Regulatory Guide 5.25

Design Considerations for Minimizing Residual Holdup of Special Nuclear Material in Equipment for Wet Process Operations

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Issue date:	06/30/1974
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RG-5.25
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June 1974 U.S. ATOMIC ENERGY COMMISSION

REGULATORY GUIDE

DIRECTORATE OF REGULATORY STANDARDS

REGULATORY GUIDE 5.25 DESIGN CONSIDERATIONS FOR MINIMIZING

RESIDUAL HOLDUP OF SPECIAL NUCLEAR MATERIAL

IN EQUIPMENT FOR WET PROCESS OPERATIONS

A. INTRODUCTION

and storage, (3) precipitation, (4) slurry transfer, and (5)

liquid-solid separations.

Section 70.22 "Contents of applications," of 10

B. DISCUSSION

CFR Part 70, "Special Nuclear Material," requires, among other things, that each application for a license to 1. Background possess at any one time more than one effective kilogram of special nuclear material (SNM) contain a full Past experie nee and current observation of the unit description of the applicant's program for control of and operations used in operating systems at plants for accounting for SNM which will be in his possession chemical conversion, fuel fabrication, scrap recovery, under license, including procedures fol controlling SNM

and fuel reprocessing indicate that publication of general during its processing or use in the facility. Section 70.51, guidance for equipment design could assist in achieving

"Material balance, inventory, and records requirements," the degree of material control that is essential for requires, among other things, that certain licensees satisfactory protection of SNM. In processing, SNM may conduct their nuclear material physical inventories in accumulate as a sizable deposit which increases during compliance with specific requirements set forth in

10 CFR Part 70. processing, or SNM may accumulate only during draindown. For a given process, mode of operation, and type of material, the amount of holdup may fluctuate The control of and material balance accounting for near some characteristic value. In other cases, the SNM can be made more effective by reducing residual quantity accumulated may continue to increase as holdup in process equipment following draindown or operation continues and become apparent as residual following draindown and cleanout. This would lessen the holdup only upon draindown or cleanout.

severity of problems associated with determination of the residual holdup component of a physical inventory It is often difficult to determine the quantity of and would reduce the component of uncertainty SNM holdup with sufficient precision and accuracy to contributed by residual holdup to a physical inventory. meet the MUF and LEMUF requirements of Section

70.51. This determination usually includes locating, sampling, identifying, and analyzing the SNM.

This regulatory guide describes design features and Appropriate design not only could assist in reducing characteristics acceptable to the Regulatory staff for residual holdup and consequent need for determination, minimizing the residual holdup of SNM after draindown but also could assist in increasing the effectiveness of or cleanout of equipment used in wet process draindown and cleanout, if necessary.

operations. These features and characteristics are expected to facilitate physical inventory measurements and ameliorate material balance uncertainties without interfering with process operations. In particular, this Regulatory Guide 5.8, "Design Considerations for guide is addressed to operations including (1) liquid Minimizing Residual Holdup of SNM in Drying and Fluidized Bed Operations," is a parallel guide.

blending and gas-liquid contacting, (2) liquid transfer Copies of published guides may be obtained by request indicating the divisions USAEC REGULATORY GUIDES Washington, D.C. 20545, desired to the US. Atomic Energy Commission, for the public Attention: Director of Regulatory Standards. Comments and suggestions Regulatory Guides we issued to describe and make mvailable to improvements in these guides are encouraged and should be sent to the Secretary specific parts of methods acceptable to the AEC Regulatory staff of implementing staff in of the Commission, U.S. Atomic Energy Commission, Washington, D.C. 20545, regulations, to delineate techniques used by the the Commission's Attention: Chief, Public Proceedings Staff.

guidance to evaluating specific problems or postulated accidents, or to provide applicants. Regulatory Guides are not substitutes for regulations and compliance those set out in The guides are issued in the following ten broad divisions:

with them is not required. Methods and solutions different from the guides will be acceptable if they provide a basis for the findings requisite to 1. Power Reactors

6. Products

6. Pro rts the issuance or continuance of a permit or license by the Commission. 2. Research and Test Reactors

7. Transportation

3. Fuels and Materials Facilities

8. Occupational Health

4. Environmental and Siting 9. Antitrust Review to accommodate Published guides will be revised periodically, as appropriate, 5. Matwrials and Plant Protection 10. General comments and to reflect new information or experience.

With unknown or imprecisely known quantities of beneficial to consider the effects of residual holdup early residual holdup in equipment, the effectiveness of a in the stages of equipment design, particularly if material balance as a control mechanism is seriously impaired. Minimizing the quantity of material retained shutdown and cleanout could be avoided for an entire in process equipment generally enhances the automated process (e.g., chemical conversion facility) or effectiveness of a material protection program in the a remotely operated process (e.g., fuel reprocessing plant).

following ways.

2. Unit Operations a. Quality of Physical Inventories This guide is addressed to reducing residual SNM

The extent to which inaccuracy and holdup in five unit operations common to wet chemical uncertainty in measured residual holdup detracts from a physical inventory depends on the amount of holdup processes. These are described in the following and the uncertainty in that amount. Therefore, the paragraphs. For purposes of this discussion, the term

"significant amounts" refers to those quantities which influence of this uncertainty on the LEMUF (limit of may cause difficulty in satisfying the inventory quality error on material unaccounted for) can be reduced requirements of Section 70.51.

directly by reducing residual holdup. By reducing the quantity of material that cannot be measured well, the quality of the physical inventory 2 is improved. In a. Liquid Blending and Gas-Liquid Contacting addition, the contribution of unmeasured holdup to the Gas-liquid contacting refers to the reaction of a MUF (material unaccounted for) can be reduced. gas with a liquid to yield a liquid product. An example of a gas-liquid reaction is the hydrolysis of uranium In general, one of the influential factors which hexafluoride to form an aqueous solution of uranyl must be controlled to achieve a satisfactory inventory is fluoride, which then may pass to a precipitation the presence of residual holdup and its influence on operation.

inventory uncertainty. For a process amenable to dynamic inventory techniques, in particular, credibility Liquid blending is used, for example, to in the technique itself would be increased by reducing or produce a uniform mixture of uranium and plutonium removing the uncertainty of residual holdup. nitrate solutions which subsequently may pass to a coprecipitation operation or be transferred to a fluid bed b. Susceptibility of SNM to Diversion drier. To prevent the formation of polymeric species of plutonium during mixing, control of the temperature Reduction of the quantity of residual holdup and acidity of plutonium nitrate or of mixed nitrates is following draindown or draindown and cleanout of necessary.

process equipment decreases the quantity of SNM which is susceptible to diversion during sampling and A distinguishing characteristic of gas-liquid identification and subsequent separation, recycle, or contacting and liquid blending is that the bulk material recovery as appropriate. is a liquid; 'solids normally are not expected to be Decreasing the residual holdup limits the effort present. In general, draindown of equipment used for necessary to establish the presence of residual material the operations can be enhanced significantly if and to remove it for a physical inventory. Consequently, accompanied by rinsing. To remove residual deposits of the amount of time SNM is accessible and the number of any plutonium polymer formed, additional cleaning may people who need access to it are reduced, and the be necessary.

opportunity for unauthorized individuals to gain access to SNM during this stage of a physical inventory is b. Liquid Transfer and Storage reduced. Where the effects of residual holdup are negligible, an in-process or dynamic inventory method Liquids containing SNM are transferred and stored throughout a number of chemical conversion might be utilized, thereby reducing direct contact (i.e.,

processes and fuel reprocessing steps. For example, accessibility) of inventory personnel with SNM.

uranium and plutonium nitrate solutions or uranyl fluoride solutions are transferred between vessels. Also, Automated processes have the effect of directly limiting personnel access to SNM during normal waste solutions may be transferred from liquid-solid separating operations to temporary storage tanks or operation. A dynamic or in-process inventory may be evaporating ponds. Tanks are utilized for feed conducted for an automated process line; this would adjustments, dissolution, accountability, settling, surge, continuously limit access to SNM. Consequently, it is and product collection.

2 Regulatory Guide 5.13, "Conduct of Nuclear Material In general, a low level of residual holdup can be Physical Inventories," addresses the subject of conducting achieved if equipment used for transfer and storage of physical inventories for nuclear material. liquids is flushed out or rinsed after draining. However,

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precipitation of solids or buildup of salt on vessel walls 3. Holdup in Liquid Blending and Gas-Liquid may resist meager attempts at rinsing. Contacting Many types of contactors (e.g., mixer-settlers, mixer c. Precipitation columns, scrubbers, etc.) are used for liquid blending and gas-liquid reactions to. produce liquid products.

In precipitation reactions, SNM in aqueous Although pulse columns may be preferred for solution is converted to solid form by the addition of a liquid-liquid contacting, centrifugal contactors have the precipitating agent. The resulting solid initially is in advantage of low holdup volume. Therefore, a small suspension but may undergo' settling. Holding or aging decrease in inventory error can be realized by using tanks may be used for purposes such as crystal growth, centrifugal contactors rather than pulsed columns.

chemical adjustment, or buffer storage. Disadvantages of centrifugal contactors are thay they are expensive and must be constructed to small tolerances.

This type of unit operation is used for the Furthermore, the kinetics of some reactions a&e not conversion of uranyl fluoride to ammonium diuranate favored by the use of centrifugal contactors.

(ADU); uranyl nitrate to ADU; plutonium nitrate to plutonium peroxide, oxalate, or hydroxide; and mixed Liquid holdup in liquid blending and gas-liquid uranium-plutonium nitrates to mixed ADU-plutonium contacting equipment can occur at low spots in lines, in hydroxide. An additional application is the conversion pump cavities, and in vessels without bottom outlets.

of uranium-containing and/or plutonium-containing Internally mounted equipment such as mixers, baffles, solutions to sols. and spray rings provide additional surfaces where material can collect. However, as is true for most In general, draindown of equipment used for processes in which solids are absent, liquid products precipitation operations may leave a significant quantity generally can be readily removed by gravity, i.e., by of residual holdup. simply draining and flushing.

More complex problems are encountered when d. Slurry Transfer plutonium in solution forms polymeric species of a colloidal or gelatinous character that makes their Slurry transfer is the movement of a liquid in removal from equipment difficult. Acidification can, at which solid or semisolid ma(erials are suspended. An least partially, resolubilize the polymer, but kinetics example is the transfer of slurries from precipitation fimit the rate at which this occurs. To improve the operations (mentioned in section B.2.c. above) to ability of a facility to meet accountability requirements, separating or drying operations. Gels or sols containing it may be necessary to provide cleanout capability in uranium and/or plutonium also may be transferred as those units of equipment where polymers could slurries. conceivably form.

Draindown of equipment used for this 4. Holdup in Liquid Transfer and Storage operation without cleanout may leave a significant quantity of material as holdup. Liquids are stored in various kinds of vessels and, are transferred to process equipment through piping systems by means of gravity, pumps, steam or air jets, air lifts, or e. Liquid-Solid Separations vacuum. When liquid is transferred by any 6f the above means, holdup-pro6bleis can result from the existence o f Unit operations currently utilized to achieve stagnant zones, low- points in lines, or. .irikomplete liquid-solid separation, including dewatering or solvent drainisng of equipment. As for the previous uiit removal, are centrifugation, filtration, and settling. operation, internally mounted equipment .such as Liquid-solid separations separate bulk liquids from mixers, baffles, and spray rings provide surfaces where suspensions or slurries of solids and consolidate the solid material can collect. Therefore, equipment design material as a damp cake'for subsequent operations. By effectively could be directed toward improved, draining, means of liquid.solid separations, SNM-containing supplemented by provisions for rinsing and flushing.

material from enrichment or fuel reprocessing plants may be converted to'a form suitable for fuel fabrication.

Draindown of the equipment may leave a- significant Gravity flow of material in a process is beneficial quantity of residual holdup. since it provides a degree of self-action (automation) for draining and flushing operations. Feed solution pumped to the highest point in a process would then cascade

-downward through the process network. Transfer lines Operations that result in a dry solid product for the entire process would be sloped for better overall (e.g., drying and fluidized bed operations) are not drainage. However, even with an entire system designed included in this unit operation and are the subject of a inherently for free drainage, excessively flushing out the separate regulatory guide. '

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wet end of a process to reduce the quantity of SNM in Use of antioxidants and efficient agitation can assist the equipment for inventory purposes can produce a in preventing these problems of holdup. The large quantity of dilute solution that is unsuitable for composition of the materials of construction as well as processing. Consequently, vacuum transfer and removal the condition of the interior surfaces of vessels (e.g.,

of solutions may be preferable. roughness or texture) may equally influence residual holdup prevention. The differences between these two More onerous holdup problems include the buildup factors may indeed be subtle.

of sludges in the bottoms of tanks used for accountability, transfer, or storage and the residual jet Where deposits form on equipment surfaces, heels that remain after such tanks are emptied. ultrasonic treatment can be effective for removing Dissolution tanks have been constructed of stainless steel deposits. Such a cleaning technique may be needed if and Teflon-coated stainless steel (for other than other methods of altering process conditions (e.g., use of irradiated service); the latter is preferred for purposes of surfactants) or modifying process equipment (e.g.,

reducing surface accumulation. Storage tanks and other electrostatically charging polyethylene vessels or vessels should be accessible for the installation of sensing maintaining polished internal surfaces) are ineffective.

devices such as dip tubes or inductive and sonic level Unfortunately, anomalous situations may arise if it detectors. This recommendation should be considered in is not possible to identify a deposit sufficiently to view of other factors such as shielding and protecting understand its properties. For example, flaking of vessels containing SNM from severe weather by deposits and consequent plugging of piping downstream embedding the vessels in concrete. can be decreased by flushing precipitator vessels with acid between batch runs. However, reduced plugging can

5. Holdup in Precipitation be a result not only of the acid dissolving the deposits but also of the acid causing the deposits to be more adherent. More adherent deposits are less likely to flake Slurries and suspensions formed by precipitation off and plug the equipment, but large quantities may can be removed readily from vessels by simple draining if accumulate.

settling does not occur. Loosely adhering solids on vessel walls can be dislodged by flushing. In sustained 6. Holdup in Slurry Transfer operations, however, solids may deposit on and adhere to surfaces in a manner that makes removal' difficult. Slurries are transferred from one process vessel to Agitation, which is provided plrincipally to enhance another by methods that are essentially the same as particle agglomeration, reduces but does not eliminate those used to transfer liquids. However, holdup this deposition of solids. In the preparation of sols using problems are more complex for slurry transfer because precipitation as a process step, agitation is necessary to of a tendency of the suspended solids-to settle out of the resuspend the precipitate. The amount of deposited carrier liquid. Although different materials exhibit solids usually is sufficiently large to necessitate total different settling characteristics, a critical velocity exists cleanout for a physical inventory. below which particles begin to settle out. Such settling is most likely to occur at shutdown or when flow rates are reduced because of abnormal operations. In such Several troublesome problems are related to residual situations, pumps and valves may act as sites in which holdup during precipitation and digestion. Where solids can accumulate or be trapped.

internally coated vessels are used for processing (e.g.,

Teflon-coated glass for fuel-particle preparation), a Cavities and recesses in pumps used to transfer positive seal should be assured between the lining and" slurries or suspended solids can collect significant the vessel walls to prevent accumulation of particles ini quantities of solid material that are difficult to fluish out.

annular spaces between the two surfaces. Another Transferring material by jets or gas lifts may minimize problem can be the oxidation of intermnfdiate -this difficulty.

compounds to undesirable compounds that may be gummy and insoluble. This could cause plugging of When screw conveyors are used to transfer moist equipment and process piping if not controlled. For pastes, a coarse intermediate cleandut may be necessary example, PuF 3 may oxidize to PuF 4

• 2.5H 2 O. In for operational reasons, i.e., to prevent subsequent addition, some process intermediates (e.g., PuF 3 ) or plugginrg of the process line. Additionally, a more interferents (e.g., polymers of plutonium) have a complete cleanout may be needed at the end of each tendency to deposit on the surfaces of vessels used for run. Because frequent cleanouts are necessary for precipitation and digestion. Plugging can be caused when operational reasons alone, a paste transfer method flakes or globules of the deposits break loose from the necessitating less interruption is desirable.

surface and flow to a constriction such as an outlet or other piping. A more serious consequence of such 7. Holdup in Liquid-Solid Separations deposits of SNM may be the hazard from accumulation of large yet unknown quantities. Unit operations used for the separation of liquids

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and solids are centrifugation, filtration, and settling of Parts of the separation system exposed to slurries. A wide variety of devices is used for this centrates and filtrates usually can be drained readily, but operation. The type selected is dependent on the nature simple flushing probably does not remove solids of the material being processed, the throughput rate, and adequately. Cleanout of plate-and-frame filter presses in the liquid content of the feed and product. Holdup particular can be difficult since centrates and filtrates problems are discussed below in connection with the each contain suspended solids, and sustained normal type of equipment and the characteristics of the process operation results in holdup of solids.

material.

C. REGULATORY POSITION

In facilities with high throughputs, two centrifuges in series are typically used for separation. A For purposes of facilitating the measurement and/or primary centrifuge for separation and recovery of bulk recovery of residual special nuclear material held up in solids is upstream from a clarifying centrifuge for process equipment and to improve the accuracy and removal and recovery of residual trace solids. The reliability of a physical inventory, the amount of SNM

principal purpose of the primary unit is to produce a held up in equipment should be minimized. The design concentrated solid product having a relatively low water of equipment used to carry out physical or chemical or solvent content. The second centrifuge serves changes on special nuclear material by wet operations, principally for clarifying the centrate (i.e., the centrifuge including liquid blending, gas-l4quid contacting, liquid effluent) from the first centrifuge. In processes in which transfer and storage, precipitation, slurry transfer, and the centrate from the first unit is not recycled through liquid-solid separation, should incorporate features that the fuel preparation process, the clarification step serves minimize residual holdup. Some appropriate equipment to recover residual SNM before the centrate is design features and characteristics whose use is generally transferred to waste treatment.

acceptable to the Regulatory staff for this purpose are described in the following paragraphs. These should be Most of the material held up in a centrifuge implemented to the extent practicable. Usage also after draindown exists as unremoved solids. In a batch should be consistent with quality assurance, health, and basket-type centrifuge, holdup is normally small after nuclear safety codes that may be applicable.

unloading by normal procedures. However, in a solid-bowl continuous centrifuge equipped with a helical 1. General Design conveyor to remove solids, any solids deposited on the surfaces of the flights of the conveyor, on bowl surfaces in the clearance space between the flights of the a. Vessels, piping, valves, and accessory equipment conveyor and the bowl, and on surfaces of the should be designed to minimize undrained volume and solids-discharge cavity are difficult to remove. Simple should be free draining where practicable.

flushing is not likely to be effective in dislodging solids, b. Inside surfaces of equipment should be free of either from surfaces contacted by the flush or surfaces crevices,, cracks, protrusions, and other irregularities that inaccessible to the flush. Comparable difficulties occur 'J could entrap material.

with other types of centrifuges, especially continuous c. Surfaces that contact SNM should be selected centrifuges having complex unloading mechanisms. and coated, polished, or machined to prevent or resist the adherence of liquids or solids.

b. Filters d. Overlapping metal surfaces in contact with In facilities having low throughputs or in process material should be avoided except where sealed facilities handling highly enriched uranium or by welding; internal welds should be ground flush with plutonium, dewatering may be effected by continuous inner surfaces. Exceptions may be gasketed openings (e.g., rotary) filters or batch filters. For reasons of such as inspection and cleanout doors or ports.

criticality control, this equipment is typically small in e. The internal angles, corners, and recesses should size. Following draindown, less material may be held up be rounded with a radius larger than a minimum radius, in filters than in centrifuges. for example, one fourth inch.

f. Seams that may promote corrosion should not Although batch filters and drum filters have be used.

readily exposed surfaces that can be cleaned out by g. Materials of construction that contact SNM in simple flushing or mechanical removal, it is difficult to any form should be selected to minimize corrosion, clean out other types of filters, e.g., plate-and-frame dissolution, or erosion of surfaces during operation or presses. Leakage and bypassing of material can occur during contact with rinse solutions used for cleaning.

around the edges of a filter drum used in a continuous h. Structural integrity should be adequate to resist process line; pan filters have better cake removal than do formation of leaks, cracks, and crevices due to stresses drum.ffilters. In filters such as those,'using a metal grid to such as thermal and vibratory stresses. Accordingly, support a paper filter medium, fines can lodge in the valves and pumps should be installed so as to minimize interstices of the equipment. stresses on attached piping and vessels.

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i. The influence of operating variables such as f. Equipment such as product and centrate material flow rate, pH, concentration, and temperature collection vessels or chambers of centrifuges should be should be evaluated to reduce undesirable formation of designed to contain material without loss by foaming, holdup (e.g., caking or sticking) that might be induced splatter, or formation of sprays in wet processes.

by operating in an undesirable range of operating conditions.

j. Flow control valves should have a minimum of 3. External Design internal holdup or obstruction to flow and should be installed in a location and position that enhances a. Visual access should be provided to all surfaces draining of the entire piping network. or spaces where material is likely to accumulate;

kl. Pipe lines for slurries or suspensions should be alternatively, clearance should be provided to permit sized according to process flow requirements so that external use of nondestructive assay instruments or flow velocity is above the critical velocity at which internal probes to detect the presence of SNM or to settling can Occur. identify the location of residual material not visually

1. Material that contains solid forms of SNM, e.g., accessible. 3 slurries and filtrates, should be transferred continuously b. Liquid transfer systems or vessels should have to avoid settling. drains and valves installed at the lowest points to permit m. Process units should be closely coupled and draining -by gravity or other means. The stagnant sized, with minimal intervening holdup tanks. volumes that may collect in drain lines and between tees n. Equipment design should eliminate as many and drain valves should be kept to a minimum. Transfer areas of stagnation and residual accumulation of lines should have adequate slope to permit draining of solutions and slurries as possible (e.g., in order to process solutions after shutdown. If a pump is used, a facilitate the capability for conducting dynamic drain equipped with a valve should be installed at the inventories). 1 rw point of the transfer line.

c. Equipment used to transfer solutions from

2. Internal Design storage tanks should be provided with adequate check valves to prevent siphoning or suction of process a. Equipment should have a minimum of internal solutions into the steam or air supply lines. This components upon which process material can collect. equipment includes steam jets, steam lines, air lifts, gas For example, bowls, product chambers, and centrate purge lines, and vacuum relief valves.

collection chambers of centrifuges should be designed to d. If vacuum transfer of liquids is used, the be free of nonessential protrusions and ledges. vacuum pumps should be protected from corrosive Additional surfaces in the form of helical conveyors, vapors or SNM-containing liquids by suitable traps and liquid accelerating bars, and devices for removing slurries filters. If other transfer methods such as liquid piston should be kept to a minimum. pumps are employed, these should also be protected.

b. The use of internal mechanical agitators in e. Although seals and drain valves should be blenders should be avoided. If agitators are used, they designed to be leaktight under normal conditions and to should be designed to permit surfaces to drain freely and be free of crevices and cavities, provision should be made to present minimum surface for the collection of solid for the collection of material leaking through seals and particles. Seals such as self-sealing packing glands and valve seats when abnormal conditions exist.

cone pressure seals for maintaining a tight seal around f. Gravity transfer of liquid slurries from one stirring shafts should necessitate minimal maintenance. vessel to another and of wet solids, centrates, and c. Sensing devices such as thermocouples or level filtrates from centrifuges and filters should be used in detectors should be installed in a manner that minimizes preference to the use of transfer containers. If pumping the amount of solid material that can be retained on the of liquids or slurries is necessary, gas lifts should be used, surfaces of such devices. provided the disengagement of gas does not result in d. Extended surfaces such as packing (e.g., excessive foaming or entrainment. Pumps should be Raschig rings, Berl saddles, etc.) should *be avoided. designed to minimize cavities and stagnant volumes. All Permanently mounted process equipment internals that pumps should be mounted for maximum drainage and cannot be removed for cleaning should be designed to designed for minimal cavities and undrained volumes.

allow rinsings and normal contents of vessels such as g. Equipment should be arranged so that liquid blenders to drain freely from the bottom of the connecting piping follows the shortest practical route equipment. If extended surfaces are necessary, the with the fewest number of bends and fittings.

licensee should 'be able to demonstrate that an h. The piping network should be designed to allow acceptable limit of error can be obtained, either by free drainage to accumulation points.

rinsing or by removal of packing.

e. All lower portions of vessels such as liquid blenders and storage tanks should be sloped (e.g., tanks 3 Regulatory Guide 5.23, "In Situ Assay of Plutonimn may have conical or dished bottoms) to allow liquids to Residual Holdup," provides additional methods and procedures drain freely. regarding measurements.

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4. Design for Accomodating Cleanout This is particularly important for vessels hindlin2 plutonium-containing solutions that can form polymeric a. Equipment such as precipitators and digestors compounds which may settle.

-, should be provided with access ports, removable covers, g. Wash or flush lines and spray rings should be or removable sides to allow visual inspection of the connected at high points of transfer lines and piping internal surfaces. networks or upper zones of interconnected vessels to b. Access ports or removable panels should be permit flushing of accumulated solids.

provided, to allow cleaning of internal surfaces by h. Drain valves should be installed at low points in

1 appropriate methods such as brushing, vacuuming, vessels and piping systems, Pumps for the nini-"

washing, scraping, or rinsing to remove, dislodge, or network should be designed to facilitate disassemYl' f,-r dissolve SNM particles. complete cleanout.

c. Equipment should be provided with fittings for i. Interconnecting piping and pumps shmol '-

connections for washdown and rinsing of internal capable of being cleaned by flushing with clean draininas surfaces of vessels and pipes. Steam, water, or from storage or process vessels. Where nece-saN'.

appropriate chemical solutions should be used to separate flushing lines should be connected to tr'-i-de dislodge, dissolve, or otherwise remove all particulate lines to assist in cleaning.

process material, residual liquid, and condensed vapors j. Storage vessels should be provided ,ith remaining on internal surfaces of the equipment. separate bottom drain valves that permit their contents Quick-connect (-disconnect) couplings should be utilized or wash solutions to be removed without affectine in process lines where frequent cleanout is necessary. interconnected vessels.

d. Provisions should be made for flushing and . k. Provisions (e.g., instrumentation) should he draining and for removing and collecting rinsings in made to permit verification that all material ha3 .1--i removed from transfer lines.

which SNM may be entrained or dissolved. Removal of material from centrifuge bowls, product collection 1. Jets should be installed so as to completely chambers, and transfer lines should be facilitated by empty vessels such as liquid storage tanks. To further designs that permit disassembly. Also, distribution decontaminate vessels, air and steam sparges should be installed as necessary.

devices for flush solutions should be designed and arranged to allow flush solutions to contact the interior m. The use of filters whose components muit ie surfaces and cavities of the process equipment and of disassembled for recovery of solids (for exa'-nle.

auxiliary devices inside the equipment. Flush lines to plate-and-frame filter presses) should be avoided.

plutonium-containing vessels and equipment should be n. Filter media should be removable or be cir-.c, connected only to acidified solution sources. of being backwashed in situ. Removable filter rmw2ii e. Supplementary internal mechanical equipment should be treated by leaching or by combustion and not permanently mounted such as scrapers, agitators, leaching for the recovery and determination of SNM.

atomizers, and rinsers should be capable of being o. The composition of flush solutions for disassembled and removed for cleaning and inspection. equipment containing residual plutonium should "'e f. Bottom outlets and drain plugs should be controlled to avoid polymerization or precipitation te2..

selectively located to facilitate draindown and cleanout. adequate acidification).

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