Information Notice No. 89-32: Surveillance Testing of Low-Temperature Overpressure-Protection
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
March 23, 1989
Information Notice No. 89-32: SURVEILLANCE TESTING OF LOW-TEMPERATURE
OVERPRESSURE-PROTECTION SYSTEMS
Addressees:
All holders of operating licenses or construction permits for
pressurized-water reactors (PWRs).
Purpose:
This information notice is being provided to alert addressees to potential
operability problems due to lack of inservice testing of power-operated relief
valves (PORVs) in their low-temperature overpressure-protection (Ltop) mode.
It is expected that recipients will review the information for applicability
to their facilities and consider actions, as appropriate, to avoid similar
prob-lems. However, suggestions contained in this information notice do not
consti-tute NRC requirements; therefore, no specific action or written response
is required.
Description of Circumstances:
Beaver Valley: During an inspection (Inspection Report No. 50-334,
412/86-20), NRC inspectors noted that technical specifications (TS) require
that over-pressure protection be provided by two PORVs with a nominal trip
setpoint of less than or equal to 350 psig whenever the temperature of a
non-isolated reactor coolant system (RCS) cold leg is less than or equal to
275�F. The TS surveillance requirement only addresses stroking the operable
PORV each time the plant enters Mode 5 (cold shutdown) unless that PORV has
been tested within the preceding three months.
The licensee analyzed two cases for an overpressure accident scenario: (1) a
mass input case and (2) a heat input case. The most restrictive PORV opening
time was identified as the mass input accident which would require a valve to
open within 2.5 seconds. An NRC safety evaluation report (SER) dated April 4,
1983 found this analysis to be acceptable. A review of the licensee's mainte-
nance surveillance procedure indicated that the nominal trip setpoint of less
than or equal to 350 psig was addressed, but the stroke time was not.
Plant TS and procedures had not implemented PORV stroke times as assumed in
the analysis. The licensee performed an evaluation using data from the
station's ASME Valve Stroke Log, when compared to SER stroke time assumptions.
The licensee
8903170419
.. IN 89-32
March 23, 1989
Page 2 of 3
concluded that the resulting maximum RCS pressure would still have been within
specified limits. However, the licensee initiated several procedural improve-
ments to address PORV stroke testing.
Turkey Point: The staff inspected the licensee's overpressure mitigation
system (OMS) (Inspection Report Nos. 50-250, 251/88-14 and 88-26). The PORV
electronics operability and setpoints are verified before being aligned for
low-pressure operations. The inspectors reviewed the stroke times for the
Unit 3 and 4 PORVs from May 1984 through May 1988. These tests were performed
in accordance with the licensee's inservice test (IST) program. The IST
require-ment for each PORV is to fully stroke within 15 seconds. The stroke
times reviewed ranged from less than 2.0 seconds up to 6.41 seconds. These
stroke times are well below the 15-second IST criterion. However, in analyses
sup-porting license amendments, a relief valve opening time of 2.0 seconds was
assumed in calculating the setpoint overshoot for the mass input case. The
heat input case assumed a relief valve opening time of 3.0 seconds. The PORVs,
on average, were not meeting the design-basis stroke time.
The licensee requested relief from the TS requirement in order to prepare for
the eventual refueling outage that would place one of the units within the
operating regime of the OMS. The request extended to the next refueling
outage for each of the units in order to allow the licensee time to resolve
this issue. The licensee requested that Westinghouse perform an analysis to
determine the magnitude of the overshoot considering the following transients:
1) the start of an idle reactor coolant pump with the secondary water
temperature of the steam generator less than or equal to 50�F above the RCS
cold-leg temperature; 2) the start of a high pressure safety injection pump
and its injection into a water-solid RCS and 3) the inadvertent start of two
charging pumps with a loss of letdown. The safety evaluation demonstrated
that with a PORV opening stroke time up to 3.45, the OMS could mitigate the
most limiting transient (spurious start of a SI pump). The licensee has
completed a design change for Unit 4 and is planning to implement the design
change on Unit 3 during the next refueling outage. This design change will
ensure that the PORVs will open in time to prevent exceeding the 10 CFR 50,
Appendix G limits. The surveillance procedures supporting the TS were changed
so that future stroke time testing will use an acceptance criterion that is
consistent with the design basis.
Shearon Harris: NRC inspectors assessing operational performance (Inspection
Report No. 50-400/88-34) noted a discrepancy concerning the testing of the
pressurizer PORVs. An IST procedure specified that the PORVs were to be
stroke tested from the open to closed position with a maximum stroke time of
2.0 seconds. The licensee tested the PORVs in accordance with an 18-month
surveil-lance test for pressurizer PORV operability. Although no safety
analysis credit was taken for the PORVs at power operation, they were required
to provide overpressure protection (by opening on demand) during
low-temperature operation. Shearon Harris utilizes two of the three PORVs for
the Ltop system.
.. IN 89-32
March 23, 1989
Page 3 of 3
The design basis of the licensee's Ltop is to protect the RCS from
overpressure when the transient is limited to: (1) start of an idle reactor
coolant pump with secondary-side water temperature less than 50�F above RCS
cold-leg temper-ature or (2) start of a charging safety injection pump and its
injection into a water-solid RCS. The PORV setpoints were calculated to
maintain the RCS below the maximum allowable system pressure given in 10 CFR
50 Appendix G. The setpoint calculations assumed a valve opening time of 2.0
seconds in determin-ing the possible overshoot. The inspectors noted that if
the actual valve opening times were greater than 2.0 seconds, then the
pressure overshoot could be greater than originally calculated. A significant
increase in valve opening time could result in the 10 CFR 50 Appendix G limits
being exceeded during a design-basis transient.
The PORVs were stroked in the open direction so that the licensee could
perform the time-to-close test. However, the surveillance procedure did not
require that the time to open be determined, and this was not done.
Discussion:
The basic issue in these three cases is that the licensee's inservice testing
of its low-temperature overpressure-protection (Ltop) systems may be inade-
quate. Stroke time requirements used in analyses of the licensee's Ltop
systems were not being transferred into IST requirements and eventually into
surveillance test procedures. The ASME Code, Section XI, paragraph IWV-3400,
requires valves to be exercised to the position required to fulfill their
function. Therefore, not testing the Ltop PORVs in the open direction is a
concern.
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 tech-
nical 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: Milton Shymlock, RII
(404) 331-5542
Thomas McElhinney, Res. Insp., Turkey Pt.
(305) 245-7669
Attachment: List of Recently Issued NRC Information Notices
.. Attachment
IN 89-32
March 23, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
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
89-27 Limitations on the Use 3/8/89 All holders of OLs
of Waste Forms and High or CPs for nuclear
Integrity Containers for power reactors,
the Disposal of Low-Level fuel cycle
Radioactive Waste licenses and
certain by-product
materials licenses.
89-26 Instrument Air Supply to 3/7/89 All holders of OLs
Safety-Related Equipment or CPs for nuclear
power reactors.
89-25 Unauthorized Transfer of 3/7/89 All U.S. NRC
Ownership or Control of source, byproduct,
Licensed Activities and special
nuclear material
licensees.
89-24 Nuclear Criticality Safety 3/6/89 All fuel cycle
licensees and
other licensees
possessing more
than critical
mass quantities of
special nuclear
material.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
..
Page Last Reviewed/Updated Tuesday, March 09, 2021