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WSRC-RP- 8 9-1357

INCIDENTS AT THE SAVANNAH RIVER SITE WASTE TANK FARMS (U)

WSRC-RP--89-1357

DE92 009545

by

William C. Perkins and William S. Durant i_"! _ _,_ " _ _:__,"

MARi 6 1992Westinghouse Savannah River CompanySavannah River Site

Aiken, SC 29802

December., 1989

A paper proposed for presentation at theDOE/ANL Training Course on the Prevention

of Significant Nuclear Events

and for publication in the course notes.

This paper was prepared in connection with work done underContract No. DE-AC09-88SR18035 with the U.S. Department of

Energy. By acceptance of the paper, the publisher and/or

recipient acknowledges the U.S. Government vs right toretain a nonexclusive, royalty-free license in and to any

copyright covering this paper, along with the right to

reproduce and to authorize others, to reproduce all or

part of the _,-opyrighted paper.

t

WSRC-RP-89-1357

INCIDENTS AT THE SAVANNAH RIVER SITE WASTE TANK FARMS

William C. Perkins and William S. Durant

ABSTRACT

This paper describes process incidents that have occurred at theSavannah River Site waste tank farms.

INTRODUCT ION

The Savannah River Site has experienced a number of loss of

containment incidents, during waste transfers in the waste

management areas. Varying amounts of equipment damage,

environmental insult, and radiation exposure occurred during these

example incidents. These incidents are brought to the attentionof personnel in the DOE complex in hopes that by sharing these

experiences, others will be able to prevent a recurrence in theirfacilities. [Slide i]

DISCUSSION

General

At Savannah River, high-level liquid waste is held in large

underground tanks in two tank farms, one in H-Area and one in F-Area. The first eight tanks in each area were constructed in

1952. The last tank, Number 51, was completed in 1981. A typical

tank holds about one million gallons in double-walled containmentwith induced draft, HEPA-filtered ventilation. [Slides 2 and 3]

The traditional unit operations are : receipt, transfer,

evaporation, and storage. In addition, ion exchange completes the

decontamination of evaporator overheads (condensate). The wastes

are in alkaline form at high salt contents. The majorconstituents are sodium salts. The principal radioactive

components of the liquid concentrate are Sr-90 and Cs-137. Tank-to-tank transfers are made through underground double-walled

piping. [Slides 4 and 5]

Our worst waste releases have occurred during waste transfer

operations. This paper describes three of these incidents.

[Slide 6] These were not tank failures.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agencythereof, nor any of their

employees, makes any warranty, expressor implied, or assumesany legal liability or responsi-bility for the accuracy, completeness,or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-ence herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof, The views...4 opinions of .... =................ du .oi. nr.ccssariiy state or refiect those oi the

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WSRC-RP-89-1357

Tank 13 Release

In December 1983, about I00 gallons of liquid waste (containing

about 600 Ci of Cs-137) leaked onto the top of Tank 13 in the H-Area Waste Tank Farm.

At the time, Tank 13 was the feed tank for the waste evaporator.

The feed pump inside Tank 13 was being started as part of the

evaporator startup procedure. The evaporator had been shut downfor several days during which we experienced some record-settingcold weather. Several frozen instrument and flushwater lines had

been repaired. [Slide "7]

To start the feed pump, an operator primed it with flushwater. Ashe closed the flushwater valve inside the riser, he noticed water

leaking near another flushwater valve outside the riser. He

closed the second valve also, and the leak stopped. By the time

he was able to report the leak, the waste release was already in

progress. [Slide 8]

That outside valve was normally left open by procedure so that

flushwater pressure was maintained in that line. Then, if theinside valve leaked while the pump was running, water would leak

into the waste, rather than waste backing up in the water line

Unfortunately, the inside valve did leak (or was not completely

closed by the operator). It was also found later that the leak he

saw was coming from a flange gasket (located between the valves)that had failed under pressure from ice while the line had been

frozen. [Slides 9 and I0]

As waste was being pumped to the evaporator, some waste leaked

into the flushwater line through the inside valve and escaped

around the failed flange gasket.

One hour after the pump was started, the evaporator was full. The

Control Room Operator closed an automatic valve stopping flow to

the evaporator, but leaving the pump running in the recycle mode.At about the same time, a radiation alarm sounded at Tank I0, some

125 yards away from Tank 13. Health Protection personnel checkedand found radiation coming from the direction of Tank 13.

A supervisor, informed of the alarm, requested a check of the Tank13 area and ordered that the storm-water sewers in that area be

diverted to the retention basin. When the Health Protection

personnel reported high radiation readings at Tank 13, the feed

pump was shut down. The pump had been running for almost twohours at that point.

A massive effort, mobilized in response to this release, followed

in several phases over the next eighteen months. [Slide ii]

The first phase involved containment of the wastes to prevent

further spread of radioactive contamination. A dam was thrown

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"_ WSRC-RP-89.1 357

across the storm water drainage ditch, and the impounded waste was

pumped to the Retention Basin. A dike, at first of sandbags andlater of concrete, was placed around the top of the tank. Insidethe dike, a sump and sump pump returned waste and flushes to the

tank. Temporary shielding and television cameras were some of themeasures used to minimize exposure of workers to radiation.

With temporary containment in place, the tank top was flushed withlarge amounts of water and then cleaned with oxalic acid and

commercial cleaning solutions. Later, about 1400 cubic yards ofasphalt and soil were excavated and removed.

Because the waste had seeped into the concrete on the top of thetank, almost 140 cubic feet of concrete had to be removed. The

concrete was removed by a combination of sanding, sandblasting,and chipping.

Waste water was sent to the Retention Basin during the cleanup.

Over 15 million gallons of water had to be decontaminated by ionexchange.

The cleanup was accomplished with a total radiation dose to

personnel of only 58 rem, in spite of radiation fields measuringI00 R/hr. No worker uptakes of airborne radioactive material

occurred from this incident. Less than 300 mCi of activityreached a nearby stream emptying into a plant creek, but no

measurable activity reached the river. Evaporator operationresumed six months after the release.

The causes of this release were:

• unusually cold weather for an unusually long time (as low as7°F, subfreezing for over 36 hours),

• failure of electric heating on the exposed water line (there

was no failure indic;_tor in the circuit),

• failure of a flange gasket because of pressure from ice while

the line was frozen (gasket may have been oversized),

• a leaking seat on the flushwater valve inside the riser (or

failure to close this valve completely), and

• procedural violation by field operator: closing the flushwater'valve outside the riser.

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WSRC-RP-89-1357

The consequences of this accident were aggravated by severalfactors :

• Failure of the radiation monitor at Tank 13 confused diagnosisefforts and delayed responses.

• Rain on the night of the release promoted waste runoff to thestorm water drains.

The measures taken to prevent a recurrence of this experienceincluded:

• Improved flushwater valves were installed.

0 Special winterizing measures in effect before the accident were

improved and are to be verified, especially when unusuallysevere weather is forecast.

• A method (indicator light) was provided where needed for

verification that heat tracing (on exposed flushwater lines) isworking.

• A pressure gauge and switch were installed to give an alarm ifwaste backs up in the flushwater line.

• Containment dikes (with leak-detection sumps) were provided atkey tank farm locations.

• Containment huts were provided on the top of feed tanks.

• Operator training was improved. The operator, who closed the

flushwater valve because of the leaking flange, had goodintentions, but acted contrary to procedure. Procedures were

expanded to include reasons "why" whenever appropriate.

• Two radiation monitors were provided for feed pump risers.

4

I

WSRC-RP-89-1357

Tank 9 Release [Slide 12]

In May 1967, over 200 gallons of waste (containing about 2000 Ciof Cs-137) overflowed from a riser and onto the top of Tank 9 inH-Area.

At the time, the evaporator was concentrating supernate fromanother waste tank, and Tank 9 was the receiver tank for the

evaporator bottoms (concentrate) . Evaporator bottoms weretransferred to a gravity-drain line discharging into a riser on

Tank 9_ Normally, the waste fell through the riser into the tank,

where the salts (primarily sodium nitrate) would precipitate as

the liquid cooled.

The rate of concentrate removal slowed sharply on the morning of

May 14. Under normal procedures, the concentrate transfer line

was backflushed with water, but the temperature at the outlet of

the water line did not decrease as expected from previousbackflushes. Difficulty was again experienced in an attempt to

empty the evaporator. A second backflush was also unsuccessful.

The foreman and an operator investigated and found that waste had

overflowed from the riser to the lip of a storm sewer about 50

feet away. A small quantity had entered the sewer.

The storm sewer effluent was impounded by construction of a dam

near the storm sewer outfall. Impounded water was pumped to aretention basin. Some waste, however, reached the creek.Measurements in the creek showed that about 27 curies (of Cs-137)

passed 0.8 mile downstream, 16 curies passed 1.7 miles downstream,

and 0.9 curies passed 5 miles downstream. None was detected inthe river. Most of this activity remains in the bed of the creek,

although about one curie desorbs annually and reaches the swampbetween the creek and the river.

Approximately 1200 square feet inunediately adjacent to the riserwere severely contaminated with radiation levels as high as I00

R/hr. The spill area was covered with dirt and sprayed with

asphalt to reduce the radiation intensity and prevent additionalwaste from reaching the sewer. Temporary shielding was placed

around the riser. A sump and pump were placed near the riser•

The storm sewer was flushed with water. This water was pumped to

a seepage basin until June 23. Excavation and backfill operations

continued until July 19. About 450 cubic yards of contaminateddirt was removed to a burial ground. This incident resulted in a

total personnel dose of about 85 rem.

The cause of this release was overevaporation of the waste (the

specific gravity was 1.47 at 109 degrees C) and pluggage of theriser with salt crystals. No buildup of salt had been expected,

but photographs taken later confirmed that the two-foot diameterriser had been completely plugged. Obviously, the deposition

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WSRC-RP-89-1357

characteristics of the concentrated waste had been grosslyunderestimated. In addition, there was no radiation monitor

installed near the riser, so there was no early warning of thewaste release°

Modifications were made to this system (to preclude recurrence ofthis release), which included:

I. The bottoms discharge line was extended deeper into the tank so

that concentrate discharges into the tank proper, not into theriser.

2o Radiation monitors were installed at tank risers.

3. Instrumentation was installed to sound an alarm in response to

rising liquid in the riser.

4= A viewing port was installed in the riser to facilitate

inspections inside the riser.

2j_fer Line Release [Slide ]3]

In 1960, an emergency transfer line was installed between theannulus of waste tank 16 and waste tank 14. Tank 16 had developed

leaks in the primary wall, and this line was used to transfer

185,000 gallons from the annulus. The line was 2-inch carbonsteel and was covered with an asphalt-coated earthen berm. The

line was not used again until 1972 when an estimated i000 gallons

was transferred. On May 23, 1977 the line was reactivated for the

purpose of removing about 112,000 pounds of salt from the annulusof tank 16 during a tank cleaning program. The radiation levelwas about IR/hr (at 5 cm from the berm) during the ensuingtransfers.

The first indication of any difficulty was on July 29, 1977 when a

one-foot-diameter, eight-inch-deep depression wa;_ observed in the

berm midway between the tanks. The depression was investigated

and surveyed by Health Protection personnel. Radiation at the

depression was 4.5 R/hr. As a precautionary measure, 3/4 inchlead shielding was placed over the depression.

During a subsequent transfer on August i, steam was observed

rising from the berm depression 55 minutes after the transfer had

begun. The transfer was stopped immediately and the area aroundthe depression was surveyed. The condensate, which wet an area

two feet by 1.5 feet on the side of the berm, radiated 10R/hr at 3inches and had transferable contamination as high as 200 mrad/hr.

The line was uncovered and found to be unjacketed 2-inch carbon

steel pipe. Personnel inspected the pipe at the failure site

through binoculars and determined that failure was due tocorrosion. Maximum radiation within the excavation around the

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WSRC-RP-89-1357

transfer line was 120 R/hr. Accumulated radiation dose to all

personnel eventually reached 8.6R.

About i00 cubic yards of soil containing an estimated 500 curies

of 137 cesium, representing up to 400 gallons of salt solution,was removed from the berm and transferred to the burial ground.

Monitoring wells in the area are routinely sampled, and the

samples showed no increase in activity. Surface water runoff fromthe tank 16 area had been diverted to the retention basin since

May. No increased activity was detected in the retention basin.

Although the physical cause of the leak was general corrosion of

the carbon steel pipe, a number of factors contributed to the

incident. The pipe had never been coated with an exterior

waterproofing material. Additionally, there was no secondary

containment around the pipe. It had been assumed that the pipewas encased when the authorization was written to allow its use in

May 1977; however, this was not verified. Record prints showingconstruction details of the transfer line were not available.

Follow-up to this incident included the following measures: i)The contaminated berm and transfer pipe were removed and replaced

with a jacketed line. 2) All waste transfer lines that did notmeet current standards were identified and either upgraded or

abandoned. 3) All transfer lines for which reference prints could

il not be found were unearthed.

i_ LESSONS LEARNED [Slide 14]

i These incidents contain many lessons. The following comments are

i an attempt to sun_narize them:

_I • Radioactive materials are insidious and persistent in a questto escape containment; therefore, great diligence must be

" exercised to prevent their escape.

• When unusually cold weather is predicted, outdoor facilitiesneed extra winterizing.

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• Heat tracing on water lines exposed to cold weather should have

indicators (lights) to verify operation.

• After unusually cold weather, outdoor facilities need thorough

inspection and testing for proper operation.

• Where personnel safety in involved, backup monitors are needed.

• Lines carrying high-salt liquids should maintain temperaturecontrol from end to end.

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WSRC-RP-89-1357

• Careful configuration control is a necessity to ensure that

systems used by other organizations are what they are supposedto be.

• Systems that have not been used for an extended period of time

should be functionally tested before use.

• Unusual events should be thoroughly investigated.

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