United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-31: Buildup of Enriched Uranium in Ventilation Ducts and Associated Effluent Treatment Systems

                                                        SSINS No.:  6835
                                                            IN 85-31 

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                           WASHINGTON, D.C. 20555 

                               April 19, 1985 

Information Notice No. 85-31:  BUILDUP OF ENRICHED URANIUM IN VENTILATION
                                  DUCTS AND ASSOCIATED EFFLUENT TREATMENT 
                                  SYSTEMS 

Addressees: 

All uranium fuel fabrication licensees. 

Purpose: 

This information notice is provided to alert recipients of a potentially 
significant problem pertaining to criticality safety at enriched uranium 
fuel fabrication plants. It is expected that recipients will review the 
information for applicability to their facilities and consider actions, if 
appropriate, to preclude a similar problem occurring at their facilities. 
However, suggestions contained in this information notice do not constitute 
NRC requirements; therefore, no specific action or written response is 
required. 

Description of Circumstances: 

This notice provides information regarding a potential for the buildup of 
uranium in ventilation ducts and associated effluent treatment systems of 
enriched uranium fuel fabrication plants. For nuclear criticality safety 
purposes, licensees establish controls to prevent a buildup of enriched 
uranium in unsafe or unfavorable geometry ventilation equipment and other 
effluent treatment systems. 

On two occasions recently, significant quantities of highly enriched uranium
were found in unfavorable geometry effluent ducts and treatment systems as a 
result of settling or deposition of uranium-bearing solids. 

In one event, uranium-bearing solids or vapors were picked up in the ventil-
ation system and deposited on the inside of the ventilation ducts and scrub-
ber walls above the water line. The deposition appears to have increased as 
the air stream cooled and when air changed direction in elbows. The accumul-
ation above the water line appears to have resulted from splashing and sub-
sequent drying of scrubber liquid on the scrubber walls. To control this 
situation the licensee initiated a surveillance program to identify accumu-
lations of uranium in the effluent system and to take appropriate corrective
actions when uranium buildup 



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                                                           IN 85-31 
                                                           April 19, 1985 
                                                           Page 2 of 2 

exceeded predetermined limits. Also, a program was initiated to identify the
uranium source and to take remedial actions to prevent the uranium from 
entering the system. 

In another event, uranium solids were deposited in unfavorable geometry 
ducts as a result of changes in the speed or direction of air flows. 
Periodic cleaning of the ducts prevented a significantly large accumulation 
of uranium. As a control measure, the licensee initiated a visual inspection 
and a radiation detection surveillance program to identify significant 
accumulation of uranium in unfavorable geometry ventilation and effluent 
treatment systems. 

Discussion: 

These incidents are significant to nuclear criticality safety because 
enriched uranium accumulated in excess of acceptable quantities in 
ventilation and effluent treatment s stems of unfavorable geometry. The lack 
of an adequate licensee program for detecting, locating, and estimating the 
quantity of the depositions was the major contributing factor. 

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the Reg-
ional Administrator of the appropriate NRC regional office or this office. 



                                   James G. Partlow, Director 
                                   Division of Inspection Programs 
                                   Office of Inspection and Enforcement 

Technical Contact:   Douglas Sly 
                     (301) 492-4783 

Attachment:  List of Recently Issued IE Information Notices 
Page Last Reviewed/Updated Tuesday, November 12, 2013