ML19323B674

Development of Process for Removing Kr-85,C-14 & Other Contaminants from Off-Gas of Fuel Reprocessing Plants, Presented at 14th Erda Air Cleaning Conference

ML19323B674
Person / Time
Site:	Crane
Issue date:	04/24/1980
From:	Eby R, Stephenson M UNION CARBIDE CORP.
To:
Shared Package
ML19323B642	List: ML19323B645 ML19323B647 ML19323B649 ML19323B651 ML19323B654 ML19323B657 ML19323B662 ML19323B667 ML19323B670 ML19323B674 ML19323B677 ML19323B680 ML19323B684
References
RTR-NUREG-0662, RTR-NUREG-662 K-GD-1398, NUDOCS 8005140057
Download: ML19323B674 (15)

Text

14th ERDA AIR CLEANING CONFERENCE 8 005140M 7 K-GD-1398 DEVELOPMENT OF THE FASTER PROCESS FOR RE::OVING KRYPTON-85, CARSON-14, AND OTHER CONTAMINANTS FROM THE OFF-GAS OF FUEL REPROCESSING PLANTS

• M.

J.

Stephenson and R.

S.

Eby Union Carbide Corporation Nuclear Division Oak Ridge Gaseous Diffusion Plant Oak Ridge, Tennessee Abstract The Oak Ridge Gaseous Diffusion Plant has the primary responsi-bility for the development of the FASTER (Fluorocarbon Absorption System for Treating Effluents from Reprocessors) process for applica-tion to LMFBR and LWR fuel reprocessing plants.

Krypton-85 removals in excess of 99.9% and carbon-14 as carbon dioxide removals greater than 99.99% have been obtained in a development pilot plant.

So far, pilot plant tests show that the presence of other reprocessing plant off-gas components does not appreciably affect the general operability or removal efficiency of the process.

Tests also indicate that the one process designed for krypton and carbon removal may be even more effective in removing other fission products and objectionable chemi-cal contaminants such as nitrogen dioxide.

Elemental and organic l

iodine removals in excess of 99.99% and nitrogen dioxide removals over 99% were recently achieved.

Higher process decontaminations are possible.

Trapping studies show that 13X molecular sieves are very i

effective in removing the fluorocarbon vapor from the process product stream.

I.

Introduction Stringent emission standards are being formulated to limit the release of various volatile fission products from nuclear fuel cycle facilities.

At this time, the viability of the nuclear fuel cycle rests, in part, on how well the industry can effectively manage all the associated nuclear wastes.

The long-lived isotopes of krypton and carbcn are of particular concern because the control technology has not yet been adequately demonstrated for removing either of these two fission products from the of f-gas of comn.ercial nuclear 'uel repro-cessing plants.

The generally straightforward problem of off-gas decentamination is greatly complicated in this case by the presence of other common reprocessing plant off-gas components such as nitrogen oxides (NO, N20, NO2), carbon dioxide, water, iodine, various organics, ruthenium tetroxide, and particulates.

In the case of carbcn-14, it is generally assumed that the volatile form of carbon will be carbon dioxide, although admittedly, quantities of carbon monoxife and light organics such as methane could also be present.

t

• This document is based on work performed at the Oak Ridge Gaseous Diffusion, Plant operated by Union Carbide Corporation, Contract W-7'05 eng 26 with the U.

S.

Energy Research and Development Administration.

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exchangers, and several refrigeration compressors.

Physical and chemical traps are also installed for solvent recovery and final product separation and purification.

Details of the process and development pilot plant are available in several program reports [3,4,5),

III.

Experimental Program Plan As currently envisioned, the krypton-85/ carbon-14 removal pro-cess will be the final step in an integrated chain of processes designed to collectively decontaminate fuel reprocessing plant off-gas.

The integrity and reliability of any off-gas decontamination system will undoubtedly be the subject of much scrutiny.

Legitimate concern will be expressed not so much about how well the off-gas train will function in a normal operation, but about the overall conse-quenccs of abnormal operation and the capability of the individual prccesses to meet the challenges imposed by irregular or otherwise uncontrolled feed conditions.

In this context, several fundamental questions need to be answered:

(1) what happens in the evert the upstream primary removal equipment fails and large amounts of other fissica products and chemical contaminants inadvertently pass down-stream; (2) can the downstream process (es) be relied upon as a short-term backup rystem to remove the other radioactive components from the reprocessing plant off-gas in case of such a failure; and (3) how well can the fluorocarbon process function as the princry removal facility for iodine and other fission products including ruthenium oxides, and chemical contaminants such as nitrogen dioxide.

Pilot P ant work is currently being directed toward exploring these points l

by establishing the general process behavior of feed gas components such as nitrogen oxides, iodine, methyl iodide, and water, and defining the effects of these components on the general operability and overall performance of a process designed for krypton-85 and carbon-14 removal.

Figure 3 gives the relative solubilities of various volatile feed gas components in the process solvent, refrigerant-12.

Xenon and carbon dioxide are the most soluble of this group, while helium is the least.

Figure 4 gives the predicted distribution coefficients of important feed gas components'that are classified as high boiling components relative to the solvent.

Those components more volatile than refrigerant-12 end up in either the process vent with the less soluble components, such as nitrogen and oxygen, or in the process product stream with the more soluble volatile components, such as kryp;cn and carbon dioxide; while the less volatile components, i.e.,

iodine and nitrogen dioxide, collect in the solvent still reboiler.

Water, not shown in figure 4, is more volatile than iodine but significantly less volatile than methyl iodide.

Because krypton and xencn removals in exces of 10' were achieved previously, high process rem:cals were projected "r the even less volatile feed gas com:Onents.

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14th ERDA AIR CLEANING CONFERENCE K-GD-1398 DEVELOPMENT OF THE FASTER PROCESS FOR REMOVING KRYPTON-85, CARSON-14, AND OTHER CONTAMINANTS 1

FROM THE OFF-GAS OF FUEL REPROCESSING PLANTS

• j M.

J.

Stephenson and R.

S.

Eby Union Carbide Corporation Nuclear Division i

Oak Ridge Gaseouc Diffusion plant Oak Ridge, Tennessee Abstract l

The Oak Ridge Gaseous Diffusion Plant has the primary responsi-bility for the development of the FASTER (Fluorocarbon Absorption System for Treating Ef fluents from Reprocessors) process for applica-tion to LMFBR and LNR fuel reprocessing plants.

Krypton-85 removals in excess of 99.9% and carbon-14 as carbon dioxide removals greater than 99.99% have been obtained in a development pilot plant.

So far, pilot plant tests show that the presence of other reprocessing plant off-gas components does not appreciably affect the general operability or removal efficiency of the process.

Tests also indicate that the one process designed for krypton and carbon removal may be even more effective in removing other fission products _and objectionable chemi-cal contaminants such as nitrogen dioxide.

Elemental and organic 1

iodine removals in excess of 99.99% and nitrogen dioxide removals over 99% were recently achieved.

Higher process decontaminations are

)

possible.

Trapping studies show that 13X molecular sieves are very ef fective in removing the fluorocarbon vapor from the process product l

stream.

I.

Introduction Stringent emission standards are being formulated to limit the release of various volatile fission products from nuclear fuel cycle facilities.

At this time, the viability of the nuclear fuel cycle rests, in part, on how well the industry can effectively manage all the associated nuclear wastes.

The long-lived isotopes of krypton and carben arc of particular concern because the control technology has

{

not yet bee. adequately demonstrated for removing either of these two fission procucts f rom the of f-gas of commercial nuclear fuel-repro-i cessing plants.

The generally straightforward problem of off-gas decentamination is greatly complicated in this case by the presence of other commen reprocessing plant off-gas components such as nitrogen oxides (NO, N2 0, NO2), carbon dioxide, water, iodine, various organics, ruthenium tetroxide, and particulates.

In the case of carbcn-14, in is generally assumed that the volatile form of carbon will be carbon dioxide, although admittedly, quantities of carbon monoxide and light organics such as methane could also be present.

0 -This document is based on work performed at the Oak Ridge Gaseous Diffusion Plant operated by Union Carbide Corporation, Contract W-7405 eng 26 with the U.

S.

Energy Research and Development Administration.

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Pilot Plant Test Results r-4 3,h '

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7 Krypton absorption data were obtained several' years agd and~ massy

C transfer correlations developed to describe the absorption 5phehour-2$.yj i

ena[1,2].

Most of these tests, however, were conducted with a:

$, 4y nitrogen feed gas containing only krypton.

Recentpilotplant, tests'l'?7' have been made with nitrogen feed gases containing (1) 0.1 ppm Kv, e%,.

.c (2) 0.1 ppm Kr and, in addition, between 1000 and 3000' ppm CO.gend 1.}.jf,

,0, 2. between 6000 and 7000 ppm N 0, (3) 0.1 ppm Kr and no feed gas toolor:47' 2

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(4) 0.1 ppm Xe, and (5) up to 61 carbon dioxide.

The results'of.the4e'.s

.. ' tests are summarized in figure 5.

Krypton tests were performed'withj..

g 1 to 1.5 curies of Kr-85 and gamma scintillation techniques were used r _

c o-to analyze krypton process performance.

Xenon tests were Mrformed n 3 E'

with 1 to 2 curies of Xe-133.

Refrigerant-12, carbon dioxide, and P

nitrous oxide analyses were performed with an in-l'ine infrared,a'na lyzer.

Oxygen, nitrogen, and refrigerant-12 determinations were made O

with an in-line gas chromatograph and laboratory mass spectrometer.

All tests were conducted at an absorber pressure of 300 psig, tempera-

'c ture between -25 and +10 F, solvent flow of 0.75 or 1.0 gpm, and feed

-gas flow between 7.5 and 22 scft.

.i c Pilot plant tests made with only krypton and nitrogen were repeated with high concentration of carbon dioxide and nitrous oxide y

(N20) to identify the effects of these very soluble. feed gas com-ponents on krypton distribution in the system.

The results of these i'

tests suggest that, at least for the absorption step, the presence of 1

other soluble feed gas components has no discernible ef fect on the process removal of krypton.

Of course, the soluble components con-centrate with the krypton and thereby dilute the krypton product.

This problem, however, is not a very difficult one because the. process product flow is only a small fraction of the reprocessing plant off-gas and can be handled in relatively small-scale equipment.

Several-product purification options are currently being evaluated to separate 3

and isolate the krypton-85 and carbon-14Id.

Hot-gas feed is being considered as an alternative to desubli-mation of certain feed gas components such as todine 'and water in the process gas cooler.

In absence of the gas heaf ~ exchanger, the bottom J

of the absorber column will serve as the cooling section for the in-coming feed gas and will allow the condensable and desublimable com-ponents to pass directly into solution.

Comparison of plant tests with and without the feed gas cooler shows that the~overall effect'of the hot-gas feed on the process performance is small.

Xenon and carbon dioxide removals in exce,ss of 99.99% were measured in pilot plant tests conducted at the same absorber co,ndi-tions that yielded around 99% krypton removals.

Carbon dioxide removals were a little higher than those measured for xenon.

This is consistent with component solubilities given in. figure 3.

Based on pilot plant data, HOG values for Xe and CO2 were 6 to 10 inches.

Significant amounts of carbon dioxide and xenon were found in the recycle solvent for those tests where final stripper molar L/V ratios above 2.0 existed.

The absorber performance was noti.ceably affected by the recycle concentration in those cases where process removals l

exceeded 99.99%.

Substantially better carbon dioxide removals were obtained in runs where higher stripper vapor..upflow's wers maintained.

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iodine are summarized in table I.

The methyl iodide tests were rela,-

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tively straightforward to perform and evaluate.

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prepared containing CH I tracedwith5mcofI-131andsubsequen,tly3.[(,[,

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metered into the absorber feed gas line in the amount necessaryeto-lf ? -

give the desired feed gas composition.

No transport problems werePf_

evident.

Elemental iodine, on the other hand, was difficult to feed Y

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and reluctant to move through the feed gas circuit even though the gas lines were heated.

For these tests, solid iodine containing 5 mc of I-131 was placed on a finely divided support screen inside a feed cylinder and a pickup sweep gas flow was then diverted through the cylinder and routed to the absorber.

Upon contacting the solvent, became uobile until collected in the solvent still reboiler. u I 2Elemental and organic iodine removals in excess of 10" were achievedi Gamma scintillation analytical techniques were again used to evaluate process performance.

The small amount of activity relative to the plant size and long duration of the tests largely limited the quabti.

tative capability of the counting equipment, since process removals were quite high and the off-gas in most cases contained an undectable amount of iodine.

In some cases, the absorber performance could be calculated from the amount of activity in the recycle solvent by assuming that the absorber off-gas was in equilibrium with the in -

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coming solvent.

The test results clearly show that the ef ficiency of the p'roce'ss g

I to remove methyl iodide is definitely established by the performance of the solvent purification still.

Elemental iodine, on the other.

hand, was much easier to remove from the recycle solvent.

At the 1

i,-

conditions of the still, i.e.,

-10'F, the volatility of refrigerant 12 5

rela tive to methyl iodide is 24.

This value is greater than 10 for '

elemental iodine.

Increasing the reflux ratio in the solvent still from 0.13 to 0.34 (tests 7 and 8) resulted in a significant reduction in the amount of methyl iodide in the recycle solvent and improved,the process removal efficiency by a factor of 4.

The effect of any re-cycled iodine on the process removal efficiency could not be deter-mined because the iodine recycle concentrations were below the level of detection.

The test data clearly indicate that higher-reflux

' ratios and more rectifying stages will significantly improve the recovery capability of the process.

It is important to point out that water and elemental iodine are significantly less volatile than methyl iodide, and consequently, these two components are much pasier to remove from the solvent.

Therefore, a process designed to achieve 6

a methyl iodide decontamination factor of 10 should be capable of even higher elemental iodine and water removals.

The results of the nitrogen dioxide removal experiments.are summarized in figure 6.

More than 2 months of the recent test series was devoted to studying the long-term process behavior of NO2 A,

spectrophotometric analyzer having the capability of detecting from was used for direct in-line concentration 1 to more than 6,000 ppm NO2 determinations.

Process removal eff.'<iencies between 97 and 99.9%

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Absorber Pressure, 300 psig: Absorber Temperature, -10*F; Solvent Flow, 1 gallon /minutc.

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Fluorocarbon Process Removal of Nitrogen Dioxide as a Function of Feed Gas Composition.

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were achieved.

No feed problems were encountered, and process effects due to the presence of the NO2 in the feed gas and solvent lines were not observed.

The data suggest that the removal of NO2 is strongly dependent upon the feed concentration.

This is contrary to previous experience with the less volatile components, I 2 and CH I, and the 3

more volatile components, krypton and xenon.

For one series of tests, the concentration of NO2 in the absorber off-gas remained around 20 ppm regardless of the absorber feed gas flow or inlet concentra-tion.

This, of course, again indicates inadequate removal of high boiling components from the recycle solvent.

The absorber off-gas concentration did decrease with an increase in the solvent still reflux but not to the extent that was found for the methyl iodide tests.

This was not surprising since NO2 is more volatile than CH I 3

and thereby more difficult to remove from the solvent.

Another important part of the overall ORGDP development program is evaluation of process auxiliary subsystems.

As part of this work, trapping studies were initiated to evaluate solid adsorbents for removing refrigerant-12 vapor from the process vent and krypton product.

The results of these tests are given in table II.

An ideal sorbent was identified as one that could reduce the refrigerant con-centration in the procets off-gas from a nominal 10% to less than 1 ppm.

Three sorbent materials were initially considered:

5A molecu-lar sieve, 13X molecular sieve, and H-151 alumina.

Tests were con-ducted with 3-inch-diameter traps filled to a height of 4 feet with the test material.

Initial bed temperatures were generally around 70 to 80'F.

Tests were conducted with a total gas flow (R-12 and N )

2 of 1934 scem (0.02 ft/sec superficial velocity), 11,670 seem (0.08 ft/sec), and 120,000 seem (0.8 ft/sec).

The SA molecular sieve material proved to be unsatisfactory.

Trap effluent contained 8.2 ppm before breakthrough, and the sorbent loading was only 0.5% at break-through.

The alumina bed still could not achieve the desired refrigerant vapor removal.

The trap effluent contained 10 ppm before breakthrough and refrigerant loading on the alumina varied between 2.2 and 2.9%.

On the other hand, the 13X molecular sieve proved to be an excellent trapping material for the process solvent.

The trap effluent contained less than 1 ppm R-12 and the 13X sieve loaded up to 301.

External cooling of the sorbent bed improved the loading capacity of the sieves.

Regeneration studies showed that the loaded 13X sieves could be completely regenerated with a 350 F nitrogen sweep flow of 194 1pm in 6 to 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />.

V.

Solvent Chemistry The laboratory support work is being performed at ORNL by L. M.

Toth, J.

T.

Bell, and D. W.

Fuller.

The initial program i.s designed to maluate distribution coefficients of the various feed gas components in re'.rigerant-12, look at component interactions in a multicomponent system, and identify possible corrosion conditions that could develop.

Undoubtedly, this important effort will be expanded as the program progresses.

Work in this area was only initiated recently but a substantial amount of data has already been obtained.

Several aspects of the physical and chemical behavior of I 2 in R-12 have been examined by absorption spectrophotometry in a high pressure optical cell.

Iodine in R-12 has an electronic absorption band in the visible light region at 520 nm arising from a solvated 12 molecular species.

l-t i

'\\

Table II.

Summary of R-12 Adsorption Studies for the Product 1

l'urification and Solvent Recovery Subsystems V

Total Fced Feed Ded Temp.,

Dreakthrough 11-12 in Effluent Test

Flow, Componitiont, "P

Time nefore arcak, Regeneration Scheme Number

• Adsorbent Cycle scem 1 R-12 Ritial Final _

hr "A R-125 ppm Temp.,

'F Time, hr 1

SA Sieve 1

1,934 9.5 65 s65 0.45 0.40 8.2 375 2.2

!!-151 2

1 1,934 9.5 75 s75 2.50 2.3 10.1 440 3.6 Alumina H-151 1

2 1,934 9.5 69 s69 2.00 1.9 10.7 430 1.7 Alumina H-151 4

3 11,670 10.0 77 80 0.30 1.7 19.0 420 1.5 Alumina 5

1;X Sieve 1

1,934 9.5 75 98 19.50 25.9

<1 375 4.0 6

13X Sieve 2

11,670 10.0 78 127 2.67 22.3 150**

330 6.0 7

13X Sieve 3

11,670 10.0 85 139 2.67 22.0

< 1 350 7.7 8

13X Sieve 4

11,670 10.0 68 86tt 2.92 24.8

< 1 360 6.5 9

13X Sieve 5

1.2 = 10' 3.1 73 85tt 1.17 30.6

<1 350 6.0 5

10 13X Sieve 6

1.2 x 10 3.1 73 87tt 1.12 29.5

< 1 360 6.0 8

11 13X Sieve 7

1.6 x 10 2.3 88 145 0.5 13.3

<1 360 6,0 5

12 13X Sleve 8

1.6 = 10 2.3 75 113tt 0.7 18.4

<1 340 6.0 4

e

. y

• All tests except 11 and 12 conducted at 1.5 psig in a nominal 3-inch-diameter trap with 0.0513 ft i

8 (47.6 cm') crose section. Tests 11 and 12 were made at 21 psig.

~ ' t The bulk gas is nitrogen.

.$..- )[ N h.

E 4

-l R-12 loading defined as [(1b R-12 adsorbed)/(lb adsorbent))

• 100.

Y -. N,

'3,'

1 l* The previous regeneration of 375'r for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> was not suffig, tent to regenerat'e the 13X sieve koeded hkring thh k $W previous tests hence, the high con::entration of M-12 in the af fluent.

Or-./ D/Aa+ l,

,[ n.e.d ;j i f.,," r. _'..

.r.'

., g %v ~W.n. p.

f t These. tests conducted using external bed cooling.

q., 4 yQ. 1 p.t. tw 1

g m

,. ~-,

).

s.

g Nt 7

p 15 !"..e. A,w, p < =~. NM NC Q.

l%...

_ ^

F

-s w$j q _, A,,,

g t

r

.,, n,. h,,,~ :.

4

, -

• l u p u j.,q n

e.

• e'

.t' t

't -.",,, :W D,* % a ; 4%

j l 4t b ' '* ; ?

.h

.h

. t.w.gg7g'g).

~

s r.

,c r

.3 %..,.

x m

e s

s

~

gg, m,s !.,N;m p.;g;; % 4 c_c.q,

..a

.-..,.t

" C.%

?.

P~.t'J%

'y)**

1

~

14th ERDA AIR CLEANING CONFERENCE In the absence of any added water, dilute solutions of iodine in refrigerant-12 are not expected to chemically react with either the solvent or stainless steel containment.

There is some indication, however, that refrigerant-12 solutions of iodine containing excessive amounts of free water might interact with stainless steel.

The solubility and distribution coefficient of iodine is currently being i

measured as a function of temperature.

Later, the solution effects of free water will be determined.

VI.

Conclusions Recent and more detailed pilot plant tests continue to support hypotheses orawn from earlier scoping tests and performance calcula-tions[2].

In short, the fluorocarbon-based process is versatile, has a high tolerance for feed gas impurities, and can function in a multiplicity of ways to clean up reprocessing plant off-gas and isolate the many contaminants for long-term storage and disposal.

Tests show that a process designed to remove krypton-85 and carbon-14 can also achieve high iodine, methyl iodide, water, and nitrogen dioxide decontaminations.

A comprehensive pilot plant testing program and an exhaustive solvent chemistry laboratory effort are continuing l

to fully define the capability and limitations of the PASTER process.

If the process developnent program proceeds according to schedule, sufficient information will be available within 3 years to begin final design of an LMFBR or IWR demonstration plant.

So far, no detrimental 1

effects due to the presence of the various feed gas components in the fluorocarbon process have been uncovered except maybe a possible cor-rosion problem that could develop in a stainless steel system if free water is present.

Materials of construction will be selected after the solvent chemistry work has been completed and possible corrosion mechanisms identified.

Substantially more testing is required at this point before the process can be fully evaluated.

VII.

References fl]

J.

R.

Merriman, Analysis of a Multicompcnent Gas Absorption System with Carrier Gas Ccabsorption, U.S.E.R.D.A.

Report KY-G-300, j

Paducah, Kentucky (1975).

4 i

[2]

M.

J.

Stephenson, et al.,

" Experimental demonstration of the selective absorpticn process for Kr-Xe removal", Proceedings of the Twelfth AEC Air Cleaning Conference, 11-27 (1973).

l

[3]

M.

J.

Stephenson, et al.,

" Absorption process for removing krypton from the off-gas of an LMFBR fuel reprocessing plant", Proceedings of the Thirteenth AEC Air Cleaning Conference, 263-275 (1975).

[4]

M.'J.

Stephenson, et al., Fluorocarbon Absorption Process for the Recovery of Krypton from the Off-Gas of Fuel Reprocessing Plants, U.S.E.R.D.A.

Report K-GD-1390, Oak Ridge, Tennessee (1976).

[5]

M.

J.

Stephenson and R.

S.

Eby, ORGDP Selective Absorption Pilot Plant for Decontamination of Fuel Reprocessing Plant Off-Gas, j

U.S.E.R.D.A.

Report K-1876, Oak Ridge, Tennessee (In Progress).

i

~,,

.