380:, which has a 6.57 hour half-life, the production of Xe remains constant; at this point, the Xe concentration reaches a minimum. The concentration then increases to the new equilibrium level (more accurately steady state level) for the new power level in roughly 40 to 50 hours. During the initial 4 to 6 hours following the power change, the magnitude and the rate of change of concentration is dependent upon the initial power level and on the amount of change in power level; the Xe concentration change is greater for a larger change in power level. When reactor power is decreased, the process is reversed.
332:
38:
459:. The reactor burns off the nuclear poison. As this happens, the reactivity and neutron flux increases, and the control rods must be gradually reinserted to counter the loss of neutron absorption by the Xe. Otherwise, the reactor neutron flux will continue to increase, burning off even more xenon poison, on a path to
634:
With little change in overall power level, these oscillations can significantly change the local power levels. This oscillation may go unnoticed and reach dangerous local flux levels if only the total power of the core is monitored. Therefore, most PWRs use tandem power range excore neutron detectors
418:
by inserting neutron-absorbing control rods, the reactor neutron flux is reduced and the equilibrium shifts initially towards higher Xe concentration. The Xe concentration peaks about 11.1 hours after reactor power is decreased. Since Xe has a 9.2 hour half-life, the Xe concentration gradually decays
383:
Iodine-135 is a fission product of uranium with a yield of about 6% (counting also the I produced almost immediately from decay of fission-produced tellurium-135). This I decays with a 6.57 hour half-life to Xe. Thus, in an operating nuclear reactor, Xe is being continuously produced. Xe has a very
422:
The temporarily high level of Xe with its high neutron absorption cross-section makes it difficult to restart the reactor for several hours. The neutron-absorbing Xe acts like a control rod, reducing reactivity. The inability of a reactor to be started due to the effects of Xe is sometimes referred
619:
An initial lack of symmetry (for example, axial symmetry, in the case of axial oscillations) in the core power distribution (for example as a result of significant control rods movement) causes an imbalance in fission rates within the reactor core, and therefore, in the iodine-135 buildup and the
623:
In the high-flux region, xenon-135 burnout allows the flux to increase further, while in the low-flux region, the increase in xenon-135 causes a further reduction in flux. The iodine concentration increases where the flux is high and decreases where the flux is low. This shift in the xenon
531:
The probability of capturing a neutron before decay varies with the neutron flux, which itself depends on the kind of reactor, fuel enrichment and power level; and the Cs / Xe ratio switches its predominant branch very near usual reactor conditions. Estimates of the proportion of Xe during
607:
Large thermal reactors with low flux coupling between regions may experience spatial power oscillations because of the non-uniform presence of xenon-135. Xenon-induced spatial power oscillations occur as a result of rapid perturbations to power distribution that cause the xenon and iodine
556:
s, which corresponds to a half-life of about one hour. Compared to the 9.17 hour half-life of Xe, this nearly ten-to-one ratio means that under such conditions, essentially all Xe would capture a neutron before decay. But if the neutron flux is lowered to one-tenth of this value, like in
470:; during a run-down to a lower power, a combination of operator error and xenon poisoning caused the reactor thermal power to fall to near-shutdown levels. The crew's resulting efforts to restore power placed the reactor in a highly unsafe configuration. A flaw in the
347:
for absorption. Because absorbing neutrons can detrimentally affect a nuclear reactor's ability to increase power, reactors are designed to mitigate this effect; operators are trained to properly anticipate and react to these transients. In fact, during World War II,
463:. The time constant for this burn-off transient depends on the reactor design, power level history of the reactor for the past several days, and the new power setting. For a typical step up from 50% power to 100% power, Xe concentration falls for about 3 hours.
611:
The instantaneous production rate of xenon-135 is dependent on the iodine-135 concentration and therefore on the local neutron flux history. On the other hand, the destruction rate of xenon-135 is dependent on the instantaneous local neutron flux.
375:
value for that reactor power in about 40 to 50 hours. When the reactor power is increased, Xe concentration initially decreases because the burn up is increased at the new higher power level. Because 95% of the Xe production is from decay of
608:
distribution to be out of phase with the perturbed power distribution. This results in a shift in xenon and iodine distributions that causes the power distribution to change in an opposite direction from the initial perturbation.
410:
is >10 years, and it is not treated as a radioisotope.) Thus, in about 50 hours, the Xe concentration reaches equilibrium where its creation by I decay is balanced with its destruction by neutron absorption.
615:
The combination of delayed generation and high neutron-capture cross section produces a diversity of impacts on nuclear reactor operation. The mechanism is described in the following four steps.
532:
steady-state reactor operation that captures a neutron include 90%, 39%–91% and "essentially all". For instance, in a (somewhat high) neutron flux of 10 n·cm·s, the xenon cross section of σ =
423:
to as xenon-precluded start-up, and the reactor is said to be "poisoned out". The period of time that the reactor is unable to overcome the effects of Xe is called the "xenon dead time".
627:
As soon as the iodine-135 levels build up sufficiently, decay to xenon reverses the initial situation. Flux decreases in this area, and the former low-flux region increases in power.
834:
481:
designs might be able to extract Xe from the fuel and avoid these effects. Fluid fuel reactors cannot develop xenon inhomogeneity because the fuel is free to mix. Also, the
384:
large neutron absorption cross-section, so in the high-neutron-flux environment of a nuclear reactor core, the Xe soon absorbs a neutron and becomes effectively stable
624:
distribution is such as to increase (decrease) the multiplication properties of the region in which the flux has increased (decreased), thus enhancing the flux tilt.
719:
583:. Fission produces Xe, Xe, and Xe in roughly equal amounts but, after neutron capture, fission caesium contains more stable Cs (which however can become
772:
745:
831:
870:
729:
489:
to leave the fuel salts. Removing Xe from neutron exposure improves neutron economy, but causes the reactor to produce more of the
630:
Repetition of these patterns can lead to xenon oscillations moving about the core with periods on the order of about 24 hours.
701:
482:
852:
800:
335:
Graph showing the concentration of Xenon and the reactivity of the nuclear reaction from the moment the reactor is shutdown.
912:
427:
360:. Wu's soon-to-be published paper on Xe-135 completely verified Fermi's guess that it absorbed neutrons and disrupted the
485:
demonstrated that spraying the liquid fuel as droplets through a gas space during recirculation can allow xenon and
474:
system inserted positive reactivity, causing a thermal transient and a steam explosion that tore the reactor apart.
966:
649:
525:
490:
415:
961:
929:
971:
504:(Cs) produced in the fuel, and it is practical to handle them separately (fission yield is appr. 6% for both).
309:
operation. The ultimate yield of xenon-135 from fission is 6.3%, though most of this is from fission-produced
500:
condenses in a separate tank after the decay of Xe, and is physically separate from the 30.05 year half life
151:
781:
754:
343:, the presence of Xe as a fission product presents designers and operators with problems due to its large
117:
344:
460:
580:
478:
372:
588:
467:
946:
686:
331:
725:
644:
561:
reactors, the ratio would be 50-50, and half the Xe would decay to Cs before neutron capture.
254:
250:
111:
104:
50:
672:
446:
increases many orders of magnitude and the Xe begins to absorb neutrons and be transmuted to
60:
874:
867:
856:
838:
513:
431:
357:
306:
282:
353:
887:
294:
183:
87:
955:
439:
430:
control authority is available, the reactor can be restarted, but the xenon burn-out
310:
204:
161:
70:
868:
Utilization of the
Isotopic Composition of Xe and Kr in Fission Gas Release Research
443:
368:
349:
230:
226:
176:
849:
807:
584:
521:
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493:
435:
340:
302:
298:
209:
576:
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517:
377:
326:
314:
239:
221:
721:
Women In Their
Element: Selected Women's Contributions To The Periodic System
448:
399:
386:
361:
278:
125:
564:
Xe from neutron capture ends up as part of the eventual stable fission
486:
290:
286:
270:
774:
DOE Fundamentals
Handbook: Nuclear Physics and Reactor Theory Volume 2
747:
DOE Fundamentals
Handbook: Nuclear Physics and Reactor Theory Volume 2
37:
17:
596:
592:
528:, while a Xe that does capture a neutron becomes almost-stable Xe.
673:"Livechart - Table of Nuclides - Nuclear structure and decay data"
565:
558:
471:
330:
274:
575:
Nuclei of Xe, Xe, and Xe that have not captured a neutron all
568:
which also includes Xe, Xe, and Xe produced by fission and
635:
to monitor upper and lower halves of the core separately.
780:. U.S. Department of Energy. January 1993. Archived from
753:. U.S. Department of Energy. January 1993. Archived from
305:
under reactor conditions), with a significant effect on
367:
During periods of steady state operation at a constant
352:
suspected the effect of Xe, and followed the advice of
850:
CANDU Fundamentals: 20 Xenon: A Fission
Product Poison
687:""Xenon Poisoning" or Neutron Absorption in Reactors"
496:. The long lived (but 76000 times less radioactive)
947:"Xenon Poisoning" or Neutron Absorption in Reactors
237:
220:
215:
203:
182:
160:
150:
124:
110:
103:
86:
69:
59:
49:
44:
888:"The Influence of Xenon-135 on Reactor Operation"
477:Reactors using continuous reprocessing like many
466:Xenon poisoning was a contributing factor to the
548:barn) would lead to a capture probability of
371:level, the Xe concentration builds up to its
8:
30:
36:
339:In a typical nuclear reactor fueled with
700:Benczer-Koller, Noemie (January 2009).
661:
364:that was being used in their project.
29:
893:. Westinghouse Savannah River Company
7:
667:
665:
414:When reactor power is decreased or
434:must be carefully managed. As the
419:back to low levels over 72 hours.
289:and it is the most powerful known
25:
801:"Xenon, A Fission Product Poison"
718:Lykknes, Annette (2019-01-02).
483:Molten Salt Reactor Experiment
1:
572:rather than neutron capture.
321:Xe effects on reactor restart
281:of about 9.2 hours. Xe is a
832:Xenon decay transient graph
806:. candu.org. Archived from
526:long-lived fission products
988:
702:"Chien-shiungwu 1912—1997"
650:Shutdown (nuclear reactor)
603:Spatial xenon oscillations
508:Decay and capture products
491:long-lived fission product
356:in contacting his student
324:
255:Complete table of nuclides
873:October 19, 2013, at the
591:) and highly radioactive
249:
35:
930:"Xenon-135 Oscillations"
512:A Xe atom that does not
65:xenon-135, 135Xe, Xe-135
855:July 23, 2011, at the
837:June 24, 2018, at the
336:
917:www.nuclear-power.net
620:xenon-135 absorption.
345:neutron cross section
334:
886:Roggenkamp, Paul L.
724:. World Scientific.
397:. (The half life of
813:on February 3, 2007
581:isotopes of caesium
479:molten salt reactor
461:runaway criticality
32:
589:neutron activation
468:Chernobyl disaster
438:are extracted and
337:
301:; up to 3 million
31:Xenon-135, Xe
967:Isotopes of xenon
645:Isotopes of xenon
514:capture a neutron
269:) is an unstable
260:
259:
251:Isotopes of xenon
112:Natural abundance
16:(Redirected from
979:
962:Fission products
934:
933:
926:
924:
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909:
903:
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96:
79:
40:
33:
27:Isotope of xenon
21:
987:
986:
982:
981:
980:
978:
977:
976:
972:Neutron poisons
952:
951:
943:
941:Further reading
938:
937:
928:
921:
919:
911:
910:
906:
896:
894:
890:
885:
884:
880:
875:Wayback Machine
866:
862:
857:Wayback Machine
848:
844:
839:Wayback Machine
830:
826:
816:
814:
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803:
798:
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784:
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771:
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766:
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743:
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732:
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671:
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605:
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541:
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533:
524:, one of the 7
510:
453:
451:
450:
449:
447:
404:
402:
401:
400:
398:
391:
389:
388:
387:
385:
358:Chien-Shiung Wu
329:
323:
307:nuclear reactor
283:fission product
253:
238:
194:
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188:
171:
168:
166:
142:
140:
135:
128:
90:
73:
28:
23:
22:
15:
12:
11:
5:
985:
983:
975:
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969:
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953:
950:
949:
942:
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936:
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860:
842:
824:
791:
787:on 2013-02-14.
764:
760:on 2013-02-14.
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678:
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652:
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632:
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628:
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621:
604:
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509:
506:
452:
426:If sufficient
403:
390:
325:Main article:
322:
319:
295:nuclear poison
258:
257:
247:
246:
243:
235:
234:
224:
218:
217:
213:
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207:
205:Decay products
201:
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186:
184:Binding energy
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133:
122:
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10:
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809:
802:
799:Crist, J. E.
795:
792:
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756:
749:
748:
741:
738:
733:
731:9789811206306
727:
723:
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311:tellurium-135
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162:Excess energy
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68:
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62:
58:
54:
52:
48:
43:
39:
34:
19:
920:. Retrieved
916:
907:
895:. Retrieved
881:
863:
845:
827:
815:. Retrieved
808:the original
794:
782:the original
773:
767:
762:, pp. 35–42.
755:the original
746:
740:
720:
713:
695:
681:
633:
614:
610:
606:
574:
563:
530:
511:
476:
465:
444:neutron flux
442:is reached,
436:control rods
425:
421:
413:
382:
369:neutron flux
366:
354:Emilio Segrè
350:Enrico Fermi
338:
266:
262:
261:
227:Decay energy
130:
105:Nuclide data
92:
75:
913:"Xenon-135"
587:on further
502:caesium-137
498:caesium-135
440:criticality
373:equilibrium
341:uranium-235
297:(2 million
293:-absorbing
216:Decay modes
145:0.02 h
956:Categories
922:2017-09-19
897:18 October
817:2 November
656:References
577:beta decay
570:beta decay
518:beta decay
516:undergoes
428:reactivity
327:Iodine pit
315:iodine-135
240:Beta decay
222:Decay mode
432:transient
416:shut down
362:B Reactor
279:half-life
263:Xenon-135
126:Half-life
118:synthetic
871:Archived
853:Archived
835:Archived
789:, p. 35.
639:See also
88:Neutrons
487:krypton
291:neutron
287:uranium
277:with a
271:isotope
71:Protons
45:General
728:
51:Symbol
18:Xe-135
891:(PDF)
811:(PDF)
804:(PDF)
785:(PDF)
778:(PDF)
758:(PDF)
751:(PDF)
705:(PDF)
595:than
566:xenon
559:CANDU
472:SCRAM
303:barns
299:barns
275:xenon
245:1.168
197:0.028
61:Names
927:and
899:2013
819:2011
726:ISBN
550:2.65
542:2.65
540:cm (
534:2.65
313:and
193:.476
156:3/2+
152:Spin
141:9.14
579:to
520:to
285:of
273:of
231:MeV
199:keV
191:398
177:keV
169:413
167:−86
134:1/2
116:0 (
958::
915:.
664:^
599:.
597:Cs
593:Cs
585:Cs
554:10
546:10
538:10
522:Cs
494:Cs
456:Xe
407:Xe
394:Xe
317:.
267:Xe
210:Cs
99:81
82:54
55:Xe
932:.
925:.
901:.
821:.
734:.
707:.
689:.
675:.
552:×
544:×
536:×
378:I
265:(
233:)
229:(
195:±
189:8
174:4
172:±
143:±
136:)
131:t
129:(
120:)
95:)
93:N
91:(
78:)
76:Z
74:(
20:)
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