Skip to Main Page ContentSkip to SearchSkip to Site Map NavigationSkip to Footer Links- Home
- FAQ
- Glossary
- Facility Locator
- What's New
- Site Help
- Index A-Z
- Contact Us
- Browse   Aloud
- Email Updates
Search NRC   Report a Safety Concern- Nuclear   Reactors    - Power Reactors
  - Research & Test     Reactors
  - Operating Reactors
  - Operator Licensing    - New Reactors
  - Advanced Reactors
  - Operator     Licensing for New Reactors    - Nuclear Reactor     Quick Links 
- Nuclear   Materials    - Special Nuclear Material
  - Source Material
  - Byproduct Material
  - Med, Ind, &     Academic Uses    - Source Materials Facilities
  - Uranium Recovery
  - Fuel Cycle Facilities
  - Materials     Transportation    - Nuclear     Materials Quick Links 
- Radioactive   Waste    - Low-Level Waste
  - Waste Incidental to     Reprocessing
  - High-Level Waste
  - Uranium Mill Tailings    - Low-Level Waste Disposal
  - High-Level Waste Disposal
  - Storage of Spent     Nuclear Fuel
  - Transporation of     Spent Nuclear Fuel    - Radioactive Waste Quick     Links 
- Nuclear   Security    - Domestic Safeguards
  - Information Security    - Radioactive Material     Security
  - Contact   Us 
- Public   Meetings & Involvement    - The NRC Approach to     Open Government
  - About Meetings Open to     the Public
  - Conferences & Symposia    - Documents for Comment
  - Facilitating Stakeholder Involvement
  - NRC Information Quality Guidelines
  - Subscribe to     E-mail Updates    - Commission     Schedule
  - Public Meeting Schedule
  - Adjudications     (Hearings) 
- NRC Library    - Basic References
  - Document     Collections
  - ADAMS Public     Documents
  - Public Document Room
  - Get Copies of     Documents    - FOIA &     Privacy Act Requests
  - Photos &     Video
  - Records     Management 
  - Withholding of     Sensitive Information
  - FAQ Index    - Electronic Hearing Docket 
- About NRC    - The     Commission
  - Governing     Legislation
  - Plans, Budget, & Performance
  - Organization &     Functions
  - Locations
  - History
  - Values    - Direction-Setting     & Policymaking
  - Radiation     Protection
  - Fire     Protection
  - How We Regulate
  - Emergency     Preparedness & Response
  - Public     Affairs
  - Congressional     Affairs    - International     Programs
  - State & Tribal     Programs
  - Alternative     Dispute Resolution Programs
  - Employment     Opportunities
  - Contracting     Opportunities
  - Grant Opportunities
  - Civil   Rights 
PrintHome > NRC Library > Document Collections > Generic Communications > Information Notices > 1993 > IN 93-67 Bursting of High Pressure Coolant Injection Steam Line Rupture Discs Injures Plant Personnel                                 UNITED STATES                         NUCLEAR REGULATORY COMMISSION                     OFFICE OF NUCLEAR REACTOR REGULATION                            WASHINGTON, D.C.  20555                                August 16, 1993NRC INFORMATION NOTICE 93-67:  BURSTING OF HIGH PRESSURE COOLANT INJECTION                                    STEAM LINE RUPTURE DISCS INJURES PLANT                                         PERSONNELAddresseesAll holders of operating licenses or construction permits for nuclear powerreactors.PurposeThe U.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to remind addressees of the hazards associated with steam drivencoolant injection systems such as the high pressure coolant injection (HPCI)system and the reactor core isolation cooling (RCIC) system at BWRs and theauxiliary feedwater system at PWRs.  It is expected that recipients willreview the information for applicability to their facilities and consideractions, as appropriate, to avoid similar problems.  However, suggestionscontained in this information notice are not NRC requirements; therefore, nospecific action or written response is required.  BackgroundThe purpose of HPCI steam exhaust rupture discs is to protect the HPCI turbinecasing and associated exhaust piping from an overpressure event if the normalexhaust path to the suppression pool becomes blocked.  At Quad Cities Station,two 40.6-cm [16-inch] stainless steel discs are installed in series with a6.4-cm [2.5-inch] spacer between them to allow for a pressure sensorinstrumentation line.  The pressure sensor, while serving no control function,actuates an alarm in the control room at 68.9 kPa [10 psig] to alert theoperators that the inner disc is leaking.  The normal range of the HPCIexhaust steam pressure is 172 to 207 kPa [25 to 30 psig].  The HPCI highexhaust pressure turbine trip setpoint is 689 kPa [100 psig] and is sensed bypressure sensors located downstream from where the section of pipingcontaining the rupture discs branches off from the exhaust piping.  Thesection of piping containing the rupture discs is mounted vertically over theturbine exhaust and vents directly to the HPCI room.  Pressure greater than1034 kPa [150 psig] in the exhaust line will cause the inner disc to ruptureand impact the outer disc, releasing steam into the HPCI room.Description of CircumstancesDuring a quarterly inservice test of the HPCI pump at the Commonwealth EdisonQuad Cities Station, Unit 1, on June 9, 1993, the exhaust steam line rupture 9308100248.                                                            IN 93-67                                                            August 16, 1993                                                            Page 2 of 4discs burst, releasing steam into the HPCI room, burning, and slightlycontaminating, five workers.  The rupture discs burst within one second afterthe turbine was started.  Fire doors between the Unit 1 and Unit 2 HPCI roomswere blown off their hinges into the Unit 2 HPCI room.  Both sets of doubledoors that are part of the secondary containment boundary were also blownopen.  The floor latch on the inner containment door was bent; the outer doorswere also slightly damaged, but were repaired, closed and sealed approximately35 minutes after the event.  The steam release was terminated by automaticisolation of the steam supply line on high HPCI turbine area temperature about20 seconds into the event.DiscussionUpon investigating the event, the licensee determined that water hadaccumulated in the turbine casing because the drain system level switches forthe Unit 1 HPCI system had failed.  In April 1992, the licensee performed areliability-centered maintenance study which recommended the level switches beincluded in the preventive maintenance program but the recommendation had notbeen acted on at the time of the event.  The Unit 2 HPCI drain system levelswitches were also found to be inoperable.The slug of water created during the HPCI turbine roll passed from the turbinecasing to the vertical exhaust line and compressed the air in the 40.6 cm [16 inch] line containing the rupture discs.  The resulting pressure pulsecaused the inner rupture disc to burst, which impacted the outer disc asdesigned and caused it to burst as well.  The exhaust line pressure sensors,located in the horizontal 61 cm [24 inch] exhaust line that tees off from thevertical 40.6 cm [16 inch] rupture disc line, did not detect a high pressure(see Figure 1).  The pressure switches were within tolerance and should haveimmediately isolated the steam supply upon sensing a high exhaust pressurebefore the rupture discs burst.  The fact that a high exhaust line pressurewas not detected indicates two possible causes for the disc rupture.  Eitherthe inner rupture disc was degraded and burst at lower-than-design pressure,or the pressure pulse actually exceeded the design pressure and caused thedisc to burst, relieving the exhaust line pressure before the downstreampressure sensors detected a high pressure condition.While inspection of the rupture discs did not reveal any degradation fromcorrosion or aging, the vendor, Black Sivalls & Bryson, Inc, stated that thediscs are warranted for one year of service under normal conditions.  The HPCIand RCIC rupture discs at Quad Cities Station had been in service for 20 yearsand were not part of any scheduled inspection or preventive maintenanceprogram.  When consulted about the event, the vendor advised against using thespare discs in the plant storeroom because they were purchased at the sametime as the failed discs.  The licensee later replaced the failed discs withnew units.  Before this event, the licensee recently replaced a HPCI rupturedisc during a refueling outage at the Dresden Station, a plant similar to QuadCities, after finding a crack in the disc during an inspection.  The rupturediscs were inspected at the Dresden station as part of an enhancement to thepreventive maintenance program that was recommended by a reliability-centeredanalysis..                                                            IN 93-67                                                            August 16, 1993                                                            Page 3 of 4The steam injured five workers, four of whom were participating in the HPCIpump surveillance test.  The fifth, and most severely injured worker was ahealth physics technician in the room on routine rounds, who was not aware ofthe danger posed by the surveillance test.  The test procedure contained nospecific guidance on room occupancy.  Interviews with the workers revealedthat they had performed the surveillance in the past and were familiar withthe process.  This familiarity may have led to a relaxed attitude towardpersonal safety.  The workers stated that during previous surveillances theysometimes evacuated the room before rolling the turbine, or stood near thedoors to be ready to escape.  The licensee made no routine announcement overthe plant paging system to alert plant personnel before the HPCI turbinestart, and the workers were not prepared for the turbine to start.A lack of constant communication between the workers and the control room mayhave contributed to the personnel injuries.  If a control room operator hadbeen in contact with the workers in the HPCI room during the turbine roll, theworkers would have been aware of the impending turbine start and, after start,the steam supply might have been manually isolated or the turbine manuallytripped before the automatic isolation caused by the high area temperature inthe HPCI room.  When the Unit 1 HPCI rupture disc failure caused the fire doors to be blownoff their hinges and into the Unit 2 HPCI room, one of the doors impacted apipe hanger in the room and moved it 5.1 centimeters [2 inches].  If the steamrelease had resulted from a high energy line break from the inlet side of theHPCI steam line instead of the exhaust line, the damage to the Unit 2 HPCIsystem could have been more severe.  While high energy line breaks have beenanalyzed for safety systems at all plants, the doors to rooms containing highenergy steam lines may not have been included in the analysis.  For example,at Duane Arnold Energy Center, the licensee discovered that while the HPCI andRCIC rooms were qualified for pressures of 26.2 kPa [3.8 psig], the doorsbetween these rooms and the reactor building would yield at 6.9 kPa [1 psig].The licensee for the Quad Cities Station will implement a preventivemaintenance schedule for both the HPCI and RCIC rupture discs and the levelswitches.  The licensee will review the surveillance test procedure andevaluate the missile hazard created by the fire doors.  The licensee replacedthe rupture discs for the Unit 2 HPCI and RCIC systems with new ones after theevent at Unit 1 and is considering burst testing the removed discs todetermine if they are degraded..                                                            IN 93-67                                                            August 16, 1993                                                            Page 4 of 4This information notice requires no specific action or written response.  Ifyou have any questions about the information in this notice, please contactthe technical contact listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.                                    /s/'d by CIGrimes/for                                    Brian K. Grimes, Director                                    Division of Operating Reactor Support                                    Office of Nuclear Reactor RegulationTechnical contacts:  Clark Vanderniet, RIII                     (708) 790-5594                     David Skeen, NRR                     (301) 504-1174Attachments:1.  Figure 1, "Simplified Layout of Quad Cities Station HPCI Turbine Exhaust       Steam Line"2.  List of Recently Issued NRC Information Notices.Page Last Reviewed/Updated Tuesday, November 12, 2013Home- News   Releases
- Event   Reports
- ADAMS
- Open Gov
- Digital   Government
- Students   & Teachers
- Photos &   Video
- For Developers
About Us- Strategic   Plan
- Budget &   Performance
- Perf   & Accountability Rept
- History of the   NRC
- EMPLOYMENT
- NRC   Ethics
- Agency Status
- Contact Us
Popular Documents- Info   Digest
- Factsheets   & Brochures
- Forms
- Electronic   Submittals Application
- NRC   Reports – NUREG
- NRC   Regulations – 10-CFR
- Inspection   Reports
- Plain   Writing
- Enforcement   Actions
- RULEMAKING   DOCUMENTS
Stay Connected- Blog
- Chat
- Twitter
- YouTube
- Flickr
- GovDelivery
- RSS
Regulations.govUSA.govRecoveryFOIANo Fear EEOInspector GeneralSite MapAccessibilityPrivacy PolicySite DisclaimerFor Employees