Information Notice 2007-32, Out of Service Equipment Connected to in Service Process Line Results in Fissile Solution Spill at Fuel Cycle Facility
ML072530077 | |
Person / Time | |
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Issue date: | 10/15/2007 |
From: | Pierson R NRC/NMSS/FCSS |
To: | |
References | |
IN-07-032 | |
Download: ML072530077 (10) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555 October 15, 2007 NRC INFORMATION NOTICE 2007-32: OUT-OF-SERVICE EQUIPMENT CONNECTED
TO IN-SERVICE PROCESS LINE RESULTS IN
FISSILE SOLUTION SPILL AT FUEL CYCLE
FACILITY
ADDRESSEES
All licensees authorized to possess a critical mass of special nuclear material.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of a criticality safety concern regarding failure to fully disconnect out-of-service
equipment from operational equipment at fuel cycle facilities. NRC expects that licensees will
review this information and consider actions, as appropriate, to avoid similar problems.
Suggestions contained in this IN are not NRC requirements; therefore, no specific action or
written response is required.
DESCRIPTION OF CIRCUMSTANCES
An NRC licensee that operates a fuel cycle facility with high-enriched uranium (HEU)
processes, constructed a new facility to convert HEU compounds into concentrated uranyl
nitrate (UN) solution, and process the UN solution through a solvent extraction system, for final
purification. The new solvent extraction system included a tray dissolver and filter system in
two large gloveboxes. The tray dissolver glovebox system, as shown in Figure 1, was designed
to recover small amounts of uranium from various sources and return filtered UN solution
directly to the solvent extraction system.
Delays in the construction of the new facility placed schedule pressure on the licensee. The
tray dissolver glovebox system, installed during facility construction, was considered non- essential to process startup, and finalization of equipment installation was delayed. The tray
dissolver glovebox system was connected to a main HEU solution transfer line which was
connected to the solvent extraction system collection vessel. The tray dissolver glovebox
system was flagged as out-of-service but was not isolated from the main HEU solution
transfer line.
Before initiating operation of the new HEU process system, the licensee conducted reviews of
the newly constructed facility, including requiring process engineers to compare installed piping
and valves to design drawings. During this process, an engineer mistook a diverter valve in the
tray dissolver filter glovebox for a block valve, and the associated as-built drawing was changed
to reflect the error. The incorrect drawing gave the impression that the tray dissolver filter
glovebox was isolated from other process lines and the error was not detected during
subsequent readiness reviews. The diverter valve directed flow towards a sample point, and
could not have impeded solution flow in the process line.
Figure 1 Tray Dissolver Filter Glovebox Equipment Arrangement
Licensee startup procedures included hydrostatic testing of process equipment with natural
(non-enriched) UN solution. On several occasions after system startup, operators observed and
reported yellow solution in the tray dissolver filter glovebox, and these instances were attributed
to the hydrostatic testing. The solutions in the filter glovebox were assumed to be natural UN
solution and were recovered, but not sampled. After a few years of operation, the licensee decided to move the unused tray dissolver glovebox
system to a new location in the facility. UN solution was found in the system filters and
operators drained the system without a specific work procedure and thus did not sample the
solution in the filters, restore the original valve line-up, or fully re-tighten the filter cover bolts.
The next day a large HEU solution transfer took place through the transfer line to the solvent
extraction system collection vessel. Approximately 37 liters of concentrated HEU solution
spilled into the filter glovebox, through the glovebox drains, and to the floor of the facility.
Licensee operators observed the spill as it passed under a door, investigated, observed solution
spraying from the tray dissolver filters, and took corrective actions that terminated the event.
The tray dissolver filter glovebox was an unfavorable geometry configuration. To protect
against criticality in its gloveboxes, the licensee normally installed two glovebox drains
consisting of 1-inch or greater diameter tubes, and implemented controls to assure that the
drains were not blocked during operation. The tray dissolver glovebox was constructed with the
drains, but because the system was considered out-of-service, no controls were implemented to
prevent blockage of the drains. Subsequent to the spill event, the licensee discovered that tools
and cleaning material had been stored in the tray dissolver filter glovebox and had partially
obstructed one of the drains.
To protect against criticality during spill events, the licensee had surveyed the facility floor and
eliminated or directed flow away from solution collection points. During investigations
conducted immediately after the event, the licensee discovered an elevator pit, near the path of
the solution flow, which was not protected against solution ingress. The elevator pit was an
unfavorable geometry configuration.
SUBCRITICAL MARGIN
NRC considers this spill to be significant because the mass involved exceeded the minimum
critical mass for the fissile solution. A minimum critical mass is a theoretical value used to
analyze safety margin for events involving fissile material. For a solution, the minimum critical
mass is determined based on a critical reflected sphere of the solution. An approximate value
for a critical sphere can be taken from Figure 2 which is Atlantic Richfield Hanford Company
Criticality Handbook (ARH 600), Volume 2, Figure III.B.6(100)-1. The as-found solution can be
represented by UN solution containing 170 grams uranium-235 (U-235) per liter. Figure 2 shows that UN solution at 170 grams U-235 per liter has a minimum critical mass of 1.4 kilograms. 37 liters of UN solution at 170 grams U-235 per liter results in approximately 6.5 kilograms of U-235 which exceeds the minimum critical value of 1.4 kilograms.
Although the volume of spilled solution would not have attained the critical slab height at the
collection points, the mass spilled in the event would have been sufficient to sustain criticality in
a slab configuration of sufficient thickness. An approximate value for a critical slab can be taken
from Figure 3 which is ARH 600, Volume 2, Figure III.B.5(100)-1. The most likely way to reach
the critical slab would have been with additional process solution since 200 liters were available
in the transfer that led to the spill. Critical slab heights were estimated based on the actual
process solution by filling both collection points with process solution until the critical height was
determined. The estimated critical slab height in the glovebox is approximately 4.1 inches and Figure 2 Spherical Critical Mass for UN Solution
is attained with 130 liters of process solution. The estimated critical slab height in the elevator
pit is approximately 3 inches and is attained with 100 liters of solution. A critical slab height can
be determined based on the mass actually spilled by converting that mass into a concentration
based on the two estimated critical volumes.
The mass in the 37 liters spilled can be converted from 170 grams U-235 per liter in 37 liters to
48 grams U-235 per liter in 130 liters or 63 grams U-235 per liter in 100 liters. Figure 3 shows
that the minimum critical slab height at 48 grams U-235 per liter is approximately 4.2 inches and
that the minimum critical slab height at 63 grams U-235 per liter is approximately 3.4 inches.
This analysis demonstrates that the height of a critical slab at the collection points would not be
affected significantly by reducing the uranium concentration of the process solution. This
supports the conclusion that sufficient mass was available during the event to attain criticality if
a suitable geometry had been reached. Figure 3 Critical Slab Height versus Solution Concentration
DISCUSSION
When handling licensed material, licensees must completely understand the material flowpath.
In the above spill, the licensee lost control of configuration and did not clearly understand the
flowpath of HEU solution. No safety controls existed to preclude inadvertent criticality.
Criticality did not occur because the spilled solution did not assume a favorable configuration.
NRC is concerned that fuel cycle licensees have configuration management and start-up
procedures that detect and preclude starting a process with out-of-service equipment cross- connected to in-service equipment. NRC is also concerned that licensees use formal work
processes such as written procedures to accomplish work related to licensed activities.
The failure to develop, maintain, and fully integrate management measures, operating
procedures, and criticality, radiological, fire, and chemical controls can lead to uncontrolled
process operations as in the above spill event. NRC safety inspections typically include review of the licensee safety audit program, to ensure that analytical assumptions are regularly
reviewed in all areas. NRC safety inspections also routinely review licensee configuration
management programs, to ensure that plant changes are controlled, and design and as-built
information are updated to accurately reflect criticality safety assumptions and controls.
This information notice does not require any specific action or written response. Please direct
any questions about this matter to the technical contact below.
/RA/
Robert C. Pierson, Director
Division of Fuel Cycle Safety
and Safeguards
Office of Nuclear Material Safety
and Safeguards
Technical Contact:
Dennis Morey, NMSS
301-492-3112 E-mail: dcm@nrc.gov
Enclosure:
List of Recently Issued FSME/NMSS Generic Communications of the licensee safety audit program, to ensure that analytical assumptions are regularly
reviewed in all areas. NRC safety inspections also routinely review licensee configuration
management programs, to ensure that plant changes are controlled, and design and as-built
information are updated to accurately reflect criticality safety assumptions and controls.
This information notice does not require any specific action or written response. Please direct
any questions about this matter to the technical contact below.
/RA/
Robert C. Pierson, Director
Division of Fuel Cycle Safety
and Safeguards
Office of Nuclear Material Safety
and Safeguards
Technical Contact:
Dennis Morey, NMSS
301-492-3112 E-mail: dcm@nrc.gov
Enclosure:
List of Recently Issued FSME/NMSS Generic Communications
ML072530077 OFC FSCC/TSB Tech ED FSME FCSS/TSB FCSS FCSS
NAME D.Morey E.Kraus: fax A.McIntosh D.Jackson J.Giitter R.Pierson
DATE 9/ 20 /07 9/ 12 /07 9/ 11 /07 9/ 25 /07 10/15/07 10/15/07 OFFICIAL RECORD COPY Recently Issued FSME/NMSS Generic Communications
Date GC No. Subject
Addressees
02/02/07 IN-07-03 Reportable Medical Events Involving All U.S. Nuclear Regulatory Commission
Patients Receiving Dosages of medical use licensees and NRC Master
Sodium Iodide Iodine-131 less than Materials Licensees. All Agreement State
the Prescribed Dosage Because of Radiation Control Program Directors and
Capsules Remaining in Vials after State Liaison Officers.
Administration
02/28/07 IN-07-08 Potential Vulnerabilities of Time- All U. S. Nuclear Regulatory Commission
reliant Computer-based Systems licensees and all Agreement State
Due to Change in Daylight Saving Radiation Control Program Directors and
Time Dates State Liaison Officers.
03/13/07 IN-07-10 Yttrium-90 Theraspheres and All U.S. Nuclear Regulatory Commission
Sirspheres Impurities (NRC) Medical Licensees and NRC Master
Materials Licensees. All Agreement State
Radiation Control Program Directors and
State Liaison Officers.
04/04/07 IN-07-13 Use of As-Found Conditions to All licensees authorized to possess a
Evaluate Criticality-related Process critical mass of special nuclear material.
Upsets at Fuel Cycle Facilities
05/02/07 IN-07-16 Common Violations of the Increased All licensees who are implementing the
Controls Requirements and Related U.S. Nuclear Regulatory Commission
Guidance Documents (NRC) Order Imposing Increased Controls
(EA-05-090), issued November 14, 2005 and December 22, 2005.
05/21/07 IN-07-19 Fire Protection Equipment Recalls All holders of operating licenses for nuclear
and Counterfeit Notices power reactors and fuel cycle facilities;
except those licensees for reactors that
have permanently ceased operations and
who have certified that fuel has been
permanently removed from the reactor
vessel; and except those licensees for
decommissioned fuel cycle facilities.
06/11/07 IN-07-20 Use of Blank Ammunition All power reactors, Category I fuel cycle
facilities, independent spent fuel storage
installations, conversion facility, and
gaseous diffusion plants. Date GC No. Subject
Addressees
IN-07-23 Inadvertent Discharge of Halon All holders of operating licenses for nuclear
1301Fire-suppression System from power reactors, except those who have
Incorrect and/or Out-of-date permanently ended operations and have
Procedures certified that fuel has been permanently
removed from the reactor vessel. All
holders of licenses for fuel cycle facilities.
07/19/07 IN-07-25 Suggestions from the Advisory All U.S. Nuclear Regulatory Commission
Committee on the Medical Use of (NRC) medical-use licensees and NRC
Isotopes For Consideration to Master Materials Licensees. All Agreement
Improve Compliance With Sodium State Radiation Control Program Directors
Iodide I-131 Written Directive and State Liaison Officers.
Requirements in 10 CFR 35.40 and
Supervision Requirements in 10
CFR 35.27
08/13/07 IN-07-26 Combustibility of Epoxy Floor All holders of operating licenses for nuclear
Coatings at Commercial Nuclear power reactors and fuel cycle facilities
Power Plants except licensees for reactors that have
permanently ceased operations and who
have certified that fuel has been
permanently removed from the reactor
vessel.
03/01/07 RIS-07-03 Ionizing Radiation Warning Symbol All U.S. Nuclear Regulatory Commission
licensees and certificate holders. All
Radiation Control Program Directors and
State Liaison Officers
03/09/07 RIS-07-04 Personally Identifiable Information All holders of operating licenses for nuclear
Submitted to the U.S. Nuclear power reactors and holders of and
Regulatory Commission applicants for certificates for reactor
designs. All licensees, certificate holders, applicants, and other entities subject to
regulation by the U.S. Nuclear Regulatory
Commission (NRC) of the use of source, byproduct, and special nuclear material
03/20/07 RIS-07-05 Status and Plans for Implementation All NRC materials licensees, Radiation
of NRC Regulatory Authority for Control Program Directors, State Liaison
Certain Naturally-occurring and Officers, and NRCs Advisory Committee
Accelerator-produced Radioactive on the Medical Uses of Isotopes
Material
04/05/07 RIS-07-07 Clarification of Increased Controls All U.S. Nuclear Regulatory Commission
for Licensees That Possess (NRC) licensees issued NRCs Order
Collocated Radioactive Material Imposing Increased Controls and all
During Transportation Activities Radiation Control Program Directors and
State Liaison Officers Date GC No. Subject
Addressees
05/04/07 RIS-07-09 Examples of Recurring Requests for All holders of, and applicants for, a: (1) 10
Additional Information (RAIs) for 10 CFR Part 71 certificate of compliance
CFR Part 71 and 72 Applications (CoC) for a radioactive material
transportation package; (2) 10 CFR Part 72 CoC for a spent fuel storage cask; and (3)
10 CFR Part 72 specific license for an
independent spent fuel storage installation
(ISFSI).
06/27/07 RIS-06-27, Availability of NRC 313A Series of All U.S. Nuclear Regulatory Commission
Suppl. 1 Forms and Guidance for Their (NRC) medical-use licensees and NRC
Completion Master Materials licensees. All Radiation
Control Program Directors and State
Liaison Officers.
05/15/07 RIS-07-10 Subscriptions To New List Server
For Automatic Notifications Of All U.S. Nuclear Regulatory Commission
Medical-Related Generic (NRC) medical-use licensees and NRC
Communications, Federal Register Master Materials licensees. All Radiation
Notices And Newsletters Control Program Directors and State
Liaison Officers.
Note: A full listing of generic communications may be viewed at the NRC public website at the following address:
http://www.nrc.gov/Electronic Reading Room/Document Collections/Generic Communications