ML20055C709
| ML20055C709 | |
| Person / Time | |
|---|---|
| Site: | 07001113 |
| Issue date: | 05/29/1990 |
| From: | Winslow T GENERAL ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9006070369 | |
| Download: ML20055C709 (4) | |
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i May 29, 1990 1
U.S. Nuclear Regulatory Commission
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Document Control Desk 4
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Dear Sir:
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Subject:
30-Day Incident Report -
ADU Clarifier Overflow Tank Pump Explosion In accordance with 10 CFR 20.405 (a) (1) (iv) and (c'f2), GE Nuclear Fuel and Components Manufacturing hereby submits w.a required report for the April 29, 1990, incident involving,the pump i
explosion.
l Summary On Sunday, 4/29/90, at approximately 4:30 a.m.,
a pump servicing line 4 ammonium diuranate (ADU) clarifier. overflow tank appeared to have exploded.
A subsequent investigation found that a weak solution of ammonium nitrate had been concentrated in the pump-which had been inar*vertently lef t in operation.
The down stream valve was closed such that the " dead headed" pump had heated and concentrated the solution until there was'a rapid thermal.
l decomposition resulting in the separation of the' pump housing halves.
All ADU systems were shut down from 4/20 to 5/4 until the cause of the incident was identified and corrective actions taken to assure safe operation.
There were no injuries or overexposures resulting fron the incident and no other equipment damage.
Incident Description On 4/27/90, at approximately 5:00 a.m.,
line 4 ADU weekly production was shut-down for cleaning per normal procedures.
The 4
piping and clarifier were flushed out with nitric acid, recirculated, and then pumped to a receiver tank for processing 00 f'
I U. S. Nuclear Regulatory Commission Document Control Desk May 29, 1990 Page 2 upon restart.
The piping down stream from the clarifier overflow tank pump was manually valved.out and a recirculation line valve was partially opened (ball valve handle at 45').
The pump was left on or turned on soon afterwards.
The solution left in the piping was a combination of ammonia, water, and nitric acid.
Investigations performed after the explosion found that the down stream valve allowed approximately 20 gallons of solution in the piping to leak back to the pump and that the recirculation valve was nearly closed, even though the valve handle position implied it was partially open.
The " dead headed" pump, over a period of approximately 43 hours4.976852e-4 days <br />0.0119 hours <br />7.109788e-5 weeks <br />1.63615e-5 months <br />, boiled off the water in the solution which had leaked back to the pump and resulted in a concentrated solution of ammonium nitrate.
Running hot, the pump heated the concentrated ammonium nitrate until there was a rapid thermal decomposition.
The decomposition resulted in a rapid pressure increase which blew the 6" Wilfley pump casing apart at the center gasket which was held together i
with eight bolts.
The auction half of the pump struck a steel pipe, bending it 15', and skidded off for another 16 feet before coming to rest.
No other equipment sustained damage.
The outlet half of the pump and impeller remained intact.
No personnel were in the immediate area at the time of the incident and localized contamination was cleaned up per routine work area procedures.
Within three hours of the explosion, a multifunctional investigation team was assembled.
An investigation was initiated l
that included pictures of the accident site.
Samples were pulled of all liquid and solid deposits in and around the pump and i
associated piping.
Industrial and Radiation Safety personnel were notified.
Due to the potential damage exceeding $2,000, tPe NRC i
Operations Center was notified per 10 CFR 20.403 (b) (4) on 4/29/90 at approximately 2:30 p.m.
Conclusions and Actions Taken The ADU system, including line 4, remained shut down from 4/29 to 5/4 until other potential sources of ammonium nitrate were identified and applicable corrective actions taken.
Mr. Bill Cruice, an expert in explosions from Hazards Research Corporation, Mt.
Arlington, N.J., was contracted to evaluate the findings and make recommendations.
All operations in the fuel manufacturing process were reviewed by Mr. Cruice to determine locations where
F I
U. S. Nucicar Rtgulctory Commission Document Control Desk
'. May 29, 1990 Page 3 l
ammonium nitrate could be produced and accidentally concentrated.
These locations included the ADU lines, uranium recovery unit (URU), waste treatment, and associated HVAC systems.
Corrective actions were completed or planned activities were made to address each of these areas.
i 1
i on-site and off-site analyses of the samples taken from the pump and associated piping confirmed the presence of concentrated ammonium nitrate.
These samples included floor liquids, air sample filters, crystals found on the floor, and smears from internal pump parts.
The presence of concentrated ammonium l
nitrate was positively identified with infrared spectroscopy.
Mr.
Cruice confirmed that the incident description above could have caused the explosion.
No ignition or detonation occurred.
A rapid thermal decomposition in a confined space resulting in a l
rapid pressure increase caused the pump halves to separate.
Short term corrective actions for the ADU acid flush procedure were to water flush piping before and after the addition of nitric acid to I
prevent the possibility of accumulation of ammonium nitrate in pumps.
Further, the replacement of the recirculation valves with l'
restricting orifices in the clarifier underflow and overflow should prevent the " dead heading" of the pumps in these applications.
A checklist was prepared that will require a physical verification of pump operation after the acid flushes.
Mr. Cruice confirmed that these actions were appropriate to prevent the conditions necessary to cause a recurrence.
Since all process and storage tanks are vented to a central scrubber exhaust system, selected ductwork was opened and samples taken of any deposits.
Analysis of accumulated material in the filter housings down stream of scrubbers found detectable levels j
of ammonium nitrate.
Mr. Cruice noted that the cake would not thermally decompose without the introduction of high heat levels.
The risk of violent reactions in the area appeared low.
Corrective actions taken consisted of:
1.
Startup of ADU operations was initiated on 5/4 under additional procedural controls.
Pump status is now routinely checked using written checklists and tanks are not permitted to operate when nearly empty.
Where the ammonium hydroxide and nitric acid solutions could be mixed in the ADU flush',
additional water flush and drain steps were added.
2.
In addition, on line 5 a FroVox program was written to interlock the pumps with respective tank level indicators to
' shut the pumps off on low level, which might prevent a concentrating condition.
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L U. S. Nuclo2r R0gulatory Commission Document Control Desk.
May 29, 1990 Page 4 3.
The ADU and URU (Uranium Recovery) operators were informed on why the incident occurred and the importance of following the l
modified procedures to prevent the accident from recurring.
Uranium recovery (URU) operators were also informed about these issues.
4.
Physical modifications to equipment included:
a.
.The. clarifier overflow pump valves in the ADU lines were removed and replaced with restricting orifices in the recirculation loop where solids were not present.
b.
To prevent pump " dead heading", pump suction and selected discharge valves were either removed or tagged open for similar pumps depending on the size of storage tanks and associated maintenance needs.
c.
In places where automatic valve-positions could be manually overridden, pumps were fitted with switches which prevent continuous operation without " hands-on" activation by the operator.
5.
Procedural controls were added to prevent any work in the ductwork or filter. housings until accumulations were either evaluated or cleaned out by sweeping or washing.
Radiation Protection personnel who evaluate Radiation Work Permits' (R.WPs) which are required for any ventilation work, were also notified of the new restrictions.
6.
NF&CM also notified other domestic uranium fabricators, ANI, and our foreign associates of the pumo explosion in order to warn of the potential safety concern.
In addition, long term cgrrective actions are being evaluated to augment or replace procedural controls.
j We would be pleased to discuss this matter further with you and your staff if deemed necessary.
Sincerely, GE NUCLEAR ENERGY i
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Preston Winslow. Manager Licensing & Nuclear Materials Management
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G. Troup - NRC Region II TPW-90-085 f
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