Information Notice 1995-03, Loss of Reactor Coolant Inventory and Potential Loss of Emergency Mitigation Functions While in a Shutdown Condition
| ML003727420 | |
| Person / Time | |
|---|---|
| Issue date: | 07/03/2000 |
| From: | Marsh L Operational Experience and Non-Power Reactors Branch |
| To: | |
| Benner, Eric | |
| References | |
| IN-95-003, Suppl 2 | |
| Download: ML003727420 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
July 3, 2000
NRC INFORMATION NOTICE 95-03, SUPPLEMENT 2: LOSS OF REACTOR COOLANT
INVENTORY AND POTENTIAL LOSS
OF EMERGENCY MITIGATION
FUNCTIONS WHILE IN A
SHUTDOWN CONDITION
Addressees
All holders of operating licenses for nuclear power reactors except those who have ceased
operations and have certified that fuel has been permanently removed from the reactor vessel.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice supplement
to alert addressees to insights from inspections related to losses of reactor coolant while the
reactor is in a hot, pressurized, shutdown condition with the potential for adversely affecting
accident mitigation capability. It is expected that recipients will review the information in this
supplement for applicability to their facilities and consider actions, as appropriate, to avoid
similar problems. However, suggestions contained in this information notice supplement are
not NRC requirements; therefore, no specific action or written response is required.
Background
Information Notice 95-03, "Loss of Reactor Coolant Inventory and Potential Loss of Emergency
Mitigation Functions While in a Shutdown Condition," issued on January 18, 1995, discusses an
incident at Wolf Creek involving the loss of reactor coolant while the reactor was in a hot, pressurized, shutdown condition. At Wolf Creek, all residual heat removal (RHR) and
emergency core cooling system (ECCS) pump suction lines are supplied by a common suction
header. When the loss of reactor coolant occurred, hot reactor coolant system (RCS) water
was introduced into this common suction header between the refueling water storage tank
(RWST) and the RHR and ECCS pumps. This hot water flashed to steam, resulting in a
steam/water mixture in the header. Had an ECCS actuation occurred, this mixture could have
been introduced into the suction of the ECCS pumps. If operators had not been able to
terminate the event, the hot water in the suction piping may have led to steam binding, which
could have adversely affected the pumps in both ECCS trains. In addition, water flashing to
steam in the header and the RWST could have caused serious mechanical damage to the RHR
piping and the RWST as a result of water hammer. Finally, the flow path from the RCS through
the RWST establishes a containment bypass path.
IN 95-03, Supp. 2 The NRC issued Generic Letter (GL) 98-02, "Loss of Reactor Coolant Inventory and Associated
Potential for Loss of Emergency Mitigation Functions While in a Shutdown Condition," on
May 28, 1998, to request that addressees (1) perform an assessment to determine if their
ECCSs include certain design features, such as a common pump suction header, which can
render the systems susceptible to common-cause failure and if this susceptibility is found, (2)
prepare, with consideration of plant-specific design attributes, a description of the features of
their Appendix B quality assurance program (for example, the methods used to verify valve
position; the controls in place to ensure compliance with plant surveillance, maintenance, modification, and operating procedures; and the adequacy of operator training for such
activities) that provide assurance that the safety-related functions of the RHR system and the
ECCS will not be adversely affected by activities conducted at hot shutdown.
This information notice supplement discusses additional insights that have been gained from
NRC inspections performed in response to GL 98-02.
Discussion
Licensee and staff analyses of the Wolf Creek event assumed failure to isolate the RCS
draindown path. If this were to occur, within 5 minutes, the reactor vessel water level could
drain to the bottom of the hot leg, and, as a consequence, the operating RHR pump would lose
suction, cavitate, and fail. Continued boiloff would result in uncovering of the core in less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Failure to quickly isolate the flow path could also result in the RWST suction header filling
with steam, which would continually discharge into the RWST. This steam could lead to water
hammer events with the potential for mechanical damage to pump components, piping, and
tank structural components.
A special NRC report dated March 1995 and titled "Reactor Coolant System Blowdown at Wolf
Creek on September 17, 1994" (AEOD/S95-01), identified 19 loss-of-coolant events that have
occurred at reactors during shutdown. Of these 19 events, only 2 have taken place at
temperatures and pressures sufficient to result in voiding RWST piping. Considering
pressurized-water reactor operating experience, the staff estimated the initiating event
frequency may be equal to or greater than 1E-3 per reactor year. The initiating event frequency
and the heavy dependence upon short-term operator action highlight the importance of careful
planning, the accuracy of administrative procedures, and disciplined adherence to those
procedures.
GL 98-02 focused on requesting that affected licensees take adequate protective measures to
minimize the likelihood of a Wolf Creek type event. The generic letter was not intended to
address all aspects related to recovery from a shutdown loss-of-coolant accident (LOCA).
However, during NRC inspections performed in response to GL 98-02, the staff identified a
potentially generic weakness regarding the procedures used to mitigate a Wolf Creek type
event that licensees may wish to review.
At one facility, the procedure used to recover from a hot, pressurized shutdown LOCA directs
operator actions that could increase the probability that ECCS equipment would be disabled
and could delay recovery from the LOCA. Specifically, for entry conditions in which the
pressurizer level is less than 10 percent or RCS subcooling is less than 32 degrees C (58 degrees F), and the RWST level is greater than 27 percent, that is, a Wolf Creek type scenario,
IN 95-03, Supp. 2 closure of the RHR hot-leg isolation valves are not explicitly directed early in the procedure, and, as such, the LOCA is not terminated. The procedure subsequently directs alignment of
the suction of the operating centrifugal charging pump to the common suction header, potentially exposing it to hot reactor coolant and rendering it inoperable. If that centrifugal
charging pump is rendered inoperable, the operator is expected to evaluate aligning the suction
of the second centrifugal charging pump to the common suction header, exposing it to the
same conditions which rendered the first centrifugal charging pump inoperable. This
progression continues with the two safety injection pumps, potentially rendering them
inoperable, also, and could ultimately result in a significant loss of ECCS capability.
Related Generic Communications
ÿ
GL 98-02, "Loss of Reactor Coolant Inventory and Associated Potential for Loss of
Emergency Mitigation Functions While in a Shutdown Condition," May 28, 1998.
ÿ
Information Notice 95-03, "Loss of Coolant Inventory and Potential Loss of Emergency
Mitigation Functions While in a Shutdown Condition," January 18, 1995.
ÿ
Supplement to Information Notice 95-03, March 25, 1996.
This information notice requires no specific action or written response. However, recipients are
reminded that they are required to consider industry-wide operating experience (including NRC
information notices), where practical, when setting goals and performing periodic evaluations
under Section 50.65, "Requirements for monitoring the effectiveness of maintenance at nuclear
power plants," of Part 50 of Title 10 of the Code of Federal Regulations. 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.
/RA/
Ledyard B. Marsh, Chief
Events Assessment, Generic Communications
and Non-Power Reactors Branch
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical contact:
Eric J. Benner, NRR
301-415-1171 E-mail: ejb1@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
IN 95-03, Supp. 2 closure of the RHR hot-leg isolation valves are not explicitly directed early in the procedure, and, as such, the LOCA is not terminated. The procedure subsequently directs alignment of
the suction of the operating centrifugal charging pump to the common suction header, potentially exposing it to hot reactor coolant and rendering it inoperable. If that centrifugal
charging pump is rendered inoperable, the operator is expected to evaluate aligning the suction
of the second centrifugal charging pump to the common suction header, exposing it to the
same conditions which rendered the first centrifugal charging pump inoperable. This
progression continues with the two safety injection pumps, potentially rendering them
inoperable, also, and could ultimately result in a significant loss of ECCS capability.
Related Generic Communications
ÿ
GL 98-02, "Loss of Reactor Coolant Inventory and Associated Potential for Loss of
Emergency Mitigation Functions While in a Shutdown Condition," May 28, 1998.
ÿ
Information Notice 95-03, "Loss of Coolant Inventory and Potential Loss of Emergency
Mitigation Functions While in a Shutdown Condition," January 18, 1995.
ÿ
Supplement to Information Notice 95-03, March 25, 1996.
This information notice requires no specific action or written response. However, recipients are
reminded that they are required to consider industry-wide operating experience (including NRC
information notices), where practical, when setting goals and performing periodic evaluations
under Section 50.65, "Requirements for monitoring the effectiveness of maintenance at nuclear
power plants," of Part 50 of Title 10 of the Code of Federal Regulations. 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.
/RA/
Ledyard B. Marsh, Chief
Events Assessment, Generic Communications
and Non-Power Reactors Branch
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical contact:
Eric J. Benner, NRR
301-415-1171 E-mail: ejb1@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
Accession Number #ML003727420
- see previous concurrence
Document name: G:\\REXB\\EJB1\\IN9503S2.WPD
To receive a copy of this document, indicate in the box C=Copy w/o attachment/enclosure E=Copy with attachment/enclosure N = No copy
OFFICE
REXB
TECH ED
RII
RII
SRXB
NAME
E Benner*
B Calure*
R Gibbs*
P Frederickson*
M Razzaque*
DATE
6/9/2000
6/8/2000
6/16/2000
6/21/2000
6/23/2000
OFFICE
SRXB
REXB
NAME
J Wermiel*
L Marsh
DATE
6/27/2000
07/03/2000
/
/2000
/
/2000
/
/2000
[OFFICIAL RECORD COPY]
___________________________________________________________________________________
OL = Operating License
CP = Construction Permit
Attachment
IN 9503 - Supp. 2 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information
Date of
Notice No.
Subject
Issuance
Issued to
________________________________________________________________________________
2000-09
Steam Generator Tube Failure
Indian Point Unit 2
06/28/2000
All holders of operating licenses
for nuclear power reactors except
those who have ceased
operations and have certified that
fuel has been permanently
removed from the reactor vessel
2000-08
Inadequate Assessment of the
Effect of Differential
Temperatures on Safety-
Related Pumps
5/15/2000
All holders of operating licensees
for nuclear power reactors
2000-07
National Institute for
Occupational Safety and
Health Respirator User Notice:
Special Precaustions for Using
Certain Self-Contained
Breathing Apparatus Air
Cylinders
4/10/2000
All holders of operating licenses
for nuclear power reactors, non- power reactors, and all fuel cycle
and material licensees required to
have an NRC-approved
2000-06
Offsite Power Voltage
Inadequacies
3/22/2000
All holders of operating licenses
for nuclear power reactors, except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor
2000-05
Recent Medical
Misadministrations Resulting
from Inattention to Detail
3/06/2000
All medical licensees
2000-04
1999 Enforcement Sanctions
for Deliberate Violations of
NRC Employee Protection
Requirements
2/25/2000
All NRC licensees
2000-03 High-Efficiency Particulate Air
Filter Exceeds Mass Limit
Before Reaching Expected
Differential Pressure
2/22/2000
All NRC licensed fuel-cycled
conversion, enrichment, and
fabrication facilities