Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 86-60
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 28, 1986
Information Notice No. 86-60: UNANALYZED POST-LOCA RELEASE PATHS
Addressees:
All nuclear power reactor facilities holding an operating license or a
construction permit.
Purpose:
This information notice is being provided to alert recipients to a
potentially significant problem pertaining to substantial possible leakage
of radioactive water flowing in pipes outside containment after a
loss-of-coolant accident (LOCA). The NRC expects that recipients will review
this notice for applicability to their facilities. Suggestions contained in
this notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Reference:
NUREG-0737: "Clarification of TMI Action Plan Requirements," November
1980. Item III.D.1.1: Integrity of Systems Outside Containment Likely
to Contain Radioactive Material for Pressurized Water Reactors and
Boiling-Water Reactors.
Description of Circumstances:
On August 2, 1985, the licensee at Haddam Neck Nuclear Power Plant reported
to the NRC that two potential post-LOCA release paths from containment had
been identified:
1. The following potential post-accident release path resulted from TMI
Action Plan modifications completed in 1981. The release path can come
about in two ways (Figure 1):
a. When the charging system is running and normally aligned, borated
water is injected from the volume control tank (VCT) to the
reactor coolant pump (RCP) seals past the thermal barrier and into
the reactor cooling system (RCS). Some of the seal injection water
flows through the Number 1 seal and returns through a filter and
the seal water heat exchanger to the charging pump suction.
Because a charging pump is operating, the seal water return header
does not pressurize. In the post-LOCA situation, the system
operates essentially the
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IN 86-60
July 28, 1986
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same except the injection water is drawn from the refueling water
storage tank (RWST) rather than the VCT and the charging pumps
will automatically start only if normal power is available. To
preserve for the operator the option of running the RCPs after an
accident, the licensee removed automatic safety injection and
containment isolation signals to the isolation valves for the RCP
auxiliaries [i.e., seal water (valve A in Figure 1), thermal
barrier, and oil cooler returns]. These isolation valves remain
remotely operable from the control room.
Under post-accident conditions, if offsite power is lost, the
charging pumps stop and are not automatically restarted. With no
operator action, the unisolated RCP seal water return line will
pressurize from the seal leakage that is normally routed to the
charging pump suction. This line relieves to the VCT at 140 psig;
eventually the VCT will overflow to the waste treatment system. If
no action is taken to stop the seal water leakage, a flow path for
highly radioactive fission products to the plant stack would
eventually exist through the waste treatment system. Manual
isolation of the seal water return header (closure of valve A in
Figure 1) to the VCT or manual start of a charging pump would
terminate the scenario.
b. At some time after a LOCA when 100,000 gallons have been pumped
from the RWST, the ECCS will take suction from the containment
sump (recirculation mode). If the RCS pressure exceeds the shutoff
head of the residual heat removal (RHR) pumps, the charging system
will be manually aligned to take a suction on the RHR system and
discharge to the RCS at a higher pressure. In this mode of
operation, if the seal return header isolation valve (valve B in
Figure 1) downstream of the relief valve to the VCT were to be
manually closed or to fail closed (for example, on loss of control
air), the seal water return header would again pressurize to the
point of safety relief at 140 psig.
The licensee informed plant operators of these potential post-accident
release pathways, of expected indications, and appropriate actions to stop
the leakage (either start a charging pump or isolate the return line, based
on operator judgment).
2. The second release path is related to the post-LOCA recirculation mode.
The licensee had considered only RHR system leakage outside containment
as a source of radioactive release during sump recirculation. Because
the charging system may also be used in this recirculation, it could be
moving highly radioactive water outside containment. Previously, the
licensee was monitoring RHR system leakage to assure that it was below
the Technical Specification, but not the charging system leakage. The
licensee has now expanded its surveillance to include both systems.
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IN 86-60
July 28, 1986
Page 3 of 3
Discussion:
These release paths are associated with low frequency events, but because
the associated offsite doses may be significant, licensees may want to
consider these release paths and other release paths that may be unique to
their plants in post-LOCA analyses. Such release paths are related to the
referenced TMI Action Plan item for a program to reduce to
as-low-as-reasonably-achievable (ALARA) levels the leakage from systems
outside containment that would or could contain highly radioactive fluids
during a serious transient or accident.
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Vern Hodge, IE
(301) 492-7275
Attachments:
1. Figure 1
2. List of Recently Issued IE Information Notices
