ML110050073
| ML110050073 | |
| Person / Time | |
|---|---|
| Site: | Framatome ANP Richland |
| Issue date: | 12/28/2010 |
| From: | Link R AREVA NP |
| To: | Document Control Desk, Office of Nuclear Material Safety and Safeguards |
| References | |
| 46447, REL:10:033 | |
| Download: ML110050073 (4) | |
Text
A December 28, 2010 AR EVA REL:10:033 U.S. Nuclear Regulatory Commission Director, Office of Nuclear Material Safety and Safeguards Attn: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Thirty-day Follow-up Report to December 2, 2010 Incident Reported Under 10 CFR 70.50 (b)(2) (NRC Event 46447); AREVA NP Inc. Richland Facility; License No. SNM-1227; Docket No. 70-1257 On, December 2, 2010,. the-AREVA NP Inc. Richland facility reported that following an acid wash of the Ammonia Recovery:Facility(ARF)Stripper a-lab analysis of the wash-solution indicated that 8 kg of uranium had been recovered.
The initial report (NRI( Event No.45310) was made because the plant condition met the reporting criterion in 10 CFR.70 Appendix A (b)(1).
.This 30-day follow-up report is being submitted in accordance with 10 CFR 70 Appendix A (b).
Caller Identification This condition was reported to. the NRC Operations Center by Robert E. Link, AREVA Environment Health Safety & Licensing Manager, on December 2, 2010 at 1739 EST (509 375-8409).
Date, Time, and Exact Location of Incident The reportable condition was determined to exist on December 2, 2010 at approximately 0715 hours0.00828 days <br />0.199 hours <br />0.00118 weeks <br />2.720575e-4 months <br /> local time. This condition involved the ARF Stripper column, which is located in the ARF Building.
Incident Description On December 2, 2010 at about 0715 local time, a Process Engineer informed Nuclear Criticality Safety (NCS) that he had confirmed that an acid wash of the ARF stripper column had recovered 8 kg of Uranium. The acid wash was expected to have removed all significant quantities of uranium from the system. This resulted in a review of the adequacy of the ISA treatment for the ARF stripper column.
Safety Significanceof'the incident The safety impact of this condition is low. The amount of U recovered, approximately 8 kg, is less than25% of a. minimum critical mass in spherical. geometry: The concentration of the liquid was about 1 gram U per liter. The'8 kg constitutes an approximate ten-year. accumulation since the last column acid wash in 2001. Based on the accumulation rate over the past 10 years, AREVA NP INC.
An AREVA and Siemens company 2101 Horn Rapids Road, Richland, WA 99354 Tel.: 509 375 8100 - www.areva.com
USNRC REL:10:033 December 28, 2010 Page 2 another 30 years of accumulation would be required without any removal during maintenance before achieving a critical mass in spherical geometry.
Processing activities were suspended at the time of discovery and remained suspended until an appropriate processing path was identified with appropriate controls in place.
Incident Response Actions A number of actions were taken in direct response to this incident, as follows:
The acid wash solution was collected in a storage tank and will be processed through the Miscellaneous Uranium Recovery System (MURS).
" A gamma spectroscopy analysis of the equipment was performed to verify acceptable U content in the Stripper column and associated equipment.
A second acid wash was completed to remove any residual U and the resulting solution was analyzed and was processed through the normal waste water process.
A second gamma spectroscopy analysis of the equipment was performed to verify acceptable U content and to establish a baseline for future analyses.
Appropriate internal and regulatory notifications were made.
An apparent cause analysis (ACA) was initiated.
Interim and Near-Term Corrective Actions Interim and/or near-term corrective actions that have been taken or are in progress include:
Held ISA Team meeting to evaluate the condition discovered in ARF. (Complete)
Added appropriate accident sequences to the NCSA/ISA for the ARF including the establishment of appropriate IROFS. (Complete)
Initiated changes to the ISA Summary, PHA, and P&ID so that the ARF is clearly understood to be under the regulatory requirements of 10CFR70 subpart H. (ECD:
1/31/2011)
Inspected the ARF sumps for accumulation of solids. (Complete)
Implemented new IROFS and management measures as required to prevent significant U accumulation in ARF. (Complete)
Incident Cause The ACA identified a single Root Cause: The ISA Team failed to identify that a gradual accumulation of uranium in the ARF Stripper Column and its ancillary equipment was a credible mechanism for creating a nuclear criticality hazard. The ISA Team failed to identify this mechanism because team consensus was based on previous plant experience. This experience, which was confirmed by sampling of the process waste for uranium, was that the upstream chemical precipitation followed by two stages of centrifugation, filtration and processing through two stages of ion exchange would ensure sufficiently low uranium concentrations to prevent buildup in this equipment.
The likely mechanism(s) for the U accumulation in the ARF Stripper Column is one of or a combination of the following:
- 1. Insoluble ADU crystallized in the ADU effluent surge tanks (Tanks 713A and 713B) or in the ARF feed tank when the uranium concentration in the effluent exceeded the solubility limit
USNRC REL:10:033 December 28, 2010 Page 3 for uranium in a basic system (pH above 8) and the solids were suspended in the ADU process effluent. The solid uranium was pumped to the ARF distillation column where it deposited on the distillation column horizontal plates.
- 2. Soluble uranium in the +6 valence state at its solubility limit was concentrated by boiling in the distillation column. The concentration was increased above the solubility limit which caused uranium to crystallize on the distillation column surfaces that were wetted by the solution.
- 3. Soluble uranium with a +6 valence state was reduced to much less soluble +4 valence state uranium due to the presence of iron in the caustic used in the process. The +4 uranium then crystallized on the distillation column surfaces.
Regardless of the potential causes of the accumulation, periodic acid washing will remove accumulated U-bearing solids from the process equipment.
Corrective Actions to Prevent Recurrence Periodic acid washing with confirmation of effectiveness by a gamma spectroscopy analysis and visual inspection of selected areas has been established for this equipment. (Complete)
Update the ISA/PHA procedures to include a section/list of lessons learned from oversights and discovered inadequacies in ISAs/PHAs. (ECD: 2/15/2011)
Training of ISA/PHA team leaders to the revised procedure is planned. (ECD:
2/28/2011)
Review the specific facts associated with this event with all EHS&L members and Process Engineers directly involved with the ISA process. Remind them of the importance of using the human performance tool of a questioning attitude while executing safety analyses and performing reviews of safety documentation. (ECD:
2/15/2011)
Re-evaluate the other points where SNM is declared sufficiently separated from process streams to be outside of 1 OCFR 70 subpart H requirements and verify that a sound technical basis is provided for the declaration. (ECD: 2/28/2011)
The interim corrective actions in progress and the corrective actions to prevent recurrence listed above are expected to be completed by February 28, 2011.
AREVA management continues to evaluate additional actions that may be needed to adequately address other potential generic implications of this plant condition.
If you have questions about this incident or AREVA NP's associated response, please contact me on 509-375-8409.
Very truly yours, R. E. Link, Manager Environmental, Health, Safety, & Licensing
/mah
USNRC REL:10:033 December 28, 2010 Page 4 cc: U.S. Nuclear Regulatory Commission, Region II Attn: M. D. Sykes, Chief Fuel Facility Branch 3 Marquis One Tower, 23 T85 245 Peachtree Center Avenue N.E. Suite 1200 Atlanta, GA 30303-8931