Information Notice No. 89-36:Excessive Temperatures in Emergency Core Cooling System Piping Located Outside Containment
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
April 4, 1989
NRC INFORMATION NOTICE: NO. 89-36: EXCESSIVE TEMPERATURES IN EMERGENCY
CORE COOLING SYSTEM PIPING LOCATED
OUTSIDE CONTAINMENT
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to an event that
involved the potential for reactor coolant system (RCS) leakage outside con-
tainment. A check valve serving as the inboard containment isolation valve
in a high-pressure injection (HPI) system injection line failed to seat pro-
perly after termination of HPI flow, allowing RCS backflow into HPI system
piping that was not qualified for RCS temperatures. The HPI system piping
was exposed to fluid temperatures in excess of design temperatures, resulting
in stresses that exceeded the allowable limits for Class 1 piping according
to the American Society of Mechanical Engineers Boiler and Pressure Vessel
Code (ASME Code), Section III. Recipients are expected to review the infor-
mation for applicability to their facilities and consider actions, as appro-
priate, 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:
On January 20, 1989, at Arkansas Nuclear One, Unit 1 (ANO-1), a failure of the
main generator exciter resulted in a generator lockout and subsequent trips of
the main turbine and the reactor. Upon loss of power to plant loads from the
main generator, one of the two non-safety-related 6.9 kV buses failed to auto-
matically fast transfer from the unit auxiliary transformer to the startup
transformer; this failure caused two of the four reactor coolant pumps (RCPs)
to trip on undervoltage. A failure of one of the main feedwater (MFW) pumps
to runback to minimum speed and a failure of a MFW block valve and control
valves to close after the reactor trip resulted in overfeed of the once
through steam generators; this overfeed caused a slight overcooling (11�F) of
the RCS. The operators manually started one HPI system pump to maintain
pressurizer level above the heater cutoff point. The pump was secured 2
minutes later; however, check valve MU-34B in the "B" HPI line did not seat
properly (see Figure 1). The existing RCP configuration (i.e., two pumps
running and two
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. IN 89-36
April 4, 1989
Page 2 of 3
pumps tripped) created a differential pressure across MU-34B that caused RCS
backflow into the HPI system piping outside containment. The flow path ran
from the RCS and outside containment via MU-34B, through the crossover pipe
to the "C" HPI line, and then back inside containment to the RCS via MU-34C
as shown in Figure 1. The HPI system piping upstream of MU-34B was not qua-
lified for RCS temperatures. Subsequent analysis by the licensee (assuming
a RCS temperature of 545� F) showed that the temperature effects resulted in
stresses that exceeded ASME code-allowable limits for Class 1 piping. The
HPI system piping was qualified for RCS pressure but was only designed for
a temperature of 145� F. The licensee became aware of RCS leakage outside
containment when tape attached to the HPI piping began to melt, smolder and
smoke, activating a local smoke detector and the associated control room
alarm.
Discussion:
The primary concerns are that the failure of a check valve to seat properly
exposed piping located outside containment to RCS temperature and that the
piping was not designed for RCS temperatures. Furthermore, the check valve
serves as the inboard containment isolation valve, but valve testing
(consisting of visual inspection and vertical stroke of the valve disc) was
not adequate to reveal the excessive wear problem that led to its failure.
Because the piping outside con-tainment was not monitored to detect RCS
in-leakage (e.g., high temperature alarms), the piping potentially could be
exposed to RCS temperatures for long periods without being detected. It is
important for addressees to note the need for piping to be qualified for
potential inservice conditions and that the as-sociated components, that are
part of the reactor coolant pressure boundary, are subject to applicable ASME
Code requirements which include, in part, leak detection, isolation and
periodic testing.
Corrective actions proposed by the licensee include installation of a second
check valve in each HPI line inside containment, installation of temperature-
monitoring instrumentation in the HPI lines outside containment between the
containment penetration and the first outboard check valve, replacement of
all piping that was determined to be overstressed from high temperature during
the event, and leak rate testing for all check valves in the HPI lines inside
containment.
Subsequent review by the licensee identified HPI system pipe supports that
are not qualified for the maximum temperature to which the associated piping
could be exposed when the HPI system is used in the piggyback mode of
operation. The licensee is upgrading the pipe supports. It is important that
system piping be analyzed and qualified for the maximum temperature and
pressure to which it could be exposed, regardless of whether credit is given
in the final safety analysis report (FSAR) transient/accident analysis for the
associated mode of operation.
. IN 89-36
April 4, 1989
Page 3 of 3
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the
technical contacts listed below or the Regional Administrator of the
appropriate regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Rick Kendall, NRR
(301) 492-3140
Yueh-Li Li, NRR
(301) 492-0915
Attachments:
1. Figure 1 - ANO High Pressure Injection System Flow Path to the Reactor
Coolant System (Simplified Diagram)
2. List of Recently Issued NRC Information Notices
. Attachment 2
IN 89-36
April 4, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-86, Operating with Multiple 3/31/89 All holders of OLs
Supp. 1 Grounds in Direct Current or CPs for nuclear
Distribution Systems power reactors.
89-35 Loss and Theft of Un- 3/30/89 All U.S. NRC
secured Licensed Material byproduct, source
and special
nuclear material
licensees.
89-34 Disposal of Americium 3/30/89 All holders of an
Well-Logging Sources NRC specific
license
authorizing well-
logging activities.
89-33 Potential Failure of 3/23/89 All holders of OLs
Westinghouse Steam or CPs for PWRs.
Generator Tube
Mechanical Plugs
89-32 Surveillance Testing 3/23/89 All holders of OLs
of Low-Temperature or CPs for PWRs.
Overpressure-Protection
Systems
89-31 Swelling and Cracking 3/22/89 All holders of OLs
of Hafnium Control Rods or CPs for PWRs
with Hafnium
control rods.
89-30 High Temperature 3/15/89 All holders of OLs
Environments at or CPs for nuclear
Nuclear Power Plants power reactors.
89-29 Potential Failure of 3/15/89 All holders of OLs
ASEA Brown Boveri or CPs for nuclear
Circuit Breakers power reactors.
During Seismic Event
89-28 Weight and Center of 3/14/89 All holders of OLs
Gravity Discrepancies or CPs for nuclear
for Copes-Vulcan power reactors.
Air-Operated Valves
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
..
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