United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-19: Potential Loss of Effective Volume for Containment Recirculation Spray at PWR Facilities

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                               March 14, 1990


Information Notice No. 90-19:  POTENTIAL LOSS OF EFFECTIVE VOLUME FOR
                                   CONTAINMENT RECIRCULATION SPRAY AT 
                                   PWR FACILITIES


Addressees: 

All holders of operating licenses or construction permits for pressurized 
water reactors (PWRs). 

Purpose: 

This information notice is intended to alert addressees to the possible loss 
of effective volume for containment recirculation spray caused by the 
entrapment of water in the refueling canal of 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 do not constitute NRC 
requirements; therefore, no specific action or written response is required.  
This information notice resolves and completes action on Generic Safety 
Issue 95, "Loss of Effective Volume for Containment Recirculation Spray." 

Description of Circumstances: 

In 1983, the NRC staff resident inspector at H. B. Robinson Unit 2 
questioned the licensee's practice of leaving the refueling canal drain 
valve in the closed position during plant operation.  The specific concern 
was that if the refueling canal drain valve in a PWR dry containment is 
closed during plant operation and the plant experiences a loss-of-coolant 
accident (LOCA), that fraction of the containment spray which falls into the 
refueling canal would be prevented from returning to the containment 
emergency sump.  Eventually the entire volume of the refueling canal could 
be filled with water, preventing that amount of water from being available 
for the post-LOCA recirculation mode for containment and reactor cooling. 

A subsequent investigation by the H. B. Robinson licensee revealed that 
Westinghouse had intended the refueling canal drain valve to be open during 
operation.  However, operation with the valve closed was found to have 
negligible safety significance because the maximum volume of water that 
could be entrapped in the refueling canal was small relative to the large 
volume of water available from the refueling water storage tank.  
Nevertheless, the licensee decided to operate the plant with the valve open 
and revise plant procedures accordingly.



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                                                            IN 90-19
                                                            March 14, 1990
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The staff reviewed the licensee's response and corrective action (operation 
with the drain valve open) and found them acceptable.  Further, the staff 
considered the potential generic implications of this issue.  Of particular 
concern was whether there are large spaces that might entrap the 
recirculation water and whether this water can be adequately drained to the 
containment sump.  The staff addresses this concern in the design review 
under Standard Review Plan (SRP) Section 6.2.2, "Containment Heat Removal 
System."  However, there are PWR plants that were not reviewed under SRP 
Section 6.2.2 to determine if the entrapment of containment recirculation 
water could occur.  There are 27 PWR plants licensed before SRP Section 
6.2.2 was issued.  Other PWR plants were reviewed under SRP Section 6.2.2, 
but plant procedures may not have been explicitly evaluated for this safety 
matter. 

Safety Significance: 

The principal concern is the potential for the entrapment of containment 
spray water in operating PWRs.  The concern arises because if a sufficient 
volume of spray water is prevented from returning to the containment 
emergency sump, adequate flow in the containment spray recirculation and 
emergency core coolant recirculation mode may not be provided.  Insufficient 
flow to the sump can result in inadequate net positive suction head to the 
containment spray and low pressure safety injection pumps.  Subsequently, 
proper post-LOCA containment cooling and reactor core cooling can be 
disabled. 

In the NRC staff's evaluation of Generic Safety Issue 95, the staff 
concluded that the safety significance of this issue depends primarily upon 
whether entrapment of an unacceptable volume of containment spray water 
could occur during the recirculation phase.  Licensees may wish to review 
the adequacy of their procedures for ensuring proper water drainage to the 
containment emergency sump.  Requiring that the refueling canal drain valves 
be open while the reactor is operating or other comparable provisions may be 
appropriate.  In this connection, we note that the current plant technical 
specifications for PWRs with ice-condenser containments include operability 
and surveillance requirements for the refueling canal drain valve during 
power operation. 

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 NRR project manager. 




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contact:  Chang-Yang Li, NRR
                    (301) 492-0875

Attachment:  List of Recently Issued NRC Information Notices
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