Information Notice No. 89-77: Debris in Containment Emergency Sumps and Incorrect Screen Configurations
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
November 21, 1989
Information Notice No. 89-77: DEBRIS IN CONTAINMENT EMERGENCY SUMPS
AND INCORRECT SCREEN CONFIGURATIONS
Addressees:
All holders of operating licenses or construction permits for pressurized
water reactors (PWRs).
Purpose:
This information notice is intended to alert addressees to potential
problems resulting from inadequate housekeeping and insufficient
surveillance of containment emergency recirculation sumps. 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.
Description of Circumstances:
During the recovery period after a loss-of-coolant accident, following
injection of emergency coolant from the refueling water storage tank, water
is collected within the containment emergency recirculation sump to be
pumped back into the reactor coolant system. The emergency sump structures
are designed to provide for a continuous flow of water to the recirculation
pumps by preventing the entry of air or debris, thereby protecting the
recirculation pumps from damage due to loss of net positive suction head or
entrained solid material. To provide guidance for sump designs, the NRC
staff issued Regulatory Guide 1.82, "Water Sources for Long-Term
Recirculation Cooling Following a Loss-of-Coolant Accident," dated June
1974, which was revised in November 1985. Regulatory Guide 1.82 emphasizes
the need for inservice inspection of emergency core cooling sump components,
including debris interceptors, vortex suppressors, and sump outlets. The
staff also expressed the need for emergency sumps to be protected from
debris in Standard Review Plan 6.2.2 and Generic Letter 85-22, "Potential
for Loss of Post-LOCA Recirculation Capability Due to Insulation Debris
Blockage." PWR standard technical specifications and the technical
specifications of many plants require visual inspection of the containment
emergency sump and verification that the suction inlets to the recirculation
pumps are not restricted by debris. Sump components, including trash racks
and screens, must also be inspected. The surveillance interval is typically
18 months.
On June 16, 1988, following a recirculation flow verification test, loose
parts and debris were found in the containment sump, the recirculation
pumps, and the suction piping of Surry Units 1 and 2. Some of the items
were large enough to
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November 21, 1989
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have caused pump damage or flow degradation. In addition, some of the sump
screens were found to have gaps, which could have allowed additional loose
material to enter the sump. One screen was found to be missing. Following
investigation of the event by the licensee and the NRC staff, the licensee
incorporated sump surveillance requirements similar to those of PWR standard
technical specifications into their plant procedures. The NRC issued a
notice of violation and proposed imposition of a $50,000 civil penalty.
On July 8, 1989, the licensee for the Trojan facility discovered numerous
items in the containment sump. The NRC was informed of this condition on
July 12, 1989. On July 14, 1989, after containment had been closed out, an
NRC inspector and the licensee found additional debris. On July 17, 1989,
the top sump screen and portions of the inner screen were found to be
missing. On July 19, 1989, the NRC identified additional missing and
damaged inner sump screens. Debris had previously been found in the Trojan
sump during a 1988 outage. In 1980, a residual heat removal pump was jammed
by a welding rod between the impeller and the casing ring demonstrating the
potential safety significance of loose debris in the containment emergency
sump. The Trojan Technical Specifications contain periodic inspection
requirements for the containment emergency sump and sump screens. The
licensee's inspection procedures for the containment emergency sump did not
have adequate inspection criteria. The NRC issued a notice of violation and
proposed imposition of a $280,000 fine for a severity level II violation.
As a result of the problems identified at the Trojan facility, the NRC
resident inspector recently performed an inspection of the Diablo Canyon
sump and sump screens, including a comparison of the design drawing to the
actual arrangement of the sump screens. Debris was found in the Unit 1 and
Unit 2 sumps, and the sump screen arrangement on the design drawing was
found to be incorrect. The sump screens were not configured in accordance
with the FSAR drawing. The Diablo Canyon Technical Specifications contain
periodic inspection requirements for the containment emergency sump and sump
screens. Initial findings indicate that plant procedures for sump
inspection were not sufficient or detailed enough to assure adequate
inspections.
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: Walton Jensen, NRR
(301) 492-1190
Attachment: List of Recently Issued NRC Information Notices
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