Information Notice 2005-22, Inadequate Criticality Safety Analysis of Ventilation Systems at Fuel Cycle Facilities: Difference between revisions

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{{#Wiki_filter:UNITED STATES
{{#Wiki_filter:UNITED STATES


NUCLEAR REGULATORY COMMISSION
===NUCLEAR REGULATORY COMMISSION===
 
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS


WASHINGTON, D.C. 20555 July 29, 2005 NRC INFORMATION NOTICE 2005-22:                 INADEQUATE CRITICALITY SAFETY ANALYSIS
===WASHINGTON, D.C. 20555===
July 29, 2005 NRC INFORMATION NOTICE 2005-22:


===INADEQUATE CRITICALITY SAFETY ANALYSIS===
OF VENTILATION SYSTEMS AT FUEL CYCLE
OF VENTILATION SYSTEMS AT FUEL CYCLE


Line 34: Line 35:
addressees to a safety concern arising from inadequate criticality safety analysis of ventilation
addressees to a safety concern arising from inadequate criticality safety analysis of ventilation


systems at fuel cycle facilities. It is expected that recipients will review the information for
systems at fuel cycle facilities. It is expected that recipients will review the information for


applicability to their facilities and consider actions, as appropriate, to avoid similar problems.
applicability to their facilities and consider actions, as appropriate, to avoid similar problems.
Line 49: Line 50:
differences between otherwise similar systems, analyzed under a single broad criticality
differences between otherwise similar systems, analyzed under a single broad criticality


analysis, were not recognized by criticality safety analysts. The first instance was noted
analysis, were not recognized by criticality safety analysts. The first instance was noted


subsequent to a backflow event in an off-gas line from a uranium dissolver. The licensee used
subsequent to a backflow event in an off-gas line from a uranium dissolver. The licensee used


a single criticality safety analysis for ventilation systems in the facility. The ventilation analysis
a single criticality safety analysis for ventilation systems in the facility. The ventilation analysis


took credit for off-gas piping typically having either a siphon break and a drain, or two drains.
took credit for off-gas piping typically having either a siphon break and a drain, or two drains.
Line 61: Line 62:
modification for the off-gas line on the uranium dissolver such that only one drain was in the
modification for the off-gas line on the uranium dissolver such that only one drain was in the


system. During preparation of the facility criticality safety analysis, criticality safety analysts
system. During preparation of the facility criticality safety analysis, criticality safety analysts


failed to recognize that the design difference defeated the siphon break so that double
failed to recognize that the design difference defeated the siphon break so that double
Line 71: Line 72:
uranium dioxide powder in a high-efficiency particulate air (HEPA) filter housing where no
uranium dioxide powder in a high-efficiency particulate air (HEPA) filter housing where no


uranium was expected. The licensee determined that what criticality safety analysts thought
uranium was expected. The licensee determined that what criticality safety analysts thought


was a breathing air-ventilation system was also connected to a process off-gas line from a hood
was a breathing air-ventilation system was also connected to a process off-gas line from a hood


on a uranium oxidation furnace. The licensee identified a design difference in the system in
on a uranium oxidation furnace. The licensee identified a design difference in the system in


that ventilation and off-gas lines were connected differently, as they approached the HEPA
that ventilation and off-gas lines were connected differently, as they approached the HEPA


filter, than was customary in the remainder of the plant. The licensee had several broad
filter, than was customary in the remainder of the plant. The licensee had several broad


criticality safety analysis packages related to ventilation and process off-gas, grouping them as
criticality safety analysis packages related to ventilation and process off-gas, grouping them as


breathing air, dry off-gas, and wet off-gas. The criticality safety analysts failure to recognize
breathing air, dry off-gas, and wet off-gas. The criticality safety analysts failure to recognize


the design difference in duct connections in one part of the plant from other areas of the plant
the design difference in duct connections in one part of the plant from other areas of the plant
Line 89: Line 90:
led to the incorrect determination that the system was breathing air and criticality was not
led to the incorrect determination that the system was breathing air and criticality was not


credible. This incorrect determination resulted in the failure to implement criticality safety
credible. This incorrect determination resulted in the failure to implement criticality safety


controls typical for off-gas ventilation in the plant.
controls typical for off-gas ventilation in the plant.
Line 98: Line 99:
masses of fissile material are required to analyze accident scenarios leading to criticality and
masses of fissile material are required to analyze accident scenarios leading to criticality and


provide reliable controls to assure that inadvertent criticality events are highly unlikely. When
provide reliable controls to assure that inadvertent criticality events are highly unlikely. When


processes, systems, equipment, or procedures are repeated in a facility, licensees frequently
processes, systems, equipment, or procedures are repeated in a facility, licensees frequently
Line 104: Line 105:
elect to combine similar processes, systems, equipment, or procedures into a single criticality
elect to combine similar processes, systems, equipment, or procedures into a single criticality


analysis. The safety concern arises when modifications resulting in minor design differences
analysis. The safety concern arises when modifications resulting in minor design differences


between otherwise similar systems defeat the credited double-contingency arrangement or non- credibility determination.
between otherwise similar systems defeat the credited double-contingency arrangement or non- credibility determination.
Line 112: Line 113:
controls for groups of ventilation and process off-gas systems that were similar in form and
controls for groups of ventilation and process off-gas systems that were similar in form and


function. While crafting the analyses, developing the criticality safety controls, and
function. While crafting the analyses, developing the criticality safety controls, and


implementing the credited controls, licensee criticality safety analysts failed to recognize design
implementing the credited controls, licensee criticality safety analysts failed to recognize design
Line 124: Line 125:
placing an additional column into the system that effectively defeated the siphon break for the
placing an additional column into the system that effectively defeated the siphon break for the


uranium dissolver. The criticality safety review for this design change looked at the analysis for
uranium dissolver. The criticality safety review for this design change looked at the analysis for


the process, but did not consider the impact that the change would have on off-gas ventilation.
the process, but did not consider the impact that the change would have on off-gas ventilation.
Line 134: Line 135:
Minor design changes during construction of new processes or facilities are common at fuel
Minor design changes during construction of new processes or facilities are common at fuel


cycle licensees and may have a subtle effect on criticality controls. Licensees should consider
cycle licensees and may have a subtle effect on criticality controls. Licensees should consider


actions, as appropriate, to mitigate this vulnerability. These actions could include reviewing all
actions, as appropriate, to mitigate this vulnerability. These actions could include reviewing all


criticality safety analyses that group similar systems, to assure that all assumptions regarding
criticality safety analyses that group similar systems, to assure that all assumptions regarding


the forms and functions of the systems are valid for all applications. Actions could also include
the forms and functions of the systems are valid for all applications. Actions could also include


verifying that the design change review process is adequate to trigger an in-depth criticality
verifying that the design change review process is adequate to trigger an in-depth criticality
Line 153: Line 154:
Licensees should consider whether their ISA/SAR provides an adequate integrated review of
Licensees should consider whether their ISA/SAR provides an adequate integrated review of


ventilation and related systems. This IN requires no specific action nor written response. If you have any questions about the
ventilation and related systems. This IN requires no specific action nor written response. If you have any questions about the


information in this notice, please contact the technical contact listed below.
information in this notice, please contact the technical contact listed below.


/RA/
/RA/
                                      Robert C. Pierson, Director
  Robert C. Pierson, Director


Division of Fuel Cycle Safety
Division of Fuel Cycle Safety
Line 171: Line 172:


===Dennis Morey, NMSS===
===Dennis Morey, NMSS===
                        301-415-6107 E-mail: dcm@nrc.gov
301-415-6107 E-mail: dcm@nrc.gov


Attachment: List of Recently Issued NMSS Generic Communications This IN requires no specific action nor written response. If you have any questions about the
Attachment: List of Recently Issued NMSS Generic Communications This IN requires no specific action nor written response. If you have any questions about the


information in this notice, please contact the technical contact listed below.
information in this notice, please contact the technical contact listed below.


/RA/
/RA/
                                      Robert C. Pierson, Director
  Robert C. Pierson, Director


Division of Fuel Cycle Safety
Division of Fuel Cycle Safety
Line 191: Line 192:


===Dennis Morey, NMSS===
===Dennis Morey, NMSS===
                        301-415-6107 E-mail: dcm@nrc.gov
301-415-6107 E-mail: dcm@nrc.gov
 
Attachment:  List of Recently Issued NMSS Generic Communications
 
ADAMS ACCESSION #: ML051890406 OFC
 
FCSS/TSG
 
Tech ED
 
FCSS/TSG
 
FCSS
 
NAME
 
DMorey:dw
 
Ekraus: by fax


Attachment: List of Recently Issued NMSS Generic Communications
MGalloway


ADAMS ACCESSION #: ML051890406 OFC                FCSS/TSG          Tech ED            FCSS/TSG          FCSS
RPierson


NAME              DMorey:dw          Ekraus: by fax    MGalloway        RPierson
DATE


DATE                07/ 08 /05       07/ 12 /05         07/ 20 /05       07/ 29 /05
07/ 08 /05
07/ 12 /05
07/ 20 /05
07/ 29 /05


Attachment Recently Issued NMSS Generic Communications
Attachment Recently Issued NMSS Generic Communications


Date         GC No.                 Subject
Date
 
GC No.
 
Subject


==Addressees==
==Addressees==
07/13/05     RIS-05-13   NRC Incident Response and     All licensees and certificate
07/13/05 RIS-05-13
 
===NRC Incident Response and===
the National Response Plan
 
===All licensees and certificate===
holders.
 
07/11/05 RIS-05-11
 
===Requirements for Power===
Reactor Licensees in


the National Response Plan    holders.
===Possession of Devices===
Subject to the General


07/11/05      RIS-05-11    Requirements for Power        All holders of operating licenses
===License Requirements of 10===
CFR 31.5


Reactor Licensees in          for nuclear power reactors and
===All holders of operating licenses===
for nuclear power reactors and


Possession of Devices        generally licensed device
generally licensed device


Subject to the General        vendors.
vendors.


License Requirements of 10
06/10/05 RIS-05-10  
                            CFR 31.5
Performance-Based
06/10/05     RIS-05-10   Performance-Based             All industrial radiography


Approach for Associated       licensees and manufacturers and
===Approach for Associated===
Equipment in 10 CFR 34.20


Equipment in 10 CFR 34.20    distributors of industrial
===All industrial radiography===
licensees and manufacturers and
 
distributors of industrial


radiography equipment.
radiography equipment.


04/18/05     RIS-05-06   Reporting Requirements for   All material licensees possessing
04/18/05 RIS-05-06
 
===Reporting Requirements for===
Gauges Damaged at
 
===Temporary Job Sites===
All material licensees possessing
 
portable gauges, regulated under
 
10 CFR Part 30.


Gauges Damaged at            portable gauges, regulated under
6/23/05 IN-05-17


Temporary Job Sites          10 CFR Part 30.
===Manual Brachytherapy===
Source Jamming


6/23/05      IN-05-17    Manual Brachytherapy          All medical licensees authorized
===All medical licensees authorized===
to possess a Mick applicator.


Source Jamming                to possess a Mick applicator.
05/17/05 IN-05-013 Potential Non-conservative


05/17/05      IN-05-013    Potential Non-conservative    All licensees using the Keno-V.a
===Error in Modeling Geometric===
Regions in the


Error in Modeling Geometric  criticality code module in
Keno-v.a Criticality Code


Regions in the               Standardized Computer Analyses
All licensees using the Keno-V.a


Keno-v.a Criticality Code    for Licensing Evaluation (SCALE)
criticality code module in
                                                          software developed by Oak


Ridge National Laboratory
===Standardized Computer Analyses===
for Licensing Evaluation (SCALE)
software developed by Oak


===Ridge National Laboratory===
(ORNL)
(ORNL)
05/17/05     IN-05-012   Excessively Large Criticality All licensees authorized to
05/17/05 IN-05-012
 
===Excessively Large Criticality===
Safety Limits Fail to Provide


Safety Limits Fail to Provide possess a critical mass of special
===Double Contingency at Fuel===
Cycle Facility


Double Contingency at Fuel    nuclear material.
===All licensees authorized to===
possess a critical mass of special


Cycle Facility
nuclear material.


Note: NRC generic communications may be found on the NRC public website, http://www.nrc.gov, under Electronic Reading Room/Document Collections.}}
Note: NRC generic communications may be found on the NRC public website, http://www.nrc.gov, under Electronic Reading Room/Document Collections.}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Latest revision as of 17:30, 15 January 2025

Inadequate Criticality Safety Analysis of Ventilation Systems at Fuel Cycle Facilities
ML051890406
Person / Time
Issue date: 07/29/2005
From: Pierson R
NRC/NMSS/FCSS
To:
References
IN-05-022
Download: ML051890406 (5)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, D.C. 20555

July 29, 2005 NRC INFORMATION NOTICE 2005-22:

INADEQUATE CRITICALITY SAFETY ANALYSIS

OF VENTILATION SYSTEMS AT FUEL CYCLE

FACILITIES

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 alert

addressees to a safety concern arising from inadequate criticality safety analysis of ventilation

systems at fuel cycle facilities. It is expected that recipients will review the information for

applicability to their facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this IN are not new NRC requirements; therefore, no

specific action nor written response is required.

DESCRIPTION OF CIRCUMSTANCES

Recently, two events occurred at NRC-licensed fuel cycle facilities involving the failure to

implement criticality safety controls on process off-gas or ventilation systems when minor

differences between otherwise similar systems, analyzed under a single broad criticality

analysis, were not recognized by criticality safety analysts. The first instance was noted

subsequent to a backflow event in an off-gas line from a uranium dissolver. The licensee used

a single criticality safety analysis for ventilation systems in the facility. The ventilation analysis

took credit for off-gas piping typically having either a siphon break and a drain, or two drains.

However, a concern about off-gas accumulation in an enclosed area led to a design

modification for the off-gas line on the uranium dissolver such that only one drain was in the

system. During preparation of the facility criticality safety analysis, criticality safety analysts

failed to recognize that the design difference defeated the siphon break so that double

contingency was not established.

The second instance was noted when a fuel cycle licensee observed an accumulation of

uranium dioxide powder in a high-efficiency particulate air (HEPA) filter housing where no

uranium was expected. The licensee determined that what criticality safety analysts thought

was a breathing air-ventilation system was also connected to a process off-gas line from a hood

on a uranium oxidation furnace. The licensee identified a design difference in the system in

that ventilation and off-gas lines were connected differently, as they approached the HEPA

filter, than was customary in the remainder of the plant. The licensee had several broad

criticality safety analysis packages related to ventilation and process off-gas, grouping them as

breathing air, dry off-gas, and wet off-gas. The criticality safety analysts failure to recognize

the design difference in duct connections in one part of the plant from other areas of the plant

led to the incorrect determination that the system was breathing air and criticality was not

credible. This incorrect determination resulted in the failure to implement criticality safety

controls typical for off-gas ventilation in the plant.

DISCUSSION

Under 10 CFR Parts 70 and 76, certain licensees processing, storing, or handling critical

masses of fissile material are required to analyze accident scenarios leading to criticality and

provide reliable controls to assure that inadvertent criticality events are highly unlikely. When

processes, systems, equipment, or procedures are repeated in a facility, licensees frequently

elect to combine similar processes, systems, equipment, or procedures into a single criticality

analysis. The safety concern arises when modifications resulting in minor design differences

between otherwise similar systems defeat the credited double-contingency arrangement or non- credibility determination.

In the two events described, the two licensees used a single criticality safety analysis to develop

controls for groups of ventilation and process off-gas systems that were similar in form and

function. While crafting the analyses, developing the criticality safety controls, and

implementing the credited controls, licensee criticality safety analysts failed to recognize design

differences between the systems that defeated some of the assumptions or credited controls

used in some portion of the facility.

In the first instance, a design change occurred, during construction of the system, that involved

placing an additional column into the system that effectively defeated the siphon break for the

uranium dissolver. The criticality safety review for this design change looked at the analysis for

the process, but did not consider the impact that the change would have on off-gas ventilation.

In the second instance, contractors were constructing a new facility, and criticality safety

analysts did not recognize design differences in the ventilation system.

Minor design changes during construction of new processes or facilities are common at fuel

cycle licensees and may have a subtle effect on criticality controls. Licensees should consider

actions, as appropriate, to mitigate this vulnerability. These actions could include reviewing all

criticality safety analyses that group similar systems, to assure that all assumptions regarding

the forms and functions of the systems are valid for all applications. Actions could also include

verifying that the design change review process is adequate to trigger an in-depth criticality

safety review for changes arising during construction.

The Part 70 integrated safety analysis (ISA) and the Part 76 safety analysis report (SAR)

provide an integrated approach to assure that inter-relationships between accident scenarios

and their controls are appropriately evaluated during related design and change activities.

Licensees should consider whether their ISA/SAR provides an adequate integrated review of

ventilation and related systems. This IN requires no specific action nor written response. If you have any questions about the

information in this notice, please contact the technical contact listed 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

301-415-6107 E-mail: dcm@nrc.gov

Attachment: List of Recently Issued NMSS Generic Communications This IN requires no specific action nor written response. If you have any questions about the

information in this notice, please contact the technical contact listed 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

301-415-6107 E-mail: dcm@nrc.gov

Attachment: List of Recently Issued NMSS Generic Communications

ADAMS ACCESSION #: ML051890406 OFC

FCSS/TSG

Tech ED

FCSS/TSG

FCSS

NAME

DMorey:dw

Ekraus: by fax

MGalloway

RPierson

DATE

07/ 08 /05

07/ 12 /05

07/ 20 /05

07/ 29 /05

Attachment Recently Issued NMSS Generic Communications

Date

GC No.

Subject

Addressees

07/13/05 RIS-05-13

NRC Incident Response and

the National Response Plan

All licensees and certificate

holders.

07/11/05 RIS-05-11

Requirements for Power

Reactor Licensees in

Possession of Devices

Subject to the General

License Requirements of 10

CFR 31.5

All holders of operating licenses

for nuclear power reactors and

generally licensed device

vendors.

06/10/05 RIS-05-10

Performance-Based

Approach for Associated

Equipment in 10 CFR 34.20

All industrial radiography

licensees and manufacturers and

distributors of industrial

radiography equipment.

04/18/05 RIS-05-06

Reporting Requirements for

Gauges Damaged at

Temporary Job Sites

All material licensees possessing

portable gauges, regulated under

10 CFR Part 30.

6/23/05 IN-05-17

Manual Brachytherapy

Source Jamming

All medical licensees authorized

to possess a Mick applicator.

05/17/05 IN-05-013 Potential Non-conservative

Error in Modeling Geometric

Regions in the

Keno-v.a Criticality Code

All licensees using the Keno-V.a

criticality code module in

Standardized Computer Analyses

for Licensing Evaluation (SCALE)

software developed by Oak

Ridge National Laboratory

(ORNL)

05/17/05 IN-05-012

Excessively Large Criticality

Safety Limits Fail to Provide

Double Contingency at Fuel

Cycle Facility

All licensees authorized to

possess a critical mass of special

nuclear material.

Note: NRC generic communications may be found on the NRC public website, http://www.nrc.gov, under Electronic Reading Room/Document Collections.


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