Bulletin 91-01: Reporting Loss of Criticality Safety Controls
OMB No: 3150-0009 NRCB 91-01 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS WASHINGTON, D.C. 20555 October 18, 1991 NRC BULLETIN 91-01: REPORTING LOSS OF CRITICALITY SAFETY CONTROLS Addressees All fuel cycle and uranium fuel research and development licensees. Purpose This bulletin requests that addressees inform the Commission of their criteria and procedures that assure the prompt evaluation and reporting of the degradation of any controlled parameters used to prevent nuclear criticality to licensee management and the immediate reporting to the Commission of any significant degradation of such controls as required by 10 CFR 20.403(a). A written response to this bulletin is required. Background On October 3, 1990, all licensees who possess more than a critical mass quantity of special nuclear material were informed of the need for management attention to the establishment and maintenance of their nuclear criticality safety program (Information Notice No. 90-63, attached). That Notice referred to previous Information Notice No. 89-24, dated March 6, 1989, also on the subject of criticality safety. The Commission needs assurance that proper attention is being addressed to these important criticality concerns. Also, licensees must assure that significant degradation of any controls used to prevent criticality is promptly reported to management, and as required by 10 CFR 20.403(a)(1), to the Commission, to assure that appropriate actions are taken to prevent further system degradation. Description of Circumstances In May 1991, a process upset occurred in the solvent extraction portion of a uranium recycle unit of a fuel manufacturing operation. The process upset caused the accumulation of enriched uranium in favorable geometry tanks in a waste processing area. When these tanks filled, their uranium contents were transferred, in some instances without sample measurement, to an unfavorable geometry tank waste accumulation tank, and then to a second, unfavorable geometry waste treatment tank. Although the upset was observed by operators late on an evening shift, the process was not shut down until around 5:30 the next morning, when measurements indicated high uranium concentrations in the favorable geometry tanks. A high concentration of uranium was measured in the waste treatment tank at 7:00 a.m. 9110180125 . NRCB 91-01 October 18, 1991 Page 2 of 5 Licensee management was made aware of the incident later that morning, and a technical evaluation/recovery team was established. The NRC was notified of the incident around 3:45 p.m. that day. A criticality incident did not occur, but the margin of safety was reduced. The licensee removed the excess uranium from the waste treatment tank over a period of several days using centrifuge techniques. The licensee's investigation team concluded that there were several areas of operational control which were significant contributors to the incident, including: (1) failure to always follow procedures or inadequate procedures; (2) insufficient supervision and/or technical support of operations; (3) lack of adequate overchecks/audits on conformance with criticality safety control requirements; and (4) inadequate records systems. The Commission's investigation is reported in NUREG-1450. Discussion of Safety Significance Because of the above event and knowledge of similar circumstances at other licensed activities, the Commission is concerned that there may be insufficient attention by licensees to the need for internal reporting and prompt evaluation of failures of controlled parameters related to criticality safety. The Commission is also concerned that licensees may not have procedures in place to assure compliance with the requirements under 10 CFR 20.403 to report immediately to the Commission any significant failure of criticality safety controls. As discussed in the appendix to this bulletin, several controls may be used to maintain a controlled parameter for preventing a criticality excursion. If substantial control over a controlled parameter is lost, the event should be reported to the Commission. Following are specific examples of events related to criticality control that should be reported to the Commission immediately: 1. Complete loss of a controlled parameter. 2. Substantial degradation of a controlled parameter. 3. Failure of a controlled parameter previously identified by the Commission or the licensee's criticality safety specialists as requiring reporting upon failure. 4. Determination that a criticality safety analysis was deficient in evaluating actual plant conditions and necessary controlled parameters were not established. . NRCB 91-01 October 18, 1991 Page 3 of 5 5. An unusual event or condition for which the severity and remedy are not readily determined. Reports of such events must be made to the NRC Operation Center, which is staffed 24 hours per day, and to the appropriate Regional Administrator. Some types of events, though not warranting reporting to the Commission, nevertheless merit attention within the licensee's own organization, particularly by the criticality safety specialists. The Commission intends that all events involving degradation of criticality controls be reported for evaluation within the licensee's organization. Since some events which can occur in process systems and their relative importance to criticality safety cannot be determined before the event, criteria are needed in order to make the judgment as to whether the event should be reported to the Commission as required by 10 CFR 20.403(a). Each recipient of this bulletin, therefore, should assure that as to the extent of degradation, licensees are encouraged to report to the Commission. If initial indications of an event do not seem to warrant Commission notification, but further developments prove it to be more serious, the Commission should be immediately notified at that point. Addressees are also reminded that all necessary corrective actions must be taken promptly, regardless of any reporting action. Reports to the Commission do not require that corrective actions be completed prior to reporting. Requested Action Addressees are requested to evaluate their criticality safety criteria and procedures, modify them as appropriate to assure that events involving degradation of controls will be promptly evaluated and reported to licensee management and NRC as appropriate, and provide a description of their criteria and procedures to NRC. In completing this evaluation, licensees should include the following: 1. Based on your current analyses of criticality safety, and any further criticality analyses that may be necessary for this determination, identify and examine each individual controlled parameter whose failure could contribute to a decrease in criticality control. For each individual controlled parameter, determine whether or not degradation of the system of controls would constitute a significant loss of effectiveness. Loss of a single controlled parameter should be considered to have occurred upon total failure or substantial degradation of the control. 2. Any list of methods of control, such as indicated in the appendix, should be considered from the point of view of importance to maintaining its associated controlled parameter. The possibility of combinations of loss of more than one control should be considered; i.e., are some controls likely to fail simultaneously and what is the level of significance of such an occurrence? . NRCB 91-01 October 18, 1991 Page 4 of 5 3. Whenever an event occurs in which criticality safety controls do not function entirely as expected, a management-established reporting system should ensure that proper levels of licensee management will be promptly informed. This reporting system will allow plant and safety management to evaluate the significance of a criticality event precursor and to take appropriate action. Significant loss of control may dictate activation of the Emergency Plan during the evaluation and recovery activities. Reporting Requirements Within 90 days of the receipt of this bulletin, pursuant to 10 CFR 70.22(d), each recipient shall provide the Commission with a statement describing its reporting criteria and management implementation procedures for evaluation and reporting related to loss of criticality safety controls which meet the requirements of 10 CFR 20.403(a). The statement should indicate the means whereby responsible licensee management will be made aware of any relevant failures, the criteria used by licensee management to determine the importance of those failures to criticality safety, and the related reporting levels. The statement should also indicate how the determination will be made that a controlled parameter is sufficiently degraded such that any Emergency Plan procedures will be activated and indicate how the implementation of these procedures for reporting will be documented. Implementing procedures and documentation will be reviewed during NRC inspection. The written reports required above shall be submitted to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, D.C. 20555. In addition, a copy shall be submitted to the appropriate Regional Administrator. The reporting requirements for reports in response to this bulletin are covered by OMB clearance number 3150-0009, which expires May 31, 1994. The estimated average number of burden hours is 80 person hours per licensee response, including those needed to assess the new recommendations, search data sources, gather and analyze the data, and prepare the required letters. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to the Information and Records Management Branch, Division of Information Support Services, Office of Information Resources Management, U.S. Nuclear Regulatory Commission, Washington, DC 20555, and to the Paperwork Reduction Project (3150-0009), Office of Information and Regulatory Affairs, NEOB-3019, Office of Management and Budget, Washington, DC 20503. On November 19, 1991, the Commission will sponsor a workshop concerning reporting of criticality safety events. The location for the workshop will be announced as soon as arrangements can be made. . NRCB 91-01 October 18, 1991 Page 5 of 5 If you have questions about this matter, please contact one of the technical contacts listed below. Richard E. Cunningham, Director Division of Industrial and Medical Nuclear Safety Office of Nuclear Material Safety and Safeguards Technical contacts: George H. Bidinger, NMSS (301) 492-0683 Robert E. Wilson, NMSS (301) 492-0126 A. Thomas Clark, NMSS (301) 492-3424 Attachments: 1. Information Notice No. 90-63, "Management Attention to the Establishment and Maintenance of a Nuclear Criticality Safety Program" 2. Appendix - Principals of Criticality Safety 3. List of Recently Issued NMSS Bulletins 4. List of Recently Issued NRC Bulletins . Attachment 2 NRCB 91-01 October 18, 1991 Page 1 of 1 APPENDIX PRINCIPALS OF CRITICALITY SAFETY The basic tenet of nuclear criticality prevention is that at least two, unlikely, independent, and concurrent changes in process conditions must occur before a criticality accident is possible. This is the so-called "double contingency" principle in ANSI/ANS-8.1-1983. Controls or systems of controls are used to limit process variables in order to maintain safe operating conditions. A list of these typical controls is presented below. The analysis for criticality safety should identify the multiple scenarios by which nuclear criticality can occur. Then controlled parameters and their supporting methods of control must be established to prevent each scenario. A defense-in-depth of two or more controlled parameters is necessary to make criticality unlikely, thereby satisfying the double contingency principle. If a controlled parameter is lost or is substantially degraded, the special nuclear material could threaten to cause exposures to radiation or release of radioactive materials as described in 10 CFR Part 20.403(a) and should be reported immediately to the Commission. Several controls may be involved in maintaining a controlled parameter. For example, a large tank used to receive process solution containing a fissile material might use Raschig rings for one control parameter and concentration limits for another. Both parameters may have several related controls to assure that their loss is highly unlikely. The Raschig rings may be inspected before and after installation, both as to boron content and volume fill level. There may be several controls on concentration, such as initial feed preparation, in-line monitors, and sampling and analysis. The product of all the controls combined provide the "highly unlikely" character of the failure of the controlled parameters. STANDARD CONTROLLED PARAMETERS AND TYPICAL SUPPORTING CONTROLS Controlled Parameters Typical Supporting Controls � Favorable Geometry - Configuration control - Periodic examination (Quality Assurance) - Spacing � Use of Poisons - Configuration control - Neutron absorption measurement - Periodic examination and analysis - Concentration � Mass - Batch size weighing, sampling and analysis - Volume and density measurements � Concentration - Dual sampling and dual analysis - On-line monitoring � Automatic Engineered - Temperature Systems - Pressure - Moisture .
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