US3080262A

US3080262A - Process for removal of radioactive contaminants from surfaces

Info

Publication number: US3080262A
Application number: US804573A
Authority: US
Inventors: Newman Kenneth Walter
Original assignee: Purex Corp
Current assignee: Purex Corp
Priority date: 1959-04-07
Filing date: 1959-04-07
Publication date: 1963-03-05
Anticipated expiration: 1980-03-05

Description

BhdilfifiZ Patented Friar. 5, i953 fine This invention relates to the radioactive decontamination of surfaces on which are deposited radioactive materials, and is particularly concerned with removal of radioactive contaminants from the surfaces of components of nuclear power generating equipment.

Atomic reactor systems for power generation include as a major portion of the system a high temperature high pressure water recirculation loop or piping and associated equipment from the pile to the steam generating plant. Each such loop system, in addition to the loop piping, is composed of a number of components such as valves, pumps, agitators, flanges and the like, which require a substantial amount of contact maintenance work.

During operation of the system, fuel element ruptures occasionally occur in the reactor, resulting in the introduction of uranium dioxide and fission products into the high temperature water in the loop. Such radioactive contamination sources circulated by the loop water tend to accumulate on the internal surface of the loop piping and associated equipment. Such accumulation of radioactive contaminants increases to the extent that, in the absence of proper decontamination, expo-sure rates for personnel involved in contact maintenance of the equipment, poses a major problem.

In operation of the loop system the water in the high temperature high pressure loop piping also reacts with the base metal of the loop, which may be carbon or stainless steels, or cobalt, titanium or zirconium alloys, forming in situ on the internal surface of the loop components a tight obdurate adherent scale, and also forming an oxide of some unknown composition with said base metal or their alloying elements, which settles out as a loose deposit or crud on the surface of the tight adherent scale. The aforementioned radioactive contamination products tend to settle into and to become occluded in these scale deposits. Most of the high intensity radioactive emitters accumulate in the tight adherent scale on the internal surface of the loop. The less intense forms of radioactivity present in the loop water tend to become entrapped in the loose scale or crud.

Ineffective decontamination of the loop system and assoicated equipment of nuclear generating systems has hampered necessary maintenance of these systems and causes frequent costly shutdowns in operation. The tight adherent scale formed on the internal surface of the components of this system is extremely dimcult to remove. However, it has been found, surprisingly, that removal of the tightly adherent scale and crud formed on the internal surface of the loop in nuclear power generating systems does not necessarily result in removal of radioactive contaminants since said contaminants may redeposit on the internal surface of the equipment during such scale removal. Hence the basic decontamination problem is the removal of the contaminating products from the loop system regardless as to whether scale deposits are or are not removed during the decontamination process.

Various prior art methods have been tried in an effort to solve the aforementioned decontamination problem, including sand blasting, electrolytic procedure, and use of a variety of chemical treating baths such as hydrofiuoric acid, ammonium per sulfate, alkaline permanganate, ammonium citrate, ethylenediamine tetraacetic acid, hexamethylene tetramine, hydrazine and sulfamic acid solutions, with some degree of effectiveness, but without producing the desired high degree of decontamination and freedom from corrosion desired in practice. In practically all of these prior art processes, the decontamination factor, defined as the ratio initial activity final activity was relatively low, that is, of the order of about 2 to 4.

It is an object of this invention to remove radioactive contaminants from surfaces, particularly from the internal surface of equipment employed in nuclear reactors or power generating systems.

Another object of the invention is the removal of radioactive contaminants from the scale formed on the internal surface particularly of the loop piping and associated equipment employed in nuclear reactors or power generating systems.

it is still another object to effect removal of radioactive contaminants from metal surfaces, with or without simultaneous removal of scale formed on such surfaces.

A still further object is the removal of radioactive contaminants from the internal surface of nuclear power generating equipment, resulting from contact of said surface with high pressure high temperature Water circulating through the loop of the system and carrying radioactive emitters such as fission products.

A still further object is the removal of radioactive contaminants from the internal surface of loop piping and associated equipment of a nuclear power generating system, together with both tight and loosely adherent scale formed on such surfaces, said contaminants having been deposited on said surface chiefly by the high pressure high temperature water circulated in said loop piping from the reactor to the power generating components of the system.

Still another object is to provide efficient processes for carrying out the aforementioned removal of radioactive contaminants employing chemical treating baths in rela tively short treating periods and resulting in high decontamination factors for the surfaces of the components treated.

Another particularly important object is the provision of processes for radioactive decontamination as aforementioned, employing treating baths having practically no corrosive effect on the base metal of the surface treated.

Other objects of the invention will be apparent from the following description of the invention.

1 have found that I can effectively remove radioactive contamination pursuant to the above objects, by contacting the surfaces to be decontaminated with an alkaiine solution containing an alkali and an aikanolamine, designated solution A. For best results and in preferred practice solution A also preferably contains a. complexing agent. I preferably also contact the surface requiring decontamination with an alkaline oxidizing solution, especially one which contains as essential components an alkali and a permanganate, and also preferably, but not necessarily, an alkali metal fluoride, and designated solution B. in preferred practice, I follow the aforementioned treatment of the surface to be decontaminated with an acid treatment, preferably an aqueous nitric acid solution, designated solution C. As will be noted hereinafter in greater detail, the surface to be treated can be contacted with solution A followed by solution B, or vice versa. In certain instances treatment with solution A alone results in effective decontamination, in which case treatment with solutions B and C can be dispensed with. In some cases, after treatment with solutions A and B in that sequence, this may be followed by treatment again in solution A,

although preferably the two initial treating steps are followed by treatment in the aforementioned acid solution C, or an equivalently functioning non-corrosive solution when the particular acid solution employed, e.g. nitric acid, is corrosive to the particular base metal involved, as described more fully hereinafter.

It is noteworthy that treatment of the contaminated surface according to the invention process is effective for practically complete removal of radioactive contaminants from metal surfaces, which contaminants may emit any one or more of the forms of radiation alpha, beta or gamma, and resulting in a high decontamination factor, irrespective of the presence of any scale on such surface, and whether or not the radioactive contaminants are present in such. scale. However, the invention process generally results in removal not onlyv of radioactive contaminants, but simultaneously also of scales of the type usually formed on the internal surface of water circulation equipment in the loop piping of nuclear power generating systems. Thus, such scale, both tightly adherent and loose, can be removed together with the source of radioactivity, but such scale removal is not necessary for achieving the primary result, namely, decontamination. Thus, for example, the outer surface of the nuclear power generating components often contains radioactive surface contaminants which can be removed substantially in the absence of any scale on such outside surface. The process of the instant invention achieves marked improvement over prior art processes, as will be shown hereinafter, while prroducing substantially no corrosion of the base metal surface.

Solution A, which is preferably employed as the first treating step for contacting the surface to be decontaminated, is preferably applied as a concentrated alkali solution of alkali metal hydroxide, e.g., KOH, complexing agent such as acetic acid or hydroxy acetic acid, and alkanolamine, e.g., triethanolamine. If desired, such solution can be used also in diluteform.

In the highly alkaline solution A the amount of alkaline material employed may range from about 5 to about 55% of alkali metal hydroxide based on the weight of the solution. Preferably, from about to about of alkali, most desirably potassium hydroxide, is used to obtain the desired high alkalinity.

In these solutions there also are incorporated preferably compounds in. the form of certain complexing agents or salts, to act in conjunction with the alkali. These salts are derived from an aliphatic hydroxy acid such as hydroxy'acetic acid, lactic, citric, tartaric, gluconic, glyceric, malic, glycollic acid and saccharic acid. When the free acids are incorporated in the alkaline solution, the corresponding alkali metal salts will be formed. These salts or mixtures of these salts may be employed for the above purpose. Low molecular weight fatty acid such as acetic or propionic acid may also be employed. These latter salts, however, are not as useful in such solutions as are the salts of the hydroxy acids referred to above. They may be used effectively particularly if used together with the hydroxy acids. The soluble salts of the above acids also can be employed, preferably the potassium or sodium salt, for example potassium or sodium acetate or potassium or sodium glycollate. The quantity of these complexing salts added to the solution may vary, but generally from about 1 to about by weight of such complexing agents can be present in the treating solution in water, amounts of about 4 to about 40% usually being employed. These salts can be used separately or in admixture with each other, and function to a degree in complexing scale components, e.g., oxides of the base metal, and in complexing radioactive contaminants to facilitate removal of the scale and the radioactive contaminants.

Also, alkanolamines are employed in the above alkaline solutions preferably containing the salts of the aliphatic hydroxy acids or low molecular weight fatty acids. As 'ilkanolamines the polyalkanolamines are preferably employed, particularly those which form stable dispersions or solution in the water system of the composition at the operating temperatures of 200 to 300 F. and are not decomposed by pyrolysis at such temperatures under the conditions of proposed use. Examples of suitable polyalkanolmonoamines with their boiling points and vapor pressures (at 20 C.) of the pure compounds are set out below.

Other suitable polyalkanolrnonoamines are hydroxypropyl diethanolamine, hydroxyethyl diiso-propanolamine, N,N-dihydroxethyl glycine, and glycol or polyglycol derivatives of triethanolamine and polyetherglycol derivatives. of triethanolarnine having the general constitutional formula (C H CHZOXGH where a+b+c equals from 3-6, both inclusive. Triethanolamine or homologues thereof wherein one or two of the hydroxyethyl groups are replaced by hydroxypropyl groups should be present either alone or together with one or more other suitable monoamines or polyamines described below.

I may also use alkanolpolyarnines, preferably polyalkanolpolyamines, having boiling points above 400 F. and similar low vapor pressures such as the polyalkanolpolyamines referred to below. Alkanolpolyamines may be used to partially replace the alkanolrnonoarnines in like weight proportions or the alkanolpolyamines may be employed in additional weight proportions tothe polyalkanolmonoamines in the manner described hereinbelow to assist and improve the removal of radioactive emitters and scale deposits where the latter are present.

In preferred practice wother alkanolamine, preferably an alkanolpolyamine, is also incorporated with the poly alkanolmonoamine. The result is an improvement in overall decontamination ability and performance.

Examples of suitable alkanolpoly-amines for purposes of the invention have the following general formula:

1 /Rs N(OHzCHZNRS)n-CHZCH N where n equals 0 to 4, preferably 0 to 1. R R R R and R may be hydrogen, hydroxyethyl, hydnoxypropyl, or carboxymethyl groups. Where It equals 0 there is at least one hydroxy ethyl group present, and where there is only one hydroxyethyl group there is also present at least one car-boxymethyl group, and preferably two or three carboxymethyl groups. Where It is 1 or more, there are a plurality of hydroxyalkyl groups present, e.g 2 or more. All of these groups may be hydroxyethyl groups or hydroxypropyl groups, or a portion of these hydroxyalkyl groups may be hydroxyethyl and the remainder hydroxypropyl. Where there are two hydroxyalkyl groups present, there may also be present one or more carboxyrriethyl amazes groups. The hydroxypropyl structure can be any of the following structures:

Structure (1) is the grouping preferably employed.

Examples of suitable specific alkanolpolyamines where n equals 0 are tabulated below:

6 cresol and cresylic acid, polyatomic phenols such as dihydroxy benzenes and its homologues, triatomic phenols such as pyrogallol and its homologues, and higher polyphenols, which are sufficiently acid to form salts with alkali at the concentrations employed which are soluble in these aqueous compositions at the temperature of the treatment, say, at 125300 F. The alkali metal salts which are effective in this respect are the salts of phenol itself, the ortho, meta and para dihydroxy benzenes, and of the trihydroxy benzenes such as pyrogallic acid. These materials are generally compatible with the alkali solutions.

The alkanolpolyamines listed in Table Ia have boiling points above 400 F.

Of the above compounds in Table la the tetra-kis N-hydroxyethyl ethylene diamine (compound 13), the tetrakis N-hydroxypropyl ethylenediamine (compound 15), N-monohydroxyethyl, N-trihydroxypropyl ethylene diamine (compound 16), and N-dihydroxyethyl, N-dihydroxypropyl ethylene diamine (compound 17) are of particular importance. Examples of polyalkanolpolyamines where n is 1 or more are pentahydroxyethyl diethylene triamine, hexahydroxyethyl triethylene tetramine and heptahydroxyethyl tetraethyl pentamine.

Preferably these alkanolpolyamines should not be so extensively substituted as to disadvantageously impair their solubility and stability in the alkaline solution or to disadvantageously alter their characteristics as an alkanolpolyamine.

The amount of alkanolamine employed, which may be polyalkanolmonoamine alone, or which may include both polyalkanolmonoamine in combination with aikanolpolyamine, is generaily in the range or" about 2.5 to about preferably about 10 to about 30%, by weight of the solution. Where, as in preferred practice, the alkanolmonoamines are employed in admixture with alkanolpolyamines, the range of ratios of the amounts of monoamine to polyamine by weight can be between about 1 part monoamine to 1 part polyamine, to about parts mono amine to 1 part polyamine, but preferably this range of ratios is between about 1:1 to about 10:1.

Phenols, which may be in the form of alkali metal phenates such as the potassium and sodium phenates, may also be added, if desired, to the above alkaline solution, preferably containing complexing salt and alkanolamine. Thus, the phenols, i.e., the monatomic phenols, are suitable such as hydroxybenzene and its homologues including Hence, such materials can be employed as additive to the treating reagent. Such phenates may be employed in amounts ranging up to about 20% by weight of the alkaline solution, generally about 3 to 15%.

A preferred alkaline solution of this type designated solution A can be produced by adding the ingredients listed below to water in the amount noted below.

In solution the acetic and hydroxy acetic acids will form the corresponding potassium salts.

The following illustrative solution, designated solution A' may also be employed.

Weight percent Solution A of solution Potassium hydroxide 17 Triethanolamine 15 Water 68 However, solution A is not a preferred form of treating solution.

Substantial decontamination of radioactive emitters can be realized in many cases using solution A, -e.g., solution A alone, Without further treatment. Thus, for example,

decontamination of carbon steel can be accomplished without appreciable corrosion simply by treatment in solution A However, best results are obtained employing solution B in conjunction with solution A.

The temperature of treatment using solution A is preferably about the boiling point of the solution, for example, in some instances about 280 F., or higher, although temperatures lower than 280 F. also can be employed. Time of treatment may vary greatly depending on the specific composition of the bath, its concentration and temperature, and the nature of the radioactive contamination and of the surface being treated. The period of treatment may thus vary from as low as 15 minutes to as much as 48 hours or longer.

Following treatment with solution A, the surface to be decontaminated is then preferably treated in the alkaline permanganate bath, which has an oxidizing action and is particularly effective for removal of radioactive contamination together with tightly adherent scale, where the latter is present, as in the case of decontamination of loop piping and associated nuclear equipment. Such permanganate solution contains an alkali metal hydroxide, e.g., sodium or potassium hydroxide, and a soluble permanganate, preferably alkali metal, e.g., potassium or sodium permanganate, as oxidizing agent. This composition may also contain an alkali metal carbonate. The amount of alkali metal hydroxide employed may range from about 1 to about 25% by Weight of solution, preferably about 10 to about 25 the amount of permanganate from about 0.4 to about 12% by weight of solution, preferably about 3 to about 9%. The amount of alkali metal carbonate employed may range from to about 15%, usually about 5 to 15% when used.

A typical solution of this type, designated solution B is as follows:

1 Gallon.

A preferred type of alkaline permanganate solution is one which contains a Water soluble inorganic fluoride derived from any source which produces fluoride-contain ing ion in strong alkaline solution. The fluoride may be a simple fluoride such as the alkali metal fluoride sodium or potassium fluoride, or ammonium fluoride, or I can employ soluble bifluorides such as sodium bifluoride, or complex fluorides such as alkali metal or ammonium fluoborates and silicofiuorides. These complex fluorides decompose in the alkaline-permanganate system to produce the fluoride ion in the solution. The amount of fluoride compound which I employ is generally in the range of about 0.25 to about 8% by weight of the solution, usually about 0.75 to 6%. However, for any specific fluoride ion source employed, it is preferred not to employ an amount substantially greater than the amount which is soluble in the particular alkaline permanganate solution utilized.

A typical solution of this type, designated solution B is formed by adding to water in a concentration of 2 lbs.

I have also found that by adding a minor amount of asoluble, e.g., alkali metal or ammonium, chromate to solution B, the solution, which in the absence of such chromate is corrosive to certain cob-alt alloys such as Stellite #6 and #12, is thereby rendered non-corrosive to such alloys. The amount of chromate compound employed in the solution is usually about 0.1 to about 4.0% by Weight of the solution. Alkali permanganate solutions containing chromate can be prepared from dry solid compositions composed of the above noted essential components .in admixture. In such compositions the amount of alkali metal hydroxide is preferably about 15 to about by weight of the composition, a kali metal or ammonium fluoride is about 1 to about 15%, alkali permanganate is about 2 to about 45% and alkali chromate is about 1 to about 10%. Such composition is generally dissolved in water in a range of about 2 ounces to about 4 pounds per gallon. of water to make up working solutions whose components are substantially within the ranges noted above.

The temperature of treatment in the alkaline permanganate solution is generally in the range of about to about 220 F preferably 180 to 200 F. Time of treatment is from say about 15 minutes to about 1 /2 hours.

While in preferred practice, treatment of the radioactively contaminated surface with solution A is carried out first, followed by treatment with solution B, this sequence can be reversed, with treatment in solution B carried out prior to treatment with solution A.

Also, while not necessary in all instances, in preferred practice the surface to be decontaminated is then treated in an aqueous acid solution C for passivating said surface and removing any oxide stain deposited during treatment with the permanganate solution. Preferably an aqueous nitric acid solution is employed, e.g., an aqueous nitric acid solution equivalent to about 5 to about 40%, preferably about 18 to about 30%, by volume of 42 degrees B. nitric acid solution. Additives can be incorporated in such nitric acid solution. For example, acetic, tartaric, citric, m-alic or adipic acids can be included, and also soluble fluorides such as ammonium or alkali metal fluorides and bifluorides, and complex fluorides such as fluoborates, fiuosilicates, fluotitanates or fluozirconates. Wetting agents such as Nacconol -(an alkylbenzene sulfonate having about 12 to about 18 carbon atoms in the chain) can be added also. Temperature of treatment in these aqueous nitric acid solutions may be room'temperacture or higher, and time of treatment may vary from about 5 to about 30 minutes.

Nitric acid-containing solutions can be empl' yed safely on stainless steels of the 300 series and on cobalt alloys such as Stellite 6 and 12, titanium and its alloys, zirconium and its alloys, such as Zircalloy 2, and the like, but cannot be employed safely on carbon steels or 400 series stainless steels. On stainless steels of the 300 series, for example, corrosion is very minor, e.g., on the order of about 0.01 to about 0.05 mil.

In place of aqueous nitric acid solutions, I can use as solution C aqueous solutions of oxalic, chromic, citric, phosphoric or sulfamic acids. Use of these acids requires different temperatures and time of treatment. For example, with phosphoric acid, an elevated treating temperature of about 160 F. is employed, and with oxalic acid a temperature of about F. Preferred ranges of the aforementioned alternative acids employed are about 10 to about 30% citric acid, about 5 to about 10% oxalic acid, about 3 to about 25% phosphoric acid, about 2 to about 25 sulfamic acid, and about 2 to about 15% chromic acid, by weight of solution.

Generally, after each of the treatments with solutions A, B or C noted above, the surface of the part being decontaminated is rinsed free of adhering solution.

The following are examples of practice of this invention. In such examples 1 nad. is equivalent to 1 roentgen. The rad. is a standard measurement of alpha beta and gamma radiation and the roentgen, designated R. is a standard of measurement of gamma radiation. Both terms rad. and roentgen esignate the same intensity of radiation. The term mrad. designates millirad, and the term mr. designates milliroentgen. One mr. corresponds to about 2000 to about 3000 counts per minute.

EXAMPLE 1 A Thorex slug dissolver in the form of a 550 gallon vessel 54" in diameter by 59 hi h, is equipped with 16 nozzles from various inlets, outlets and sampling lines. The bottom portion of the tank is equipped with a jacket for heating or cooling, and the upper part with an open top jacket for safety and shielding.

The Thorex dissolver was previously decontaminated by a first prior ant procedure using treatments with 30% nitric acid, alternated with 20% caustic-2% sodium tartrate solution. This procedure required 11 nitric acid treatments and 7 caustic-tartrate treatments to reduce the background radio activity to 6000 mr./hr. Further reduction to 2000 mr./hr. was accomplished using three passes of 30% nitric acid containing 4% sodium fluoride, but further treatment using the latter solution failed to reduce the background activity. The corrosion specimens which were removed from the tank showed 32,000 mr./hr. at contact. The total time consumed in the decontamination of the dissolver to the 2000 inn/hr. background activity was 17 days.

EXAMPLE 2 The dissolver tank of Example 1 was again placed in use and after 26 months of such use, the dissolver was again subjected to radioative decontamination by a second procedure employing three solutions for treatment, namely solution A solution B and an aqueous solution of nitric acid equivalent to 30% by volume of 42 B6. nitric acid, designated solution C Solution A and then solution B were each recirculated in the tank for one hour at boiling temperature, and solution C was then recirculated in the tank at 30 to 40 C. for the same period. Each step was followed by a vigorous water flush.

Two complete cycles of the above procedure were made but the radioactivity remaining after the first cycle was negligible, showing one cycle to be adequate. The radiation level was reduced at the end of the first cycle from approximately 10,000 R./hr. at contact with the tank, to 70 mr./hr. at contact with the tank. The actual time required for decontamination was one week, due to the simultaneous circulation of solutions A B and C through other vessels also for decontamination thereof. However, a period of treatment for the dissolver using solutions A B and C can be completed in two days, and would permit sufficient decontamination to permit direct maintenance of the equipment.

The above second procedure of the invention described in Example 2 not only reduced the amount of residual radioactivity remaining after treatment compared to that remaining after treatment by the prior art first procedure described in Example 1, but in addition produced a sub stantial saving in manpower and chemicals, and also the cost of handling the radioactive solutions leaving the plant was materially reduced from about 3000 gallons of solution for the first procedure of Example 1 to 700 gallons for the second procedure of Example 2.

EXAMPLE 3 The following cycles listed in Table II were individually tested for decontamination effectiveness on loop piping and associated equipment of a nuclear reactor, including valves and pumps, for the time and at the temperature shown below in Table II. The material of construction of such equipment was 304 stainless steel. The percentages of nitric acid given are in terms of percent by volume of 42 B. nitric acid. Other percentages are in terms of percent by weight.

Table 11 Solution Tcmpera- Time tom (1) E61,; formaldehyde solution, rinse with Ambient.. 5 min.

wa er. (2) Hexamine, sulfuric acid solution, rinse with Boiling... 1 hr.

water, repeat cycle twice. (3) 25% NaOl-l, 3% KMNOr solution, rinse with do 1 hr.

water, 10% HNO3, 3% ferrous ammonium sulfate, rinse with water, repeat cycle twice. (4) 5% HNOa solution do. 1 hr. (5) NaOH, H302 solution, rinse with 10% HNOa, {35 C 30 min. rinse with water. C 15 min. (6) 10% N32C1'2O7, 30% HNO; solution, rinse 60 C 30 min.

with water. (7) 6% NaOH, 1 tartaric acid solution, 30 C 5 min.

rinse with water, 5% oxalic acid solution, rinse with water, 28% HNOa, 7% Nail, rinse with water, re eat cycle twice. (8) 20% tHNO3, 3% H solution, rinse with Ambient... 2 hrs.

\va er. (9) 20% HNOa, 3% HF solution, (surface started 80 C 30 min.

0 c (10) Nazclgoy, H SO4 solution, water riusc. 0--.. 2 hrs.

All of the above solutions or cycles were found to be inadequate for decontaminating the equipment. A combined cycle including procedure 6 followed by procedure 7 of Table II removed most of the soft smearable contamination, but would not remove the hard beta and gamma emitters, or the film containing such emitters.

EXAMPLE 4 A number of components from a nuclear reactor similar to the parts treated in Example 3 were treated as follows:

The parts were each first treated in solution A above, under agitation, for 30 minutes to 1 hour at 133 to 135 C.

The parts were then treated in an agitated overflowing water rinse.

The parts were then treated in an agitated bath 13 formed by dissolving composition B in water in a concentration of 3.8 lbs. per gallon of water, for 30 minutes to 1 hour at 102 C.

The parts were then treated in an agitated overflowing water rinse.

The parts were then treated in an aqueous bath (solution C composed of 34.5% by volume of 40 Baum nitric acid and 14% of a solution C as follows:

Percent by Solution 0 weight NH HF 28.6 Glacial acetic a id 14.4 Nacconol (alkyl benzene sulfonate wetting agent containing from about 12 to 18 carbon atoms in the alkyl chains) 0.3 Water 56.7

Solution C was used at a temperature of 30 to 45 C. for 5 to 30 minutes.

The parts were finally treated in an agitated overflow-- ing water rinse.

Substantially no corrosion of the 304 stainless steel parts listed in Table III was detected as result of the decontamination treatment.

1 1 EXAMPLE 5 Three pieces of equipment, one a pot about 5 feet in diameter and 7 feet high, the second a dissolver tank about 7 to 8 feet in diameter and about 9 feet high, both having steam coils therein, and a pump, all of this equip ment being stainless steel, was decontaminated in the manner described below. The dissolver tested 6,000 mrad/ hr. of radioactivity at a distance of 10 feet prior to decontamination. The radioactivity of the pot was 1450 m-rad./hr. at a distance of 6 feet, and that of the pump was 2000 mrad./hr. at a distance of 200 feet.

The three pieces of equipment were each treated first in solution A then in solution B followed by treatment in solution C at the temperatures and for the periods of duration substantially as given in Example 2.

Following treatment in the manner noted above, the radioactivity reading of the pot was reduced to 30 rnrad.

per hour, the dissolver reduced to less than 6 mrad. per

hour and the pump to 150 mrad./hr. No corrosion of the base metal of these parts Was observed.

EXAMPLE 6 Carbon steel sample parts exposed to radioactive contamination in a loop of a nuclear reactor or power -gener-' ating system were treated for 30 to 60 minutes in solution A at about 135 F. The samples were then rinsed and found to be substantially decontaminated without any significant amount of corrosion of the base metal.

EXAMPLE 7 A series of one inch square 304 stainless steel coupons were exposed in the loop piping of a nuclear power generating system for 30 days at 235 C. The coupons were removed and subjected first to the action of solution A then to the action of solution B and finally to the action of a solution C an aqueous nitric acid solution having a concentration equivalent to25% by volume of 42 B. nitric acid.

The temperature and time of treatment in these baths, and the decontamination and corrosion results in terms of mils of penetration are set forth in Table IV below:

12 EXAMPLE 8 A at 80 C., followed by (3) treatment in a solution of 6.0

molar nitric acid containing 5% hydrogen peroxide, at room temperature. A D.F. (decontamination factor) of 22 was thus obtained. A similar stainless steel coupon holder previously subjected to the same radioactive contaminating conditions as the above coupon holder was subjected to process (Y) including treatment with solutions A B and C substantially according to the procedure described in Example 2 above. A D.F. of 59 was obtained, as contrasted to a DR of 22 obtained by the above described prior art procedure, showing markedly improved decontamination by the instant process.

The above process (X) was tested for radioactive decontamination of carbon steel coupons substituting N21 S O treatment as the third step, and obtaining a DP. of 19.5. Similarly contaminated carbon steel coupons subjected to process (Y) of the invention, with Na S O solution also substituted for the nitric acid treatment of the third step, resulted in a much higher D.F. of 88.

Hence process (Y) is seen to be substantially more effective than process (X) for radioactive decontamination of both stainless steel and carbon steel.

EXAMPLE 9 Table IV Final con- Base Sample Time, Temp.. tamination, metal 0. Initial contamination Baths min. 0. counts per penetramrn. tion in mils A1 30 135 1, 000 1 5,900 mradJhr. incl. mrjhr B, 15 100 .010

c, 5 25 10o A1 30 135 500 2 5,200 mrad./hr. incl. 60 mr./hr B 15 15 .0084

C 5 25 l00 A1 30 130 2,000 3; 6,250 mrad./hr. incl. 60 Inn/hr B 30 100 1, 000 0088 C 5 25 l00 A1 30 135 500 4 6,500 mradJhr. incl. mrJhr {B 15 .0103

C3 5 25 100 A; 30 1, 000 5 7,200 mracL/hr. incl. 85 Inn/hr B 15 100 0103 03 5 25 100 A 30 2, 000 6 7,300 mradJhr. incl. 100 Inn/hr H B, 15 100 0282 From the results in 'Table IV it 1s seen that radioactive 65 Percent y I decontammatlon In each case was reduced to a very low Solutlon C 4- Welght level even after the initial treatment in bath A (see particularly samples No. 2 and 4), and was reduced to an 75% phosphoric acid solution 96.0

Mixture of coal tar bases (still bottoms) 0.8 Triton X-l00 (a polyethoxylated nonylphenol nonionic wetting agent) 0.8 Mercapto benzthiazole 0.08 Water 2.32

Following rinsing, the parts were observed to be practically free of radioactive contamination without corrosion of its 'base metal.

accuses 13 EXAMPLE Mixture of coal tar bases (still bottoms) 0.80 Triton X-100 0.80 Mercapto benzthiazole 0.08 Citric acid 5.0

Water 2.32

Results similar to those of Example 9 were obtained.

EXAMPLE 11 Percent by Composition 3' Weight Potassium hydroxide, KOH 69.8 Sodium fluoride, NaF 7.4- Potassium permanganate, KMnO 19.8 Sodium chromate, Na CrO 3.0

The specimens were then treated in solution C at to C. for about half an hour, and then rinsed.

The parts were found to be decontaminated and the amount of corrosion to the base metal of the Stellite 6 and 12 samples was very minor, of the order of about 0.001 to 0.01 mil.

EXAMPLE 12 Specimens of stainless steel having an oxide scale deposit and contaminated with tightly bound radioactive emitters, were treated with an acid pickle composed of an aqueous solution of HCl and HNO The oxide deposit was substantially entirely removed, but the radioactive contamination was only slightly reduced.

Similar stainless steel specimens having a scale deposit thereon including tightly bound radioactive contaminants in the scale deposit, were subjected first to treatment with solution A according to the procedure of Example 6, and then to treatment with solutions B and C accord ing to the procedure of Example 9. The scale deposit was substantially entirely removed, and also practically all of the radioactive contaminants were removed,

Thus, it is apparent that the degree of scale removal and decontamination are not necessarily related, and removal of scale is not necessarily accompanied by good decontamination employing prior art treating solutions. However, when the invention process, including treatment for example with solutions A B and C is employed, efiicient decontamination is achieved, and which is accompanied also by substantial or complete removal of scale.

EXAMPLE 13 Components of a loop of an atomic reactor contaminated with radioactive emitters were first treated in solution A given below for about an hour at the temperature of boiling of the solution.

Percent by Solution A weight Potassium hydroxide 30.7 Triethanolamine 12.4 Tetrahydroxyethyl etliylenediamiue 4.5

Monohydroxyethyltrihydroxypropyl ethylenediamine 6.7 Acetic acid 11.7 Potassium acid tartrate 1.9 Water 32.1

The parts were treated in solutions B and C at temperatures and for the time periods set forth in Example 2 for these solutions.

The components following the above treatment were found to be practically completely decontaminated.

EXAMPLE 14 The procedure of Example 13 is repeated employing in place of solution A the following alternative solutions:

Percent by Solution A weight Potassium glycolate 22.5 Potassium acetate 6.5 lotassium hydroxide 16.7 Potassium phenoxide 5.8 Triethanolamine 13.8

Water 34.7

Solution A Sodium hydroxide 12 Sodium acetate 12 Potassium glycolate 15 Triethanolamine 15 Water 46 Solution A Potassium hydroxide l4 lotassium acetate 8 Potassium glycolate 20 Potassium acid tartrate 2 Triethanolamine 10 N,N'-dihydroxyethyl ethylenediamine 5 Water 41 Percent by Solution A weight Potassium hydroxide 15 Potassium acetate 8 Potassium glycolate 2O Triethanolamine 12.5 N,N,N,N-tetrakis Z-hydroxypropyl) ethylenecliamine 2.5

Water Balance Substantially complete decontamination is obtainable for each of the components so treated.

EXAMPLE 15 EXAMPLE 16 The procedure of Example 13 is repeated, employing in place of solution B solution B Decontamination results similar to those of Example 13 are obtainable.

EXAMPLE 17 The procedure of Example 13 is repeated, using in place of solution B solution B or solution 13 Solutions 13.; and B are aqueous solutions of composition B' dissolved in water in a concentration of 1 lb. per gallon and 4 lbs. per gallon, respectively. Results similar to the results of Example 13 are obtainable.

1 5 EXAMPLE 1s The procedure of Example 13 is repeated, employing in place of solution C solution A Effective decontamination of the components is obtainable, except that decontamination is not as complete as in the case of Examples 13 and 14.

From the foregoing it is apparent that I have developed a process for efilcient radioactive decontamination of surfaces, particularly the surfaces of components employed in nuclear reactor systems, such as the loop piping and associated equipment. The improved decontamination results are accomplished on various types of ferrous and non-ferrous metals and alloys, including carbon and stainless steels and alloys such as cobalt, titanium and zirconium alloys. These improved decontamination results are achieved Within relatively short treating periods and without any material corrosion of the base metal. The process has the additional advantage of removing any tight adherent scale as well as loose scale deposited on the metal surface and Within which the source of radioactive contamination may be bound. Further, the compositions and solutions employed in the process are readily prepared.

The term consisting essentially of as used in the definition of the ingredients present in the compositions claimed is intended to exclude the presence of other materials in such amounts as to interfere substantially with the properties and characteristics possessed by the composition set forth but to permit the presence of other materials in such amounts as not substantially to atfect said properties and characteristics adversely.

While I have described particularly embodiments of my invention, it should be understood that various modifications and adaptations thereof may be made Within the spirit of the invention as set forth in the appended claims.

I claim: 7

1. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali and an alkanolamine, and removing radioactive contaminants from said surface.

2. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of from about 5% to about 55% by Weight of an alkali metal hydroxide, from about 1 to about 45% by weight of an agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids, and from about 2.5 to about by Weight of an alkanolalmine, and removing radioactive contaminants from said surface.

3. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali and an alkanolamine and then contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate.

4. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali, an alkanolalmine and a complexing agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids and then contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate.

5. A process effective for removal of radioactive contaminants emit-ting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of from about 5% to about 55% by weight of an alkali metal hydroxide, from about 1 to about 45 by weight of an agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids, and from about 2.5 to about 30% by weight of an alkanolamine and then contacting said surface with an aqueous solution consisting essentially of from about 1 to about 25% alkali metal hydroxide and about 0.4 to about 12% alkali metal permanganate.

6. A process effective for removal ofradioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of from about 15% to about 40% by weight of an alkali metal hydroxide, from about 4 to about 40% by weight of an agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids, and from about 10 to about 30% by weight of an alkanolarnine, and then contacting said surface with an aqueous solution consisting essentially of from about 10 to about 25% alkali metal hydroxide and about 3 to about 9% alkali metal permanganate.

7. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of from about 5% to about 55% by weight of an alkali metal hydroXide, from about 1 to about 45% by weight of an agent take-n from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids, and from about 2.5 to about 30% by weight of a mixture of a polyalkanolmonoamine and an alkanolpolyamine, and then contacting said surface with an aqueous solution consisting essentially of from about 1 to about 25 alkali metal hydroxide, about 0.4 to about 12% alkaii metal permanganate, and about 0.25% to about 8% of a soluble inorganic fluoride.

8. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali, an alkanolamine and a complexing agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular Weight fatty acids, then contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate, and then contacting said surface with an aqueous solution consisting essentially of a member of the group consisting of citric, oxalic, phosphoric, sulfamic and chromic acids.

9. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali, an alkanolamine of the group consisting of polyalkanolmonoamines and alkanolpolyamines and a complexing agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids, then contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate, and then contacting said surface with an aqueous solution consisting essentially of a member of the group consisting of citric, oxalic, phosphoric, su-lfamic and chrornic acids.

10. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of from about 5% to about 55% by weight of an alkali metal hydroxide, from about 1 to about 45 by weight of an agent taken from the group consisting of soluble salts of molecular weight fatty acids, and from about 2.5 to

about 30% by weight of an alkanolamine, then contacting said surface with an aqueous solution consisting essentially of from about 1 to about 25% alkali metal hydroxide and about 0.4 to about 12% alkali metal permanganate, and then contacting said surface with an aqueous solution consisting essentially of a member of the group consisting of nitric, citric, oxalic, phosphoric, sulfamic and chromic acids.

11. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of from about 5% to about 55% by weight of an alkali metal hydroxide, from about 1 to about 45 by weight of an agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids, and from about 2.5 to about 30% by weight of an alkanolamine, then contacting said surface with an aqueous solution consisting essentially of from about 1 to about 25% alkali metal hydroxide and about 0.4 to about 12% alkali metal permanganate, and then contacting said surface with an aqueous solution consisting essentially of nitric acid in a concentration equivalent to about 5 to about 40% by volume of said solution of 42 B. nitric acid.

12. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of from about 15% to about 40% by weight of an alkali metal hydroxide, from about 4 to about 40% by weight of an agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids, and from about to about 30% by weight of an alkanolamine, then contacting said surface with an aqueous solution consisting essenu'ally of from about 10 to about 25% alkali metal hydroxide and about 3 to about 9% alkali metal permanganate, and then contacting said surface with an aqueous solution consisting essentially of nitric acid in a concentration equivalent to about 18 to about 30% by volume of said solution of 42 B. nitric acid.

13. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from surfaces of ferrous and nonferrous metals, which comprises contacting said surfaces with an aqueous solution which consists essentially of from about 5% to about 55% by weight of an alkali metal hydroxide, from about 1 to about 45 by weight of a soluble salt of an acetic acid compound of the group consisting of hydroxy acetic acid and acetic acid, and from about 2.5 to about 30% by weight of an alkanolamine, and removing radioactive contaminants emitting alpha, beta or gamma radiation from said surfaces.

14. A process efiective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from surfaces of ferrous and nonferrous metals, which comprises contacting said surfaces with an aqueous solution which consists essentially of from about 5% to about 55% by weight of an alkali metal hydroxide, from about 1 to about 45% by weight of a soluble salt of an acetic acid compound of the group consist-ing of hydroxy acetic acid and acetic acid, and from about 2.5 to about 30% by weight of triethanolamine, and removing radioactive contaminants emitting alpha, beta or gamma radiation from said surfaces.

15. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from surfaces of ferrous and nonferrous metals which comprises contacting said surface at elevated temperature :ith an aqueous solution which consists essentially of from about 5% to about 55% by weight of an alkali metal hydroxide, from about 1 to about 45% by weight of a soluble salt of an acetic acid compound of the group consisting of hydroxy acetic acid and acetic acid, and from about 2.5 to about 30% by weight of a polyalkanolmonoamine, then contacting said surface at elevated temperature with an aqueous solution consisting essentially of from about 1 to about 25% alkali metal hydroxide, about 0.4 to about 12% alkali metal permanganate, and about 0.25% to about 8% of a soluble inorganic fluoride, and then contacting said surface with an aqueous solution consitsing essentially of nitric acid in a concentration equivalent to about 5 to about 40% by volume of said solution of 42 B. nitric acid.

16. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from surfaces of ferrous and nonferrous metals which comprises contacting said surface at elevated temperature with an aqueous solution which consists essentially of from about 15 to about 40% by weight of an alkali metal hydroxide, from about 4 to about 40% by weight of a soluble salt of hydroxy acetic acid, and from about 10 to about 30% by weight of triethanolamine, then contacting said surface at elevated temperature with an aqueous 'solution consisting essentially of from about 10 to about 25% alkali metal hydroxide, about 3 to about 9% alkali metal permanganate, and about 0.75 to about 6% of an alkali metal fluoride, and then contacting said surface with an aqueous solution consisting essentially of nitric acid in a concentration equivalent to about 18 to about 30% by volume of said solution of 42 B. nitric acid.

17. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from surfaces of ferrous and nonferrous metals which comprises contacting said surfaces at elevated temperature with an aqueous solution which consists essentially of from about 15 to about 40% by weight of an alkali metal hydroxide, from about 4 to about 40% by weight of a soluble salt of hydroxy acetic acid, and from about 10 to about 30% by weight of triethanolamine, then contacting said surface at elevated temperature with an aqueous solution consisting essentially of from about 10 to about 25 alkali metal hydroxide, about 3 to about 9% alkali metal permanganate, and about 0.75% to about 6% of an alkali metal fluoride, and then contacting said surface with an aqueous solution consisting essentially of about 3 to about 25% phosphoric acid.

18. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali, an alkanolamine and a soluble salt of an aliphatic hydroxy acid, and then contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate.

19. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali, triethanolamine, and a complexing agent taken from the group consisting of soluble salts of the aliphatic hydroxy acids and soluble salts of the low molecular weight fatty acids, and then contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate.

20. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali, an alkanolamine and a soluble acetate, and then contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate.

21. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an al- .kali, an alkanolamine and a soluble glycolate, and .then

contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate.

22. A process efiective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface which comprises contacting said surface with from a cobalt alloy surface, which comprises contacting said surface with an aqueous solution which consists ess ential'ly of an alkali and an alkan-olarnine, and then contacting said surface with -a solution consisting essentially of an alkali, an oxidizing agent in the form of a soluble permanganate, and a soluble chromate.

24. A process effeotivefor removal of radioactivecontaminants emitting alpha, beta or gamma radiation from a ucobalt al-loy surface, which comprises contacting said surface with an aqueous solution which consists essentially of an alkali and an alkanolamine, and then contacting said surface with :a solution consistinglessentially v ofifro rn about 1 to about 2 5% alkali metal hydroxide, about 0.4 to about 12% alkali metal permanganate, and about 0.1 to about 4.0% of a soluble chromate.

25. A process effective for removal ofradioactivecon- ,taminants emitting alpha, beta or gamma radiation from a cobalt alloy surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali and an alkanolamine, and then contacting said surface with a solution consisting essentially of from about 1 to about 25% alkali metal hydroxide, about 0.4 to about 12% alkali metal permanganate, and

about 0,110 about 4.0% of an alkalimetal chromate, and

jthencontacting said surface with an aqueous acid solution.

26. A process effective for removal of radioactive contaminants emittingalpha, beta or gamma radiation from a surface which comprises contacting said surface with an aqueous solution which consists essentially of an alkali and an alkanolamine and then contacting said surface with a solution consisting essentially of an alkali and an oxidizing agent in the form of a soluble permanganate, and then contacting said surface with an aqueous nitric ,acid solution.

References Cited in'thefile of this patent UNITED STATES PATENTS 1,899,734- Stockton Feb. 28, 1933 2,408,096 Pierce Sept. 24, 1946 "2,584,017 Dvorkovitz J an. 29, 1952 2,653,860 Mayer Sept. 29, 1953 2,843,509 Arden July 15,1958 2,852,419 Overholt etal Sept. 16, 1 958 2,924,576 Bersworth Feb. -9, 1960 OTHER REFERENCES iContamination and Decontamination of NuclearPow- ,cr Reactors, AEC Document APAE No.43, vol. I (pages 33-36 relied on).