Event Notification Report for October 11, 2000

24-HOUR 91-01 BULLETIN VIOLATION OF MASS CONTROL

"On 10/10/00 at about 11:30 a.m. while sorting drums of 'wet waste' in the Modular Extraction/ Recovery Facility (MERF), SPC process operators found three sock filters that contained larger than expected amounts of sludge. These sock filters came from two separate waste drums that had been packaged in 1993 or early 1994. Per Criticality Safety Specifications and Standard Operating Procedures, the process operators removed the sludge from the filters and placed it into three separate 4-gallon containers. Operators sampled the material in each of the containers and sent the samples to the SPC laboratory for analysis. The 4-gallon containers were transferred from MERF to an authorized storage location for moderated material. The lead process operator contacted the process engineer who in turn contacted Criticality Safety."

"On 10/11/00 at about 10:45 a.m., the SPC laboratory reported the percent U in the sludge. The results are summarized in the following table."

"Container # Net Wt.(kg) %U %235U Grams U Grams 235U

56696 15.4 71.4 3.55 10,979.8 389.8

56697 8.7 74.4 1.88 6,635.8 123.1

56698 13.9 72.4 1.89 10,111.2 191.3

Total 38.1 NA NA 27,626.8 704.2 "

"The total 235U present in the process batch at MERF (in the sock filter sludge plus other waste material) was calculated to be 895.9 grams, which exceeds the 790 gram 235U limit for the facility by about 106 grams."

"This data also indicates an infraction of the 200 g 235U mass control limit placed on individual waste drums on the waste storage pad."

"Safety Significance Of Event:"

"The safety significance of this event is low. The mass of uranium present in the process batch of waste drums being sorted in MERF was less than a safe mass (45% of critical) for the enrichments actually present. The actual enrichment of the materials involved was less than 3.6% 235U, however if the facility enrichment limit of 5 wt.% 235U is assumed, the total 235U mass was about 51% of a minimum critical mass. The information derived from the MERF infraction reveals an infraction of the mass control limit for drums on the storage pad."

"The criticality safety limit on surface density restricts a vertical stack of waste drums to 626 grams 235U. This is controlled by limiting any drum in a three tier array of waste drums to 200 grams 235U. If the two drums containing sock filters and another drum at the 200 g 235U limit were present in a three tier stack, the total mass in the stack would have been approximately 965 g 225U. A criticality area density is over 550 g 235U per sq. ft. which corresponds to 1,512 g 235U in a 2.75 sq. ft. area, the footprint area of a single drum. This is less than 64% of a minimum critical surface density."

"Potential Criticality Pathways:"

"For criticality to occur in a single waste drum requires a minimum of about 40 kg U02 enriched to 5 wt.% 235U. Current SOPs require sorting of waste and NDA assay before waste can be moved to the waste pad."

"To exceed an allowed surface density for stacked drums on the waste pad would require more than 600 grams 235U in a vertical stack of drums. This surface density limit would result in drum arrays that are substantially subcritical."

"For criticality to occur in the processing equipment in MERF would require a minimum of 40 kg U02 enriched to 5 wt.% 235U. Before such large amounts could be processed in this equipment, the operating staff would have to fail to perform the following actions required by the applicable criticality safety specification (CSS) and SOPs:
* re-sort the waste and remove all uniquely identifiable quantities of uranium,
* shred cartridge filters, HEPA filters and similar items
* re-assay the sorted and shredded waste
* remove any material in excess of 250 grams 235U mass from the mass controlled area and stage it to become part of the next process batch to be processed through the MERF equipment."

"Controlled Parameters:"

"For the MERF process, the controlled criticality parameter is mass. Per the SPC operating license, mass control as the only controlled parameter is allowed provided:"

"1. The work station shall be limited to one safe batch, where a safe batch is defined as no more than 0.45 of the minimum critical mass of the material in process;"

"2. No more than one safe batch may be moved at one time when introducing or removing material from a workstation;"

"3. Individual safe batches shall be spaced a specified minimum distance apart;"

"4. A record shall be maintained of the SNM inventory at each mass-limited workstation; and"

"5. SNM inventory control shall assure material buildup over time will not cause the batch limit to be exceeded."

"In MERF the mass limit is 790 g 235U, < 45% of a minimum critical mass at 5 wt.% enriched. An inventory of the material processed through the facility is maintained and the facility is inspected by operating and engineering personnel for potential holdup after each batch is processed through the facility. The following controls are used to ensure compliance with the 790 g 235U mass limit:"

"Prior to being considered for a process batch, each drum / HEPA filter has a three party check or an electronic comparison between two separate record systems to ensure that the mass assigned to the drum is free from transcription / transposition errors. If sufficient data does not exist, the drum or HEPA must be recounted."

"Target batch size is limited to 250 g 235U."

"SPC operating staff selects a batch of drums and transfer them to a locked location."

"SPC engineering staff verifies the target batch size of 250 g 235U is not exceeded."

"SPC Process Operator and Supervisor or lead technician verify the drums in the locked area are part of the designated batch and that the target batch size of 250 g 235U is not exceeded."

"Operating staff then resorts the waste to identify any uniquely identifiable quantities of U compounds prior to processing the waste through the washer."

"After resorting and shredding cartridge filters, HEPA filters and similar items, the material in the process batch is recounted using NDA. Any material in excess of 250 g 235U is set aside outside the mass controlled area and becomes a part of the next process batch."

"Estimated Amount, Enrichment, and Form Of Licensed Material:"

"The licensed material is urania sludge. The total 235U present in the process batch was calculated to be 895.9 grams. This is 51% of the minimum critical mass for this type of material enriched to 5 wt.% 235U. The actual material involved was enriched to less than 3.6 wt% 235U."

"Nuclear Criticality Safety Control(s) Or Control Systems and a Description of the Failures Or Deficiencies:"

"The filters came from two separate waste drums that had been packaged in 1993 or early 1994. Although waste segregation/accumulation controls were not as robust at that time as they are presently, wastes placed in such drums were required by criticality safety instructional card to contain only contamination levels of uranium. Therefore, sock filters containing this much U bearing material should not have been placed in a waste drum. The NDA system used to determine the U content of waste drums does not provide accurate results for concentrated high density materials such as the sludge contained in the sock filters. This is a known limitation of the NDA system. SPC currently takes extra precautions to ensure that the use of NDA is compatible with the known limitations of this equipment and that the waste matrix in the waste drums is adequately similar to that in the standard used to calibrate the NDA system. As previously stated, in 1993 and 1994 the procedures for segregating and processing waste were not as stringent as they are now."

"Corrective Actions To Restore Safety Systems and When Each Was Implemented:"

"The MERF process operators promptly segregated, sampled, and then removed from MERF the sludge accumulations discovered in the waste drums, thereby restoring compliance with the mass control limit for the facility."

"SPO operating, engineering and safety personnel have reviewed all other stored containerized waste types and have confirmed that only wet waste drums may be subject to this type of failure. This determination is based on the date of generation of the other drums in storage and the types of material in the drums."

"As a precautionary measure, SPC operating personnel have started placing wet waste drums on the waste storage pad into a single tier storage array. Because record keeping requirements dictate that the storage location of each drum be accurately recorded, this action is expected to be completed in about 1 week."

"Additional corrective actions are still being evaluated."

The licensee will notify NRC Region 4.