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.
9003080213
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IN 90-19
March 14, 1990
Page 2 of 2
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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