By S.S. Shetty and J.M. Gilkison
Westinghouse Savannah River Company
Reprinted from the American Glovebox Society
publication "The Enclosure"
Vol. 6, No. 1 - February 1993
| Abstract: This paper presents the results of a study of alternative methods for replacing Sphincter designed gloveports in gloveboxes. In addition, the paper discusses modifications that are required on metal glovebox wall panels to allow replacement of the Sphincter gloveports. A review of Westinghouse Savannah River Co. (WSRC) maintenance records showed that gloveports manufactured by Central Research Laboratories provide the lowest risk of failure. This assessment is based on the records of glove-to-port seal life and air in-leakage. These records also indicate that glove changes are made in shorter times with fewer workers that required by alternate gloveport designs studied. These attributes culminate in a significant decrease in radiation exposure and assimilation risk of maintenance personnel replacing gloves. Further, the Central Research design reduces the number of expendable hardware parts required to achieve a glove replacement. This reduction in expendable materials can result in a significant reduction in contaminated waste volume generated during a glove replacement. |
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Gloveboxes such as those used in the WSRC FB-Line mechanical line are used to confine hazardous and radioactive materials. Processes within the gloveboxes are usually regulated by exterior controls. However, some routine operations, many off-nominal operations, and maintenance of equipment within the gloveboxes are performed inside the gloveboxes, via gloveports. Access to the interior of the gloveboxes is achieved through gloveports installed in the sides of the glovebox cabinets. These gloveports contain gloves that will accept the operator's hands and arms. A mechanical seal is maintained between the glove and the gloveport to confine materials inside the gloveboxes. The confinement aspects of the gloveport seal are augmented by a differential pressure between the interior and exterior. The pressure within the glovebox is negative to the exterior so air leakage past the gloveport seals is toward the interior of the gloveboxes.
The differential pressure creates airflow into the glovebox. The in-leakage of moist air from the exterior of the glovebox may adversely affect the production of some high-quality products. Therefore, the gloveport seals and the gloves must prevent significant quantities of air from leaking into the gloveboxes as well as confine the hazardous materials.
The gloveports in the mechanical line gloveboxes are installed in two levels. The gloveports installed in the upper, operational levels are installed in windows. The gloveports in the lower level are installed in metal panels.
Three gloveport designs are used in the mechanical line gloveboxes. These are:
| Design | Manufactured by |
|---|---|
| Central Research Laboratories |
Central Research Laboratories 250 Highway 19 Red Wing, MN 55066 |
| Sphincter | No longer in business |
| Zollinger | Overly Manufacturing Co. P.O. Box 70 Greensburg, PA 15601 |
Each of these gloveport designs have been used successfully at the SRS. However, many of the Sphincter design gloveports in the mechanical line gloveboxes have deteriorated after many years of use. This deterioration increases air leakage past the glove seals. The primary causes of the air in-leakage are excessive dimensional tolerances in the gloveport parts, and deterioration of elastomer O-rings used to affect the seal. Further, Sphincter no longer manufactures gloveports or replacement parts. As a result, a program is now underway to determine the best solution to minimize air in-leakage and improve on the Sphincter design.
Gloveport failure data for mechanical line was provided by the Savannah River Technology Center (SRTC), Safety Analysis and Risk Management Department (SA&RM). The keyword survey search of the database contained contamination, assimilation, rupture, and puncture occurances associated with mechanical line operations and maintenance.
The results of this study indicate that gloveports manufactured by Central Research Laboratories provide the overall best reliability at SRS. This assessment is based on several factors, including glove-to-port seal life and air in-leakage past the gloveport seals. These records also indicated that glove changes can be made in shorter times with fewer workers than required by the Sphincter and Zollinger designs. These attributes culminate in a significant decrease in radiation exposure and assimilation risk of maintenance personnel replacing gloves. Furthermore, the Central Research design reduces the number of expendable hardware parts required to achieve a glove replacement. This reduction in expendable materials can result in a significant reduction in contaminated waste volume generated during a glove replacement. Based on this information, the Central Research gloveport design was judged to be superior to the other two designs for the mechanical line application.
The review of the operating information and maintenance records for FB-Line mechanical line indicated that the Zollinger gloveports provided satisfactory containment when well maintained but required more frequent replacement of gloves. These records showed these gloveports to have a greater propensity for air in-leakage around the seal. The need for more frequent replacement in turn resulted in more radiation exposure to personnel replacing gloves.
Sphincter no longer manufactures gloveports and was not considered to be a viable future source for gloveports or replacement parts.
The following is a comparison of the Central Research gloveports and the Zollinger gloveports.
Gloves in Central Research gloveports can be changed by one maintenance person usinga special tool provided by the manufacturer. (Note: additional personnel from Health Protection may be required to monitor the operator's activities.) With this tool, a new glove is forced into the gloveport. As the new glove moves into the gloveport, the old glove is forced out of the gloveport and into the glovebox interior. As the old glove is forced into the glovebox interior, the O-ring seal for the old glove wipes the ID of the gloveport. This action removes any gross contamination from the ID surface ahead of the new glove seal. A confinement seal is maintained throughout the operation - initially by an O-ring associated with the old glove followed by an O-ring associated with the replacement glove. The maintenance personnel do not have any direct contact with the old glove assembly during the glove changing operation. The operation takes as little as 20 minutes to perform a single glove change.
In contrast, changing gloves in a Zollinger gloveport requires two maintenance personnel to contact the old glove assembly. These personnel must perform the following operations:
Typically, a glove change in a Zollinger gloveport requires about 60 minutes to perform a single glove change operation.
The same gloveport can be used to transfer items, including the old glove assembly, in or out of the glovebox with the Central Research design.
The Zollinger design does not provide this versatility.
The Central Research gloveport design allows a diaphragm plug to be installed in the gloveport instead of a glove. The plug can be used to replace a glove during extended times when a glove is not required in the gloveport. In addition, the diaphragm can be used to mount sealed bulkhead service couplings for electrical, hydraulic, or pneumatic connections into a glovebox.
The Zollinger design does not provide this versatility.
The Central Research gloveport design allows a window to be installed in the gloveport instead of a glove. The window may contain shielding materials if desired.
The Zollinger design does not provide this versatility.
The Central Research design allows a safety cover to be installed in the gloveport. These safety covers can provide enhanced fire protection and can confine gases that can potentially permeate through the gloveport.
The Zollinger design does not provide this versatility.
Conversion of gloveports between manufacturer designs is relatively simple for the window mounted gloveports. Therefore, the use of the existing inventory of Zollinger gloveports is suggested prior to a total conversion to Central Research gloveports. Conversion to the Zollinger window mounted gloveports will allow the consumption of the existing inventory of Zollinger gloveport parts. After the inventory of Zollinger parts is depleted, these gloveports can be readily converted to the Central Research design.
Conversion of the metal panel mounted gloveports is complicated because many of the gloveports are welded to the metal panels. The gloveports need to be cut from the panels or the entire panel including the gloveport will need to be replaced. The conversion would be performed in a radiologically controlled area by "Q" cleared personnel. Confinement huts will be required to perform this operation. Maintenance personnel will be required to wear plastic suits with fresh air supplies. Thus, the conversion of the gloveports will be expensive. It would not be cost effective to convert these gloveports to the Zollinger design and then later reconvert them to the Central Research design. Thus, the direct conversion of the metal panel mounted Sphincter gloveports to Central Research gloveports is recommended.
Two concepts for converting metal panel Sphincter gloveports to Central Research gloveports are:
The clamp-in style is available with either aluminum or stainless steel components; however, the material types should not be mixed in the same gloveports. This style can be mounted in metal, plastic, or glass panels. the weld-in style is available only with stainless steel components and is the style recommended for mounting in metal panels.
The gloveport design furnished by Central Research Laboratories is superior to the Zollinger or Sphincter designs (for use in the WSRP FB line). Based on WSRC operating experience, the Central Research design provides better resistance to air leakage past the glove-to-gloveport seals. Further, glove replacement with this design can be performed in shorter time with a resultant decrease in the radiation exposure of personnel performing the installation. The design also provides more versatility than the other two designs assessed. This versatility includes the capability of converting the gloveport to a bagging port, a shielded window, or a sealed port. The design allows safety shields to be installed and allows purging of air during glove replacement to minimize the volume of air transferred to the glovebox during a glove change.
The Sphincter design is not considered to be a viable alternative. This manufacturer no longer makes gloveports or replacement parts for gloveports. Two concepts for converting the Sphincter gloveports in window and metal glovebox panels were provided by the study.
The Zollinger design had greater incidence of air leakage past the glove-to-gloveport seals than the Central Research design based on mechanical line experience. This design also requires more personnel and longer times to replace gloves than required by the recommended design. However, the Zollinger gloveport will provide acceptable service when properly installed and maintained.
Sharad S. Shetty is a Senior Engineer for the Westinghouse Savannah River Company. In his current position, Mr. Shetty acts as a systems engineer in the Engineering and Projects Division of the Savannah River Site, Aiken, SC. He has a Masters of Engineering degree in Industrial Engineering from the University of Pittsburgh. Mr. Shetty has over 16 years industrial experience including 9 years with Department of Defense and Department of Energy projects as well as projects in the petrochemical and pulp and paper industries.
Joseph M. Gilkison is a Principal Engineer for the Westinghouse Savannah River Company. He has a Masters of Engineering degree in Metallurgical Engineering from the University of Illinois. Mr. Gilkison has 29 years experience including 19 years in the commercial nuclear industry and at the Savannah River Site.
AGS Editor's Note: This article represents the findings of a study at SRP and additional factors should be considered when selecting a gloveport system for any application. The preferences stated in this article represent conditions including significant potential radiation exposure, high maintenance overhead costs, high waste processing and disposal costs, and other factors not present in many facilities. Overall cost of the gloveport system, operator exposure hazard, maintenance cost, frequency of use, consequences of containment loss, versatility of gloveport system, and other factors must be weighed in the decision on which system to use. The AGS does not endorse products or ensure their suitability or reliability. This article presents the findings of the authors and not the society and is published to present information to the membership and encourage information exchange and discussion about this topic. Please feel free to respond to this article with letters or additional articles to present your viewpoint. American Glovebox Society