Packaging of Plutonium Metal and Oxide in the ARIES Project

The objective of the Advanced Recovery and Integrated Extraction System (ARIES) Project is to demonstrate technology to dismantle plutonium pits fi-om excess nuclear weapons, convert the plutonium to a metal ingot or an oxide powder, package the metal or oxide, and veri@ the contents of the package by nondestructive assay. The packaged weapons plutonium will be converted to mixedoxide reactor fuel or immobilized in ceramic forms suitable for geologic storage. The packaging of the material must therefore be suitable for storage until the material is further processed. A set of containers for plutonium metal and oxide has been developed to meet the needs of the ARIES process and the Department of Energy requirements for long-term storage. The package has been developed and qualified with the participation of private companies.


Introduction
Removal of nuclear weapons from the stockpiles of the United States and Russiz along with the need l%r stabilization of plutonium residues from production plants, has required development of containers fm safe storage of plutonium, potentially over a period of decades. schedule requirements of the ARIES Project demanded that containers be available in 1998. To meet this schedule, a simple design was developed for containem that would meet DOE-STD-3013. At the beginning of ARIES container development the 1994 version of this standard (1) was in force. The 1996 version of the standard(2) did not introduce requirements that could not be met by the design in progress.
The development of the container design was iterative, with consultation with potential container manut%tums providing assurance that the containers could be easily and cost-effectively manufactured. Bodies and tops for both inner (material) and outer (boundary) containers were designed to be manuthctured by standard deep drawing methods. Containers were designed in two sizes to meet project requirements, having a 6.5-in. height and a 10-in. heighb oth with 4.92-in. diameters.
A weldment was developed to meet the requirements cf ASME IX: Boiler and Pressure Code (3). Plutonium metal or oxide is inserted into the material container, and the container is welded in a glove box. The inner container is then decontaminated by electrolytically removing a l%v atomic layers from the surfime of the stainless steel along with associated radionuclides. The inner container is removed from the decontamination station and the glove box line after decontamination has been confirmed to less than 20 dpm/100 cmz removable contamination and total contamination of 500 dprn/100 cm2, as required by 10 CFR 835, Appendix D (4). The inner container is then welded into the outer containc~. After every welding operation and decontaminatio~the container is leak checked to assure leak tightness to 107 std-cc/sec He, as required by ANSI N14.5 (5).
These storage containers can accept plutonium metal or plutonium oxide prepared to the requirements of DOE-STD-3013-96 (2). Multiple types of convenience containers can be used for plutonium oxide.

Design Requirements
The primary criteria used in the design of the storage package were obtained from DOE-STD-3013-96 (2). Additional requirements wexe imposed by the ARIES nondestructive assay (NDA) module. The design requirements are summarized below.
A minimum of Wo nested scaled containers. At least one container remains leak-tight as defined by ANSI N14.5 after a free drop horn a 9-m height Container materials are resistant to corrosion in the anticipated storage environment not combustible or organic.
Atmosphere inside containers precludes re-stabilizing the material contents. Containers will be leak-tight as defined in ANSI N14.5. Containers allow fm ND& material verification, inspection and surveillance. Containers will be permanently marked. Design hydrostatically proof-tested to 1.5 times the calculated theoretical maximum pressure, remaining leak-tight after the test. Inner container sized to fit into outer container with clearance for welding. Inner container allows fbr nondestructive indication d 100 psi pressure buildup or less. Exterior surfaces of the inner and outer containers and interior surf%e of outer container are &e of external contamination as defined by 10 CFR 835, Appendix D.
Maximum outside diameter of the outer container is 12.5 cm, and the maximum external height is 25.4 cm. Convenience container includes no organic materials.

Fabrication and WeIding
The container paclqge consists of three containers fm plutonium oxide, and two for plutonium metal. The ,:.. iiuwrmost container (convenience container) fm plutonium oxide is a crimp-sealed fd pack can containing no elastomem. The inner and outer containers are welded Type 304L stairdess steel. The outer diameter of the outer container for both 6.5-and 10-in. sizes is 4.92 in. The outer container has a pintle fixture on the top for robotic handling. The wall thickness of the inner container for both sizes is a minimum of 0.040 in.; fm the outer container, a minimum of 0.080-iu. All containers have a 3/8-iu. radius of curvature joining the cylinder top and bottom to the sides. Figure 1 shows the 10-in. container paclmge. The containers zne permanently marked with a laser marker. Markings are both human-and machine-readable.
Several fabrication methods, including deep drawing, spinning, and flow forming, were considered fbr the fabrication of storage package.
Industrial firms were consulted fm their recommendations on ease of tkbrication. After evaluation of manufacturing feasibility, COS$ reliability, and repeatability, deep drawing was selected as the manufwturing process for both the inner and outer containers. Issues related to can roundness, container wall thickness, alignment between can and li~were aU addressed early in development.
The inner and outer containers are sealed with a full penetratio~autogenous weld. The weldment is performed with a gas tungsten arc process and meets the requirements of the ASME Section IX: Boiler and Pressure Vessel Code (3).
All weldments are ptiormed in a heliumatmosphere with anoxygenconcentration of less than 50 ppm. Helium shield gas is used to aid in heat transfm and weld penetration act as an oxygen barrier, and to keep the torch cool. Pulsed current is supplied by a programmable controller and power supply. The containers are welded in the vertical position. The can is rotated while the torch remains stationary. A tixture was thbricated to keep the lid aligned with the can body and maintain constant electrode-to-surface spacing.
The weld joint fm both containers is a butt joint with no filler material added. Anon-radioactive tongsten electrode is used fm both containem. Pulsed current was used to minimize weld puddle sagging. The pulse peak current used fw the inner container was 150 amps and fm the outer container, 175 amps. The average current is 34 amps for the inner container and 75 for the outer container.
A part of the requirements of ASME Section IX: Boiler and Pressure Vessel Code (3), weld samples were subjected to tensile tests and &&and-root bending moment tests, and photomicrographs of the welds were taken. The weld meets container sealing requirements for DOE-STD-3013-96 (2). Because the containers am welded in a helium atmosphere, helium gas is encapsulated in the containers, which meets the DOI?-STD-3013-96 requirement fm a nonreactive atmosphere (2). The helium atmosphere also allows for leak checking the weld joint by placing the container in a vacuum chamber and detecting the presence of helium.

Testing
A comprehensive testing plan included all requirements specified in DOE-STD-3013-96 (2) and additional tests to obtain data on the handling characteristics and strength cf the containers. Drop, crush and pressurization tests were specified.
All container parts were fiabncated by Toledo Metal Spinning Company, Toledo, Ohio. Befm being welded, the containers were loaded with a non-radioac,tive metal payload to simulate plutonium oxide or metal loading. The container assemblies were welded at the Los Alamos NationaI Laboratory. Tke containers were leak checked atkr welding. All of the 76 containers welded fix testing had a leak rate of less than 1x1O-9 std-cc/sec at one atmosphere. A Varian Portatest II leak detector was used.
The results of the tests follow.

Four-Foot Drop
Test. The purpose of this test was to determine the integrify of the container after a drop typical cf what might be sustained in processing. This test is not required by DOE-STD-3013-96 (2). Two inner containers cf each size loaded with 4.5 kg of simulated metal and two loaded with 4.5 kg of simulated oxide were dropped tium 122 cm (4 ft). Visual examination of the containers after the drop test revealed minor scratches. Helium leak testing showed that all contaiuem were leak-tight to less than 1 x 109 .st&w/sec after the tes~and the presence of helium in the containers was verified.

Nine-Meter Drop
Test. This test is required by DOE-STD-3013-96 (2). Three stomge packages of each size loaded with 4.5 kg of simulated metal and three loaded with 4.5 kg cf simulated oxide were dropped from 9 meters (30 tl). Visual examination of the containem after the drop test nwealed minor deformations. Helium leak testing showed that all outer containers were leak-tight to less than 1 x 10-9 stdcdsec afler the tes~and the presence of helium in the containers was verified.
Inner Container Crush Test. These tests were done to determine the strength of the design in possible handIing incidents. They are not required by DOE-STD-3013-96 (2). For each size, one crush test was conducted using two pairs of inner cans filled with 4.5 kg of simulated metal; another was conducted with 4.5 kg of simulated oxide. One test tied the impacting container in a vertical orientation, and the other test held it horizontal. The impacting container was released km a height of 61 cm (2 ft). Visual examination of the containers after the test revealed minor scmtches. Helium leak testing showed that all outer containers were leak-tight to less than 1 x 10-9 std-cc/sec after the test and the presence of helium in the containers was verified Storage Packrge Crush Test. These tests were done to determine the strength of the design in possible handling incidents. They are not required by DOE-STD-3013-96 (2). For each size, one crush test was conducted using two pairs of storage containem filled with 4.5 kg of simulated meta~I I . . another was conducted with 4.5 kg of simulated oxide. One test fixed the impacting package in a vertical orientation% and the other test held it horizontal. The impacting package was released fium a height of 3 meters (10 ft). Visual examination of the storage paclmges * the test revealed minor deformations. HeIium leak testing showed that all outer containers were leak-tight to less than 1 x 10-9 std-CCISCC after the test and the presknce of helium in the contaimm was verified.
Hydrostatic Tests. Hydrostatic testing is required to 1.5 times the theoretical maximum pressure calculated as specified by DOE-STD-3013-96 (2) fm the outer container. In addition, the deflection of the ends of the irmer containem will be used to indicate pressures of less than 100 psi, as required by DOE-STD-30 13-96 (2). Hydrostatic tests wem conducted on five inner and five outer containers of both sizes. The change in container height was measured as the pressure was graduaUy increased to 750 psi. The pressure was finther increased on three of each container until the container burst. For an internal pressure of 100 psi, the total length of the inner 6.5-in. container increases approximately 0.120 in., and the total length of the inner 10-in. container increases approximately 0.090 in. For an internal pressure of 500 psi, the length of the 6.5-in. outer container increases approximately 0.150 in. fm an internal pressure of 500 psi, and the length of the 10-in. outer container increases approximately 0.150 in.
Burst tests were done to acquire data on material strength. They are not required by DOE-STD-3013-96 (2). The three imer 6.5-in. containers burst at pressures of 3456, 3513, and 3492 psi. The three inner 10-in. containem burst at pressures of 3230,3002, and 3451 psi. The three outer 6.5in. containers burst at pressures of 6444, 5345, and 6068 psi. The three outer 10-in. containers burst at pressures of 7496, 7400, and 6010 psi. Failure for all containers except the 10-in. outer containem initiated at the pressure fitting welded into the container for the test. Because these fittings are not apart of the container as it will be use~these burst pressures are minimum values that can be expected under actual working conditions. The 10-in. outer containers failed at the circumferential weld.

Conclusions
The design of long-term plutonium containem fm the ARIES Project includes a minimum of tsvo nested sealed containers hbricated of corrosion resistant stainless steel. The containers are welded in a helium environment and = leak-tight as defined by ANSI N14.5.
The containers, including the convenience C* are &e of organic material. The container storage paclmge has successfully passed the drop and pressurization specified in DOE-STD-3013-96 as well as additional handling and material strength tests. The design chamcteristics of the container package and the successfid testing allow us to state that the containers meet DOE-STD-3013-96.