So they say the resonant frequency of the main steam line is the cause for the SRV failure. How do we know if something dangerous is going on with the MSL causing abnormal vibrations. If might be a crack developing or maybe even damage with the loop vibration snubbers. Maybe nothing is wrong with the SRVs...except the main steam lines are vibrating a lot more than they have been in the past. Are we setting ourselves up for a MSL break before the MSIVs?
I guess the rule are, you got to prove those valves were unsafe behind a barrier, instead you prove to the community these valves are safe.
These new valves were allowed to operate with a common mode failure due to design and poor quality components.
All this secrecy with this from the beginning was predicated on the fear the poor quality components in the SRV effecting the operability of other plants with target rock srvs. Remember within a month with the new valves one started leaking...
Pilgrim Nuclear Power Station LER: SRV-3B Safety Relief Valve Declared Inoperable Due to Leakage and Setpoint Drift
On Sunday January 20, 2013, at 2050 hours with the reactor at 100% core thermal power (RMSS in RUN), PNPS declared SRV-3B inoperable and entered Technical Specification (TS) 3.6.D.2 requiring an orderly re- actor shutdown such that reactor coolant pressure is less than 104 psig within 24 hours. On Monday January 21, 2013, at 1300 hours (16 hrs and 10 minutes) reactor coolant pressure was lowered to less than 104 psig. SRV-3B had been declared inoperable consistent with PNPS procedures that state an SRV is inoperable if the first stage pilot thermocouple temperature is 350 F below its baseline temperature. This LER Supplement provides the determination of cause for the leakage. The cause of the SRV leakage was that the natural fre- quency of the pilot assembly was close to a resonant frequency of the valve assembly when installed on the PNPS main steam line, that had failed to be considered in the design of the SRV. A contributing cause was wear and looseness of parts in the main stage of RV-203-3B.
The reactor was depressurized and a new pilot valve assembly was installed on SRV-3B. On January 22, 2013, at 1015 hours reactor restart was commenced. On January 24, 2013 at 0312 hours 100% core thermal power was achieved.
This LER also reports the as-found setpoint of one SRV pilot valve tested was less than the minimum pres- sure required by TS 3.6.D.1.
This event had no impact on the health and/or safety of the public.
So this is how Pilgrim explained it in the
first LER with these new SRVs.
The enclosed Supplement Licensee Event Report (LER) 2011-007-01, "Safety Relief Valve Declared Inoperable Due to Leakage
There was no evidence of a design defect that could be the root cause for the onset of leakage. The basic design of this 3-stage valve is mature and had been in operation since 1970.
The newest frames it like this.
Licensee Event Report 2013-002-01, SRV-3B Safety Relief Valve Declared Inoperable Due to Leakage and Setpoint Drift
The industry has experienced numerous instances where SRV leakage has occurred at other plants with other Target Rock Model three stage safety relief valves.
What I have seen over the years is truthfulness and integrity
is totally unregulated with license Event report. They generally must submit one,
god help you if you don’t...but the substance of the LER can be falsified at
will and the NRC will never call a utility on it.
They will tell any any mistruth in order to protect saying up a power with defective nuclear safety componets.
On Sunday January 20, 2013, at 2050
hours with the reactor at 100% core thermal power (RMSS in RUN), PNPS
declared SRV-3B inoperable and entered Technical Specification (TS) 3.6.D.2
requiring an orderly reactor shutdown such that reactor coolant pressure is
less than 104 psig within 24 hours. On Monday January21, 2013, at 1300 hours (16 hrs and 10
minutes) reactor coolant pressure was lowered to less than 104 psig.
SRV-3B had been declared inoperable
consistent with PNPS procedures that state an SRV is inoperable if the first
stage pilot thermocouple temperature is 350 F below its baseline temperature.
This LER Supplement provides the determination of cause for the leakage. The
cause of the SRV leakage was that the natural frequency of the pilot assembly
was close to a resonant frequency of the valve assembly when installed on the PNPS
main steam line, that had failed to be considered in the design of the SRV. A
contributing cause was wear and looseness of parts in the main stage of
RV-203-3B.
The reactor was depressurized and a
new pilot valve assembly was installed on SRV-3B. On January 22, 2013, at
1015 hours reactor restart was commenced. On January 24, 2013 at 0312 hours
100% core thermal power was achieved.
This LER also reports the as-found
setpoint of one SRV pilot valve tested was less than the minimum pressure required
by TS 3.6.D.1.
This event had no impact on the health and/or safety of
the public.
BACKGROUND:
As background, the pressure relief
system includes four (4) SRVs and two (2) spring safety valves (SSVs). During Refueling
Outage (RFO-1 8), in April/May, 2011, the four SRVs were replaced with Target
Rock Model 0867F 3-stage SRVs. The SRVs discharge through their individual
discharge piping, terminating below the minimum uppression pool (torus) water level.
The four SRVs are installed on the main steam piping in containment between the
reactor pressure vessel and the flow restrictors.
The 3-stage SRV contains a pilot (also
called the first stage), a second stage, a main stage, and an air operator.
To monitor these valves for leakage,
Pilgrim installed thermocouples at the pilot (first stage), at the second stage,
on the tailpipe near the valve (4.5' to 6' away), on the tailpipe far from the
valve (-20' away) and at the pilot bellows. Procedure 2.2.23, "Automatic
Depressurization System", provides guidance for interpreting the thermocouple
data and determining valve operability based in part on testing performed by
Target Rock.
Subsequent to installation in RFO-1 8
and prior to this event, Pilgrim experienced minor second stage pilot valve leakage
from SRV RV-203-3C on May 18, 2011 and November 25, 2011. Also, on December 26,
2011, SRV RV- 203-3D first stage pilot valve experienced leakage while
operating at full power. The SRV was declared inoperable and the plant was
shutdown on December 26, 2011 in accordance with TS 3.6.D.2 and RV-203-3C was
replaced entirely, and the RV-203-3D pilot assembly was replaced (LER
2011-007-00).
EVENT DESCRIPTION:
On Sunday January 20, 2013, at 2050
hours with the reactor at 100% core thermal power (RMSS in RUN), PNPS declared
SRV-3B inoperable and entered Technical Specification (TS) 3.6.D.2 requiring
the initiation of an orderly reactor shutdown such that reactor coolant
pressure is less than 104 psig within 24 hours. On Monday January 21, 2013, at
1300 hours (16 hrs and 10 minutes) reactor coolant pressure was less than 104
psig. SRV-3B had been declared inoperable consistent with PNPS procedures that
state an SRV is inoperable if the pilot stage thermocouple temperature is 350
F below its baseline temperature.
While at full power, indication of a
steam leak across the first stage pilot of RV-203-3B was identified. The leakage
was evaluated and in accordance with criteria specified in procedure 2.2.23, specifically,
if the pilot stage thermocouple temperature is 35 degrees F below its baseline
temperature (with a smaller decrease at the second stage thermocouple) and
cannot be explained by a corresponding downpower, the SRV is inoperable. The safety
relief valve was subsequently declared inoperable and the Limiting Condition
for Operation (LCO) for Technical Specification (TS) 3.6.D.2 was entered. Per
TS 3.6.D.2 the plant was shutdown and reactor coolant pressure was below 104
psig within 24 hours.
CAUSE:
The SRVs were purchased new,
installed, and tested for the first time in April/May 2011 during RFO-1 8.
Following an extensive investigation,
it was determined that the cause of the SRV leakage was that the natural frequency
of the pilot assembly was close to a resonant frequency of the valve assembly
when installed on the PNPS main steam line. This was not considered in the
Entergy specification or the Target Rock design of the valve.
A contributing
cause was wear and looseness of parts in the main stage of RV-203-3B.
EXTENT OF CONDITION:
This condition potentially
applies to all four three stage SRVs that were installed in RFO 18. During
Cycle 19 operation,Pilgrim has observed leakage from RV-203-3B, 3C, and
3D.
- On May 18, 2011 and November 25, 2011, SRV RV 203-3C second stage pilot valve minor leakage was observed. This condition did not cause inoperability of the valve. SRV RV-203-3C was replaced during the December 26, 2011 shutdown.
- On December 26, 2011, SRV, RV-203-3D first stage pilot valve experienced leakage that exceeded the operability criteria while operating at full power. The plant was shut down as required by TS 3.6.D.2, RV 203-3C and 3D were repaired and the plant returned to full power operation. The cause of the pilot leakage was later determined to be a combination of the natural frequency issue and weakening of the pilot bellows spring. This bellows spring had a through wall failure during testing at an offsite test facility in March 2013. This failure was the subject of a Target Rock 10 CFR, Part 21 (Reference 1).
- On January 20, 2013, Pilgrim experienced the event described in this Licensee Event Report, first stage pilot valve leakage of SRV, RV-203-3B. The plant was shutdown as required by TS 3.6.D.2. The pilot valve was replaced with a refurbished pilot and the plant was returned to full power operation.
- On February 3, 2013, RV-203-3B first stage pilot valve leakage was identified while at full power. Reactor power was lowered to 80% and at 1000 psig pressure, the pilot was reseated. An Operability Determination with a compensatory measure was implemented to maintain the reactor power at 80% and reactor pressure at 1000 psig. An Operations Decision Making Issue (ODMI) was implemented to monitor and take corrective actions. During the forced outage on February 8, 2013, caused by a loss of offsite power due to a major winter storm, RV-203-3B first stage pilot valve was replaced with a new pilot valve and the plant was returned to power operation. The cause of the pilot leakage was determined to be a combination of the natural frequency issue and weakening of the pilot bellows spring. This bellows spring had a through wall failure during testing at an offsite test facility in March 2013. This failure was the subject of a Target Rock 10 CFR, Part 21 (Reference 1).
The removed RV-203-3B pilot valve was
sent to Wyle Laboratory for testing.
As-found test results for the SRV, RV
203-3B pilot valve were:
Pilot S/N SRV Position As-Found Deviation 23 RV-203-3B 1112 psig (-)3.8%Technical Specification 3.6.D.1 requires the as-found setpoint to be within 1155±34.6 psig (1120.4 psig to 1189.6 psig). The as-found setpoint was less than the minimum pressure specification required by TS 3.6.D.1. This test result was entered into the corrective action program as a separate event, and is included in this LER since the condition was discovered within 60 days from the initial discovery of pilot leakage. Accordingly, this as-found value being out of Technical Specification setpoint is reported in this LER pursuant to 10 CFR 50.73(a)(2)(i)(B).
The third pilot on RV-203-3B began
leaking on February 26, 2013. Leakage was controlled by reducing power and
pressure per the ODMI. This pilot was replaced during the Spring 2013 RFO. The
cause of the pilot leakage was that the pilot assembly had a natural frequency
that was close to a resonant frequency of the valve assembly when installed on
the PNPS main steam line.
CORRECTIVE ACTIONS:
The following corrective actions were
taken to address this event related to leaking RV-203-3B:
- The SRV-3B pilot was replaced with a refurbished and tested pilot.
- PNPS Procedure was revised to reduce reactor power and pressure to stop leakage per an ODMI as described in "Extent of Condition."
The following corrective actions are
being taken to address the results of review of Extent Conditions:
- To minimize the possibility of further pilot leaks, all currently installed pilots (and replacements if necessary until the long term corrective action can be taken) have been set at the high end of their allowed set pressure band.
- The recommendations of the Target Rock 10 CFR, Part 21 are being followed.
- The only PNPS pilot with a bellows spring from the same material and heat treatment certifications as the failed bellows was removed from the plant. Detailed metallurgical analysis did not identify any intergranular cracks such as those identified in the failed bellows.
- PNPS has ordered new pilot assemblies with enhancements designed by Target Rock to raise the natural frequency of the pilot and make it more resistant to steam system vibration (References 2 and 3). These pilots include the bellows replacement recommended by the 10 CFR, Part 21. PNPS plans to install these pilots during the spring of 2015 RFO.
SAFETY CONSEQUENCES:
The leaking SRV pilot valves and the
plant shutdown to repair the SRV in accordance with Technical Specification 3.6.D.2
posed no threat to the public health and safety.
All leakage from the valve was
collected in plant systems, the suppression pool (torus), and processed in
accordance with normal station practices.
Pilgrim has installed temperature
monitoring to provide sufficient indication of SRV leakage to ensure that
timely actions can be taken to ensure that the plant is maintained in a safe
condition. Procedure 2.2.23 provides the instructions and guidance for
interpreting and responding to SRV temperature indications. Based on these
instructions, the plant was shutdown. The SRV would have been able to respond
if needed to meet its core cooling or reactor pressure vessel over protection
functions. As a result, the plant safety was maintained. The risk of operating
with a leaking SRV is characterized by an increased chance of having an
inadvertently opened SRV with increased chance of that valve failing to
reclose. Assuming the plant operated for 24 hours with this condition, this
results in a change in core damage frequency of less than 1.OE-7. The impact of
setpoint drift (0.8% below the 3% tolerance) is considered to be bounded by
delta change in core damage frequency of less than 1.OE-7.
PREVIOUS EVENTS:
Prior to Cycle 19, there were no
leakage or setpoint drifts occurrences with three stage safety relief valves
since the new design was installed in April/May, 2011, during Refueling Outage
18 for all four safety relief valves.
During Cycle 19, Pilgrim observed
minor leakage from the second stage pilot valve of RV-203-3C. Also, first stage
pilot valve leakage was observed from RV-203-3D which was confirmed, plant was
shutdown as required by TS 3.6.D.2, and first stage pilot valve was replaced.
This event is described in LER 2011-007-00. During the outage for RV-203-3D,
the entire RV 203-30 was replaced with a new valve assembly.
The industry has experienced numerous
instances where SRV leakage has occurred at other plants with other Target Rock
Model three stage safety relief valves.
OE33766 - Three Stage Safety Relief
Valve Pilot Leakage just below Normal Operating Pressure - Plant Hatch. The
plant Hatch installed the same model 3-stage SRVs in Unit 2 in April 2011.
Hatch experienced numerous pilot leaks during 2011. On some occasions, leakage
was reduced by power and/or pressure reductions. Hatch Unit 2 had some success
through power and/or pressure reductions and operating for several months after
reseating the first stage pilot valve through power and/or pressure reductions.
OE26394 & OE26892 - Planned
Shutdown due to a three stage Safety Relief Valve Leak - Peach Bottom Unit 3
OE32805 - Safety Relief Valve
Temperature Phenomenon – Fitzpatrick
OE34730 - Target Rock 3 Stage Main
Steam SRV Bore to Seat Misalignment - Limerick 2
OE19219 - Plant Shutdown Due to
Increasing Tailpipe Temperature - Duane Arnold
ENERGY INDUSTRY IDENTIFICATION SYSTEM
(EIIS) CODES:
COMPONENTS CODES
Valve, Relief RV
SYSTEMS
Main Steam SB
REFERENCES:
2. Target Rock Technical Evaluation of
Replacement Items TERI 075, "Technical Evaluation of Pilot Assembly 304095-1
Replacing Pilot Assembly 303977-1 for 0867F-001," Target Rock, Revision A,
January 14, 2013.
4. Condition Report CR-PNP-2013-0378, Safety Relief Valve
RV-203-3B, Pilot Leakaqe.
No comments:
Post a Comment