Hatch SRVs: Demonstrated Component Unreliability

Update

So the manufacturing gap defect was also seen in 2016 at unit 1. The exact same defect in 2017 at unit 2. Are you sure these guys are nukes?  

May 26,2016

Edwin I. Hatch Nuclear Plant Licensee Event Report 2016-004-00

SOUTHERN«\ NUCLEAR A SOUTHERN COMPANY NL-16-0772

Safety Relief Valves As Found Settings Resulted in Not Meeting Tech Spec Surveillance Criteria

On March 30, 2016, Unit 1 was at 1 00 percent rated thermal power (RTP) when "as-found" testing results of the 3-stage main steam safety relief valves (SRVs) indicated two of the eleven Unit 1 SRVs had experienced a setpoint drift during the previous operating cycle which resulted in their failure to meet the Technical Specification (TS) opening setpoint pressure of 1150 +1- 34.5 psig as required by TS Surveillance Requirement (SR) 3.4.3.1. The test results showed that two SRVs were slightly out of spec low due to setpoint drift. 

The SRV pilots were disassembled and inspected while investigating the reason for the drift. SNC has determined that the abutment gap closed pre-maturely. The pre-mature abutment gap closure is most likely due to loose manufacturing tolerances leading to SRV setpoint drift. 

...Look at all these quality issues in the LERs at the bottom? In three stage, then two stage, then back to three stage. A new platinum coating in the seat and disc on first use failed on roughness of the base metal. Issues with the gape abutment last reporting period remained uncorrected. 

These valves are lucky to be cycled once in 18 months. It would be highly unlikely these valves getting cycle three times in 18 months. These are extremely light duty safety valves. Why all the problems. 

Did they do any testing like cycling the valves with these for 200 times like in the worst accident.       

Edwin I. Hatch Nuclear Plant licensee Event Report 2017-(){)4-()() Safety Relief Valves' As Found Settings Resulted in Not Meeting Tech Spec Surveillance Criteria

On June 30 2017, with Unit 2 at 100 percent rated thermal power {RTP), "as-found" testing of the 3-stage main steam safety relief valves (SRVs) (EBS Code RV) showed that two of the eleven main steam SRVs that were tested had experienced a drift in pressure lilt setpoint during the previous operating cyde such that the anowable technical specification (TS) surveillance requirement (SR) 3.4.3.1 limit of 1150 +/- 34.5 psig had been exceeded. Below is a table illustrating the Unit 2 SRVs that failed as found testing results alter being removed tom service during the Spring 2017 refueling outage.

MPL

2821-F013C

2821-F013E

Event cause Analysis

Drift

-39 psig

-49 psig

The SRV pilots were disassembled and inspected while investigating the reason for the drift It was found that the abutment gap closed prematurely during testing using a linear variable differential transformer (l von to measure pilot stroke distance. The pre-mature abutment gap closure is most likely due to loose manufacturing tolerances leading to SRV setpoint drift.

So they are incapable of detecting a manufacturing defect in the below.

LER 1-2016·004 Identified multiple SRV setpoint drift for 2 of Ole 11 SRVs. Corrective actions included revising vender specifications to tighten as-left tolerances of abutment and pre-load gap, increase the minimum set for abutment pressure at the high end of specification, and tighten diametrical and face run-out tolerances for bellows assembly on pre-load spacer mounting end. 

LER 2-2015..004 identified multiple SRV setpolnt drift for 2 of the 11 SRVs. Corrective actions included replacement of the 2-stage SRVs with 3-stage SRVs which typically do not exhibit set point drift. The selpoint drift was out of spec high while the event discussed in LER 1-2016-004 have failed to meet acceptance criteria by drifting out of spec low. 

LER 1-2014-003 identified multiple SRV setpoint drift for 5 of the 11 SRVs. Corrective actions included replacement of the 2-stage SRVs with 3-stage SRVs which typically do not exhibit set point drift. The setpoint drift was out of spec high while the event discussed in LER 1-2016-004 have failed to meet acceptance criteria by drifting out of spec low. 

LER 1·2012-004 identified multiple SRV setpoint drift for 8 of the 11 SRVs. Corrective actions included replacement of the 2-stage SRVs with 2-stage SRVs whose pilot discs had undergone a platinum surface treatment which was considered at that time to be the lorig term fix for this corrosion bonding issue.