DOE/RL-97-59
Revision 0

FINAL REPORT JULY 26, 1997
ACCIDENT INVESTIGATION BOARD REPORT ON THE MAY 14, 1997, CHEMICAL EXPLOSION AT THE PLUTONIUM RECLAMATION FACILITY, HANFORD SITE, RICHLAND, WASHINGTON

APPENDIX A

Memorandum for the Appointment of the Accident Investigation Board

 

APPENDIX B

Performance of Barriers

Table B-1. Performance of Barriers.
Barrier Purpose Performance
Concentration of Chemicals Maintain chemical make-up specification for solvent extraction process Barrier failed because the surveillance procedure did not require checking the chemical make-up specification; because the system was not designed for long-term storage. Therefore, the facility was operating in an un-analyzed condition.
Standby Plan Place PRF in safe configuration Barrier failed because the standby plan did not address the cold chemicals in the Room 40 tanks, therefore the chemicals were stored long-term.
PRF Room 40 long-term shutdown procedure Place PRF Room 40 into safe configuration Barrier failed because management did not use procedure, therefore the HN and HNO3 solution was not drained into plastic drums.
Weekend Shutdown Procedure Place PRF Room 40 into safe configuration for storage of chemicals during short term shutdown of solvent extraction process Barrier failed because procedure limited storage to two weeks, therefore, the Facility line management violated the storage limitation requirement.
Safety Authorization Basis To operate the facility in a safe manner Barrier failed because management did not conduct an unreviewed safety question screen.
Lessons Learned To prevent recurrence of events by providing feedback Barrier failed because PFP line management failed to implement corrective actions from lessons learned from prior events involving HN and HNO3.
Process Hazard Analysis To define the safe operating parameters of the chemical process Barrier failed because PFP line management did not initiate a hazards analysis for long term-storage of HN and HNO3 solution.
Training Program To train PFP engineers, operators, and managers to recognize potential hazards in the work place Barrier failed because PFP training and qualification programs did not include lessons learned from prior events involving HN and HNO3
PFP Line Management Maintain facility operations within the safety envelope Barrier failed because PFP line management failed to implement the PRF Room 40 Long Term Shut Down Procedure, resulting in operations outside the safety authorization basis.
RL Transition Projects Division Oversight Ensure safe operation of PFP Barrier failed because RL Oversight did not ensure that the lessons learned from the PUREX event were implemented at PFP.

APPENDIX C

Change Analysis Chart

Table C-1. Change Analysis Chart

Factors Accident Situation Prior, Ideal, or Accident-Free Situation Difference Evaluation of Effect
Explosion Chemical reaction occurred in Tank A-109 No chemical reaction Reaction between HN and HNO3 Gases/heat pressure/tank damage
Historical practices Training run suspended early Normal system shutdown Plant placed in shutdown from a different than normal status Would have eventually implemented long term shutdown and no CCX would be present
Historical practices Long term shutdown not implemented Long term shutdown would be implemented Chemicals would have been removed from Tank A-109 No explosion
Historical practices PRF left in Weekend Shutdown Left in Weekend Shutdown for no more than two weeks Plant did not implement long term shutdown after two weeks Solution would not have been available to concentrate
Exceeding authorization basis Decision made to not immediately address PRF Room 40 chemicals results in long term storage in Tank A-109 Long term shutdown of Room 40 Long term storage of chemicals in Room 40 is outside of authorization basis Allows chemical reaction resulting in explosion of Tank A-109
Lessons Learned implementation Lesson Learned from PUREX 2BX event not fully recognized or implemented Lessons Learned would have been recognized and implemented appropriate corrective actions Corrective actions not taken to prevent concentration Allows chemical reaction resulting in explosion of Tank A-109
Lessons Learned sharing Lessons Learned from 1996 Savannah River event was judged by FDH Lessons Learned Committee to be not applicable to Hanford Event would have been judged applicable and made available to Hanford facilities Corrective actions not take to prevent concentration Allows chemical reaction resulting in explosion of Tank A-109
Hazard analysis Hazard recognition in FSAR does not identify any controls Necessary controls identified in FSAR Controls in plant Operating Procedures No excessive concentration or long term storage in Tank A-109
Hazard analysis No/inadequate hazard review of decision to store solution for future use Performed USQ screen and associated hazard review performed prior to decision to store Recognition of the hazard of storage Implementing controls on storage

APPENDIX D

Technical Aspects of the Accident

HN and HNO3 Background

Hydroxylamine nitrate (HN) is used in plutonium processes for the reduction of plutonium (IV) to plutonium (III) in water-diluted nitric acid (HNO3) solutions. Reduction of the plutonium valence from IV to III changes the plutonium from extractable in organic to inextractable in organic allowing the plutonium to be separated from impurities present in the organic feed solution. The HNO3 is present to prevent plutonium from polymerizing, which would create criticality hazards.

In the PRF process, dilute HN and HNO3 are mixed in a solution. The HN and HNO3 solution is prepared in Tank A-109 in Room 40 of the PRF. The HN and HNO3 solution is automatically fed to tank 30 in the PRF canyon by a level control system on Tank 30. Tank 30 is the HN and HNO3 solution feed tank for the complexant concentrate column.

A typical batch of HN and HNO3 solution contains 3,000 pounds of solution, which is what the volume of the tank will allow. In preparation for makeup the operator subtracts any solution heel weight from 3,000 pounds and gives that information to the engineer. The engineer then provides the operator with the makeup quantity to get a 3,000-pound HN and HNO3 solution batch. At the time of makeup, the operator takes Tank A-109 off-line to prevent an incomplete batch of HN and HNO3 solution from reaching tank 30. The operator then adds the amount of water, HNO3, and HN (in that order) prescribed by the engineer. The HNO3 used is identified as CAS, which is 1.5 M nitric stored in Tank A-108. The HN is 18 wt % HN as pumped from the vendor drum. The batch is sampled and results verified and tank is placed on-line.

Evaporation Mechanism

Tank A-109 was equipped with a 1-inch overflow line that discharged to a basin below the tank, and a 1-inch vent line that connected to a ventilation header exhausting to the 291-Z-1 stack. The vent header links all of the chemical preparation tanks in Room 40 to the E-3 exhaust duct, which eventually ends up in the Building 291-Z exhaust train and out the 291-Z-1 stack. No valving exists on either the overflow line, the vent line, or the vent header; thus, a continuous air flow path from Room 40 through Tank A-109 to the vent header existed in Tank A-109.

The continuous air flow through Tank A-109 was estimated at between 2 to 5 standard cubic feet per hour. This air flow is sufficient to evaporate several pounds per day of water in Tank A-109. The observed weight loss averaged 1.3 pounds per day (see Figure 3). The evaporation of water from Tank A-109 during a 4-year period slowly increased the concentration of the remaining HN and HNO3. For purposes of analysis, it is conservatively assumed that the weight-loss observed in Tank A-109 during the storage period is primarily a result of water evaporation, thus the HN and HNO3 remained essentially the same from the time the HN and HNO3 solution was mixed until the explosion.

Reaction Chemistry

On May 14, 1997, the concentrations of HN and HNO3 in Tank A-109 exceeded those necessary to initiate an autocatalytic reaction. This rapidly propagating reaction converted the concentrated chemical solution onto gases, water vapor, and heat. The available vent and overflow connections were not adequate to relieve the pressure increase with the result that the tank internal pressure quickly exceeded the design capability of the atmospheric tank.

Laboratory experiments and other research data indicates that concentrated HN and HNO3 aqueous solution will undergo autocatalytic reactions. The specific concentrations of the reactants depends on the temperature of the solution and the presence of a metallic catalyst. The reaction is rapid and results in the evolution of gases and heat. The reaction products are nitrogen, nitrous oxide, oxides of nitrogen, and water vapor.

The Board reviewed several autocatalytic reaction events experienced at the Savannah River and Hanford sites. The events are summarized in Table D-1. These reactions occurred at a wide range of chemical concentrations. The Board could not adequately define a safety envelope for indefinite storage of these chemicals.

Table D-1. Summary of Reaction Events.

Date Location Cause Reported Chemical Concentration Result
9/19/68 Hanford, PRF, Tank A-119 Procedure violation resulting in 12 M HNO3 being added to dilute HN solution HN 1.3 M
HNO3 0.15 M 		Tank pressurized blowing solution out of chemical add port
Early 1970s Hanford, PRF, Tank A-109 Procedure violation resulting in use of Tank A-109 for make up of high acid flush instead of in a separate tank Unknown Tank pressurized, blowing chemical add port lid off of tank and indenting the ceiling
9/26/72 Savannah River, F Canyon, HAW Evaporator Sudden chemical decomposition during evaporator operations HN 0.1 M
HNO3 1.0 M		 3,000 liters of solution expelled from tank
2/14/80 Savannah River, F Canyon, Tank 5D Failed steam valve concentrates solution in Tank 5D HAS* 3.0 M
HNO3 6.4 M		 Rapid pressurization causes elbow to fail
12/3/89 Hanford, PUREX, 2BX Pipeline Solution isolated between two valves and decomposes HN 0.7 M
HNO3 1.6 M HY**		 Valve gasket fails
12/28/96 Savannah River, F Canyon, Tank 5D Strong nitric acid HN solution heated by adjacent tank HN 0.1 M
HNO3 4.5 M		 2,500 pounds of solution spilled to sump
*Hydroxylamine Sulfate
**Hydrazine

Mechanical effects of an Autocatalytic Chemical Reaction

Analysis of the incident indicates that the chemical reaction that took place would have generated a rapid (3-4 second) buildup of pressure of several hundred psi inside Tank A-109. A pressure of 200 psi exerted on a 4 foot diameter lid would generate over 350,000 pounds of force on the lid. The tank lid was 3/16-inch stainless-steel flat plate with stiffeners and twenty-eight 5/8-inch stainless-steel studs. Three failed bolts were recovered. Visual observations of the three bolts show little plastic deformation (see Exhibit A-1).

Exhibit A-1. Recovered Bolts from Tank A-109 Lid.

Five bolts were observed to have remained in the tank flange, and the tank lid has five corresponding tears where tank bolts sheared through the tank lid. It appears that once the bolts opposite of the ones that remained failed, the lid folded over the remaining bolts, pulling the bolts through the holes in the tank lid. The deformation of the lid stiffeners (metal ribs on the underside of the tank lid) tends to confirm this observation. Calculations estimate the pressure in the tank that was necessary to shear the bolts through the tank lid to be between 150 and 250 psi.

Calculations show that the cylindrical portion of the tank should be able to withstand a pressure of between 400 and 750 psi without failing. This is consistent with the observations of the tank; the cylindrical portion of the tank did not fail. The bulge on the bottom of Tank A-109 could not be measured accurately, but was estimated to be approximately a 1- to 2-inch deformation using a corner of the tank as a point of reference. Finite element calculations indicate a pressure of between 200 and 300 psi would be consistent with a 1- to 2-inch deformation of the tank bottom.

Estimating the potential gas/heat generated by the reactions and released to Room 40, a resultant room pressure of up to 2 to 3 psi would be potentially available to act on the walls of Room 40. The north, west, and south walls are 7-inch concrete walls. The east wall is sheet metal partition with three sets of interior doors (953/954/955) for entry into Room 40. The damage to the interior doors (and windows in the doors) is consistent with what would be predicted for a 2 to 3 psi pressure surge in the room. The east wall of room 41 (south of Room 40, connected by corridor 47), also sustained damage. The pressure to which the east wall of room 41 was exposed was less than the pressure inside Room 40. The positive pressure inside Room 40 would quickly dissipate as the air flowed into the corridors and stairwell and was ultimately exhausted by the building ventilation system.

The damage to the lid, bolts, tank and room is consistent with the generation of gases and heat that was predicted by the chemistry of the reaction.

APPENDIX E

References

  1. A-95-SOD-PFP-029. Bocanegra, R., W.D. Seaborg, December 20, 1995, Conduct of Operations Partial Assessment, Plutonium Finishing Plant, Site Operations Division, U.S. Department of Energy, Richland Operations Office, Richland, Washington.
  2. ARH 1746. Buckingham, J.S., A.J. Low, and R.A. Zinsli, September 18, 1970, Hazards Review: Manufacture of HN, unclassified document, Atlantic Richfield Hanford Company, Richland, Washington.
  3. BWHC 1997. Barney, G.S., June 9, 1997, Status Report on Laboratory Investigation of Tank A-109 Explosion (letter report #15F00-97-061, to M.W. Gibson and E.M. LaRock), Plutonium Process Support Laboratory, B&W Hanford Company, Richland, Washington.
  4. BWARC 1997. Peterson, D., Blake, J.E., June 6, 1997, Chemical Mix Tank (A-109) Burst Calculations (letter #03010-610-035 to G. E. Kulynych, B&W Hanford Company, Richland, Washington), Babcock & Wilcox Alliance Research Center, Alliance, Ohio.
  5. DOE 1994. September, 1994, Chemical Safety Vulnerability Assessment, Working Group Report, DOE/-0396P, U.S. Department of Energy, Washington, D.C.
  6. DOE-DP 1994. Gilbert, F.C., March 16, 1994, Guidance for Evaluating Safety Concerns Related to Potential Nitrate-Organic Safety Hazards, Memorandum to L.A. Lee, DOE DP-9, U.S. Department of Energy, Office of Defense Programs, Washington, D.C.
  7. DOE Handbook 1110-96. February, 1996,Chemical Process Hazards Analysis, DOE-HDBK-1100-96, U.S. Department of Energy, Washington, D.C.
  8. DOE Order 225.1. April 26, 1996, Change 2, Accident Investigations, U.S. Department of Energy, Washington, D.C.
  9. DOE Order 232.1. August 12, 1996, Change 2, Occurrence Reporting and Processing of Operations Information, U.S. Department of Energy, Washington, D.C.
  10. DOE Order 5000.3B. February 22, 1993, Occurrence Reporting and Processing of Operations Information, U.S. Department of Energy, Washington, D.C.
  11. DOE Order 5480.19. May 18, 1992, Change 1, Conduct of Operations Requirements for DOE Facilities, U.S. Department of Energy, Washington, D.C.
  12. DOE Order 5480.20A. November 15, 1994, Personnel Selection, Qualification, and Training Requirements for DOE Nuclear Facilities, U.S. Department of Energy, Washington, D.C.
  13. DOE Order 5480.21. December 24, 1991, Unreviewed Safety Questions, U.S. Department of Energy, Washington, D.C.
  14. DOE Order 5480.23. April 30, 1992, Nuclear Safety Analysis Reports, U.S. Department of Energy, Washington, D.C.
  15. DOE Policy 450.4. October 15, 1996, Safety Management System Policy, U.S. Department of Energy, Washington, D.C.
  16. DOE/RL-97-62. Report on the Emergency Response to the Event on May 14, 1997, at the Plutonium Reclamation Facility, Hanford Site, Richland, Washington, in preparation, U. S. Department of Energy, Richland Operations Office, Richland, Washington
  17. DOE/RL-97-63. July 26, 1997, Summary Report of the Accident Investigation Board Report on the May 14, 1997, Chemical Explosion at the Plutonium Reclamation Facility, Hanford Site, Richland, Washington, U. S. Department of Energy, Richland Operations Office, Richland, Washington.
  18. Fauske 1997. Fauske, H., June 11, 1997, Some Additional Comments on the Tank A-109 Pressurization Event (letter report #060997-A to Ron Gerton, DOE Richland Operations Office), Fauske & Associates, Inc.
  19. ICBO 1961. Uniform Building Code, International Conference of Building Officials, Whittier, California.
  20. RLID 1300.1.C. January 26, 1996, Facility Representative Program, U.S. Department of Energy, Richland Operations Office, Richland, Washington.
  21. WHC 1993. Vogt, E. C., November 30, 1993, Draft Plutonium Finishing Plant Interim Action Recommendations (external letter 9308435B R1 to J. R. Hunter), Westinghouse Hanford Company, Richland, Washington.
  22. WHC-96-1296. 1996, Unreviewed Safety Question Screening and Evaluation, Perform Inventory of Hazardous Material at PFP, Westinghouse Hanford Company, Richland, Washington.
  23. WHC-CM-1-3. January 9, 1990, Facility Shutdown, Standby, and Transfer, Management Requirements and Procedures, Section MRP 6.15, REV 0, Operations Support Services, Westinghouse Hanford Company, Richland, Washington.
  24. . WHC-CM-1-5. June 21, 1996, Identifying and Resolving Unreviewed Safety Questions, Standard Operating Practices, Section 7.3, Rev. 0, Change 2, Westinghouse Hanford Company, Richland, Washington.
  25. WHC-ZO-120-026. November 30, 1993, Plutonium Finishing Plant Chemical Prep: Perform Long Term Shutdown of PRF Chemical Prep (Room 40), Rev/Mod B-0, Westinghouse Hanford Company, Richland, Washington.
  26. WHC-ZO-181-004. August 24, 1993, Plutonium Finishing Plant, Solvent Extraction System -- Shutdown Solvent Extraction, Rev/Mod H-2, Westinghouse Hanford Company, Richland, Washington.
  27. 29 CFR 1910.119. "Process Safety Management of Highly Hazardous Chemicals," Code of Federal Regulations, as amended.
  28. 29 CFR 1910.120. "Hazardous Waste Operations and Emergency Response", Code of Federal Regulations, as amended.
  29. 29 CFR 1910.1200. "Hazard Communication", Code of Federal Regulations, as amended.