[DNFSB LETTERHEAD]
August 29, 2007
The Honorable James A. Rispoli
Assistant Secretary for Environmental Management
Dear Mr. Rispoli:
The Defense Nuclear Facilities Safety Board (Board)
acknowledges receipt of your letter of August 16, 2007, which describes your plans for
low-temperature aluminum dissolution and subsequent storage of aluminum-rich
supernate in Tank 11 at the Savannah River Site's high-level waste tank farms. The Board has reviewed the safety aspects of
using Tank 11 to store the aluminum-rich supernate and has no objections to the
Department of Energy's (DOE'S) proposed plans.
In Revision 4 of the Implementation Plan for the
Board's Recommendation 2001-1, High-Level
Waste Management at the Savannah River Site, DOE stated that additions to
Type I and Type II tanks were to be restricted to those
required to facilitate waste removal activities. As noted in the enclosure to your letter, this
proposed use of Tank 11 is not associated with a waste removal activity and
would not normally be permitted. The
Board notes that Tank 11 is one of seven Type I high-level waste tanks with
known leak sites. However, the Board
recognizes that limited space in the high-level waste tanks has forced DOE to
choose non-ideal alternatives in order to manage high-level waste at the
Savannah River Site. The aluminum-rich
supernate to be stored in Tank 11 is low-activity liquid separated from sludge
waste that is to be vitrified at the Defense Waste Processing Facility. DOE plans to store the aluminum-rich supernate
in Tank 11 until it is processed at the Salt Waste Processing Facility, once
that facility begins operation.
The Board has reviewed the safety aspects of using
Tank 11 to store the aluminum-rich supernate, and has discussed with DOE the important
actions that will be taken to minimize or mitigate the impact of a possible
leak from the tank. As described in the
enclosure to this letter, these actions include limiting the maximum level of
the waste to a level below the lowest known leak site, and implementing the
corrosion control program, tank visual inspections, leak detection requirements,
and leak response procedures. Based on
its review, the Board believes there is reasonable assurance of safety in
storing the aluminum-rich supernate in Tank 11.
Please contact me if you have any questions on this
matter.
Sincerely,
A. J. Eggenberger
Chairman
c: Mr. Jeffrey
M. Allison
Mr. Mark B.
Whitaker, Jr.
Enclosure
Enclosure
Safety
Considerations for Storage of Aluminum-Rich Supernate in Tank 11
The Defense Nuclear Facilities Safety Board (Board)
has reviewed the plans for low-temperature aluminum dissolution and subsequent
storage of aluminum-rich supernate in Tank 11. Tank 11 is a Type I high-level
waste tank with known leak sites in the upper tank wall. The Department of Energy (DOE) plans to add
the aluminum-rich supernate to a maximum level of 43 inches below
the lowest known leak in Tank 11. The
estimated cesium source term of the supernate (approximately 0.1 curie/gallon)
is significantly lower than that of the waste previously stored in Tank 11 (1.0
curie/gallon). The Board believes this
operation can be conducted safely provided that the following actions are
meticulously implemented to prevent, detect, and respond to potential leaks
until the waste in Tank 11 is processed.
1. Corrosion
Control Program. The Corrosion
Control Program in the tank farms specifies waste chemistry requirements
designed to minimize the possibility of corrosion and its detrimental effects
on tank integrity.
a. DOE will conduct
and document an evaluation of the final composition of the aluminum-rich
supernate to ensure compliance with the Corrosion Control Program. The evaluation will account for the wide
uncertainty range of the final supernate composition.
b. DOE will continue
to monitor the chemistry conditions in Tank 11 and make adjustments to meet the
requirements of the Corrosion Control Program while the supernate remains
stored in the tank.
2. Transfer Control
Program. The documented safety
analysis for the tank farms requires that transfers of waste comply with the
Transfer Control Program.
a. DOE will meet the
requirements of the Transfer Control Program to ensure that only compatible
waste will be transferred into Tank 11.
b. DOE will also
ensure that the aluminum-rich supernate in Tank 11 is not transferred
to any other tank or evaporator system in violation of the Transfer Control
Program or the evaporator waste acceptance criteria.
3. Visual Inspections. The In-Service
Inspection Program for High-Level Waste Tanks defines the requirements for
visual inspection of Type I tanks. Per
this program, the tanks must be visually inspected at least every 2 years. DOE completed a visual inspection of Tank 11
in March 2006 and found the tank walls to be in good condition except for the
two known leak sites.
a. DOE will continue
the visual inspections of Tank 11 as required by the In-Service Inspection
Program.
b. DOE will implement
real-time video surveillance in the annulus while Tank 11 is receiving waste.
4. Leak
Detection Equipment. Tank 11 is
subject to a Technical Safety Requirement that mandates operable leak detection
equipment in the tank annulus. This
detection equipment consists of a pair of conductivity probes that are linked
to a control room alarm to allow for continuous monitoring. The probes and the alarm receive a required
instrument loop test every 7 days.
a. DOE will comply
with the Technical Safety Requirement for leak detection.
5. Leak Response Procedures. The contractor maintains procedures and equipment for responding
to leaking tanks. These procedures
include, but are not limited to, the Contingency Transfer System, which is
designed to pump the annulus down to a 2 inch level at
a flow rate well in excess of any expected leak rate.
a. DOE will ensure the
leak response procedures are in place and will validate the operability of all
associated contingency transfer equipment prior to transferring waste to Tank
11.
6. Capability to Transfer Waste out of Tank 11. The
contractor also maintains procedures and equipment for responding to a leak by
removing waste from Tank 11 until the waste level has been lowered below all
leak sites. Such transfers would rely on
maintaining sufficient space in other tanks to allow receipt of the waste.
a. DOE will ensure
that adequate emergency tank space is maintained to
implement contingency transfer operations.
b. DOE will validate
the operability of the Tank 11 waste transfer pump prior to adding waste to
Tank 11, and will periodically validate operability throughout the period the
aluminum-rich supernate is stored in Tank 11.
7. Feed Specification for the Salt Waste Processing
Facility. Site analysts expect that the
aluminum-rich supernate will meet the feed specification for the Salt Waste Processing
Facility (SWPF). Once it is operational,
SWPF will provide the final disposition pathway for the supernate and DOE plans
to include the Tank 11 material in an early SWPF campaign.
a. DOE will verify by
sampling prior to transferring to Tank 11 that the waste can
be processed in SWPF. Additional
sampling during the SWPF processing campaign will ensure that the aluminum-rich
supernate meets the SWPF feed criteria.
The above actions provide assurance of safety for the
transfer of supenate from the low-temperature aluminum
dissolution process into Tank 11. The
Board withholds judgment on the storage of this aluminum-rich supernate in any
tank other than Tank 11. The Board
agrees with the stated objective of shortening the life cycle of the tank waste
system and reducing risk, as presented in the DOE letter to the Board dated
August 16, 2007.