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12 October 2012

Hanford Tank Farms Flammable Gas Safety Strategy

[Federal Register Volume 77, Number 198 (Friday, October 12, 2012)]
[Pages 62224-62225]
From the Federal Register Online via the Government Printing Office []
[FR Doc No: 2012-25064]



[Recommendation 2012-2]

Hanford Tank Farms Flammable Gas Safety Strategy

AGENCY: Defense Nuclear Facilities Safety Board.

ACTION: Notice, recommendation.


SUMMARY: Pursuant to 42 U.S.C. 2286a(a)(5), the Defense Nuclear 
Facilities Safety Board has made a recommendation to the Secretary of 
Energy concerning the Hanford Tank Farms flammable gas safety strategy.

[[Page 62225]]

DATES: Comments, data, views, or arguments concerning the 
recommendation are due on or before November 13, 2012.

ADDRESSES: Send comments concerning this notice to: Defense Nuclear 
Facilities Safety Board, 625 Indiana Avenue NW., Suite 700, Washington, 
DC 20004-2001.

FOR FURTHER INFORMATION CONTACT: Deborah H. Richardson or Andrew L. 
Thibadeau at the address above or telephone number (202) 694-7000.

    Dated: October 5, 2012.
Jessie H. Roberson,
Vice Chairman.


Hanford Tank Farms Flammable Gas Safety Strategy

Pursuant to 42 U.S.C. Sec.  2286a(a)(5) Atomic Energy Act of 1954, As 

Dated: September 28, 2012


    The Defense Nuclear Facilities Safety Board (Board) believes 
that current operations at the Hanford Tank Farms require safety-
significant active ventilation of double-shell tanks (DSTs) to 
ensure the removal of flammable gas from the tanks' headspace. A 
significant flammable gas accident would have considerable 
radiological consequences, endanger personnel, contaminate portions 
of the Tank Farms, and seriously disrupt the waste cleanup mission. 
Further, the Board believes that actions are necessary to install 
real time monitoring to measure tank ventilation flowrates as well 
as upgrade other indication systems used to perform safety-related 
    On August 5, 2010, the Board sent a letter to the Department of 
Energy (DOE) outlining issues related to the safety strategy for 
flammable gas scenarios at the Hanford Tank Farms. In its letter, 
the Board identified that the safety analyses for accident scenarios 
used non-bounding values for (1) the radiological inventory of the 
tanks and (2) the amount of waste that could be released in a major 
accident. Notwithstanding these non-conservatisms, DOE's safety 
analyses show that all of the DSTs generate flammable gas in 
sufficient quantities to reach the lower flammability limit (LFL) 
for hydrogen. Further, many of the tanks contain sufficient 
quantities of gas trapped in the waste such that the LFL could be 
exceeded if the gas were spontaneously released, which is possible 
under both normal operating and accident conditions. The current 
control strategy does not include any measures to periodically 
release the trapped gases in a controlled manner to preclude the 
accumulation of flammable concentrations.
    DOE's safety analyses show that the potential flammable gas 
scenarios warrant a credited safety control due to the dose 
consequences to workers and the public. Accordingly, the ventilation 
systems for the DSTs were previously classified as safety-
significant and credited in the documented safety analysis for the 
Tank Farms to address flammable gas scenarios. The revision of the 
safety analysis approved by DOE on January 21, 2010, and implemented 
on March 30, 2010, reduced the DST ventilation systems from safety-
significant to defense-in-depth and replaced them with a specific 
administrative control (SAC) for flammable gas monitoring.
    In its August letter, the Board noted that DOE's SAC for 
flammable gas monitoring exhibited a number of weaknesses that 
collectively rendered it inadequate as a safety control. The 
reliance on an administrative control in lieu of an engineered 
feature is also contrary to DOE's established hierarchy of controls 
as well as sound engineering practice. Further, the Board noted that 
a number of other installed systems that are (1) necessary to 
provide accurate and reliable indications of abnormal conditions 
associated with flammable gas events, and (2) serve as a direct 
input to determining whether an operator action is required were not 
appropriately classified in accordance with their safety function.
    In response to these issues, DOE, in a letter dated February 25, 
2011, informed the Board that it had revised its decision to 
downgrade the DST ventilation systems and would take action to 
restore the systems to their former safety-significant status. 
Additionally, DOE indicated that the level indication systems for 
the DST annuli and the double contained receiver tank would be 
upgraded to safety-significant.
    During the last year, the Board reviewed DOE's progress in 
meeting these commitments and addressing the Board's safety 
concerns. The Board noted that while some improvements had been made 
to the SAC used for flammable gas monitoring, it remained inadequate 
as a credited safety control. The SAC is less reliable than an 
engineered feature, remains susceptible to undetectable false low 
readings, and lacks independent verification.
    Although DOE maintains a commitment to upgrading the DST 
ventilation systems and other installed non-safety-related 
instrumentation used to perform safety functions, the Board has 
concluded that no progress has been made in these areas, and the 
schedule for upgrades continues to slip. The latest schedule, 
outlined in a letter to the Board dated April 2, 2012, reflects a 
commitment to completing the upgrades to three of the five DST 
ventilation systems by fiscal year 2014. During the Board's June 
2012 review, DOE indicated that even this was no longer a realistic 
schedule. DOE's current path forward is to upgrade only one of the 
DST ventilation systems (AY/AZ Tank Farm) by fiscal year 2015 to 
support mixer pump testing that is currently anticipated in 2016. No 
near-term procurement or installation plans are in place for the 
four other DST ventilation systems. Similarly, no plans or 
activities are proposed to upgrade the installed non-safety 
instrumentation systems being used in safety-related applications 
(e.g., the level indication systems for the DST annuli and the 
double container receiver tank).


    The Board believes that DOE needs to upgrade the DST ventilation 
systems and other instrumentation systems used for safety-related 
functions at the Hanford Tank Farms. Further, the continued reliance 
on an inadequate SAC for flammable gas control presents an 
unnecessary risk to safety. At this time, DOE does not have a means 
to provide alternate ventilation if the existing ventilation system 
becomes inoperable. The hazards posed by flammable gas releases in 
DSTs and the challenges they pose to any ventilation system are 
directly proportional to the volume of flammable gas retained within 
the DST wastes. Reducing the current inventories of flammable gases 
retained in the DST waste and keeping them small would reduce the 
future hazards posed by gas release events.


    Accordingly, the Board recommends that DOE:
    1. Take near-term action to restore the classification of the 
DST ventilation systems to safety-significant. In the process, 
determine the necessary attributes of an adequate active ventilation 
system that can deliver the required flow rates within the time 
frame necessary to prevent and mitigate the site-specific flammable 
gas hazards at the Hanford Tank Farms.
    2. Take near-term action to install safety-significant 
instrumentation for real-time monitoring of the ventilation exhaust 
flow from each DST.
    3. Take near-term action to upgrade the existing installed non-
safety-related equipment that is being used to fulfill safety 
functions at the Hanford Tank Farms to an appropriate safety 
classification. This includes instrumentation and control equipment 
whose indications are necessary for operators to take action to 
accomplish necessary safety functions.
    4. Identify compensatory measures in case any existing DST 
ventilation systems become unavailable at the Hanford Tank Farms.
    5. Evaluate means to reduce the existing inventory of retained 
flammable gases in a controlled manner. Since these gases will 
continue to be generated until the tank contents are processed, 
evaluate methods to reduce the future retention of flammable gases 
in these tanks or to periodically mix them to prevent the future 
accumulation of flammable gas inventories that could cause the tank 
headspace to exceed the LFL if rapidly released.
    The Board urges the Secretary to avail himself of the authority 
under the Atomic Energy Act (42 U.S.C. Sec.  2286d(e)) to 
``implement any such recommendation (or part of any such 
recommendation) before, on, or after the date on which the Secretary 
transmits the implementation plan to the Board under this 

Peter S. Winokur, Ph.D.,

[FR Doc. 2012-25064 Filed 10-11-12; 8:45 am]