United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 91-01: Supplement 1, Reporting Loss of Criticality Safety Controls

                                                         OMB No. 3150-0009
                                                         NRCB 91-01, Supp. 1

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                                 July 27, 1993



For Action  All fuel fabrication facilities.

For Information -  All facilities whose activities include, Hot Cell
Operations, Uranium Enrichment Operations, Uranium Fuel R&D, and Critical Mass


The U.S. Nuclear Regulatory Commission (NRC) is issuing this bulletin to 
(1) provide addressees clearer reporting criteria, (2) request that action
addressees take certain actions, and (3) require that all action addressees
report to NRC whether and to what extent the requested actions will be taken
and notify the NRC when actions associated with this bulletin are complete.

This document is not intended to address accident mitigation, emergency
response, long-term corrective actions, or license requirements.  Such actions
should be performed in accordance with the license and established


This is a follow-up to Bulletin 91-01, "Reporting Loss of Criticality Safety
Controls," which was issued on October 18, 1991.  The bulletin requested that
addressees inform the NRC of their criteria and procedures to ensure the
prompt evaluation and reporting of conditions and events involving criticality

Description of Circumstances 

The NRC staff has reviewed each licensee's response to the bulletin.  Most
responses reflected a commitment to promptly evaluate events with criticality
safety implications, report the most significant events immediately to the
NRC, and report less significant events within 24 hours.

Also, we received numerous comments on the bulletin through correspondence and
various meetings and workshops.  A major comment concerned the bulletin's
statement that loss or lack of a controlled parameter related to criticality
safety should be reported to the NRC immediately.  Several persons noted that 


                                                      NRCB 91-01, Supp. 1
                                                      July 27, 1993
                                                      Page 2 of 4 

further clarification regarding the definition of "a loss of a controlled 
parameter" is needed.  Also, several persons noted that a loss of a controlled
parameter is not always a significant event warranting an immediate report,
for example, if the event involves a small amount of special nuclear material. 
These licensees maintained that they should only report events immediately to
the NRC if there is a significant threat of a criticality accident or if the
severity of the threat cannot be readily determined.


We have considered these comments and conclude that further clarification is
warranted.  Therefore, we are clarifying that we want reported to the NRC 
immediately, those cases where (1) moderation is used as the primary
criticality control, or (2) more than a safe mass of fissionable material is
involved (regardless of the type of controls used to satisfy the double
contingency principle), and that meet one or more of the following immediate
reporting criteria.

Immediate Reporting Criteria

1.    Any event that results in the violation of the double contingency        
      principle, as defined in ANSI 8.1, and where the double contingency
      principle cannot be re-established within 4 hours after the initial
      observation of the event. 

2.    The occurrence of any unanticipated or unanalyzed event for which the
      safety significance of the event or corrective actions to re-establish
      the double contingency principle are not readily identifiable.

3.    Any case where it is determined that a criticality safety analysis was
      deficient and where the necessary controlled parameters were not
      established or maintained.

4.    Any event involving a controlled parameter previously identified by the
      NRC or the licensee as requiring immediate reporting to the NRC and
      where the double contingency principle cannot be re-established within 4
      hours after the initial observation of the event.

Events and/or conditions that satisfy the above criteria should be reported
within 4 hours from the initial observation, in accordance with 10 CFR 20.403
and 10 CFR 70.50.

All other criticality safety events that do not meet the aforementioned
criteria, but still result in a violation of the double contingency principle,
such as events where the double contingency principle is violated but control.

                                                      NRCB 91-01, Supp. 1
                                                      July 27, 1993
                                                      Page 3 of 4 

is immediately re-established, should be reported to the NRC within 24 hours
in accordance with the commitments in the responses to the bulletin.

It is expected that criticality safety events will be promptly evaluated and
that appropriate management and technical personnel will be available 24 hours
a day to perform such evaluations.

It should be emphasized that it is important that NRC be notified of events
related to criticality safety and that if there is any doubt as to whether an
event should be reported, the NRC should be contacted.

Requested Actions

Addressees are requested to review their criticality safety reporting
procedures to ensure that they meet or exceed the reporting criteria described
in this clarification of NRC Bulletin 91-01.  Questions may be directed to the
contact listed below.

Reporting Requirements

Within 60 days of this bulletin, pursuant to 10 CFR 70.22(d), each recipient
shall provide the Commission with a statement (1) confirming that their
current reporting criteria and management implementation procedures meet these
minimum criteria, or (2) describing those procedures revised to be consistent
with the reporting criteria.

Address any such written correspondence to the U.S. Nuclear Regulatory
Commission, ATTN:  Document Control Desk, Washington, D.C. 20555, under oath
or affirmation under the provisions of Section 182a, Atomic Energy Act of
1954, as amended.  In addition, submit a copy to the appropriate regional

Paperwork Reduction Act Statement

This bulletin contains information collection requirements that are subject to
the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.).  These
requirements were approved by the Office of Management and Budget, approval
number 3150-0009.

The public reporting burden for this collection of information is estimated to
average    8     hours per response, including the time for reviewing
instructions, searching existing data sources, gathering and maintaining the
data needed, and completing and reviewing the collection of information..

                                                      NRCB 91-01, Supp. 1
                                                      July 27, 1993
                                                      Page 4 of 4 

Send comments regarding this burden estimate or any other aspect of this
collection of information, including suggestions for further reducing
reporting burden, to the Information and Records Management Branch 
(MNBB-7714), U.S. Nuclear Regulatory Commission, Washington, D.C. 20555; and
to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-3019, 
(3150-0009), Office of Management and Budget, Washington, D.C. 20503.

Further clarification to this bulletin is provided in the attached responses
to specific questions raised by licensees.

If you have any questions about this matter, please contact the Operations
Branch at (301) 504-3497.

                                          ORIGINAL SIGNED BY

                                          Robert F. Burnett, Director
                                          Division of Fuel Cycle Safety
                                            and Safeguards
                                          Office of Nuclear Material Safety
                                            and Safeguards

Technical contact:  M. Klasky, NMSS
                    (301) 504-2504

1.  Questions and Answers to Bulletin 91-01
2.  List of Recently Issued NMSS Bulletins
3.  List of Recently Issued NRC Bulletins.

                                                      Attachment 1
                                                      NRCB 91-01, Supp. 1
                                                      July 27, 1993
                                                      Page 1 of 2

                    QUESTIONS AND ANSWERS TO BULLETIN 91-01

Q1.If reporting criteria currently contained in the licensee's emergency plan
cover the 91-01 requirements for immediate reporting and are consistent with
the 91-01 immediate reporting criteria, does the 91-01 procedure need to cover
only the 24-hour criteria?

A1.Yes.  No other immediate reporting would be required under 91-01.

Q2.The double contingency requirement includes all control parameters that
have previously, before the event, been identified in the nuclear criticality
safety analysis.  Therefore, if a work station has six controls, and four are
lost, is reporting required?

A2.No.  If some controls are lost, and the double contingency requirement is
still fulfilled, it is not reportable under 91-01.  However, it should be
noted that in some instances several controls may be necessary to provide an
adequate barrier.  For example, dual sampling is required when sampling is
utilized as a criticality control.

Q3.In cases where a deficiency in the criticality analysis is found, and in
the same analysis a mitigating condition not previously identified is found,
is the deficient criticality analysis reportable?

A3.Yes.  The licensee should report it.  In addition, the licensee should
prepare a corrected analysis.

Q4.If an event or condition occurs, as envisioned in criteria 2 or 3 for
immediate reporting, does the licensee have 4 hours to determine if it is
within the established safety parameters and report it to the NRC?

A4.Yes.  The licensee has a total of 4 hours to report the event or condition
to the NRC, from the time the event or condition is first noted or identified.

Q5.What determines that a controlled parameter was previously identified
formally by the NRC or licensee?

                                                      Attachment 1
                                                      NRCB 91-01, Supp. 1
                                                      July 27, 1993
                                                      Page 2 of 2

A5.Controlled parameters identified in the NRC approved section of the license
application or in a license condition would be considered formally identified
by the NRC, and those controlled parameters identified in current nuclear
criticality safety analyses would be considered formally identified by the


Safe Mass: 45 percent of the minimum critical mass of special nuclear material
for a given enrichment.

Re-establish: establish within 4 hours after the identification of the event
the conditions to assure that the double contingency principle and the pre-
established licensed conditions for that system exist.



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