GO2-10-083, Response to Request for Additional Information (RAI) Regarding Request for Relief from ASME OM Code Test Interval for a Class 2 Pressure Relief Valve
| ML101800150 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 06/18/2010 |
| From: | Oxenford W Energy Northwest |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GO2-10-083 | |
| Download: ML101800150 (4) | |
Text
ENERGY NORTHWEST W. Scott Oxenford Columbia Generating Station P.O. Box 968, PE08 Richland, WA 99352-0968 Ph. 509.377.4300 1F. 509.377.4150 soxenford @energy-northwest.com June 18, 2010 G02-10-083 10 CFR 50.55a(a)(3)
U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
References:
COLUMBIA GENERATING STATION, DOCKET NO. 50-397 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI)
REGARDING REQUEST FOR RELIEF FROM ASME OM CODE TEST INTERVAL FOR A CLASS 2 PRESSURE RELIEF VALVE
- 1) Letter G02-10-078 dated June 9, 2010, W.S. Oxenford (Energy Northwest) to NRC, "Request for Relief from ASME OM Code Test Interval for a Class 2 Pressure Relief Valve"
- 2) Phoncon to Discuss RV-06 (TAC No. ME4046) on June 15, 2010
Dear Sir or Madam:
By Reference 1, Energy Northwest requested NRC approval of proposed Relief Request RV-06 to extend the test interval for a certain Class 2 pressure relief valve on a one-time basis until the restart after refueling outage R20, which is currently scheduled for June 2011. Via Reference 2, the NRC requested additional information related to the Energy Northwest Relief Request submittal.
The Energy Northwest response to the Reference 2 request for additional information is provided in the attachment to this letter.
There are no commitments contained in this letter. If you have further questions, please contact D.W. Gregoire at (509) 377-8616.
-Vice Pres ent clear Generation and Chief Nuclear Officer
Attachment:
Response to Request for Additional Information cc:
NRC RIV Regional Administrator NRC NRR Project Manager NRC Senior Resident Inspector/988C R.N. Sherman - BPA/1399 W.A. Horin - Winston & Strawn V~UL#7
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING REQUEST FOR RELIEF FROM ASME OM CODE TEST INTERVAL FOR A CLASS 2 PRESSURE RELIEF VALVE Attachment Page 1 of 3 Response to Request for Additional Information NRC Question 1:
What was the history of the valve before it was replaced?
Energy Northwest Response:
In May 1996 and May 2003, Containment Supply/Purge (CSP) Relief Valve CSP-RV-52 (Lonergan Model LCT-13) was removed from service and bench tested. On both occasions, it passed the as-found test requirement and the valve was re-installed without requiring any repairs. In June 2007, the relief valve was again removed and tested. The valve passed the visual inspection and the set point test, but failed the as-found leakage test (60 bubbles/min vs 20 bubbles/min). It was disassembled for repair and the disc dimensions were found to be undersized. At that point, the relief valve was replaced with the Crosby OMNI 900 Model 9511817D rather than perform repair to the Lonergan Model LCT-1 3.
When removed in May 1996, May 2003, and June 2007, the Lonergan valve was found in good condition both externally and internally. There was no accumulation of corrosion materials within the valve cavity. The seat leakage failure in June 2007 was attributed to the seat dimension being undersized.
NRC Question 2:
In what type of environment is the valve located? Does the environment accelerate degradation?
Energy Northwest Response:
The valve is located in an area considered a "harsh environment" area for design purposes since the ambient conditions will experience energy changes due to a postulated Loss of Coolant Accident (LOCA) Design Basis Event (DBE) or High Energy Line Break (HELB) DBE. The relief valve is an American Society of Mechanical Engineers (ASME)Section III, Class 2 relief valve rated at 150 psi, up to 1500 F, and up to 1 x 107 RADS. The applicable Columbia Generating Station (CGS) environmental design requirements (150 psi, 1500 F and 1.85 x 106 RADS) are enveloped by the specified ASME Section III, Class 2 design capabilities, thus the relief valve is suitable for the particular design application.
The relief valve has not experienced a "harsh environment" during its service. It has been installed for 36 months and operated in a controlled, mild environment with small swings in temperature and humidity. The relief valve has been exposed to minimal radiation. The relief valve internals are exposed to air from the Control Air System (CAS) with nitrogen backup. The CAS system is sampled quarterly for air quality and results have met the air quality acceptance criteria of 40 micron maximum particulates,
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING REQUEST FOR RELIEF FROM ASME OM CODE TEST INTERVAL FOR A CLASS 2 PRESSURE RELIEF VALVE Attachment Page 2 of 3 1.0 ppm maximum hydrocarbons, and -40 F at 100 psig dewpoint. The environment has not accelerated degradation of the relief valve and the environmental conditions have been well below the design qualifications of the relief valve.
NRC Question 3:
Why was the Crosby Omni series selected? The licensee's technical equivalency may provide additional supporting justification for the relief request.
Energy Northwest Response:
The Lonergan relief valve installed at CSP-RV-52 failed its seat leakage test. The disc dimensions were found undersized. Rather than perform repair to the Lonergan and because the Lonergan was obsolete, Energy Northwest identified a new valve that met design function requirements and procured the Crosby relief valve as a replacement.
The Crosby relief valve has the same relief set point as the Lonergan. The design flow of the Crosby relief valve is in excess of the requirement for CSP-RV-52 and comparable to the Lonergan. The Crosby relief valve meets or exceeds the design requirements of CSP-RV-52, ensuring that the design function is not adversely affected.
NRC Question 4:
What is the history of similar valves (9511882A) installed at CGS? Has maintenance been performed on the similar valves and if so, what were the results? Were the valve internals found during maintenance to be in good condition?
Energy Northwest Response:
CGS has similar Crosby OMNI 900 Series valves (Model 9511882A) in use (RHR-RV-25A/B/C). These valves are used in a water application, have been tested since October 2004, and have been installed since May 2005 with no issues. Since being installed, these valves have not been required to be removed from service for testing, thus CGS has no history on maintenance or on valve internal inspections for these valves. For the Lonergan valve installed at CSP-RV-52, when removed in May 1996, May 2003, and June 2007, the valve was found in good condition both externally and internally. There was no accumulation of corrosion materials within the valve cavity.
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING REQUEST FOR RELIEF FROM ASME OM CODE TEST INTERVAL FOR A CLASS 2 PRESSURE RELIEF VALVE Attachment Page 3 of 3 NRC Question 5:
What is the impact if the valve does not perform its safety function (i.e., does not lift at desired set point)?
Energy Northwest Response:
Two failure modes can result if the relief valve does not perform its safety function:
- 1. If the relief valve opens and does not reseat, the CSP system will depressurize and the 3 inboard reactor building to wetwell vacuum breakers (CSP-V-5/6/9) will open.
- 2. If the relief valve fails to open, the CSP system could become over-pressurized and piping could rupture. The CSP system would then depressurize and the inboard reactor building to wetwell vacuum breakers would open.
NRC Question 6:
What is the risk or probability that an overpressure event would challenge the valve?
Energy Northwest Response:
The probability that an over-pressure event would challenge the valve is very low. The CAS system is regulated with several other relief valves. The likelihood of an over-pressurization of the CAS system simultaneously with all relief valves failing to lift is low. The backup nitrogen tanks also have an additional relief valve. The likelihood of an over-pressurization of the backup nitrogen tanks simultaneously with their relief valve failing to lift is low. In the event of an over-pressurization of significance, piping may rupture and the CAS air or nitrogen within the CSP system would disperse into the reactor building. Under such conditions and as stated previously, the inboard reactor building to wetwell vacuum breakers would lose pressure and open. The event would have no effect on the outboard reactor building to wetwell vacuum breakers (CSP-V-7/8/1 0) and they would remain closed.
Based on the low probability and the medium level consequences, the overall risk is low.