ML19343D413
| ML19343D413 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 04/24/1981 |
| From: | Withers B PORTLAND GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML19343D412 | List: |
| References | |
| NUDOCS 8105040434 | |
| Download: ML19343D413 (7) | |
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PORTLAND GENERAL ELECTRIC COMPANY EUGENE WATER & ELECTRIC BOARD AND PACIFIC POWER & LIGHT COMPANY 30JAN NUCLEAR PLANT Operating License NPF-1 Docket 50-344 License Change Application 74 This License Change Application is submitted in support of Licensee's request to modify Appendix A of Facility Operating License NPF-1 by
-tilowing surveillance testing of the Main Steam Isolation Valves while in the STARTUP Mode as well as in HOT STANDBY.
PORTLAND GENERAL ELECTRIC COMPANY By Bart D. Withers Vice President Nuclear Subscribed and sworn to before me this I day of April, 1981.
YAd JL Notary Public of Ordon My Commission Expires:
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PORTLAND GENERAL ELECTRIC COMPANY EUGENE WATER & ELECTRIC BOARD AND PACIFIC POWER & LIGHT COMPANY TROJAN NUCLEAR PLANT Operating License NPF-1 Docket 50-344 License Change Application 74 This License Change Application is submitted in support of Licensee's request to modify Appendix A of Facility Operating License NPF-1 by allowing surveillance testing of the Main Steam Isolation Valves while in the STARTUP Mode as well as in HOT STANDBY.
PORTLAND GENERAL ELECTRIC COMPANY By Bart D.' Withers Vice President Nuclear Subscribed and sworn to before me this /
day of April, 1981.
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TORTLAND GENERAL ELECTRIC COMPANY EUGENE WATER & ELECTRIC BOARD AND PACIFIC POWER & LIGHT COMPANY TROJAN NUCLEAR PLANT Opers. ting License NPF-1 Docket 50-344 License Change Application 74 This License Change Application is submitted in support of Licensee's request to modify Appendix A of Facility Operating License NPF-1 by allowing surveillance testing of the Main Steam Isolatica Valves while in the STARTUP Mode as well as in HOT STANDBY.
PORTLAND GENERAL ELECTRIC COMPANY a1 -
MW By Bart D. Withers Vice President Nuclear Subscribed and sworn to before me this cf N day of April, 1981.
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LCA 74 Peg 7 1 ef 4 1
LICENSE CHANGE APPLICATION Change Technical Specification 4.7.1.6 to allow for MSIV testing "while shutdown or suhequent startup..."g 2. 525'F during each reactor in HOT STANDBY or in STARTUP with Tav
, as shown in the attached replace-ment page.
REASON FOR CHANGE l
Plant Technical Specification 4.7.1.6 presently requires testing of the Main Steamline Isolation Valves (MSIVs) while in the Hot Standby Mode. The requirement to test only in Hot Standby (Mode 3) is unneces-sarily restrictive and therefore may be relaxed and made more prac'ical by allowing testing to be performed while in the Startup Mode (M,.e 2).
SAFETY EVALUATION 1.
Summary of Change The proposed change will allow testing of the MSIVs in the Startup Mode. This will increase operational flexibility as well as pro-vide the pract W 1 benefit of closing the valves with the aid of a small amount of m an flow which occurs during the Startup Mode (0- to 5 percent power). This change is a part of the overall effort aimed at improving the surveillance test performance of these valves.
2.
Discussion The MSIVs are used to recover frca steamline break and steam gener-ator tube rupture accidents. Uncontrolled steam flow from the steam generators must be limited in the event of a break in the main steam supply system piping. Any such break must not impair the integrity of the reactor heat sink or Containment Building. The proposed change to allow testing of the valves at 0- to 5 percent power was reviewed in light of the above overall requirements.
The potential for masking the inability of the MSIVs to close under no-flow conditions and the resulting consequences were examined.
The potential for degradation of the valve disk integrity was also considered.
The MSIVs are of the reverse check valve design. During normal operation, the valve is kept open against a spring force by air pressure over a piston in the actuator cylinder. In the event of manual or automatic initiation (high pressure inside Containment or high steamline flow in coincidence with low-low Tavg or with low steamline pressure), the air pressure in the cylinder is relieved and the valve is closed by the spring force and by the force of gravity due to the weight of the disk.
Steam flow will add to the closing force after the valve disk has moved off of its full open position to a point where the valve disk enters the steam flow path. Accident scenarios which involve the use of the MSIVs were examined to determine the ramifications of taking advantage of this additional steam flow force during surveillance testing.
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LCA 74 Paga 2 ef 4 MSIV closure is required in the event of a steamline break to prevent 1
an uncontrolled cooldown in the Reactor Coolant System (RCS) and to prevent overpressurizing the Containment. The change to the present testing requirement would allow closure testing with the reactor at up to 5 percent of rated power level. The signals initiating MSIV closure in steamline break cases are derived from measurement of high steam flow (the minimum setpoint >40 percent of the design steam flow at 20 percent power with a linear increase to 110 percent steam flow at 100 percent power). Hence, it is a precondition of the steamline break accident analysis that a high steam flow exists through the MSIVs when the valve closure signal is initiated. Therefore, testing with up to 5 percent steam flow would be more effective than testing with no flow for determining if the valve meets its design criteria and for idenrifying malfunctions, such as the valves sticking fully open or being so tightly bound in an intermediate position that they could fail to close during a steamline break accident. Hence, it is concluded that closure testing with up to 5 percent of rated steam flow is consistent with the accident analysis and the Technical Speci-fication bases insofar as steamline break accidents are concerned.
MSIV closure is not required for Containment isolation during a LOCA.
Rather, it is provided to assure Concaimment integrity in the event of a small steamline break inside Containment.
In such cases, analyses for more recent Westinghouse plants than Trojan have indi-cated that for the small steamline breaks inside Containment under certain combinations of break size and initial power level, the high steam flow and low steamline pressure will not always occur simul-tane ously. Therefore, in order to prevent blowdown of more than one steam generator into the Containment under these conditions, the high Containment pressure MSIV closure signal is provided.
The MSIVs are also utilized in the steam generator tube rupture analysis, which considers the effect of a double-ended break of a single tube while at 100 percent power. In that case, the analyzed system resp nse involves a rapid decrease in primary pressure that causes a reactor trip and automatic safety injection. The reactor trip causes a turbine trip, which then results in automatic opening of condenser dump valves and the Power-Operated Relief Valves (PORVs) on all steam generators.
If, however, due to the unavailability of offsite power the condenser dump were closed, turbine trip (closure of turbine stop valves) would significantly reduce steam flow through the MSIVs. In that case, closure of the MSIVs, which is a manual action in this eccident, would be under conditions of low flow. The worst single MSIV to fail open would be that associated with a faulted steam generator; if that valve failed open, it would not be possible to isolate the faulted steam generator from the steam header downstream,f the MSI7s. In that case, the downstream steam header would hava to be isolated from connections further on downstream in j
order to isolate the faulted steam generator, meaning that the condenser dump could not be used during the cooldown phase of the accident recovery. It is necessary to maintain the pressure in the faulted steam generator in order to minimize flow through the rup-tured tube and to assure subcooling in the RCS during its subsequent depres surization. Recovery from this situation could then proceed
r LCA 74 Prgt 3 ef 4 as in the case of the loss of offsite power, for which the condenser is not available anyway. The release pathways will be the same, since steam cannot be dumped to the condenser. The steam generator tube rupture accident with a loss of offsite power has been analyzed in the Final Safety Analysis Report (FSAR), and procedures exist for recove ry.
No new accident is created nor are the consequences for this accident increased.
The effect c? testing under steam flow on valve disk integrity was also considered. As a result of a conservative steamline break analysis (see J. L. Williams, PGE, to W. R. Butler, NRC, letter dated July 29, 1975), the MSIV disk material was upgraded to withstand the effects of slamming shut under steam flow conditions resulting from a double-ended, full-area guillotine steamline break accident.
Limiting the test to the Hot Standby and Startup Medes will limit the flow to 5 percent power. Since the impact forces experienced during testing will be substantially less than the design impact forces, the effect of this change on valve disk integrity should be minimal.
3.
Technical Specifications and Technical Specification Bases Paragraph 4.7.1.6 will be changed to allow MSIV testing while in the Startup Mode. The proposed change continues to require demonstration of MSIV closure within 5 seconds, which will ensure that no more than one steam generator will blow down in the event of a steamline rupture. Therefore, no changes to the Technical Specification bases are necessary.
4.
Effect on FSAR The proposed change does not affect the description of the MSIVs found in FSAR Section 5.5.5.
Surveillance testing requirements are consistent with the assumptions used in tae Chapte?: 15 accident analysis and therefore will not affect t'ae result or consequences of any previously analyzed transient. No unreviewed safety issue is involved, and no changes to the FSAR are necessary.
5.
Environmental Effect The proposed change will not affect the environmental analyses presented in the FSAR, the Environmental Report, or the final environmental statement. No unreviewed environmental matter exists, and there will be no significant impact on the environment f rom this 1
change.
SCHEDULE CONSIDERATIONS It is requested that the NRC quickly act on this LCA in order to provide the increased operating flexibility within a reasonable time period.
BASIS FOR DETERMINATION OF AMENDMENT CLASS This LCA has been determined to result in a Class III amendment in l
accordance with 10 CFR 170.22. This LCA involves a single issue and i
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IIA 74 Page 4 of 4 does not involve a significant hazard consideration. The fee for a Class III amendment is $4,000.
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