Friday, November 18, 2011

Radioactive Xenon and Nuclear Radiation

Radioactive Xenon and Nuclear Radiation

Radioactive isotopes xenon-133 and xenon-135 are typically generated by nuclear fission. Xenon-133 has half-life of 5.25 days, Xenon-135 just 9.1 hrs, so both are evidence of leakage and recent fission. Scientests have determined that 13-20 EBq of xenon-133 were released as the total inventory of noble gases after the Fukushima Daiichi accident, the largest xenon gas release not including nuclear bomb tests.   The first strong 133Xe release evidently occured immediately after the earthquake and the emergency shutdown on 11 March at 06:00 UTC, a strong indication of damage to fuel and / or reactors as such gas is not released by a normally operating power plant with all safety containment systems intact.

@@Criticality at Fukushima

%%March 11, 2011
Atmos. Chem. Phys. Discuss., 11, 28319-28394, 2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.

Xenon-133 and caesium-137 releases into the atmosphere from the Fukushima Dai-ichi nuclear power plant: determination of the source term, atmospheric dispersion, and deposition

A. Stohl1, P. Seibert2, G. Wotawa3, D. Arnold2,4, J. F. Burkhart1, S. Eckhardt1, C. Tapia5, A. Vargas4, and T. J. Yasunari6
1NILU – Norwegian Institute for Air Research, Kjeller, Norway
2Institute of Meteorology, University of Natural Resources and Life Sciences, Vienna, Austria
3Central Institute for Meteorology and Geodynamics, Vienna, Austria
4Institute of Energy Technologies (INTE), Technical University of Catalonia (UPC), Barcelona, Spain
5Department of Physics and Nucelar Engineering (FEN),Technical University of Catalonia (UPC), Barcelona, Spain
6Universities Space Research Association, Goddard Earth Sciences and Technology and Research, Columbia, MD 21044, USA

Abstract. On 11 March 2011, an earthquake occurred about 130 km off the Pacific coast of Japan's main island Honshu, followed by a large tsunami. The resulting loss of electric power at the Fukushima Dai-ichi nuclear power plant (FD-NPP) developed into a disaster causing massive release of radioactivity into the atmosphere. In this study, we determine the emissions of two isotopes, the noble gas xenon-133 (133Xe) and the aerosol-bound caesium-137 (137Cs), which have very different release characteristics as well as behavior in the atmosphere. To determine radionuclide emissions as a function of height and time until 20 April, we made a first guess of release rates based on fuel inventories and documented accident events at the site. This first guess was subsequently improved by inverse modeling, which combined the first guess with the results of an atmospheric transport model, FLEXPART, and measurement data from several dozen stations in Japan, North America and other regions. We used both atmospheric activity concentration measurements as well as, for 137Cs, measurements of bulk deposition. Regarding 133Xe, we find a total release of 16.7 (uncertainty range 13.4–20.0) EBq, which is the largest radioactive noble gas release in history not associated with nuclear bomb testing. There is strong evidence that the first strong 133Xe release started very early, possibly immediately after the earthquake and the emergency shutdown on 11 March at 06:00 UTC. The entire noble gas inventory of reactor units 1–3 was set free into the atmosphere between 11 and 15 March 2011. For 137Cs, the inversion results give a total emission of 35.8 (23.3–50.1) PBq, or about 42% of the estimated Chernobyl emission. Our results indicate that 137Cs emissions peaked on 14–15 March but were generally high from 12 until 19 March, when they suddenly dropped by orders of magnitude exactly when spraying of water on the spent-fuel pool of unit 4 started. This indicates that emissions were not only coming from the damaged reactor cores, but also from the spent-fuel pool of unit 4 and confirms that the spraying was an effective countermeasure. We also explore the main dispersion and deposition patterns of the radioactive cloud, both regionally for Japan as well as for the entire Northern Hemisphere. While at first sight it seemed fortunate that westerly winds prevailed most of the time during the accident, a different picture emerges from our detailed analysis. Exactly during and following the period of the strongest 137Cs emissions on 14 and 15 March as well as after another period with strong emissions on 19 March, the radioactive plume was advected over Eastern Honshu Island, where precipitation deposited a large fraction of 137Cs on land surfaces. The plume was also dispersed quickly over the entire Northern Hemisphere, first reaching North America on 15 March and Europe on 22 March. In general, simulated and observed concentrations of 133Xe and 137Cs both at Japanese as well as at remote sites were in good quantitative agreement with each other. Altogether, we estimate that 6.4 TBq of 137Cs, or 19% of the total fallout until 20 April, were deposited over Japanese land areas, while most of the rest fell over the North Pacific Ocean. Only 0.7 TBq, or 2% of the total fallout were deposited on land areas other than Japan.

Discussion Paper (PDF, 6457 KB)   Supplement (13 KB)   Interactive Discussion (Open, 7 Comments)   Manuscript under review for ACP  

Citation: Stohl, A., Seibert, P., Wotawa, G., Arnold, D., Burkhart, J. F., Eckhardt, S., Tapia, C., Vargas, A., and Yasunari, T. J.: Xenon-133 and caesium-137 releases into the atmosphere from the Fukushima Dai-ichi nuclear power plant: determination of the source term, atmospheric dispersion, and deposition, Atmos. Chem. Phys. Discuss., 11, 28319-28394, doi:10.5194/acpd-11-28319-2011, 2011.   Bibtex   EndNote   Reference Manager    XML

%%March 21, 2011
Radioactive Xenon 133 (5.243 day half life) has now reached the entire Eastern seaboard, and soon will likely cover the entire world. Ausbreitung der Wolke von Fukushima/Edelgas Xe-133/ (globales Bild)

%%Nov 2, 2011

Tokyo Electric Power Co. (9501.TO) said Thursday the detection of radioactive xenon at its stricken Fukushima Daiichi power plant, indicating recent nuclear fission, was not the result of a sustained nuclear chain reaction known as a criticality, as feared, but a case of 'spontaneous' fission, Kyodo News reported.
When it revealed Wednesday that it had detected at its crisis-hit No. 2 reactor xenon-133 and xenon-135, which are typically generated by nuclear fission and have relatively short half-lives, it touched on the possibility that melted fuel inside the reactor may have temporarily gone critical.

Fears of Fission Rise at Stricken Japanese Plant
By HIROKO TABUCHI Published: November 2, 2011
On Wednesday, the plant’s operator, the Tokyo Electric Power Company, said that gas from Reactor No. 2 indicated the presence of radioactive xenon and other substances that could be byproducts of nuclear fission. The presence of xenon 135 in particular, which has a half-life of just nine hours, seemed to indicate that fission took place very recently.
Trade Minister Yukuo Edano censured Japan’s nuclear regulator, the Nuclear and Industrial Safety Agency, for failing to report the discovery to the prime minister’s office for hours, according to local media reports.
The developments added to disquiet over how information related to the disaster has been handled. For almost two months after the March 11 earthquake and tsunami knocked out vital cooling systems, setting the stage for disaster, both company and government officials declared it was unlikely that any meltdowns had occurred. They finally conceded that melted fuel had likely breached containments in three reactors, and that it was likely pooled at the bottom of the vessels.
A 12-mile exclusion zone is still in effect around the plant. More than 80,000 households were displaced.
On Wednesday, Tokyo Electric said that the amount of xenon detected was small

For almost two months after the March 11 earthquake and tsunami, disaster, both company and government officials declared it was unlikely any meltdown had occurred at all at the Fukushima Daichi nuclear complex, finally conceding that the fuel had indeed slumped and had likely breached containments in three reactors.
The amount of detected xenon was small, and there was no rise in temperature, pressure or radiation levels at the reactor, Tokyo Electric said. Researchers were double-checking the data to make sure there were no errors, the company said. Experts concurred that it was possible that Tokyo Electric had made a simple error in its measurements.
But the urgent injection of boric acid underscored that the company was operating on the assumption that the measurements were valid.

%%November 3, 2011

2:24 PM Eastern Thursday November 3, 2011
Xenon / Fukushima Daiichi Reactor No. 2 - Thursday afternoon update

The information at present from TEPCO echoes that printed here this morning. Here is the latest TEPCO analysis:

-We found a possibility to detect short-half-life radionuclide such as Xe-133 and Xe-135 according to our radionuclide analysis sampled on November 1 by the gas management system of the reactor containment vessel. We continued to monitor the temperature, pressure and data from monitoring post and there was no significant fluctuation from those data. As we can't deny a possibility of fission reactions, we decided to start 
injecting boric acid water from reactor feed water system at 2:48 am on November 2 and stopped it at 3:47 pm on the same day. At around 7:20 pm on the same day, Japan Atomic Energy Agency evaluated that the TEPCO's analysis result of the short-half-life radionuclide such as Xe-133 and Xe-135 detection was valid. We consider that they were generated by the spontaneous fission on the grounds that the concentration of detected  short-half-like radionuclide (Xe-135) is low, that short-half-like radionuclide (Xe-135) was detected even after the boric acid, which stops nuclear fission chain reactions, was injected, and that the parameters of the reactor were not significantly changed.

TEPCO representatives are making, apparently, the same statements to all media outlets but are seemingly at this point not making any differentiation between spontaneous fissions of U-235 and the two Curium isotopes mentioned this morning.

Also at Unit 2... TEPCO has noted a slight increase in hydrogen concentration in the PCV at this plant. A reading of 2.7% on October 30 compares now with a reading of 2.9% on November 3rd. Because of this, TEPCO has increased the volumetric flow rate of nitrogen injection from 21 m³/hr to 26 m³/hr.

More details when available... but for now the situation is completely stable and (as I've said before) no fission chain reaction is occurring at No. 2 plant - and neither is a continued meltdown.

@@Medical uses

Xenon (Xe-133) 
Gas (fission)
Half-Life: 5.243 days
X  E N O N  -133   F I SS I O N 
R  A  D I  O C H  EM I C  A  L   X  E N  O  N   G  A  S
Xenon-133 is used for lung ventilation studies which demonstrate respiratory 
efficiency. Patients breathe the radio- active gas and scintillation cameras 
measure the amount of radioactivity found over areas of the lung. 
This procedure provides a good indication of how well the lung is 
functioning, can detect the presence of pulmonary emboli, and can assess 
chronic ventilation diseases.

@@United States
March 18, 2011, 6:37 PM ET.Radioactive Isotope Detected in California.
By Tennille Tracy
WASHINGTON–U.S. officials detected the presence of a radioactive isotope in California on Friday that appeared to come from the Fukushima nuclear-power plant in Japan, but the levels they detected were minuscule–far less than a person would normally receive  from the sun, rocks or other natural sources.
U.S. officials say the levels are consistent with their expectations and pose no risk to human health.
The Environmental Protection Agency and the Energy Department said in a statement a radiation monitor in Sacramento, Calif., detected minuscule quantities of the radioactive isotope xenon-133.  The readings validated similar ones from March 16 and 17 taken from monitors in Washington state, they said.
The agencies said the radioactive isotope appears to have come from the Japanese power plant damaged in the wake of the earthquake and tsunami there. Energy Secretary Steven Chu said earlier in the week he believed a “partial meltdown” had occurred at the plant.
The levels detected in California were about 0.1 disintegrations per second per cubic meter of air, a dose rate equal to one-millionth of what a person normally receives from rocks, bricks, the sun and other natural background sources, the statement said.
On Tuesday, EPA announced it had deployed additional radiation monitors to Hawaii, Alaska, Guam and the Northern Mariana Islands.


Some radioactive isotopes of xenon, for example, 133Xe and 135Xe, are produced by neutron irradiation of fissionable material within nuclear reactors.[7] 135Xe is of considerable significance in the operation of nuclear fission reactors. 135Xe has a huge cross section for thermal neutrons, 2.6×106 barns,[11] so it acts as a neutron absorber or "poison" that can slow or stop the chain reaction after a period of operation. This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production. Fortunately the designers had made provisions in the design to increase the reactor's reactivity (the number of neutrons per fission that go on to fission other atoms of nuclear fuel).[69] 135Xe reactor poisoning played a major role in the Chernobyl disaster.[70] A shutdown or decrease of power of a reactor can result in buildup of 135Xe and getting the reactor into the iodine pit.

Under adverse conditions, relatively high concentrations of radioactive xenon isotopes may be found emanating from nuclear reactors due to the release of fission products from cracked fuel rods,[71] or fissioning of uranium in cooling water.[72]

Radioactive contamination may also be an inevitable result of certain processes, such as the release of radioactive xenon in nuclear fuel reprocessing. In cases that radioactive material cannot be contained, it may be diluted to safe concentrations.

131mXe, 133Xe, 133mXe, and 135Xe are some of the fission products of both 235U and 239Pu, and therefore used as indicators ofnuclear explosions.
The artificial isotope 135Xe is of considerable significance in the operation of nuclear fission reactors135Xe has a huge cross section for thermal neutrons, 2.65×106 barns, so it acts as a neutron absorber or "poison" that can slow or stop the chain reaction after a period of operation. This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production. Fortunately the designers had made provisions in the design to increase the reactor's reactivity (the number of neutrons per fission that go on to fission other atoms of nuclear fuel).
Relatively high concentrations of radioactive xenon isotopes are also found emanating from nuclear reactors due to the release of this fission gas from cracked fuel rods or fissioning of uranium in cooling water. The concentrations of these isotopes are still usually low compared to naturally occurring radioactive noble gases such as 222Rn.

isotopic mass (u)
mode(s)[5][n 1]
isotope(s)[n 2]
(mole fraction)
range of natural
(mole fraction)
excitation energy
110Xe5456109.94428(14)310(190) ms
[105(+35-25) ms]
111Xe5457110.94160(33)#740(200) msβ+ (90%)111I5/2+#
α (10%)107Te
112Xe5458111.93562(11)2.7(8) sβ+ (99.1%)112I0+
α (.9%)108Te
113Xe5459112.93334(9)2.74(8) sβ+ (92.98%)113I(5/2+)#
β+p (7%)112Te
α (.011%)109Te
β+, α (.007%)109Sb
114Xe5460113.927980(12)10.0(4) sβ+114I0+
115Xe5461114.926294(13)18(4) sβ+ (99.65%)115I(5/2+)
β+, p (.34%)114Te
β+, α (3×10−4%)111Sb
116Xe5462115.921581(14)59(2) sβ+116I0+
117Xe5463116.920359(11)61(2) sβ+ (99.99%)117I5/2(+)
β+, p (.0029%)116Te
118Xe5464117.916179(11)3.8(9) minβ+118I0+
119Xe5465118.915411(11)5.8(3) minβ+119I5/2(+)
120Xe5466119.911784(13)40(1) minβ+120I0+
121Xe5467120.911462(12)40.1(20) minβ+121I(5/2+)
122Xe5468121.908368(12)20.1(1) hβ+122I0+
123Xe5469122.908482(10)2.08(2) hEC123I1/2+
123mXe185.18(22) keV5.49(26) µs7/2(-)
124Xe5470123.905893(2)Observationally Stable[n 3]0+9.52(3)×10−4
125Xe5471124.9063955(20)16.9(2) hβ+125I1/2(+)
125m1Xe252.60(14) keV56.9(9) sIT125Xe9/2(-)
125m2Xe295.86(15) keV0.14(3) µs7/2(+)
126Xe5472125.904274(7)Observationally Stable[n 4]0+8.90(2)×10−4
127Xe5473126.905184(4)36.345(3) dEC127I1/2+
127mXe297.10(8) keV69.2(9) sIT127Xe9/2-
128Xe5474127.9035313(15)Observationally Stable[n 5]0+0.019102(8)
129Xe[n 6]5475128.9047794(8)Observationally Stable[n 5]1/2+0.264006(82)
129mXe236.14(3) keV8.88(2) dIT129Xe11/2-
130Xe5476129.9035080(8)Observationally Stable[n 5]0+0.040710(13)
131Xe[n 7]5477130.9050824(10)Observationally Stable[n 5]3/2+0.212324(30)
131mXe163.930(8) keV11.934(21) dIT131Xe11/2-
132Xe[n 7]5478131.9041535(10)Observationally Stable[n 5]0+0.269086(33)
132mXe2752.27(17) keV8.39(11) msIT132Xe(10+)
133Xe[n 8][n 7]5479132.9059107(26)5.2475(5) dβ-133Cs3/2+
133mXe233.221(18) keV2.19(1) dIT133Xe11/2-
134Xe[n 7]5480133.9053945(9)Observationally Stable [n 9]0+0.104357(21)
134m1Xe1965.5(5) keV290(17) msIT134Xe7-
134m2Xe3025.2(15) keV5(1) µs(10+)
135Xe[n 10]5481134.907227(5)9.14(2) hβ-135Cs3/2+
135mXe526.551(13) keV15.29(5) minIT (99.99%)135Xe11/2-
β- (.004%)135Cs
136Xe5482135.907219(8)Observationally Stable [n 11]0+0.088573(44)
136mXe1891.703(14) keV2.95(9) µs6+
137Xe5483136.911562(8)3.818(13) minβ-137Cs7/2-
138Xe5484137.91395(5)14.08(8) minβ-138Cs0+
139Xe5485138.918793(22)39.68(14) sβ-139Cs3/2-
140Xe5486139.92164(7)13.60(10) sβ-140Cs0+
141Xe5487140.92665(10)1.73(1) sβ- (99.45%)141Cs5/2(-#)
β-n (.043%)140Cs
142Xe5488141.92971(11)1.22(2) sβ- (99.59%)142Cs0+
β-, n (.41%)141Cs
143Xe5489142.93511(21)#0.511(6) sβ-143Cs5/2-
144Xe5490143.93851(32)#0.388(7) sβ-144Cs0+
β-, n143Cs
145Xe5491144.94407(32)#188(4) msβ-145Cs(3/2-)#
146Xe5492145.94775(43)#146(6) msβ-146Cs0+
147Xe5493146.95356(43)#130(80) ms
[0.10(+10-5) s]


From Wikipedia, the free encyclopedia
Xenon-135 (135Xe) is an unstable isotope of xenon with a half-life about 9.2 hours. 135Xe is a fission product of uranium and Xe-135 is the most powerful known neutron-absorbing nuclear poison (2 million barns[1]), with a significant effect on nuclear reactor operation. The ultimate yield of xenon-135 from fission is 6.3%, though most of this is from fission-produced tellurium-135 and iodine-135.



[edit]135Xe effects on restart

During periods of steady state operation at a constant neutron flux level, the 135Xe concentration builds up to its equilibrium value for that reactor power in about 40 to 50 hours. When the reactor power is increased, 135Xe concentration initially decreases because the burn up is increased at the new higher power level. Because 95% of the 135Xe production is from decay of iodine-135, which has a 6 to 7 hour half-life, the production of 135Xe remains constant; at this point, the 135Xe concentration reaches a minimum. The concentration then increases to the new equilibrium 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 135Xe concentration change is greater for a larger change in power level. When reactor power is decreased, the process is reversed.[2]
Iodine-135 is a fission product of uranium with a yield of about 6% (counting also the iodine-135 produced almost immediately from decay of fission-produced tellurium-135).[3] This 135I decays with a 6.7 hour half-life to 135Xe. Thus, in an operating nuclear reactor, 135Xe is being continuously produced.135Xe has a very large neutron absorption cross-section, so in the high neutron flux environment of a nuclear reactor core, the 135Xe soon absorbs a neutron and becomes stable 136Xe. Thus, in about 50 hours, the 135Xe concentration reaches equilibrium where its creation by 135I decay is balanced with its destruction by neutron absorption.
When reactor power is decreased or shut down by inserting neutron absorbing control rods, the reactor neutron flux is reduced and the equilibrium shifts initially towards higher 135Xe concentration. The 135Xe concentration peaks about 11.1 hours after reactor power is decreased. Since 135Xe has a 9.2 hour half-life, the 135Xe concentration gradually decays back to low levels over 72 hours.
The temporarily high level of 135Xe with its high neutron absorption cross-section makes it difficult to restart the reactor for several hours. The neutron absorbing 135Xe acts like a control rod reducing reactivity. The inability of a reactor to be started due to the effects of 135Xe is sometimes referred to asxenon precluded start-up, and the reactor is said to be "poisoned out"[4]. The period of time where the reactor is unable to override the effects of 135Xe is called the xenon dead time.
If sufficient reactivity control authority is available, the reactor can be restarted, but a xenon burn-out transient must be carefully managed. As the control rods are extracted and criticality is reached, neutron flux increases many orders of magnitude and the 135Xe begins to absorb neutrons and be transmuted to 136Xe. The reactor burns off the nuclear poison. As this happens, the reactivity increases and the control rods must be gradually re-inserted or reactor power will increase. 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, 135Xe concentration falls for about 3 hours.[5]
Failing to manage this xenon transient properly caused the Chernobyl reactor power to overshoot ~100x normal causing a steam explosion.[citation needed] The xenon burn-out rate is proportional to neutron flux and thus reactor power. If reactor power doubles, the xenon burns out twice as quickly. The larger the rate of increase in reactor power, the faster the xenon burns out and the more quickly reactor power increases.
Reactors using continuous reprocessing like many molten salt reactor designs might be able to extract 135Xe from the fuel and avoid these effects. Fluid fuel reactors cannot develop xenon inhomogeneity because the fuel is free to mix. Also, the Molten Salt Reactor Experiment demonstrated that spraying the liquid fuel as droplets through a gas space during recirculation can allow xenon and krypton to leave the fuel salts. However, removing xenon-135 from neutron exposure also means that the reactor will produce more of the long-lived fission product caesium-135.

[edit]Decay and capture products

135Xe that does not capture a neutron decays to Cs-135, one of the 7 long-lived fission products, while 135Xe that does capture a neutron becomes stable 136Xe. Estimates of the proportion of 135Xe during steady-state reactor operation that captures a neutron include 90%,[6] 39%–91%[7] and "essentially all".[8]
136Xe from neutron capture ends up as part of the eventual stable fission xenon which also includes 136Xe, 134Xe, 132Xe, and 131Xe produced by fission and beta decay rather than neutron capture.
133Xe, 137Xe, and 135Xe that has not captured a neutron all beta decay to isotopes of caesium. Fission produces 133Xe, 137Xe, and 135Xe in roughly equal amounts, but after neutron capture, fission caesium will contain more stable 133Cs (which however can become 134Cs on further neutron activation) and highly radioactive 137Cs than 135Cs.

[edit]See also


  1. ^ Chart of the Nuclides 13th Edition
  2. ^ DOE Fundamentals Handbook: Nuclear Physics and Reactor Theory, Vol. 2, pp. 35–42.
  3. ^ DOE Fundamentals Handbook: Nuclear Physics and Reactor Theory, Vol. 2, p. 35.
  4. ^ Crist, J. E.. "Xenon, A Fission Product Poison". Retrieved 2 November 2011.
  5. ^ Xenon decay transient graph
  6. ^ CANDU Fundamentals: 20 Xenon: A Fission Product Poison
  7. ^ Utilization of the Isotopic Composition of Xe and Kr in Fission Gas Release Research
  8. ^ The Influence of Xenon-135 on Reactor Operation

[edit]Further reading

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