NRC DIRECTS STAFF TO RESOLVE POTENTIAL 

DEBRIS CLOGGING OF EMERGENCY COOLING WATER SOURCE 

The Nuclear Regulatory Commission has instructed agency staff to resolve Generic 

Safety Issue 191(GSI-191), where the containment sump, an emergency long-term cooling water 

source, could be clogged by debris accumulating after a high-pressure coolant pipe break. The 

new directions set a near-term schedule for smaller loss-of-coolant-accident (LOCA) scenarios, 

and a longer-term schedule for the less-likely larger LOCAs. The Commission also directed the 

staff to develop additional risk-informed implementing guidance for GSI-191. 

“While much has been done by the staff, and licensees have physically modified their 

sump screens, resulting in significant safety improvements, the agency needs to finally resolve 

this issue,” said Chairman Gregory B. Jaczko. “Nuclear power plants have installed larger sump 

strainers and taken steps to eliminate materials that could end up in the sump. We’re confident 

these first steps provide for continued safe operation, but we need to move forward in resolving 

the final technical issues and closing out this long-standing issue.” 

Reactor building sumps are designed to collect water lost after a pipe break, providing a 

potential source of coolant for recirculation after a reactor’s other water sources are exhausted. 

The original technical issue involved pipe-break scenarios where large amounts of fibrous 

insulation could be knocked off coolant pipes and collect in the sump, blocking recirculation. 

Sump strainer performance issues were first identified in 1979, in an NRC report, 

Unresolved Safety Issue A-43, “Containment Emergency Sump Performance.” Boiling-water 

reactors resolved the issue by installing much larger strainers, but in the late 1990s the staff 

identified new concerns for pressurized-water reactors, concerning debris generated following a 

design-basis LOCA. To address this issue, the staff developed GL 2004-02, “Potential Impact of 

Debris Blockage on Emergency Recirculation During Design Basis Accidents at PressurizedWater Reactors.” 

 

The new direction is the result of two Commission meetings in 2010 addressing GSI-191, 

and it updates previous Commission direction to staff following a 2006 meeting in which the 

staff was directed to look also at testing and schedules and make a concerted effort to look 

holistically at resolution of this issue. 

NRC NEWS

U.S. NUCLEAR REGULATORY COMMISSION

Office of Public Affairs Telephone: 301/415-8200 

Washington, D.C. 20555-0001 

E-mail: opa.resource@nrc.gov

Site: http://www.nrc.gov

No. 11-007 January 12, 2011
Forty-eight of the 69 U.S. pressurized water reactors have already used the integrated 

resolution process to develop NRC-accepted analysis and testing to show that their sumps will 

not clog. The Commission has directed the agency’s staff to continue working with industry 

representatives to perform additional testing—expected to be completed by the end of 2011—

and formulate a path forward by mid‐year 2012. In the interim, the Commission has directed the 

staff to defer further GSI-191 plant modification actions (such as fibrous material removal) until 

the tests and analyses are complete. The staff will report to the Commission in approximately 18 

months, identifying proposed policy options for resolving GSI-191. 

 The Commission expects upcoming sump performance assessments to take into account 

data including the full range of possible pipe break sizes, plant-specific compensatory measures 

and other design features that could reduce clogging risk. The Commission is also interested in 

better understanding the radiation dose that workers might receive if plants had them remove 

additional materials that could contribute to sump clogging. 

The Commission’s directions to the staff are available under “SECY 10-0113” on the 

NRC’s website at: http://www.nrc.gov/reading-rm/doc-collections/commission/srm/2010/. More 

information about the PWR containment sump issue is available on the NRC website at: 

http://www.nrc.gov/reactors/operating/ops-experience/pwr-sump-performance.html. 

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