Information Notice No. 92-85: Potential Failures of Emergency Core Cooling Systems Caused by Foreign Material Blockage
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
December 23, 1992
NRC INFORMATION NOTICE 92-85: POTENTIAL FAILURES OF EMERGENCY CORE COOLING
SYSTEMS CAUSED BY FOREIGN MATERIAL BLOCKAGE
All holders of operating licenses or construction permits for nuclear power
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the potential failure of emergency core cooling
systems (ECCS) caused by foreign material blockage. 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 are not NRC requirements;
therefore, no specific action or written response is required.
Description of Circumstances
H. B. Robinson Unit 2
On August 23, 1992, while the H. B. Robinson Nuclear Plant was in mode 4, hot
shutdown, plant personnel were performing an operations surveillance test of
the B safety injection (SI) pump. This test found that the recirculation flow
was 20 percent lower than it had been when it was last measured on July 12,
1992. Prompted by the resident inspector, the Carolina Power and Light
Company (the licensee) retested this pump on August 24, 1992, and found no
recirculation flow. The licensee also tested the A SI pump and found the
recirculation flow was 10 percent lower than when it was last measured. The
licensee declared both pumps inoperable and took the unit to cold shutdown.
On August 25, 1992, the licensee opened the B SI pump recirculation line and
removed a single piece of white plastic, about the size of a nickel, from the
Previously, on July 8, 1992, the licensee had declared the B SI pump
inoperable after a quarterly inservice inspection surveillance test found that
it was producing a recirculation flow of 11.4 Liters [3 gallons] per minute,
rather than the required 132.5 Liters [35 gallons] per minute. On July 9,
1992, the licensee shut down the plant to determine the cause of the low flow.
The licensee removed the recirculation line for the B SI pump and found that
debris was obstructing the inline orifice.
December 23, 1992
Page 2 of 3
On July 12, 1992, after flushing the B SI pump and verifying that
recirculation flows for both SI pumps were acceptable, the licensee returned
the unit to service. The licensee also tested all other ECCS pumps that could
have had contact with foreign material. The licensee believed, prior to plant
startup, that all debris had been removed.
Point Beach Unit 2
On September 28, 1992, the Wisconsin Electric Power Company (the licensee)
performed an ASME Section XI quarterly test of containment spray pumps and
valves. During the test, the licensee noted that the discharge pressure for
the A train containment spray pump was zero and that the pump was making an
abnormal noise. The test was stopped and the pump was declared inoperable.
Upon disassembly of the pump, a foam rubber plug was found blocking the
impeller suction. The licensee removed the plug and retested the pump. The
test was successfully completed and the pump was declared operable.
The licensee at H. B. Robinson determined that the foreign material found in
the SI system was a plastic material that had been used during a modification
of the Residual Heat Removal (RHR) system performed in March through
June 1992. The plastic material is manufactured by DuPont and the trade name
is Delrin-AF. At the time of the RHR modification, the plastic material had
been cut into four 23-centimeter [9-inch] diameter, circular pieces for use as
weld purge dams. However, after completing the modification, the licensee did
not account for two of the four pieces. Delrin-AF decomposes at RCS system
conditions because of reaction with the water and thermal degradation. The
licensee suspected that the purge dam pieces broke, entered the RHR piping
after breaking, and migrated into the refueling water storage tank (RWST) and
SI header during initial cavity draindown.
The licensee sent divers with cameras into the RWST to inspect for the
plastic. The divers found three fragments of Delrin-AF plastic and also other
pieces of miscellaneous debris. The location and size of the recovered
Delrin-AF material agrees with the material migration theory since all of the
pieces were larger than those recovered from the B SI pump in July and August.
The licensee inspected orifices for the SI pump minimum flow recirculation
lines and also visually inspected piping, tanks, and components to find and
remove any foreign material. Also, the licensee evaluated the potential
effect on other ECCS equipment and concluded that the ECCS equipment would
continue to be operable and reliable.
December 23, 1992
Page 3 of 3
The licensee for Point Beach Unit 2 reviewed plant records and determined that
the plug was most likely left in the piping after modifications were made to
install full flow test lines in the RHR, containment spray and safety
injection systems, during the 1991 refueling outage. The NRC reviewed the
event and determined that one train of the safety injection system piping was
rendered inoperable in the recirculation mode because of the presence of the
plug. This condition had continued for about a year and was caused by
inadequate foreign material exclusion controls during the system modifications
made in the previous outage.
The presence of small debris may not be detected by operational or post
modification testing since blockages may not appear immediately. However,
small debris may migrate into areas with smaller cross sections where the
debris could collect and cause blockage after extended operation. These
examples illustrate the consequences of failure to ensure accountability of
all materials that are used when safety systems are opened and to perform
cleanliness checks of all affected areas prior to system closure.
Related Generic Communication
On November 21, 1989, the NRC issued Information Notice (IN) 89-77, "Debris In
Containment Emergency Sumps and Incorrect Screen Configurations," which
addressed problems that could result from debris in containment emergency
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 Office of Nuclear
Reactor Regulation (NRR) project manager.
ORIGINAL SIGNED BY
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact: Eric Benner, NRR
Attachment: List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015