ML15176A708 

UNITED STATES 

NUCLEAR REGULATORY COMMISSION 

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS 

WASHINGTON, DC 20555-001 

September 2, 2015 

NRC INFORMATION NOTICE 2015-08: CRITICALITY AND CHEMICAL SAFETY EVENTS 

INVOLVING UNANALYZED CONDITIONS AND 

UNANTICIPATED UNAVAILABILITY OF IROFS AT 

FUEL CYCLE FACILITIES 

ADDRESSEES

Those holders of a materials license, certificate, approval, or registration, including those 

holders of and applicants for a source material license, under Title 10 of the Code of Federal 

Regulations (10 CFR) Part 40, “Domestic Licensing of Source Material,” or fuel cycle facility 

license under 10 CFR Part 70, “Domestic Licensing of Special Nuclear Material,” and that are 

subject to regulations in 10 CFR Part 70, Subpart H, “Additional Requirements for Certain 

Licensees Authorized To Process 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 recent operating experience involving deficiencies with evaluations of credible 

high and intermediate consequence accident sequences in facility integrated safety analyses 

(ISAs), delineation of items relied on for safety (IROFS) boundaries, and implementation of 

effective management measures to ensure the availability and reliability of IROFS. These 

deficiencies resulted in unanalyzed conditions or unavailability of IROFS established to 

minimize the likelihood of high or intermediate consequence events. 

The NRC expects recipients to review the information for applicability to their facilities and to 

consider actions, as appropriate, to avoid difficulties in compliance with regulations. 

Suggestions contained in this IN are not NRC requirements; therefore, no specific action or 

written response is required. 

DESCRIPTION OF CIRCUMSTANCES 

This IN describes four separate examples involving improper or incomplete analysis of credible 

plant conditions and identification and implementation of reliable safety controls. The events do 

not constitute a trend. However, there is general applicability with respect to the conduct of 

accident evaluations that could benefit safety when considered at other facilities. Although NRC 

staff acknowledges it is not possible to anticipate all potential process upsets, licensees should 

consider what happens in the industry to prepare for these upsets in their facilities and 

processes. This IN notes several events that have occurred recently in industry.
IN 2015-08 

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BACKGROUND 

The regulations in 10 CFR 70.61, “Performance Requirements,” establish performance 

requirements that licensees shall evaluate in their respective ISAs. Licensees must 

demonstrate that the risk of credible high- and intermediate-consequence events, which can 

significantly affect occupational or public health and safety or the environment and nuclear 

criticalities, are limited such that the likelihood of a high-consequence event is highly unlikely 

and the likelihood of an intermediate-consequence event is unlikely. This regulation also 

requires that controls designated as IROFS shall be ensured to be available and reliable to 

perform their intended function when needed through the implementation of a system of 

management measures. 

DISCUSSION 

Event 1: During periodically scheduled checks of equipment at a fuel fabrication facility, a 

licensee discovered a small amount of moisture inside an unfavorable geometry feed container 

that had been used to feed material to a dry conversion system. The system used two IROFS 

to prevent the accumulation of significant quantities of moisture (a moderator) in the 

moderator-controlled feed container. The licensee’s investigation into the event identified a 

failed dew-point sensing system that was part of a designated IROFS. This IROFS system was 

interlocked with valves that closed to stop flow if moisture content in the process exceeded the 

expected setpoint. The dew-point sensing system failure occurred because of design and 

installation errors that prevented proper operation. 

A second IROFS, also credited in the ISA to limit the risk of significant moderator accumulation, 

was found to be compromised as well. This administrative IROFS consisted of a computer 

alarm that indicated a drop in monitored holdup pressure between two isolation valves. 

A reduction in pressure in the system indicated degraded valve performance. Operators would 

be expected to act promptly because of a possible loss of integrity of the valve system. This 

IROFS was found to be unavailable because the alarm had been suppressed during previous 

system maintenance. An authorized individual suppressed the alarm in accordance with an 

approved procedure. However, the procedure did not require that suppressed alarms be reset 

or functionally tested after maintenance. This combination of failures represented an apparent 

loss of all IROFS for the accident sequence, as documented in the licensee’s ISA. 

Two aspects of this event are of particular interest for consideration by other licensees. The first 

relates to the dew-point sensor that was found to be inoperable because of moisture in the 

sampling train flow meter. While management measures are required to ensure IROFS are 

available and reliable, the surveillance established for the dew point sensor functionally tested 

the sensor output but did not verify the operation of the sampling line and the process inputs to 

the sensor. This is an example of inadequate management measures being applied to maintain 

the control’s availability and reliability. 

The second aspect similarly relates to the suppressed alarm. The alarm and resulting operator 

action were designated as an enhanced administrative IROFS. Management measures were 

applied to the IROFS; however, surveillance and testing only verified that an alarm logic signal 

was generated at the proper set point and did not verify that the operators received the alarm. 

This allowed a situation to occur in which, during maintenance, the alarm indication (a visual 

indicator on the control screen) was suppressed. This condition was then overlooked upon 

completion of the maintenance and verification that the logic signal was generated. Because 
IN 2015-08 

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the control system’s alarm was suppressed, the alarm indication was not communicated to the 

operators as intended. This is also an example of inadequate management measures 

(functional testing) being applied to ensure a control’s availability and reliability, which is 

especially important following maintenance activities. 

Event 2: Operators involved in uranium recovery at a facility initiated a cleanout of dissolver 

residue from a catch tray. The catch tray is a single continuous shallow tray beneath several 

dissolvers and filters that are used to process recoverable (although relatively small) quantities 

of highly enriched uranium. The procedure for the cleanout instructed operators to scrape or 

sponge the accumulated material in the catch tray into less than or equal to 2.5 liter (L) 

containers and handle the containers in accordance with waste handling procedures because 

the uranium content was unknown. In this instance, the operators deviated from established 

guidelines and scraped accumulated material into four to five large piles, some exceeding 2.5 L 

in volume, as an interim step before loading the material into containers. The piles were left in 

place at shift turnover and discovered by supervision during the following shift, at which point 

the abnormal condition was identified. The licensee had the material placed into 2.5 L 

containers and had them weighed and assayed before continuing operations. The licensee 

evaluated the condition and identified an accident sequence in the ISA that was believed to be 

bounding (using greater than 2.5 L containers to collect the waste). However, during 

subsequent assessment of the condition, NRC inspectors determined that none of the 

licensee’s existing evaluations adequately addressed the situation encountered. 

Of particular note in this event is that, while controls were established for dissolution and 

processing of materials, as well as for handling of waste in less than or equal to 2.5 L 

containers, the licensee failed to adequately consider credible upsets for the transitional phase 

of gathering spilled solid materials (as opposed to solutions) from the catch tray into the less 

than or equal to 2.5 L containers. The procedure being followed was inadequate to ensure that 

operators did not scrape the materials together into an unsafe geometry. Diligence must be 

exercised in assessing evolutions involving maintenance to ensure consideration is given to 

potential upsets, deviations, or unsafe conditions that can occur when transitioning from one 

subcritical state to another. The failure to analyze and establish controls for the situation did not 

ensure the process remained subcritical. The licensee’s immediate corrective action was to 

eliminate cleanout activities of the low level dissolvers until such time as the procedure could be 

revised to provide clarification and establish suitable controls to ensure subcriticality. 

Event 3: During troubleshooting of instrumentation problems associated with a resistance 

temperature detector connected to an evaporator system, the licensee identified approximately 

3 ounces of special nuclear material mixture pooled in a thermowell and junction box. The 

junction box was connected by sealed conduit to an unfavorable geometry electrical panel. The 

thermowell had developed a pinhole leak that allowed the material to enter the junction box 

through the electrical conduit. The consequences associated with possible accumulation of 

fissile solutions associated with failure of the thermowell and the electrical conduit seals had not 

been considered by the licensee, resulting in an unanalyzed condition. 

As an immediate corrective action, the licensee installed drains in all unfavorable geometry 

electrical boxes connected to process equipment by conduit. As a longer term corrective action 

for geometry control, the licensee plans to install similar drains in all existing unfavorable 

geometry electrical boxes, regardless of whether or not a box is connected to process 

equipment by conduit. The licensee is also revising procedures to ensure that drains are 

present in all unfavorable geometry boxes before installation. Once this geometry control is 

established, the relevant accident sequence involving a leak through conduit (or other such 
IN 2015-08 

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connections and penetrations in liquid bearing systems) is bounded by a previously evaluated 

sequence in the ISA. It is important that consideration be given to all potential pathways for 

fissile solution to reach unfavorable geometry, including equipment connections and electrical 

conduits. 

Event 4: During the review of operational data at a facility, the licensee staff determined that the 

original assumptions used in evaluating the potential likelihood of a credible accident sequence 

in the dry conversion process might have been nonconservative. Specifically, the licensee 

noted during review of plant records that the initiating event frequency assigned for a specific 

chemical accident sequence had occurred twice in a 17-year period. Because the licensee’s 

ISA had used an initiating event frequency of 0.1 events/year, it determined that the failure 

frequency assumed in its ISA was nonconservative. NRC staff considered this event to be 

inconsequential because the change identified in the initiating event frequency was not 

statistically significant and, as such, did not result in a failure to comply with performance 

requirements of 10 CFR 70.61. 

Nonetheless, NRC staff considers this event to be of general interest because it is appropriate 

for licensees to review operational data to validate its analysis of event sequences in their ISA 

and to look for trends that may indicate degrading performance that may need to be addressed. 

The regulation in 10 CFR 70.62(a)(3) requires licensees to maintain records of failures or 

degradation of IROFS and management measures that lead to the performance requirements 

not being satisfied. While caution must be exercised in drawing conclusions about the reliability 

and availability of IROFS from a small number of such failures, it is appropriate for licensees to 

periodically examine operational data (including failures and degradation of IROFS as well as 

occurrences of other initiating and enabling events) and reevaluate the continued validity of the 

analysis, including failure frequencies, in their ISAs, as part of maintaining safety analyses up to 

date with observed system performance. 

CONCLUSION

As stated in the Description of Circumstances section, these events do not constitute a trend; 

however, because there is general applicability with respect to the conduct of accident 

evaluations that could be of benefit to safety when considered at other facilities, the NRC 

believes that licensees might benefit from evaluation of conditions at their facilities considering 

the circumstances of these events.
IN 2015-08 

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CONTACTS 

This IN requires no specific action or written response. Please direct any questions to the 

technical contact listed below. 

/RA/ 

Marissa G. Bailey, Director 

 Division of Fuel Cycle, Safety, Safeguards 

 and Environmental Review 

 Office of Nuclear Material Safety 

 and Safeguards 

Technical Contact: Greg Chapman, NMSS/FCSE 

 301-415-8718 

 

Note: NRC generic communications may be found on the NRC public Web site, 

http://www.nrc.gov, under NRC Library/Document Collections.
IN 2015-08 

Page 5 of 5 

CONTACTS 

This IN requires no specific action or written response. Please direct any questions to the 

technical contact listed below. 

 

/RA/ 

 Marissa G. Bailey, Director 

 Division of Fuel Cycle, Safety, Safeguards 

 and Environmental Review 

 Office of Nuclear Material Safety 

 and Safeguards 

Technical Contact: Greg Chapman, NMSS/FCSE 

 (301) 415-8718 

 

Note: NRC generic communications may be found on the NRC public Web site, 

http://www.nrc.gov, under NRC Library/Document Collections 

 

 ML15176A708 

OFC PORSB PORSB MRST NMSS:FCSE NMSS:FCSE 

NAME GChapman MKotzalas AMcIntosh CErlanger MBailey 

DATE 7/6/15 7/6/15 7/10/15 8/11/15 9/2/15 

 OFFICIAL RECORD COPY