TMI-12-158, Three Mile, Unit 1, Submittal of Relief Request VR-01 Associated with the Fifth Inservice Testing (IST) Interval
| ML12292A585 | |
| Person / Time | |
|---|---|
| Site: | Three Mile Island  |
| Issue date: | 10/18/2012 |
| From: | Jesse M Exelon Generation Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| TMI-12-158 | |
| Download: ML12292A585 (7) | |
Text
10 CFR 50.55a TMI-12-158 October 18, 2012 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Three Mile Island Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-50 NRC Docket No. 50-289
Subject:
Submittal of Relief Request VR-01 Associated with the Fifth Inservice Testing (1ST) Interval Attached for your review is relief request VR-01 associated with the fifth Inservice Testing (1ST) interval for Three Mile Island Nuclear Station (TMI), Unit 1. The fifth interval of the TMI, Unit 1 1ST program complies with the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants, 2004 Edition with Addenda through OMb-2006. The fifth 1ST interval will begin on October 15, 2013. We request your approval by October 18, 2013.
There are no regulatory commitments in this letter.
If you have any questions concerning this letter, please contact Tom Loomis at (610) 765-5510.
Respectfully, Michael D. Jesse Director - Licensi Regulatory Affairs Exelon Generation Company, LLC
Attachment:
Relief Request VR-01 cc: Regional Administrator, Region I, USNRC USNRC Senior Resident Inspector, TMI Project Manager, [TMI] USNRC
Attachment Relief Request VR-01
10 CFR 50.55a RELIEF REQUEST: VR-Ol Revision 0 (Page 1 of 5)
Proposed Alternative Concerning Testing of the Pressurizer Pilot Operated Relief Valve (PORV) in Accordance with 10 CFR 50.55a(a)(3)(i)
- 1. ASME Code Component(s) Affected l-RC-RV-2, Pressurizer Pilot Operated Relief Valve (PORV), Class 1, Category B/C Component/System Function The PORV is used to control Reactor Coolant System (RCS) pressure as discussed in Three Mile [sland Generating Station (TMI), Unit 1 Updated Final Safety Analysis Report, Section 4.2.4 ("Pressure Control and Protection").
- 3. Applicable Code Requirement(s)
- ISTC-331O, "Effects of Valve Repair, Replacement, or Maintenance on Reference Values" - This section requires post-maintenance valve exercising following replacement.
- ISTC-351O, "Exercising Test Frequency" - "Power operated relief valves shall be exercise tested once per fuel cycle."
- 4. Reason for Request Pursuant to 10 CFR 50.55a(a)(3)(i), approval of a proposed alternative is requested to the above listed requirements of the OM Code. During the current fourth 1ST interval, the OM Code-required testing for the PORV is satisfied by manually stroking the valve once every operating cycle. This is performed during plant startup following a refueling outage. The valve must be stroke timed during this exercise test. TMI, Unit 1 is proposing an alternative to this required in-situ testing for several reasons.
There are several disadvantages to the in-situ testing of the PORV. The PORV is a 2.5 inch Dresser Electromatic, solenoid actuated, pilot operated relief valve. Operation of the pilot valve vents the chamber under the main valve disc which causes the main valve to open.
The PORV requires steam pressure for the main disc to open. Stroke testing the PORV during cold shutdown conditions would not exercise the main valve disc, which would not satisfy the ASME OM Code requirements. To test the PORV in-place, the RCS must be pressurized to supply the necessary fluid (steam) pressure to open the main valve disc.
10 CFR 50.55a RELIEF REQUEST: VR-Ol Revision 0 (Page 2 of 5)
Also, since the PORV design does not provide direct obturator position indication, the valve disc position must be inferred from alternate indications (tailpipe ~T, acoustic monitor, RCS pressure decrease, or quench tank pressure or level rise).
In-situ testing of the PORV would also result in an in-surge of cooler water from the hot leg of the RCS into the pressurizer. The resulting thermal cycle on the pressurizer surge line would be a thermal stress concern, as described in NRC Bulletin 88-08 ("Thermal Stresses in Piping Connected to Reactor Coolant Systems") and should be avoided.
Requiring that the PORV be tested in-place prevents plant personnel from verifying proper reseating of the main valve disc because its discharge is not accessible as it is during bench testing. Minor leakage would not be readily evident before it would cause damage to the main valve disc/seat. Excessive leakage from the pilot valve can lead to inadvertent opening of the main valve, and impair its ability to re-close.
The proposed alternative will allow testing of the PORV that is appropriate to demonstrate functionality without cycling the valve in place using reactor steam pressure. This is consistent with NUREG-0737, "Clarification of TMI Action Plan Requirements," Item ILK.3.16, "Reduction of Challenges and Failures of Relief Valves," which recommended that the number of relief valve openings be reduced as much as possible and that unnecessary challenges should be avoided.
- 5. Proposed Alternative and Basis for Use The following alternatives to the requirements stated above are proposed:
- 1) Bench testing of the PORV to satisfy valve exercise and stroke time requirements is performed at the vendor test facility prior to installation. Exercising of the valve at both the normal power operation set point and the Low Temperature Overpressure Protection (LTOP) set point (as provided in Technical Specification 3.1.12, "Pressurizer Power Operated Relief Valve (PORV), Block Valve, and Low Temperature Overpressure Protection (LTOP),,) will be verified during this testing. Measured stroke time will be based on the pressure response indication of main disc opening.
- 2) The installed valve will be removed and replaced each refueling outage, with a spare valve that has been previously bench tested.
- 3) The removed valve will be bench tested within one year of removal from the system.
- 4) In-situ exercising of the PORV will be performed only as necessary to reestablish operational readiness after maintenance on an installed valve.
10 CFR 50.55a RELIEF' REQUEST: VR-Ol Revision 0 (Page 3 of 5)
Requiring in-situ testing of the PORV unnecessarily increases the number of challenges to the PORV and results in an overall reduction in plant safety. Bench testing is preferable over in-situ testing for several reasons. Bench testing is performed at normal steam inlet conditions. Both the power operation set point and the Low Temperature Overpressure Protection (LTOP) set point (as provided in Technical Specification 3.1.l2, "Pressurizer Power Operated Relief Valve (PORV), Block Valve, and Low Temperature Overpressure Protection (LTOP)") are verified. The measurement of the PORV stroke time, verification of main disc movement, and seat leakage check can be verified more precisely under bench testing conditions.
Performing a bench test under controlled conditions allows the opportunity for accomplishing repairs to the valve while there is sufficient time for any needed repairs or additional testing without these activities affecting the unit's operating/outage schedule and without the additional dose that could result by having to remove or perforn1 work on the valve while it is attached to the ReS. If a test failure during plant startup were to occur that required cold shutdown conditions, this would result in an additional thermal cycle on the unit and additional personnel radiation exposure that could otherwise have been avoided.
Valve testing will be performed at a steam test facility, where the entire valve assembly (i.e., main valve, pilot valve, and solenoid) will be installed on a steam header in the same (vertical) orieutation as the plant installation. The test conditions in the test facility will be similar to those in the plant installation, including ambient temperature, valve insulation, and steam conditions. The valve will then be leak tested, and functionally exercised at the normal power operation set point and the LTOP pressure limit to ensure the valve is capable of opening and closing (including stroke timing), and leak tested a final time.
Valve seat tightness will be verified by a cold bar test, and if not free of fog, leakage will be measured and verified to be below design limits. If required, based on the results of "As-found" testing, the valve will be refurbished and recertified ("As-left" tested). The valve will then be shipped to the plant. If "As-found" testing is satisfactory and refurbishment is not necessary, the valve will be returned without any disassembly or alteration of the main valve or pilot valve components. A receipt inspection will be performed in accordance with the requirements of the Exelon Quality Assurance Program. The storage requirements in effect at TMI, Unit 1 ensure the valve is protected from moisture and physical damage.
Prior to installation, the valve will again be inspected for foreign material and damage. The valve will be installed, and electrically connected in accordance with a TMI, Unit 1 maintenance procedure. The procedure ensures proper reinstallation of the PORV and proper connection of controls. The post-maintenance testing then verifies operation of the solenoid-actuated pilot valve.
10 CFR 50.55a RELIEF' REQUEST: VR-Ol Revision 0 (Page 4 of 5)
The proposed alternative also provides adequate assurance that the valve stroke time will be consistently measured at the test facility. The test facility replicates the control signals to the pilot solenoid allowing it to be actuated at the pressures corresponding to when it would be actuated in the plant. Stroke timing of the solenoid-actuated pilot valve will start with the initiation of the signal to the solenoid and be based on the initial main valve obturator movement as determined by the change in steam pressure when exercised at both the normal reactor coolant system pressure limit and the lower LTOP pressure. Stroke timing will be used to ensure that the valve performs acceptably compared to its baseline and design requirements. Observation of the main disc movement at the test facility is indirect, based on evidence of steam pressure response, as it is in-situ at the plant, since there is no direct indication of the main valve position. Although this difference may result in minor differences in measured stroke time compared to those measured when installed in the plant, the stroke times measured at the test facility will be under conditions identical to when the reference values were established, making the results comparable and trendable for detecting any abnormality in valve performance. The 1ST reference values for the PORV stroke time are less than 2 seconds, and the stroke timing will be measured to at least tenths of a second even though the OM code only requires it to be measured to the nearest second.
The following is a review of PORV test history from the steam test facility which demonstrates that the PORV pilot valve opens well within the 2-second limiting stroke time allowed by ASME OM Code Section ISTC-5114(c) for rapid-acting valves:
RC-RV-2 First and Second LTOP First and Second Serial # Test Date Pressure Stroke times Normal RCS Pressure (seconds) Stroke times (seconds)
BS03989 1110412011 0.182, 0.196 0.095, 0.108 S03989 11/1112009 0.188, 0.232 0.128, 0.130 S03989 10128/2007 0.126, 0.142 0.130, 0.124 BL08905 1012212007 0.116,0.176 0.132, 0.172 BL08905 08/1012006 0.144, 0.146 0.116, 0.118 BS03839 05/07/2004 0.158, 0.156 0.094, 0.110 BL08905 OS/2412002 0.166, 0.160 0.110, 0.100 8S03989 08/3112000 0.182, 0.176 0.084, 0.076 As demonstrated above, using the provisions of this relief request as an alternative to the listed ISTC requirements will provide: 1) assurance of PORV functional capability; 2) permit detection of component degradation, and; 3) continue to provide an acceptable level of quality and safety.
10 CFR 50.55a RELIEF REQUEST: VR*Ol Revision 0 (Page 5 of 5)
- 6) Duration of Proposed Alternative The proposed alternative identified will be utilized during the fifth 1ST interval which is scheduled to begin October 15,2013 and conclude on October 14,2023.
- 7) Precedents None