ML20138D480
| ML20138D480 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 03/31/1997 |
| From: | Henson T, Hurrell S, Chris Miller External (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20138D407 | List: |
| References | |
| KY-G-558, KY-G-558-R01, KY-G-558-R1, NUDOCS 9705010135 | |
| Download: ML20138D480 (26) | |
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to GDP 97-0051 KY/G-558 Revision 1 Criteria for Transportation of Fissile Materials in Areas Without Criticality Accident Alarm Coverage at the Paducah Gaseous Diffusion Plant March 1997 4
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KYlG-558 CRITERIA FOR TRANSPORTATION OF FlSSILE MATERIALS IN AREAS WITHOUT CRITICALITY ACCIDENT ALARM COVERAGE AT THE PADUCAH GASEOUS DIFFUSION PLANT l
Revision 1 T.L.Henson Lockheed Martin Utility Services, Inc.
S. J. Hurrell Safety Solutions I
i C. S. Miller Parallax, Inc.
March 1997 1
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DISCLAIMER i
This report was prepared as an account of work sponsored by an agency of the United States Govemment. Neither the United States Govemment nor any agency i
thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not ininnge privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Govemment or any agency thereof. The views and opinions of authors expressed therein do not necessarily state or reflect those of the United States Govemment or any agency thereof.
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DATE OF ISSUE: March 1997 KY/G-558 Revision 1 S. J. Hurrell Safety Solutions C. S. Miller Parallax, Inc.
T.L.Henson Lockheed Martin Utility Services, Inc.
APPROVALS lac MP 3
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] In,?n u 3-al-97 Criticality S5fety Review Date 3[.2ifG Nu 6? Criticality Safety Manager Date Prepared by LOCKHEED MARTIN UTILITY SERVICES, INC.
Paducah Gaseous Diffusion Plant P. O. Box 1410 Paducah, Kentucky 42002-1410 for the UNITED STATES ENRICHMENT CORPORATION Under Contract No. USECHQ-93-C-0001 iii i
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Table of Contents 1.0 I N TR O D U CTI O N..............................................
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2.0 DESCRIPTION
OF FISSILE MATERIAL TRANSPORTATION OPERATIONS.1 2.1 WAS T E D R U M S..........................................
1 2.2 S AM P L E S...............................................
2 2.3 REMOVED PROCESS EQUIPMENT.........................
3 2.4 U F PRODUCT CYLINDERS................................
4 2.5 OTHER TRANSPORTATION OPERATIONS....................
5 3.0 CRITERIA FOR TRANSPORTATION OF FISSILE MATERIALS OUTSIDE C AAS C O V E RA G E............................................
5 3.1 WASTE DRUM TRANSPORTATION..........................
5 3.2 SAMPLE TRANSPORTATION...............................
6 3.3 REMOVED PROCESS EQUIPMENT TRANSPORTATION.........
6 3.4 TRANSPORTATION OF SOLID CYLINDERS...................
7 3.4.1 D E S C R I PTI O N.....................................
7 3.4.2 M ETH O D O LO G Y...................................
8 3.4.3 RESULTS OF THE CYLINDER TRANSPORTATION ANALYSIS 16 l
3.5 TRANSPORTATION OF MATERIALS OF LESS THAN A SAFE MASS, SAFE VOLUME, OR SAFE GEOMETRY................
15 3.6 TRANSPORTATION OF PACKAGES FOR WHICH CRITICALITY HAS BEEN SHOWN TO BE INCREDIBLE.........................
16 3.7 TRANSPORTATION OF PACKAGES CONTAINING s15 g 23sU....
16 3.8 TRANSPORTATION OF ITEMS ENRICHED TO LESS THAN
- 1. 0 WT 23 5 U.............................................
1 7 3.9 USE OF MOBILE DETECTORS DURING TRANSPORTATION....
17 4.0 C O N C L U S I O N S.................................................
17 R E F E R E N C E S.....................................................
18 APPENDIXA......................................................20 i
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KY/G-558, Rev.1 I
1.0 INTRODUCTION
The purpose of this evaluation is to show compliance with 10CFR 76.89 at the i
Paducah Gaseous Diffusion Plant (PGDP) during transportation activitios. Section 76.89 requires that enriched uranium materials and processes be within Criticality i
Accident Alarm System (CAAS) detection coverage. The code also states that the i
corporation may describe for the approval of the commission defined areas to be j
excluded from the monitoring requirement.' Therefore, this document will outline i
transportation activities where the quantities or configurations of uranium are controlled
~such that CAAS coverage is not warranted.
All buildings where uranium enriched greater than 1.0 weight percent 23sU is handled, 4
used, or stored at PGDP have either an installed Criticality Accident Alarm System or a justification for exclusion from alarm coverage. In some situations the building alarms l
provide coverage to some roads and areas directly outside the building walls; however, i
many of the roads and associated areas on the Paducah site do not have CAAS coverage. This report will outline the criteria that must be met during the transportation j
of fissile materials in areas without CAAS coverage.
There are several types of fissile material items transported on site at PGDP. Some of the items transported at PGDP are UF, product cylinders, removed process equipment, waste drums, samples, buggies, vacuum cleaners, among others. All of the fissile material items which are transported fall into one of the categories described in section 2.
2.0 DESCRIPTION
OF FISSILE MATERIAL TRANSPORTATION OPERATIONS 2.1 WASTE DRUMS Potentially fissile / fissile waste is generated in several facilities at the PGDP. These areas include, but are not limited to C-331, C-333, C-335, C-337, C-310, C-710, and C-720.- NCSA GEN-15 governs the generation, handling, storage, and transportation of potentially fissile waste.2 This NCSA restricts the containers used for accumulating potentially fissile waste to maximum 5.5 gallons drums or maximum 21 liter polybottles.
Unless 'a specific NCSA allows otherwise, the waste containers are required to be spaced a minimum 2 feet edge-to-edge from each other and all other fissile /potentially fissile material. The accumulation, staging, and storage of fissile /potentially fissile waste must be provided with CAAS coverage in accordance with the applicable facility TSR. After accumulation, the drums are then transported to a Temporary Fissile Storage Area (TFSA) where they are characterized in accordance with NCSA WM-01.
Drums containing less than 120 g 23sU are released from spacing controis. The 120 gram 23sU mass criterion is based on calculations using maximum 5.5 gallon waste drums which contain material enriched to 5.5 weight percent 23sU.3 This safe mass may be conservatively extrapolated to larger containers due to the lower resulting areal 1
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KY/G-558, Rev.1 density of uranium and smaller slab heights at optimum H/X ratios in the larger containers.
Waste consolidation is the repackaging of characterized low density uranium waste into 55 gallon (i.e. maximum 58 gallon) containers. Waste consolidation activities are limited to a maximum of 120 g 23sU per 55 gallon container. As stated above,120 grams 23sU is the safe mass for nominal 5 gallon and larger drums. Currently, waste characterization of fissile /potentially fissile waste is performed in C-335, C-310, and C-333. Waste drums generated in locations elsewhere must be moved to one of these three buildings to be characterized. NCSA GEN-15 gives the following rules for transporting potentially fissile wastes:
Multiple waste containers may be transported to the characterization facility simultaneously provided NCS-approved physical restraints are used to ensure a 2-foot minimum edge-to-edge spacing is maintained at all times.
No physical restraint system or containment pan is required when transporting a single waste container. The single waste container shall not be transported with other fissile material.
Waste containers shall be removed from, or loaded into the physical restraint system one drum at a time.
The physical restraint system used for the simultaneous transportation of multiple fissile waste containers shall include provisions to positively restrain the container lids and the containers themselves in place during movement.
There shall be no stacking of physical restraint systems during transportation of waste containers.
Outdoor transportation of waste containers shall be performed in dry weather or performed using a material handling vehicle or other means which provides adequate covering to ensure the containers remain dry during transportation.
2.2 SAMPLES 4
NCSA GEN-08 provides the requirements necessary to ensure fissile /potentially fissile samples are handled, stored, and transported safely from a Nuclear Criticality Safety standpoint. Samples are required to be placed in safe batches. The sample batch limits were established such that when double batched the resulting configuration is subcritical. Each sample batch is required to be spaced from other fissile /potentially
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a KY/G-558, Rev.1 fissile material. NCSA GEN-08 gives the following rules for transporting potentially fissile samples:
One batch of samples may be transported provided that the batch of samples is spaced a minimum of 2 feet edge-to-edge from all other fissile /potentially fissile material.
When multiple batches of samples are transported by vehicle each batch of samples must be securely positioned a minimum 2 feet edge-to-edge from all other fissile /potentially fissile material.
2.3 REMOVED PROCESS EQUIPMENT 5
The current issuance of Nuclear Criticality Safety Approval (NCSA) GEN-10, which is subject to change as needed for cascade maintenance operations, covers the removal, handling, and transportation of removed process equipment that is not already covered by another specific NCSA. The equipment types covered by NCSA GEN-10 are axial compressors, centrifugal compressors / pumps, converters, process gas coolers, freezer /sublimers, process gas valves, process gas pipe, expansion joints, etc. These equipment types were identified as having the potential to contain greater than a safe mass of uranium. The term safe mass is defined as the amount of material that will be just subcritical when double batched. Prior to removal from the cascade, process equipment which has not been classified as Uncomplicated Handling (UH) based on geometry must be inspected by approved methods (NDA or visual) and categorized as either UH or Planned Expeditious Handling (PEH) based on this inspection. These categories indicate whether the piece of equipment contains greater than the safe mass of uranium at its enrichment. After the equipment is removed from the cascade, it's category is verified with another NDA or visual inspection. If the category has been verified to be UH and the mass is greater than 5 pounds of uranium, a minimum two feet edge-to-edge spacing from any other containers or equipment containing fissile or potentially fissile material must be maintained at all times, including during transport. If the category is verified to be PEH, the NCSA requires that the following steps be taken:
1)
Arrange for removal, transportation (as necessary), and j
processing / decontamination prior to breaching the system.
2)
Cover all openings with fireproof covers and gasket seals to minimize intrusion of moderator.
3)
A remediation/ decontamination effort shall be started within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the first system cut. This work shall continue in such a manner that the uranium deposit is reduced below the safe mass within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after the remediation effort begins. If the remediation effort cannot be completed within this time, NCS shall be contacted and the openings to the equipment shall be covered with fireproof covers, a dry air or nitrogen 3
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buffer shall be applied, and case specific NCS guidance shall be provided i
for handling the equipment, i
- 4) PEH equipment shall be spaced a minimum of 10 feet edge-to-edge from each other and shall be spaced a minimum of 6 feet edge-to-edge from containers or non-PEH equipment containing fissile or potentially l
fissile material.
- 5) Only one piece of PEH equipment shall be transported per vehicle, the PEH spacing requirements shall be maintained during transportation (this shallinclude spacing from vehiclos containing fissile or potentially fissile material to ensure proper spacing is maintained), and the equipment shall not be transported with any other equipment containing fissile or potentially fissile material.
i 2.4 UF, PRODUCT CYLINDERS Enriched UF, is withdrawn from the cascade in building C-310 and is placed into 10-ton cylinders for shipment. Before the cylinders are allowed to be transported, they must be cooled to allow solidification of the UF., To provide for this, filled cylinders are moved to the C-310 cylinder cooling yard. Except for rare occasion, this is the only time a liquid cylinder is moved. The TSRs for the Product and Tails Withdrawal Facilities outline requirements for moving a liquid cylinder 1
1)
Liquid-filled cylinders shall not be removed from the withdrawal room without a cylinder valve protector installed.
2)
Liquid-filled cylinders shall be lifted only with overhead cranes meeting the conditions set forth in TSR section 2.3.5.2.
3)
No UF, cylinder shall be moved over another cylinder when either cylinder contains liquid UF.
l After cooling, cylinders are normally transported to C-400 to be loaded into overpacks on train cars for shipment. Cylinders are also taken on a regular schedule to Building
' C-360 for sampling and, occasionally, when the number of product cylinders to be
' shipped is large, they are transported to a long term cylinder storage yard. Section 3.4 further explains how product cylinders are transported and provides the justification for exclusion from CAAS coverage.
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KY/G-558, Rev.1 2.5 OTHER TRANSPORTATION OPERATIONS l
The transportation of UF product cylinders, samples, removed process equipment, and waste drums are described in detail in Section 2; however, these are not the only fissile materialitems which are transported at PGDP. Other items, such as Negative Air Machines (NAMs) and sample buggies, are also transported in areas without CAAS coverage. In order for an item to be transported outside of CAAS coverage, the item must fall into one of the following categories:
1.
The item contains less than a safe mass, safe volume, or is of a safe geometry.
2.
The item has been shown to be subcritical under credible process upsets.
3.
The item contains 15 grams 23sU or less and is packaged in accordance with DOT fissile excepted requirements.
4.
The item contains uranium enriched to less than 1.0 wt% 23sU.
The above criteria is described in greater detail in Section 3. Items which do not fall into one of the above categories must be transported using a mobile detection system.
The use of mobile detectors is also described in Section 3.
3.0 CRITERIA FOR TRANSPORTATION OF FISSILE MATERIALS OUTSIDE CAAS COVERAGE All the above categories of fissile materials must meet the requirements of 10CFR@76.89 during on site transportation. The following sections outline several independent criteria whereby, an exception to CAAS coverage is warranted.
3.1 WASTE DRUM TRANSPORTATION Typically, waste drum operations involve very low density uranium. Potentially fissile waste is generated in containers which have been shown to be a safe volume for its enrichment. These drums are also spaced with physical restraints to reduce the possibility of interaction. Controls have been developed in plant NCSA GEN-15 to ensure that physical restraints be used at all times when transporting more than one potentially fissile waste drum, and that if physical restraints are not used, only one drum may be transported at a time.
2 KY/S-253 discusses NCS spacing violations during transportation of fissile drums.
Most spacing violation scenarios are shown to be incredible, and the few that are not have been shown to be subcritical. Based on the arguments proposed in KY/S-253, it is judged that transportation of fissile waste drums does not require criticality alarm coverage.
Once characterized, drums which contain less than 120 grams 23sU are transported to a LLW storage area. KY/S-267 provides the basis for not needing CAAS coverage for 5
i KY/G-558, Rev.1 the storage of drums containing less than 120 grams 23sU in LLW storage areas at PGDP.' No credible criticality accident scenarios were identified in KY/S-267 for the storage of LLW. Although KY/S-267 only analyzed the storage of LLW drums, it can be used as the basis for not requiring CAAS during the transportation of LLW drums.
KY/S-267 considered the process upsets, such as a fork lift accident or earthquake, involving a large number of drums and determined that a criticality resulting from such j
an event is incredible. Based on KY/S-267, if each drum of LLW contained 120 grams 25 U, the contents of more than 10 drums are required to provide sufficient mass for a l
critical configuration. Additionally, all of the material from the drums would have to form a sphere and be optimally moderated and reflected. Although it is possible for more than 10 drums to be transported at a time, it is unrealistic to assume that 10 drums of material would be released and the contents form an optimally moderated fully reflected i
sphere. Therefore, the transportation of drums containing 120 grams 235U or less may be done outside of CAAS coverage.
3.2 SAMPLE TRANSPORTATION The handling and transportation of potentially fissile samples have been studied
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extens'ively in NCSE GEN-08.' Sample batch limits, based on the sample matrix and the maximum plant enrichment of 5.5 wt%, have been determined such that one single batch cannot be made critical. The NCSA incorporates spacing limits during transportation of more than one batch of samples that require 2 feet spacing between batches.
NCSE GEN-08 shows that the maximum subcritical mass of samples would be more than 70 lbs.' Sampling operations at PGDP typically deal with very low uranium density materials and only a few samples at a time The likelihood of transporting a great number of high density samples and concurrently having spacing violations is extremely remote. Therefore, transportation of samples does not require criticality alarm coverage.
3.3 REMOVED PROCESS EQUIPMENT TRANSPORTATION Removed process equipment labeled uncomplicated handling (UH) has been 1
specifically shown to contain less than a safe mass of uranium based on the chart in Appendix A.5 NCSA GEN-10 limits the number of pieces of UH equipment transported per vehicle to 2. Further, the evaluation performed for the NCSA demonstrates that any 2 pieces of UH equ!pment can not be made critical. Since the quantity of uranium has been specifically determined and cannot be made critical, there is no need for criticality alarm coverage during transport of UH equipment.
Removed process equipment labeled planned expeditious handling (PEH) contains either an undetermined mass of uranium or an amount greater than the safe mass based on the chart in Appendix A. This equipment requires special handling and transportation limits such as prearranged plans for removal and decontamination and 6
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l 10 feet edge-to-edge spacing from other PEH equipment. Since this equipment contains greater than a safe mass of uranium, criticality alarm coverage is necessary at l
all times until the equipment nas been decontaminated to below a safe mass. In some l
cases this decontamination can be performed without removing the equipment from building CAAS coverage (decontamination in the. building in which the equipment is i
removed from the cascade). Some equipment, however, such as converters and l
compressors, must be decontaminated in buildings other than the cascade buildings.
This requires transportation outside building CAAS coverage which will necessitate mobile alarm coverage. This type of alarm coverage is discussed further in section 3.9.
3.4 TRANSPORTATION OF SOLID CYLINDERS l
The transportation activities addressed herein involve the movement of UF, cylinders that may contain 21% 235U outside of areas provided with CAAS coverage. This section evaluates the nature of hazards associated with and the controls applied to the 21 wt %
23sU material stored to determine credibility of a criticality accident. If it can be demonstrated that a criticality accident is not credible during the onsite movement, then exclusion from CAAS coverage of plant areas through which the UF, cylinder may be moved is warranted. It should be noted that the process buildings are supplied with CAAS coverage and a justification for excluding cylinder storage yards from CAAS coverage is provided in Reference 7.
The accident initiators addressed in this justification include: transportation accidents involving low-boy haulers used to move filled solid cylinders onsite and handling accidents during the transfer of the cylinders from the low-boys to the cylinder yard storage saddle. The accident scenarios model cylinder breach and detection / mitigation j
of the accident consequences. Moderation involves the introduction of moderator, in this case water,into the cylinder. Detection involves identification of a breach in the cylinder that could permit the introduction of moderator into the cylinder. Mitigation involves a measured response to the accident conditions designed to preclude a critical configuration. In this particular case, mitigation may be as simple as covering the damaged cylinder with plastic or driving a wooden plug into the hole to preclude the introduction of water.
3.
4.1 DESCRIPTION
The PGDP product is withdrawn into 10-ton cylinders from the process cascade at Building C-310. After the UF, has solidified (approximately 5 days), these product cylinders may be moved from the Building C-310 cylinder cooldown yard to:
Building C-400 cylinder yard where the cylinders are placed in an l
overpack for offsite shipment by rail, l
A cylinder storage yard where the cylinders are temporarily stored, or 7
KY/G-558, Rev.1 Building C-360 cylinder yard where the cylinders are sampled.
It should be noted that both Building C-310, C-360, and C-400 are provided with CAAS coverage. If there is insufficient storage space at the Building C-400 storage yard, the cylinders are moved to another storage yard for interim storage. When space becomes available, the cylinders may then be moved to C-400 for packaging and offsite shipment. The storage yard currently used as interim storage is C-745-B. However, 4
this justification is applicable for movements to and from all PGDP cylinder storage yards and C-360.
Using the C-310 cylinder yard crane, the cylinders with solidified UF, are loaded onto a low-boy trailer. A low-boy is a heavy duty trailer designed to haul four or five 10-ton cylinders at one time. Once the low-boy is loaded, it is moved directly to the storage yard or Building C-360 and unloaded. The unloading at the stoiage yard is accomplished using a cylinder handler. The cylinder is placed in a saddle slightly elevated off the ground that prevents the cylinder from rolling. When the cylinder is moved to C-400 for offsite shipment, the cylinder is loaded using the cylinder handler onto the low-boy for movement. The loading and unloading of the cylinder at C-360 is accomplished using the C-360 crane. It should be noted that the equipment used to handle UF, cylinders (i.e., cranes, lifting ropes, low-boys, and cylinder grabbers) is routinely inspected for damage that might cause a cylinder to be dropped.
3.4.2 METHODOLOGY The purpose of this evaluation is to justify the exclusion of the onsite UF, cylinder transportation operation from CAAS coverage. The criticality hazards and the controls applied to the 21 wt % "U material during cylinder transportation are analyzed to 2
determine the credibility of a criticality accident. The basic approach to the evaluation is to identify the controls and any necessary conditions for criticality, identify methods of failing the controls and achieving the necessary conditions (i.e., criticality scenarios),
and estimate the frequencies of the criticality scenarios semi-quantitatively. This approach is implemented through the application of the cylinder yard criticality event tree shown in Figure 3.1. This event tree is comprised of two events that define a general criticality scenario: a cylinder breach and detection / mitigation of the breach.
The initiating event of the general event tree is "a cylinder breach." The two initiating events considered in this justification are transportation accidents and handling accidents. Each event tree sequence is assigned an endstate of either "NC," no critical configuration, or "CC," critical configuration. The methods used to estimate the frequency or probability associated with each event are discussed below. The general event tree represents handling and transportation accident scenarios and is used as a guide in determining the frequency of each criticality scenario.
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A KY/G-558, Rev.1 3.4.2.1 TRANSPORTATION ACCIDENT SCENARIO The transportation accident scenario addresses accidents involving the low-boy during movements to and from C-400, the storage yards, and C-360. The sequence of events that could result in a critical configuration include.a traffic accident in which the cylinder containment is breached, water is available for introduction into the cylinder, and the detection / mitigation of the accident fails such that water introduced into the cylinder remains in the cylinder for an extended period. Each aspect of the accident scenario is addressed in the following sections.
Accidentjnitiator The accident initiator is a traffic accident sufficiently severe that the UF, cylinder is breached permitting the introduction of water. Reference 8 indicates that as many as 800 cylinders per year might be produced at PGDP. The enriched product cylinders will originate at the withdrawal operation in Building C-310. From C-310, the cylinder may be transferred to C-400 for offsite shipment, C-745-B storage yard for interim storage, or C-360 for sampling.
Approximately 10% of the product cylinders will be sent to C-360 for sampling each year. The distance traversed from C-310 to C-400 is approximately a mile and the travel route is conservatively assumed to be outside of the range of any CAAS system.
In reality, approximately 50% of the route would be covered by the CAAS systems at C-360, C-331, and C-310. Using a two mile round-trip distance, the sampling of product cylinders to and from C-360 will result in approximately 160 cylinder-miles of travel per year.
Approximately 50% of all cylinders may reauire interim storage at a cylinder storage yard. All cylinder storage yards are within s c w of Buildings C-310 and C-400.
Therefore, the movement of these cylinders !
- nterim storage using a two mile round-trip distance will result in 800 cylinder-miies of travel per year. Again no credit was taken for the CAAS coverage provided by process buildings on the transportation route. The remaining 50% of the cylinders (400) will be transported directly to C-400 for packaging and offsite shipment. The distance between C-310 and C-400 is approximately one-half mile. Transport of the product cylinders to C-400 using a half-mile one way trip will result in 200 cylinder-miles of travel per year. No credit was taken for the CAAS coverage provided by the process buildings along the route.
Conservatively assuming only one cylinder is transported at a time (four or five cylinders can be transported by a low-boy), the total annual cylinder onsite miles covered by the 800 product cylinders is 1160 cylinder-miles. Reference 9 indicates that the frequency of all truck accidents in parking lots to be 1.29 per million miles traveled.
The cylinder transportation accident was modeled using parking lot accident frequency data because of the slow speeds (<25 mph). It should be noted that filled cylinders are transported at a maximum speed of 15 mph on the PGDP site. It was conservatively 10
KY/G-558, Rev.1 assumed that only 10% of the accidents would result in a cylinder breach. This assumption can be justified by the structural soundness of the cylinder, the rugged construction of the low-boy trailer, and the slow speed of the truck at the time of the accident. Therefore, the frequency of the initiating event is estimated:
From = 1160 cylinder-m:ies/yr x 1.29 E-06 accidents / mile x 0.10 major accidents /all accidents From = 1.5 E-04 major accidents per year.
An evaluation of 10 ton UF, cylinder integrity following drop tests has been conducted at PGDP' ". These tests involved both thin-walled (i.e.,5/16 in, wall thickness) and thick-walled (i.e.,5/8 in. wall thickness) cylinders containing a ballast that simulated the weight and characteristics of UF,'. The impact tests were made from a height of 20 feet with the cylinder in the horizontal attitude onto a solid concrete pad. Thin-walled cylinders were dropped with a horizontal impact from a height of 10 and 20 feet. Thick-walled cylinders were dropped with a horizontal impact from 20 feet. Thick-walled cylinders were also dropped with a vertical impact onto the valve end of the cylinder.
Drops were also conducted from 1 meter onto a 6-in. diameter steel piston to determine the cylinder's resistance to puncture. Following the drop tests, the integrity of the cylinders was pressure tested and the welds were dye penetrant tested. None of the 1
thin walled cylinders showed any indication of failure following the tests. The only failure involved a thick-walled cylinder being dropped onto the piston. A similar test of a thin-walled cylinder did not result in a failure. The damage to the thick-walled cylinder is believed to be a result of weakening from previous drop tests. Additional tests documented in Reference 11 indicated that another 1-meter drop test involving the valve end head striking a piston did not result in a rupture. A 30-foot drop onto the plug end at a 20 angle from the vertical also did not result in a failure. During handling operations at PGDP, no product cylinder would be lifted more than 20 feet. Operations in the cylinder storage yards do not involve lifting the cylinder more than what is necessary to clear the cylinder saddles on the transport trailer which is less than 10 feet. Rupturing a cylinder as a result of a drop in the cylinder yard is not a significant concern because of the minimallifting height and the fact that some of the cylinder yards are gravel which absorbs some of the energy from the dropped cylinder. Also, cylinders are only lifted when it is necessary to move the cylinder from the yard. The presence of personnel during cylinder lifting permits immediate identification of accidents involving a breached condition. Based on the testing documented in References 10 and 11, the probability that a cylinder would fail with a hole larger than 1 in diameter due to mishandling in the cylinder yards is considered to be extremely low.
Also, if a breach of the cylinder did occur, the location of the breach would most likely be at the bottom of the cylinder near the site of the impact mitigating the potential for direct introduction of precipitation into the cylinder.
Tests documented in Reference 12 were performed at the Oak Ridge Gaseous Diffusion Plant to determine the impact of water entering a breached cylinder filled with solid UF. These tests evaluated simulated breaches of the void region of the cylinder as well as simulated breaches of the region filled with solid UF,.
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KY/G-558, Rev.1 Tests conducted on simulated breaches in the void region of the cylinder evaluated two potential situations; one where a film of crystalline UF, was present on the interior cylinder wall and the other where no UF, was deposited on the cylinder wall. Tests of cylinders where crystalline uranium hexafluoride was present on the cylinder wall revealed that holes up to one inch in diameter in a 6.25-inch-diameter MD cylinder are almost immediately plugged with UO F, from the hydrolysis of uranium hexafluoride, 2 2 and metallic compounds formed when HF reacts with the metalin the cylinder wall. (It should be noted that holes greater than one inch were not tested.) Water agitation on the plug and jarring of the cylinder were not successfulin dislodging the plug. In cases where the plug was removed, a new plug was almost immediately formed. The rapid formation of theso plugs precluded furtherintroduction of water into the cylinder. It should be noted that the normal filling of the cylinders with UF, will result in the formation of crystalline UF, on allinterior surfaces of the cylinder wall.
Tests performed on specially prepared cylinders where no crystalline UF, was present on the cylinder wall resulted in the production of no plug. Water entered the cylinder resulting in a reaction with the solid UF,. The essentially instantaneous reaction forms j
an insoluble layer over the UF,. A thin green layer produced by metallic products formed from HF reactions covers a thicker yellow layer. This yellow layer composed of UO +2H O+HF covers an orange band of U 0 F, or UOF,. Under the orange band is 2
2 2 3 the unreacted UF. Once the water is saturated, the layers become stable at a density of 270 gull. The conclusion drawn from the chemical analysis was that instantaneous reactions result in the formation of solid layers which limit the rate of diffusion of water vapor in and HF out through the layers covering the UF. Criticality safety analysis j
models of a cylinder in which water enters the void space of the cylinder and reacts with the UF, indicate that the cylinder is subcritical."" However, since diffusion of water vapor through the insoluble layer, although slow, continues indefinitely, references 13 and 14 do not substantiate subcriticality for an unlimited period.
Tests performed where the simulated fracture was located in the region covered by solid UF, revealed that a plug similar in composition to the previous case, immediately formed. However over time the diffusion of water vapor through the plug continues to produce HF that attacks the cylinder wall. The cylinder breach and the UO F region 2 2 slowly become larger with diffusion of water vapor in and HF out through the layers covering the UF,. Reference 16 concludes that the larger cylinder breach at the Portsmouth Gaseous Diffusion Plant (PORTS) discussed in Reference 15 would have resulted in a crLical configuration had the UF, been 5% enriched. Reference 15 indicates that the reaction proceeds quite slowly with the large cylinder breach and subsequent hydration occurring over a 13-year period.
The conclusions that can be drawn from these tests and analytical models include:
small breaches of the cylinder void space an d the subsequent reaction with wet
+
air or water will result in the development of a plug that precludes the introduction of water, 12
i KY/G-558, Rev.1 larger breaches of the cylinder void space and breaches of the cylinder wall region covered by UF, will permit water to contact and hydrate the UF.,
instantaneous formation of an insoluble layer limits the rate of hydration of the l
UF., and the detection of a cylinder breach and the mitigation of any water intrusion are i
necessary in order to preclude a critical configuration.
j Since the reaction proceeds at a slow rate, the annual cylinder inspection will identify the breach before the hydration of sufficient UF, to form a critical configuration.
The following general conclusions can be drawn from an evaluation of this accident initiator:
j Transportation accidents involving product cylinders at PGDP are low frequency events (i.e.,1.5E-04/ year).
Cylinder drop tests that accelerate the cylinders to a speed of 25 mph do not result in a loss of cylinder integrity.
If a breach did occur, emergency response personnel have sufficient time to minimize the potential for UF, moderation by covering or plugging the cylinder.
Cylinder breaches that are 1 inch in diameter or less are expected to seal themselves.
While cylinder breaches greater than 1 inch may permit water to enter the cylinder, the slow rate of hydration permits recovery prior to the formation of a critical configuration.
AccidentDetection/ Mitigation This event tree event models failure of the plant to detect the accident and mitigate the accident consequences. A breached cylinder can be detected visually by the release of HF gas. Mitigation is considered to be plugging or covering the breached cylinder such that water can not enter. Such an accident is a major plant event and the emergency squad will be dispatched to the accident scene. The emergency squad is trained to plug the leak but not to spray water on the breached cylinder. Emergency response personnel have considerable time to analyze the accident and determine the appropriate recovery action. Based on this information, the probability of PGDP personnel failing to detect and take the appropriate action is conservatively considered to be less than 0.01 based on Reference 17. Given failure to detect and mitigate the accident at the time of the accident, the breach may be detected during the annual inspection. The probability of failing to detect the breach during the annualinspection is assumed to be 0.01 based on Reference 17. Therefore the probability that a breach 13
j KY/G-558, Rev.1 resulting from a transportation accident goes undetected for longer than a year is less than 0.0001.
The frequency of a transportation accident with subsequent failure to detect and mitigate the consequences within a year is estimated to be less than 1.5E-08/ year.
3.4.2.2 HANDLING ACCIDENT SCENARIO The handling accident scenario addresses breaches of the cylinder during loading and unloading of the low-boy and the storage saddle. The sequence of events that could i
result in a critical configuration include a handling accident in which the cylinder containment is breached and the detection / mitigation of the accident fails such that the moderator is introduced into the cylinder and allowed to remain in the cylinder for a period that exceeds a year. Each aspect of the accident scenario is addressed in the following sections.
Accidentinitiator The accident initiator is a handling accident sufficiently severe that the UF, cylinder is breached permitting the introduction of water. Reference 8 indicates that as many as 800 cylinders per year might be produced at PGDP. The enriched product cylinders will originate at the withdrawal operation in Building C-310. From C-310, the cylinder may be transferred to C-400 for offsite shipment, C-745-B storage yard for interim storage, or C-360 for sa,mpling. The only area not currently within CAAS coverage in which cylinder handling takes place is the interim storage area. Based on the previous discussion,400 cylinders might be moved to interim storage. Considering ono cylinder unloading and one cylinder loading at the interim storage yard, the frequency of cylinder lifts outside of CAAS coverage is 800 cy'incer lifts per year. The probability that a cylinder will be mishandled such that a breach occurs is 1.23 E-05 accidents per cylinder lift based on Reference 18.
Therefore, the frequency of the initiating event is estimated:
F om = 800 cylinders lifts / year x 1.23 E-05 accidents / lift r
F,,n,wm = 9.8E-03 lifting accidents per year.
It should be noted that this estimated frequency does not consider that the cylinder may be dropped without loss of cylinder integrity. Drop tests indicate that cylinder drops involving distances greater than the lifting height used in the cylinder yards do not result in a loss of integrity. Therefore, the calculated frequency which assumes all drops result in a loss of cylinder integrity is extremely conservative.
Accident _ Detection / Mitigation 1
This event tree event models failure of the plant to detect the handling accident and mitigate the accident conscquences. Mitigation is considered to be the covering of the breached cylinder such that water can not enter. A breached cylinder can be detected 14
l
~
KY/G-558, Rev.1 visually by the release of HF gas. Mitigation is also easily accomplished by covering the cylinder. The emergency squad will be dispatched to the accident scene. The emergency squad is trained not to spray water on the breached cylinder. Emergency response personnel have considerable time to analyze the accident and determine the i
appropriate recovery action.
1 i
As discussed in Section 3.4.2.1, tests performed on UF, cylinders indicate small
- cylinder breaches will be plugged by reaction products precluding subsequent j
introduction of UF,. Although larger breaches permit the introduction of water into the cylinder, the hydration reaction forms an insoluble layer that significantly reduces the rate of subsequent UF, hydration. This reduction in the hydration rate substantially increases the time necessary for the hydrated mass to exceed a critical mass.
Based on this information. the probability of PGDP personn'el failing to detect and take the appropriate action is conservatively considered to be less than 0.01 based on Reference 17. Given failure to detect and mitigate the accident at the time of the accident, the breach may be detected during the annual inspection. The probability of failing to detect the breach during the annual inspection is assumed to be 0.01 based on Reference 17. Therefore the probability that a breach resulting from a handling accident goes undetected for longer than a year is less than 0.0001.
s The frequency of a handling accident with subsequent failure to detect and mitigate the consequences is estimated to be less than 9.8E-07/ year.
3.4.3 RESULTS OF THE CYLINDER TRANSPORTATION ANALYSIS l
The frequency of a critical configuration was estimated by applying the values for the initiating events and the event tree events discussed in Section 3 to the event tree 4
shown in Fig. 3.1. The frequency of a transportation accident resulting in a critical configuration was estimated to be 1.5 E-08/ year. The frequency of a handling accident resulting in a critical configuration was estimated to be 9.8 E-07/ year. These values based on extremely conservative assumptions are below the threshold of credibility of 1.0 E-06/ year. Therefore, onsite UF, cylinder transportation activities do not require CAAS coverage.
3.5 TRANSPORTATION OF MATERIALS OF LESS THAN A SAFE MASS, SAFE VOLUME, OR SAFE GEOMETRY
- The term safe mass is defined as the amount of material that will just be subcritical when double batched. The safe masses of uranium for PGDP enrichments can be found on the graph included in Appendix A. Since criticality with one safe mass of uranium is not feasible, one safe mass may be transported without CAAS coverage, The safe volume is the volume that is just subcritical when double batched.
Calculations performed for GEN-08 show that for oil systems (UF, and oil was used for 15
I KY/G-558, Rev.1 l
the model) the maximum subcritical volume is 3;7 gallons.' The safe volume of ari oil l
system would be half of this value, or 1.85 gallons. Calculations performed for KY/S-222 (UO F and water was used for the model) show that the maximum subcritical 2 2 volume for non-oil systems is 5.44 gallons." The safe volume for a non-oil system would be half of this value, or 2.72 gallons. Since criticality with one safe volume of uranium is not feasible,1.85 gallons or less of fissile materials containing oil or 2.72 i
gallons or less of fissile materials not containing oil may be transported without CAAS coverage.
It is noted that any non-oil fissile material that will fit into a 5.5 gallon traximum volume drum may be so placed and transported according to the requirements for waste drums above.
Safe geometries for uranium systems are dependant on enrichment. Some examples of safe geometries used at PGDP are safe slab height dikes and containment pans and safe diameter cylinders. When uranium materials are in a container that is safe by geometry (again, based on enrichment), they cannot be made critical. Therefore, any single fissile material package whose geometric criticality safety has been documented in an approved Nuclear Criticality Safety Evaluation may be transported outside of CAAS coverage.
3.6 TRANSPORTATION OF PACKAGES FOR WHICH CRITICALITY HAS BEEN SHOWN TO BE INCREDIBLE All fissile material operations are evaluated by NCS prior to initiation of the operation.
During the evaluation process, techniques such as a What-If analysis or Hazard Operability Study are used to identify and document potential upset conditions presenting NCS concerns. An analysis for each identified process upset condition is performed to demonstrate double contingency. Application of this principle ensures that no single credible event can result in an accidental criticality or that the occurrence of events necessary to result in a criticality is not credible. Depending on the complexity of the operation, analytical methods such as Fault Tree and Event Tree Analyses are used in the evaluation process to examine potential accident scenarios.
When the determination of the likelihood of an event is questioned qualitative or quantitative estimates of event frequency are developed to support the determination. If the evaluation demonstrates that a criticality accident is not credible during the onsite transportation of the fissile material item, the item may be transported without CAAS coverage.
3.7 TRANSPORTATION OF PACKAGES CONTAINING s15 g 22sg 49CFR@173.453 provides exceptions from Nuclear Criticality Safety packaging requirements for certain types of packages during shipment. One of these types of packages is packages that contain 15 grams or less of fissile radionuclides. Therefore, transportation of packages containing s15 g 2asU does not require CAAS coverage, and l
l 16
l KY/G-558, Rev.1 can be performed in any location on the PGDP site. An example of packages meeting this criteria is equipment shipped to PGDP from other sites such as K-25. These pieces of equipment are shipped between sites under the s15 g 23sU exemption, and therefore, the exemption also applies to on-site temporary staging and shipment to final location.
3.8 TRANSPORTATION OF ITEMS ENRICHED TO LESS THAN 1.0 WT % 2 su 49CFR@173.453 provides an exception from Nuclear Criticality Safety packaging requirements for shipments of uranium enriched to less than 1.0 wt% 23sU. In addition, calculations have been performed which demonstrate that uranium enriched to less than 1.0 wt% 23sU will not go critical under all credible normal and abnormal operating conditions at PGDP.2 Therefore, items containing uranium enriched to less than 1.0 wt% 23sU may be transported without CAAS coverage.
3.9 USE OF MOBILE DETECTORS DURING TRANSPORTATION Fissile materials may be transported while outside coverage of the permanent criticality accident alarm systems if an adequate mobile detection system is used which provides coverage for all the materials being transported. The requirements of a CAAS are given in 10CFR@76.89, which states that the system must detect and annunciate a criticality that produces an absorbed dose in soft tissue of 20 rads of combined neutron and gamma radiation at an unshielded distance of 2 meters from the reacting material within 1 minute and that all monitored areas must be covered by two detectors. These requirements are met by the CAAS systems currently in use at the PGDP, including the portable systems.
During the transportation of fissile /potentially fissile material outside of CAAS coverage, if the item does not fall into any of the categories described above, the items will be transported using two continuously monitored alarming radiation detectors. Should either detector indicate a radiation level above background, personnel will evacuate the transportation vehicle, control access to the area, and notify the PSS.
4.0 CONCLUSION
S All transportation of fissile materials at the Paducah Gaseous Diffusion Plant must meet the requirements given in 10CFR@76.89. The criteria for transportation of fissile materials discussed above have shown areas where the amount of fissile materials is controlled such that the likelihood of criticality is so remote, criticality alarm coverage is not needed. As long as at least one of the above criteria is met for the transportation of fissile materials, an exception to CAAS coverage is justified.
l 17 i
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- KY/G-558, Rev.1 REFERENCES 1
10 CFR Part 76.89 2.
Baltimore, W. D. and Hurrell, S. J., Nuclear Criticality Safety Assessment of Waste Resulting from Higher Assay Operations, KYlS-253, Rev 4, September
\\
1996.
3.
Goebel, G. R., Five-gallon Drum Waste Oil Storage at 5.5 Weight Percent '*U at the Paducah Gaseous Diffusion Plant, KYlS-218, Revision 1, NCSE-207, December 1993.
Risner, V. L. and Winiarski, R. J. Jr, NCS Evaluation' for the Transport, Handling, and Storage of Fissile /Potentially Fissile Material Samples at the Paducah Gaseous Diffusion Plant, GEN-08, Rev 2, July 1996.
5.
Maurer, R. S., Nuclear Criticality Safety Evaluation for Removal and Handling of Contaminated Equipment from the Cascade at the Paducah Gaseous Diffusion j
Plant, PGDP, GEN-10 and GEN-10-01, Rev 5, October,1996.
l 6.
TechnicalJustification for the Exemption of C-746-A, C-733, C-754, C-754-A, C-333, and C-757, Waste Storage Facilities from Criticality Alarm Requirements, l
KY/S-267, Rev. 2, Lockheed Martin Utility Services, Inc., March 1997.
7.
Justification for Excluding UF6 Cylinder Storage Yards from Criticality Accident l
Alarm Coverage, KY/S-271, Lockheed Martin Utility Services, Inc., January, 1996.
8.
Letter from R. W. Schmidt to J. H. Tumer dated April 19,1994,
Subject:
Peak l
Cylinder Handling Rates For Safety Analysis, Martin Marietta Energy Services, l
Inc.
9.
Jovanis, P. P., et.al., Comparison of Accident Rates for Two Truck Configurations, Transportation Research Record 1249.
10.
Myers, J. L., et. al., Testing of Ten-Ton Capacity Uranium Hexafluoride Shipping Containers, KY-D-2032, Union Carbide Corporation, Paducah Plant, January 1964.
11.
Richardson, E. W. and Bernstein, S., Additional Testing of Ten-Ton Uranium Hexafluoride Cylinders, KY-631, Union Carbide Corporation, Paducah Plant, September 1971.
4 12.
Mallet, A. J., Waterimmersion Tests of UF6 Cylinders with Simulated Damage, Union Carbide Corporation Nuclear division, Oak Ridge Gaseous Diffusion Plant, Oak Ridge, Tennessee, November 7,1967.
l 18
KY/G-558, Rev.1 13.
Letter, E. J. Barber to Tommy Wayne Hines, " Conditions After Water Fills Ullage in 1-Ton Cylinders," Martin Marietta Energy Systems, Inc., Oak Ridge, Tennessee, December 7,1992.
14.
Letter, H. R. Dyer to P. D. Lassiter, " Additional Calculations for the Paducah Tiger," Martin Marietta Energy Systems, Inc., December 7,1992.
15.
Investigation of Breached Depleted UF6 Cylinders, POEF-2086, ORNLITM-1988, E. J. Barber et.al., Oak Ridge National Laboratory, September 1991.
16.
Assessment of Potential Critical Configurations in Breached UF6 Cylinders with 5 wt% Enriched Uranium, memorandum from H. R. Dyer (MMES) and P. B. Fox (MMES) to W. R. Brock (MMES), Martin Marietta Energy Systems, July 19,1995.
J 17.
Bums, R. S. and Turner, J. H., Method Used to Estimate Screening-Level Total j
Failure Probability for Human Error Events, KlGDPISAR-42, Martin Marietta Energy Systems, Inc., Oak Ridge, TN, July 1994.
18.
Fault Tree Analysis forPotential UF6 Release Accidents in the C-360 Toll Transfer and Sampling Facility at the Paducah Gaseous Diffusion Plant, K/GDPISAR-33, Martin Marietta Energy Systems, Inc., June 30,1993.
19.
Baitimore, W. D., SubcriticalDimensions for Water-Reflected UO,F and Water 2
Systems at 5.5 Weight Percent Enrichment, KY/S-222, Martin Marietta Utility Services, Inc., October 25,1993.
20.
Lewis, S. T., TechnicalJustification: Uranium Enriched to Less Than One Weight Percent *"U - Safe for Operations at the Paducah Gaseous Diffusion Plant, KY/S-248, Martin Marietta Utility Services, Inc., March 31,1995.
i 19
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e '
KY/G-558, Rev.1 1
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APPENDIX A Safe Mass Over a Range of Assays i
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