Revising BWR emergency procedures18 November 2013
The BWR Owners’ Group has completed a revision of emergency procedure guidelines in light of lessons from Fukushima. By Bill Williamson, Jay Lyter, Dan Roniger and Phillip Ellison
This article provides a summary of the most significant changes to Revision 3 of the Boiling Water Reactor (BWR) Owner's Group (BWROG) Emergency Procedure Guidelines. Revision 3 address lessons learned from the Fukushima Daiichi Accident and resolves most open issues identified and addressed since issuance of the last revision of the guidelines. A future revision of the guidelines is expected to address shutdown events and lessons learned from Revision 3 implementation in a few years.
The BWR Owners' Group Emergency Procedure Committee (EPC) focuses on generic issues affecting Emergency Procedures and Severe Accident Guidance (EPG/SAG) for the BWR fleet. In particular, the committee:
- Resolves issues resulting from development and implementation of EPG/SAG
- Resolves EPG/SAG implementation issues as they occur
- Facilitates a uniform understanding of EPG/SAG and their technical basis
- Improves the regulators' understanding of EPG/SAG and their technical bases
- Provides a forum for information sharing.
The committee issued Revision 3 of the Emergency Procedures and Severe Accident Guidelines early in 2013. The generic emergency procedures updates are currently being implemented as appropriate into the BWR fleet, with BWROG EPC workshops being held in the US, Europe, Mexico, Japan and Taiwan to assist with Revision 3 implementation.
The BWROG generic procedures and guidelines provide the basis for plant specific emergency actions taken by BWR licensed nuclear reactor operators. Individual utilities make use of the generic guidance to develop plant-specific procedures that take into account the variability in plant design. The generic procedures and guidelines are developed and continually enhanced in response to lessons learned from world-wide nuclear plant experience; taking into account lessons learned from drills, exercises and events. The BWROG Emergency Procedures Committee is composed of utility industry experts in plant operation, engineering, design basis and severe accidents and emergency response. The committee also has the support of contractors and vendors when appropriate.
The BWROG procedures are symptom-based and designed to respond to events as identified from the plant's instrumentation. The BWROG generic procedures are not developed and/or limited to events based on the results of risk assessment or code calculations of postulated accidents. The procedures permit the plant to respond to a wide range of events including those sequences of events whose probability of occurrence is calculated to be very small based on the use of Probabilistic Risk Assessment (PRA/PSA).
Procedures and guidelines for response to plant design basis events are addressed by Abnormal Operating Procedures (AOP), Alarm Response Procedures (ARP) and Emergency Operating Procedures (EOP). These procedures instruct the licensed plant operators on the steps necessary to maintain core cooling while taking the plant from full-power operation to a safe shutdown condition. These procedures have long been part of the plant safety response and are strictly governed by both US Nuclear Regulatory Commission (NRC) regulations as well as industry standards. The training along with the written and simulator exams for licensing reactor operators and senior reactor operators include the EOPs.
The US industry developed EOPs following the accident at Three Mile Island (TMI) and the Severe Accident Guidance was developed after the accident in Chernobyl. The SAGs were implemented as a voluntary initiative and included training and drills. The SAGs enhance the ability of the operators to manage accident sequences that progress beyond the point where EOPs and other plant procedures are applicable. The SAGs are used by licensed operators in the control room alone or with support from the plant technical support staff.
Following the terrorist actions of September 11, 2001, the US NRC required plants to develop and implement guidance and strategies to maintain or restore core cooling and containment, and spent fuel pool cooling capabilities under the conditions accompanying loss of large areas due to fire or explosion. These requirements led to the development of Extensive Damage Mitigation Guidelines (EDMG)at all US nuclear power plants. The EDMGs are used when the normal command and control structure is disabled and the use of EOPs is not feasible.
The BWROG Emergency Procedure Committee responded to and identified and applied lessons learned from the Fukushima Daiichi accident to improve the generic BWR emergency procedure guidance. The BWROG EPC members, experts in accident mitigation and response, identify open issues in the generic guidance and bring these items to the committee for resolution. Note - Any utility member can bring an emergency procedure issue to the EPC for review and discussion.
Identification of generic emergency procedure issues associated with the accident at Daiichi were thoroughly reviewed and discussed by BWROG EPC members. This is an ongoing process and items are addressed by committee members as they are identified. To support this ongoing process the EPC has been meeting quarterly since the Daiichi accident. Resolution of open issues resulted to an update to the EPG/SAG Revision 3 approved in January 2013. EPG/SAG Revision 3 was approved by all utilities on the committee. However, some open items remained, these items are being addressed in a future revision (Revision 4) of the guidelines which includes guidance for shutdown conditions. Initial work on shutdown guidance is underway.
The BWROG Emergency Procedures Committee is cooperating with other industry initiatives and addressing items associated with the US NRC's Near Term Task Force (NTTF) and interfacing with the International Atomic Energy Agency (IAEA) through its membership on improving IAEA guidance for review of BWR accident management guidance. In particular, the BWROG EPC is cooperating with a significant US industry approach - FLEX; FLEX enhances accident management capabilities based on the lessons learned from Fukushima (see also Developing the FLEX plan). The FLEX approach is described in NEI 12-06 is accepted by the US NRC with clarifications, as a method to satisfy the NRC's Order EA-12-049. The FLEX Support Guidelines (FSG) are referred to from the BWROG generic EPG/SAGs.
Significant Revision 3 changes
The BWROG EPC reviewed and made several significant and minor changes to the EPG/SAGs that were approved for issuance in Revision 3 of the guidelines. These changes were based on the lessons learned from the accident at Daiichi and resolution of open items in the EPG/SAGs since the last revision
1. Station Blackout Enhancements
Coordinate SBO procedures with EPG/SAGs; Avoid loss of Reactor Core Isolation Cooling (RCIC) High Pressure Coolant Injection (HPCI) from Reactor Pressure Vessel (RPV) depressurization; Permit use of EDMG (B.5.b) coping procedures
Limit RPV depressurization to allow extended RCIC operation; Permit local system operation; Permit defeating isolations; Adjust containment limits; Reduce primary containment pressure to maintain core cooling
- RPV Depressurization: Core cooling is highest priority. If RPV depressurization will result in loss of systems needed for core cooling:
[a] Terminate depressurization;
[b] maintain RPV pressure as low as possible. (Applies to all depressurization steps)
- EDMGs & FLEX: Authorize use of EDMG coping strategies and FLEX procedures for:
[a] RPV injection systems: [i] HPCI; [ii] RCIC
[b] RPV pressure control systems: [i] Safety Relief Valves (SRV); [ii] Isolation Condenser (IC)
- Defeat protective hardware interlocks to use all available design margin:
[a] RCIC: [i] High RPV water level; [ii] High exhaust pressure:
[b] Isolation Condenser; High area temperature
- Adjust Containment Limits: Heat Capacity Temperature; Limit Pressure Suppression Pressure; Drywell design temperature
- Reduce primary containment pressure to maintain core cooling: Reduce primary containment pressure to permit use of low pressure Portable Pump (FLEX); Maintain pressure below the Pressure Suppression Pressure to avoid loss of RCIC / HPCI.
2. Spent Fuel Pool Control
Coordinate Spent Fuel Pool control actions with RPV and containment control strategies and address Institute of Nuclear Power Operations (INPO) recommendations (IER L1-11-2)
Add Spent Fuel Pool level and temperature control sections to Secondary Containment Control
- Level: Maintain normal level using normal makeup systems; Use alternate makeup systems if necessary to maintain level above the Technical Specification Limited Condition for Operation (LCO); Isolate/repair leakage paths; Use portable sprays (FLEX)
- Temperature: Control Spent Fuel Pool temperature below the Technical Specification LCO using:
[a] Normal Spent Fuel Pool Cooling; [b] Supplemental cooling methods; [c] Cross-connects and alternative cooling lineups (FLEX)
3. Secondary Containment Hydrogen Control
Provide guidance on controlling secondary containment hydrogen; Hydrogen accumulation in secondary containment is expected during severe accident events.
Secondary containment hydrogen control section added to the SAGs
- Monitor and control secondary containment hydrogen concentration:
[a] Operate secondary containment ventilation.
[b] If secondary containment ventilation cannot be operated:[i] Operate Stand by Gas Treatment (SBGT); [ii] Create a natural circulation path
4. SAG Strategies - Containment Flooding
Remove heat from the RPV; Retain core debris in the RPV; Maintain primary containment integrity; Scrub fission products from the containment atmosphere; Minimize radioactivity releases
Primary containment flooding is implemented when RPV breach by core debris has been determined, when a large break of recirculation system exists or when Pressure Suppression Capability cannot be restored. Otherwise, Pressure Suppression Capability is maintained in order to be able to address a Design Basis Large Break LOCA or RPV breach by core debris.
The BWROG EPC continues its activities to review and address improvements to the BWR generic emergency procedures. The committee is incorporating lessons learned from the implementation of Revision 3, addressing shutdown guidance, incorporating FLEX Support Guidelines, procedure integration and providing the BWR fleet best practices from implementation. In addition, the committee is supporting the implementation of Fukushima-related items from the US NRC's Near Term Task Force Recommendations and interacting with the IAEA to improve the review of BWR emergency management procedures.
About the authors
Bill Williamson (TVA), Jay Lyter (Exelon), Dan Roniger (First Energy), Phillip Ellison (GE Hitachi Nuclear Energy). The EPC acknowledges the support of the BWROG Chairman Ted Schiffley (Exelon) and Vice Chair Lesa Hill (Southern Nuclear) in fostering BWR procedure improvements. The BWROG Emergency Procedures Committee includes members from the U.S., Japan, Mexico, Spain, Switzerland and Taiwan.
The BWROG consists of 32 total members with 20 members from the US. The BWROG has 11 committees focused on improving fleet performance for all the BWRs and 17 committees focused on items that improve the performance of specific plant designs.