Peter S. Winokur, Chairman 

Jessie H. Roberson, Vice Chaitman 

John E. Mansfield 

DEFENSE NUCLEAR FACILITIES 

SAFETY BOARD 

Joseph F. Bader 

Sean Sullivan 

The Honorable Ernest J. Moniz 

Secretary of Energy 

U.S. Depaitment of Energy 

1000 Independence A venue, SW 

Washington, DC 20585-1000 

Dear Secretary Moniz: 

Washington, DC 20004-2901 

November 1, 2013 

On September 25, 2013, the Department of Energy's (DOE) Senior Advisor for 

Environmental Management asked the Defense Nuclear Facilities Safety Board (Board) to provide its 

perspective on the safety implications of removing a portion of the radioactive liquid from tank 241-

A Y -102 at the Hanford site. The Board is unable to detennine whether any safety implications exist. 

The waste temperature in tank A Y-102 is of patticular significance to nuclear safety. The 

Board analyzed a report provided by DOE, RPP-RPT-53901 Rev. 2, Management of Supernatant 

Level in Tank 24 l-AY-102, which concludes that decanting is likely to have little effect on tank waste 

temperatures and the estimated leak rate. However, the Board determined that insufficient 

information exists to suppo1t this conclusion. Specifically, the report does not address key technical 

unce1tainties with the condition of the tank, such as: (1) the specific cause of the leak and the leak 

rate remain unknown; (2) the chemical and physical conditions at the leak site are uncertain; and (3) 

the impact from a change in temperature, pressure, or chemistry on the leak rate are also uncertain. 

If DOE proceeds with radioactive liquid decanting, the Board advises DOE to closely 

monitor for signs of increased leakage and blockage of the insulating refractory slots that distribute 

cooling air to the tank bottom. The Board also advises DOE to consider developing a more rigorous 

multi-dimensional, transient thermal analysis model to aid in understanding the safety significance of 

any observed changes in tank conditions subsequent to decanting. The enclosed repo1t contains 

additional information on the Board's evaluation. 

Enclosure 

c: Mrs. Mari-Jo Campagnone 

Sincerely, 

~.2c:-W:O- Peter S. Winokur, Ph.D. 

Chairman 
DEFENSE NUCLEAR FACILITIES SAFETY BOARD 

MEMORANDUM FOR: 

COPIES: 

FROM: 

SUBJECT: 

Staff Issue Report 

October 24, 2013 

S. A. Stokes, Technical Director 

Board Members 

M. Forsbacka, M. Horr, A. Poloski, R. Rosen, D. Shrestha 

Safety and Integrity Implications of Decanting Liquid from Hanford 

Tank 241-AY-102 

Introduction. Hanford waste tank 241-A Y-102 (tank A Y-102), the first double-shell 

tank (DST) at Hanford, was built during 1968-1970 and was placed into service in 1971. During 

a visual inspection in August 2012, Washington River Protection Solutions (WRPS) personnel 

discovered accumulations of material at three locations within the secondary confinement of tank 

A Y-102. Two accumulations were located on the floor of the tank A Y-102 annulus between the 

primary and secondary tank liners, and a third was on the primary tank dome above the 

waterline. None of the material was seen during the December 2006 and January 2007 visual 

inspections. The Department of Energy (DOE) Office of River Protection (ORP) and WRPS 

established a leak assessment team to review tank construction, review operating histories, and to 

determine the probable cause of the leak. The team met from August 28, 2012, to October 10, 

2012, to gather and analyze information, formulate tank leak and non-leak hypotheses, and 

identify the source of the accumulated floor material. WRPS personnel completed their formal 

leak assessment report in October 2012. 

Tank A Y-102 contains 151,000 gallons (57 inches) of high decay heat sludge primarily 

retrieved from single-shell tank 241-C- l 06 and 680,000 gallons (270 inches) of radioactive 

supernatant liquid on top of the sludge. DOE-ORP is making plans to remove a portion of the 

radioactive supernatant liquid due to the identified leak. DOE-ORP approved a WRPS report, 

RPP-RPT-53901 Rev. 2, Management of Supernatant Level in Tank 241-AY-102, on September 

30, 2013, which recommends decanting the radioactive supernatant liquid layer from 270 inches 

to 96 inches and maintaining the liquid level above 48 inches through future water additions if 

needed to account for evaporation. DOE's Senior Advisor for Environmental Management 

asked the Defense Nuclear Facilities Safety Board (Board) on September 25, 2013, to provide its 

perspective on the safety implications of removing a portion of the radioactive liquid from tank 

AY-102. 

Approach. In response to DOE's request, members of the Board's staff evaluated 

DOE' s plans to decant tank AY-102 supernatant liquid. This report documents the staff 

members' evaluation. RPP-RPT-53901 concluded that decanting is likely to have little effect on 

tank waste temperatures and the estimated leak rate. The staff members performed a technical 

evaluation of RPP-RPT-53901 to assess if these key conclusions are well-supported. This effort 

included reviewing supporting DOE technical reports, tank schematics, in-tank temperature data, 

and independent calculations to understand how changes in liquid level might affect waste 
temperature, the estimated leak rate, and other potential impacts on tank safety. For example, 

hydrogen generation and corrosion rates are dependent on temperature, following an Arrheniustype behavior where the reaction kinetics increase exponentially with temperature. Therefore, 

the waste temperature in tank A Y-102 is of particular significance to nuclear safety. 

Background. Figure 1 shows a schematic of a Hanford DST as shown in HNF-EP-0182, 

Waste Tank Summary Report for Month Ending December 31, 2012. The DST's primary steel 

liner rests on an insulating refractory layer on top of the floor of the secondary steel liner. The 

entire system rests on a concrete foundation. The bottom plate of the primary tank liner is 3/8-

inch thick and the bottom plate of the secondary tank liner is 1/4-inch thick. The tank annulus 

refers to the space formed between the primary tank and secondary tank liners, and extends from 

the base of the tank to the dome of the tank. The secondary tank liner is 80 feet in diameter, and 

the primary tank liner is 7 5 feet in diameter. The resulting annulus is 2-1/2 feet wide. The 

capacity of tank AY-102 is one million gallons of high-level radioactive waste. Current 

temperature monitoring capabilities for tank A Y-102 include approximately 40 operating 

the1mocouples in the tank at various heights and radial locations and thermocouples embedded in 

the concrete foundation , the refractory, and the tank dome. Additionally, ENRAFs, a type of 

level sensor, are used to measure liquid height. 

Surface Love! Probe (FIC, ENAAF ond Manual Tape) Solids Level Detector 

Camera Observation Port j ~ Dome Elevation 

Bench Mark EKhnust Stock 

Annulus Pump Pit Continuous 

----------- Air Flow Monitor 

, ..... _;~p" "" ~ _ "'- I ~ .. ,.~.,~Th·~~ ........ m ... 

Operating Llqutci Level 

Pump Pit- -- Sludge "'4_ : 

Concrete 

Steel llnere 

Figure 1. Hanford double-shell tank (from HNF-EP-0182 Rev. 297). 

Primary 

Steel 

Liner 

Secondary 

Steel 

Liner 

Reinforced 

Concrete 

Tank 

During September and October 2012, WRPS personnel collected and analyzed samples 

from two waste accumulation locations on the annulus floor. The material was radioactive, and 

its composition was consistent with tank A Y-102 waste. Detailed records for tank 241-AY-101 , 

the second DST built at Hanford, were also studied for comparison. The leak assessment team 

concluded that the likely cause of the material on the tank A Y-102 annulus floor was the result 

of a breach on the bottom of the tank's primary liner from high-temperature corrosion. Tank 

A Y-102, being a first-of-a-kind DST at Hanford, encountered numerous difficulties during its 

2 
construction period. The WRPS team concluded that these construction difficulties resulted in 

the primary tank's bottom being more susceptible to eventual failure than other DSTs 

constructed afterwards. Figure 2 shows details of the annulus, including the insulating refractory 

between the primary and secondary liners. Figure 2 also shows a diagram of the slots in the 

refractory on the tank bottom which distribute annulus ventilation air to the tank bottom for 

cooling. The total leakage volume from the primary tank, estimated on February 7, 2013, was 

190-520 gallons. A significant portion of the liquid has since evaporated, leaving 20-50 gallons 

of dry waste in the tank annulus. Figure 3 shows an image of the dried waste, labeled as "Crystal 

Nodules." 

Ventilation 

Secondary Tan k Bottom 

Air Distribution Ring 

Figure 2. Top-Hanford double-shell tank annulus (from RPP-ASMT-53793); 

Bottom-Secondary ventilation system air distribution for 241-A Y-102 

(from RPP-ASMT-53793). 

3 
Figure 3. Dried tank waste in the 241-AY-102 tank annulus (from RPP-ASMT-53793). 

Technical Evaluation of RPP-RPT-53901. The staff members found that the analyses 

contained in RPP-RPT-53901 are insufficient to determine the effect of supernatant level 

changes on waste temperatures and leak rates. RPP-RPT-53901 did not account for several key 

physical aspects of the relationship between supernatant height and heat transfer mechanisms 

that could result in a more adverse thermal condition than analyzed. For instance: 

• The analyses do not account for the reduction in the heat transfer surface area 

between the supernatant layer and primary liner wall resulting from the reduction in 

the height of the supernatant layer. 

• The analyses do not properly account for heat transfer rates varying with waste 

temperatures in accordance with Newton's law of cooling. 

• The analyses use bulk average temperatures and do not consider higher localized 

temperatures that could exceed A Y-102 corrosion control limits. 

On October 3, 2013, the staff members held a teleconference with DOE-ORP and WRPS 

personnel to discuss RPP-RPT-53901. WRPS personnel stated that the primary purpose of the 

report was to produce a general thermal analysis to support maintaining an adequate supernatant 

liquid height for this high decay heat tank. Information and analyses that could improve 

predictions of waste temperatures and leak rates due to changing supernatant liquid height 

include the following: 

4 
• Radial and axial heat transfer mechanics inside the primary liner. This includes heat 

transfer behavior between the heat generating layer of sludge, the supernatant liquid, 

the tank walls, and the ventilated air in the tank headspace. 

• Radial and axial heat transfer mechanics between the primary and secondary liners. 

This includes heat transfer behavior between the primary liner and the ventilated 

refractory layer beneath the vessel, the ventilated air space in the tank annulus, and 

the surrounding soil. 

• Both of these areas are dependent upon how the heat transfer mechanisms change 

with ventilation status. 

An analytical tool that can adequately account for these phenomena is a validated, multidimensional, transient heat transfer model. Results from such a model would be helpful in 

understanding the effects of changing the waste height due to the decanting operation and 

ventilation status on waste temperatures. The modeling approaches used by previous Hanford 

tank farm contractors in the late 1990s, are an example of the level of technical detail that could 

assess this type of complex themrnl system. These efforts did produce predictions of radial and 

axial temperature distributions in tank A Y-102 including transient effects from primary and 

secondary ventilation outages, but did not contain modeling results for the specific supernatant 

liquid decant scenario under evaluation. 

DOE' s current plan to partially decant tank A Y -102 will cause a corresponding reduction 

in hydrostatic pressure at the bottom of the primary tank liner. Although Darcy's Law predicts 

that a reduction in hydrostatic pressure would correspond to a reduction in leak rate, RPP-RPT53901 concludes the leak rate through a leakage site in the floor of the primary liner is likely 

insensitive to hydrostatic pressure because, once the liquid waste enters the presumed small leak 

opening and starts its tortuous path through the underlying refractory, pressure is quickly 

dissipated over a distance of a few inches. 

In addition to uncertainty about the impacts of reducing hydrostatic pressure by 

decanting, there are several other complicating factors that make determination of the net effect 

of decanting on the leak rate uncertain. Most of these factors are unknown or have significant 

uncertainty. They include: 

• The mechanism that led to the original tank liner failure (e.g., pitting, stress corrosion 

cracking, or preexisting flaw) and how the growth rate for this type of leak site 

increases as a result of increased waste temperatures. 

• How the size, shape, and tortuosity of the leak site and the leak flow path change due 

to hydrostatic pressure, thermal expansion, and the drying of the leaked waste. 

The complexity of the competing factors in this system is illustrated by liquid waste in 

the leak path to the tank annulus drying and forming solid deposits. For example, solid deposits 

can limit or plug the leak from the tank bottom. Conversely, because the leak path to the annulus 

is through the refractory slots, solid deposits can plug the air distribution system along the tank 

bottom (see Figure 4 ). Blockage of the refractory slots reduces air flow and limits the annulus 

ventilation air from cooling the tank bottom. Because the total volume of refractory slots is on 

5 
the order of several hundred gallons, a relatively small tank leak volume could significantly alter 

air flow in localized regions of the tank bottom. Any reduction of cooling would increase 

localized temperatures and thermal gradients on the tank bottom, potentially significantly 

increasing the corrosion rate. 

Figure 4. Close-up of dried tank waste in the refractory slot (from RPP-ASMT-53793). 

RPP-RPT-53901 acknowledges that over time, leaked waste might eventually inhibit air 

flow through the channels in the refractory. Consequently, annulus ventilation flow might be 

lost beneath the primary liner. The report states that accurately estimating temperature rise 

requires a complex three-dimensional heat transfer model, but asserts that the historic 

temperature behavior of single-shell tank 241-C-106 (the source of the tank AY-102 high heat 

sludge) can be used to bound tank A Y-102 waste temperatures if the annulus ventilation is lost. 

RPP-RPT-53901 further states that during the 1990s, the maximum solids temperature in C-106 

was 160 to 170°F and that similar temperatures should be expected in tank A Y-102 settled solids 

if the annulus ventilation system were not operated, assuming that the primary ventilation system 

continued to operate and supernatant depth was maintained at over 12 inches. This conclusion is 

only valid if, after accounting for decreases in decay heat from the 1990s, the heat transfer 

resistance from the waste in a single-shell tank to the surrounding soil is greater than or equal to 

an analogous DST. Heat transfer through the air-filled annulus in a DST to the soil is expected 

to add an additional heat transfer resistance term resulting in a higher corresponding waste 

temperature. The WRPS report did not analyze thermal transport differences between a singleshell tank and a DST. 

The primary and annulus ventilation systems provide significant heat removal for the 

sludge heat source. While these ventilation systems are in operation, decreasing the supernatant 

liquid height between 96 to 48 inches is not likely to significantly raise the temperature of the 

waste. However, as discussed above, leaked waste can inhibit operation of the annulus 

6 
ventilation system. The staff members' analysis finds that temperatures on the tank bottom 

increase significantly when the annulus ventilation system is off. Figure 5 shows that the 

temperature of the refractory layer at the tank bottom increased steadily during a test when the 

primary ventilation system was on and the annulus ventilation system was cycled off. When the 

ventilation system was cycled on, the tank bottom was rapidly cooled. 

180 

170 

160 

;:;::-

~ 150 cu 

.... 

::I 

'l;j 140 .... 

cu 

Q. 

E 130 cu 

I120 

c9 

110 0 

100 ·~ 

1/17 

Ventilation Off 

1/24 1/31 2/7 

) 

0 

2/14 

c: 

0 

c: 

0 

·.;::; 

ro 

·.;::; 

c: 

(]) 

> 

0 

0 

0 0 

0 

2/21 

Date (2008) 

0 

Ventilation Off c: 

0 

....., 

ro c: 

ooooc ."§ ooo oo I o <lJ 00 > 0 00 

00 

oO 0 

0 °

0 3/15/08: 166°F 

0 

0 

2/28 3/6 3/13 3/20 

Figure 5. Tank A Y-102 refractory temperatures from a thermocouple 21 ft from the tank centerline when 

the primary ventilation system is on and the annulus ventilation is cycled on and off (source: Tank 

Waste Information Network System). 

After a decade of additional radioactive decay after retrieval from tank C-106 in the 

1990s, on March 15, 2008, the temperature of the tank AY-102 refractory reached about 166°F 

and appeared to be steadily increasing until the annulus ventilation system was turned back on at 

the end of the test (see Figure 5). Based on these data, it is apparent that the historical C-106 

maximum solids temperature range of 160 to 170°F does not represent an upper bound for tank 

AY-102. Because the half-life of the radioisotopes primarily responsible for the decay heat in 

the tank waste is about 30 years, 5 years for additional radioactive decay from 2008 to 2013 is 

not expected to significantly change this conclusion. These data show that a prolonged annulus 

ventilation outage will raise the temperature of the tank bottom, which may lead to increased 

hydrogen generation and corrosion rates. Higher localized tank temperatures can exist between 

tank thermocouple locations. The final tank temperatures cannot be accurately predicted or 

bounded with the existing WRPS analysis. A multi-dimensional, transient thermal transport 

model would be useful in assessing tank bottom temperature increases relative to corrosion 

control limits resulting from restricted air flow on the tank bottom. 

Conclusions. DOE's analysis supporting an interim change in radioactive liquid level 

from 270 to 96 inches is insufficient to determine if there is an immediate positive or negative 

effect on the safety condition of tank A Y-102. The annulus ventilation system is a significant 

contributor in keeping the tank bottom temperatures cool. The ongoing leak in the primary liner 

of tank A Y-102 appears to have obstructed a portion of the air distribution slots immediately 

below the primary tank bottom, which is a key section of the annulus ventilation system. If a 

significant portion of this cooling air distribution system is lost, waste temperatures will increase. 

7 
Reaction kinetics increase exponentially with temperature. Hence, the potential exists for 

increased corrosion and hydrogen generation rates. 

Continued visual inspections of the tank annulus and close monitoring for variations in 

waste temperature (particularly near the tank bottom) and annulus ventilation, which can be 

indicative of increased leakage and blockage of the refractory slots that distribute cooling air to 

the tank bottom, are prudent steps if DOE proceeds with radioactive liquid decanting. Further 

analysis, including development of a more rigorous multi-dimensional, transient thermal 

transport model could provide better understanding of the significance of any observed changes. 

8