling water reactors
35:
722:criticality accidents
671:, increasing power).
472:, lowering the cost.
236:
131:
33:
1234:(Technical report).
1203:on November 29, 2007
962:; PDF; 853 kB).
160:production, and the
102:heavy-water reactors
1103:Free Patents Online
1074:"Dysprosium (Z=66)"
1054:on October 12, 2008
1048:Free Patents Online
1019:"Control Materials"
990:"CONTROL MATERIALS"
956:Mineralog. Zhurnal.
915:Xenotime-(Yb), YbPO
586:Dysprosium titanate
512:isotopic separation
390:rare-earth elements
379:pebble bed reactors
327:dysprosium titanate
124:Operating principle
104:(HWR) operate with
714:Chernobyl disaster
712:explosion and the
315:zirconium diboride
239:
152:and, thereby, the
134:
36:
706:nuclear accidents
319:titanium diboride
55:chemical elements
16:(Redirected from
1324:
1288:
1286:
1284:
1268:
1251:
1213:
1212:
1210:
1208:
1202:
1196:. Archived from
1191:
1183:
1177:
1176:
1174:
1173:
1162:
1156:
1155:
1153:
1152:
1141:
1135:
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1111:
1109:
1095:
1089:
1088:
1086:
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1064:
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1061:
1059:
1050:. Archived from
1040:
1034:
1033:
1031:
1030:
1015:
1009:
1008:
1006:
1005:
996:. Archived from
986:
980:
979:
969:
963:
936:
930:
911:
905:
904:
902:
893:
887:
877:
871:
866:
850:
840:
834:
831:
708:, including the
606:Hafnium diboride
505:neutron absorber
360:
358:
357:
350:
348:
347:
323:hafnium diboride
162:electrical power
110:breeder reactors
106:thermal neutrons
43:nuclear reactors
21:
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1327:
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1325:
1323:
1322:
1321:
1292:
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1224:Further reading
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895:
894:
890:
878:
874:
867:
863:
859:
854:
853:
846:O moderator of
845:
842:injected into D
841:
837:
832:
828:
823:
805:Nuclear reactor
796:
702:
677:
657:
630:
626:
534:
530:
525:gas centrifuges
471:
467:
463:
459:
455:
451:
447:
443:
439:
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431:
427:
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419:
415:
411:
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403:
370:burnable poison
368:The burnup of "
356:
354:
353:
352:
351:
346:
344:
343:
342:
341:
338:silicon carbide
231:
223:pressure vessel
126:
83:neutron capture
28:
23:
22:
15:
12:
11:
5:
1330:
1328:
1320:
1319:
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1304:
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1252:
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1219:External links
1217:
1215:
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1178:
1157:
1147:. Nndc.bnl.gov
1136:
1115:
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819:
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810:Nuclear safety
807:
802:
795:
792:
758:carbon dioxide
701:
698:
685:electromagnets
681:safety measure
676:
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230:
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125:
122:
86:cross sections
26:
24:
14:
13:
10:
9:
6:
4:
3:
2:
1329:
1318:
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1313:
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1207:September 25,
1199:
1195:
1188:
1182:
1179:
1167:
1161:
1158:
1146:
1145:"Sigma Plots"
1140:
1137:
1125:
1119:
1116:
1108:September 25,
1104:
1100:
1094:
1091:
1083:September 25,
1079:
1075:
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1058:September 25,
1053:
1049:
1045:
1039:
1036:
1025:on 2016-03-04
1024:
1020:
1014:
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1000:on 2016-03-04
999:
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815:Wigner effect
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800:Nuclear power
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665:chemical shim
662:
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521:boron carbide
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363:boron nitride
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154:thermal power
151:
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123:
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119:
118:Project Pluto
115:
114:fast neutrons
112:operate with
111:
107:
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99:
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91:
87:
84:
80:
76:
72:
68:
64:
60:
56:
52:
48:
44:
40:
32:
19:
1281:. Retrieved
1256:
1231:
1205:. Retrieved
1198:the original
1193:
1181:
1170:. Retrieved
1160:
1149:. Retrieved
1139:
1128:. Retrieved
1118:
1106:. Retrieved
1102:
1093:
1081:. Retrieved
1077:
1068:
1056:. Retrieved
1052:the original
1047:
1038:
1027:. Retrieved
1023:the original
1013:
1002:. Retrieved
998:the original
993:
984:
974:
967:
955:
939:
934:
922:
914:
909:
891:
880:
875:
864:
838:
829:
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717:
703:
678:
658:
610:
604:
584:
541:
509:
498:
387:
367:
331:
240:
204:
199:Neutron flux
192:
169:
166:
135:
41:are used in
39:Control rods
38:
37:
18:Control rods
994:web.mit.edu
940:Keiviite Yb
744:nitric acid
718:Homogeneous
340:, or cubic
307:boron steel
100:(PWR), and
1296:Categories
1172:2014-04-22
1151:2014-04-22
1130:2014-04-22
1029:2010-08-14
1004:2015-06-02
857:References
788:activation
661:boric acid
645:metastable
621:molybdenum
571:molybdenum
283:dysprosium
275:gadolinium
219:decay heat
170:reactivity
694:scramming
689:fail-safe
669:moderator
649:isotope U
547:corrosion
490:gamma ray
383:lithium-7
299:ytterbium
229:Materials
51:plutonium
794:See also
766:nitrogen
637:tantalum
633:tungsten
617:samarium
613:europium
563:chromium
494:tungsten
400:(Yb) (Yb
398:xenotime
374:isotopes
303:lutetium
271:europium
267:samarium
207:shutdown
205:Typical
184:shutdown
108:, while
90:energies
79:neutrons
57:such as
1283:May 29,
1265:6380030
1248:6332291
784:isotope
751:in situ
748:nitrate
726:fissile
641:hafnium
576:US Navy
567:niobium
543:Hafnium
527:over BF
486:caesium
394:yttrium
361:(cubic
295:thulium
287:holmium
279:terbium
263:hafnium
251:cadmium
148:of the
142:control
96:(BWR),
71:hafnium
63:cadmium
47:uranium
1302:Alloys
1263:
1246:
774:oxygen
770:carbon
740:borate
737:sodium
729:metals
675:Safety
591:outgas
580:corium
565:, and
555:oxygen
537:borane
478:helium
301:, and
291:erbium
259:cobalt
249:, and
247:indium
243:silver
75:indium
67:silver
1201:(PDF)
1190:(PDF)
929:; PDF
901:(PDF)
821:Notes
781:boron
733:borax
623:as Mo
535:from
517:steel
482:argon
474:Xenon
388:Some
255:boron
158:steam
73:, or
59:boron
1285:2017
1261:OSTI
1244:OSTI
1209:2008
1110:2008
1085:2008
1060:2008
954:In:
921:In:
710:SL-1
615:and
599:RBMK
597:and
595:VVER
589:not
559:iron
553:and
519:and
458:0.02
454:0.03
450:0.05
446:0.08
442:0.17
438:0.23
434:1.43
426:0.01
422:0.04
418:0.05
414:0.12
410:0.12
406:0.27
402:0.40
146:rate
144:the
772:or
762:AGR
756:In
551:tin
428:)PO
365:).
213:or
49:or
1298::
1276:.
1242:.
1238:,
1192:.
1101:.
1076:.
1046:.
992:.
944:Si
753:.
716:.
696:.
582:.
561:,
464:Si
456:Ho
452:Dy
444:Tm
440:Er
436:Lu
424:Ho
420:Tm
416:Dy
412:Er
408:Lu
372:"
321:,
317:,
313:,
297:,
293:,
289:,
285:,
281:,
277:,
273:,
269:,
265:,
261:,
257:,
245:,
92:.
69:,
65:,
61:,
1287:.
1267:.
1250:.
1211:.
1175:.
1154:.
1133:.
1112:.
1087:.
1062:.
1032:.
1007:.
950:7
948:O
946:2
942:2
917:4
903:.
844:2
735:(
629:5
627:B
625:2
533:3
529:3
470:7
468:O
466:2
462:2
460:)
448:Y
430:4
404:Y
359:N
349:B
20:)
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