·
Annual Sample: Unit 2 ‘B’ Power Operated Relief Valve (PORV)
Leakage
a. Inspection Scope
The inspectors performed an in-depth review of Dominion’s
identification and correction
of conditions adverse to quality associated with repetitive
leakage of Unit 2 PORVs since
modification and installation in 2006 during 2R17.
The inspectors assessed Dominion’s problem identification
threshold, causal analyses,
extent of condition reviews, compensatory actions, and the
prioritization and timeliness
of Dominion’s corrective actions to determine whether Dominion was
appropriately
identifying, characterizing, and correcting problems associated
with this issue and
whether the planned or completed corrective actions were
appropriate. The inspectors
compared the actions taken to the requirements of Dominion’s CAP
and 10 CFR 50,
Appendix B and assessed the effectiveness of the implemented
corrective actions.
b. Findings and
Observations
No findings were identified.
In 2006, Dominion chose to upgrade the Unit 2 Pressurizer PORV and
Operator
Assemblies to mitigate damage associated with repetitive
installation and removal to
support off-site surveillance testing of the original plant
equipment. The new PORVs
were designed to require less maintenance and to be tested in
place. During each fuel
cycle since installation, either one or both of the new PORVs have
leaked by their closed
valve seats. This condition
has resulted in Dominion isolating PORVs during each of the
last four fuel cycles. On
November 17, 2016, Dominion isolated the ‘A’ PORV due to
leakage as captured in CR1054065.
The PORVs provide overpressure protection for the reactor coolant
system (RCS) by
relieving pressure to the quench tank thereby protecting the RCS
against brittle failure.
Additionally, the PORVs are sized to ensure that departure from
nucleate boiling
specified acceptable fuel design limits are not exceeded during
analyzed events. The
rated capacity per valve is one half the capacity that prevents lifting
the RCS safety
valves during normal plant operations and transients including a
loss of load from full
power. Furthermore, this
capacity is sufficient to prevent lifting the safety valves in the
event of a continuous control rod withdrawal from low power, in
conjunction with a
pressurizer pressure trip of the reactor. Blocking or isolating a PORV will prevent the
valve from automatically opening on demand.
To correct PORV leakage Dominion has performed three recent ACEs
with limited
success. ACE 18846, from
2012, concluded that the incorrect subcomponents,
mismatched valve seats and discs, were used when maintenance
technicians swapped
out a damaged seat during installation. Dominion also identified lost bench and post-
maintenance testing opportunities in addition to training and
procedural enhancements.
In 2015, ACE 19950 found that Dominion failed to provide the
vendor adequate testing
28
requirements in the purchase order for the PORVs. Dominion further identified that the
welded in configuration of the current PORV design does not allow
for testing prior to
restoring the system. ACE
1028983, in 2016, observed that Dominion failed to take
proper action upon identification of PORV leakage due to
procedural weaknesses.
The Dominion CAP procedure, PI-AA-200, provides instructions to
station management
to ensure selection of the most appropriate causal analysis tools
during CR screening.
Consistent with previous screening, CR1054065 was screened as
Significance Level 2,
Potentially Significant Condition.
These conditions are identified as precursors to
significant events.
PI-AA-200, Attachment 6, “CAQ Screening Matrix,” recommends
consideration of a root cause evaluation (RCE) for potentially
significant repetitive
conditions. The inspectors observed that Dominion initially
elected to perform another
ACE for isolation of the ‘A’ PORV captured in CR1054065. However, consistent with a
healthy corrective action program, station staff assigned analysis
of the issue identified
that the three recent ACEs had not successfully prevented PORV
leakage and
requested elevation to a RCE to ensure the appropriate rigor. Dominion has scheduled
completion of the associated RCE (CA3048134) for February 12,
2017.