ML19254E025
| ML19254E025 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 10/09/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| TASK-05-10.A, TASK-5-10.A, TASK-RR NUDOCS 7910300522 | |
| Download: ML19254E025 (4) | |
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SYSTEMATIC EVALUATION PROGRAM
_ PLANT $YSTEMS/ MATERIALS BIG ROCK POINT Topic V-10.A Residual Heat Removal System Heat Exchanger Tube Failures The safety objective o,f this review is to assure that impurities from the cooling water system are not introduced into the primary coolant in the event of shutdown cooling system heat exchanger tube failure. This was expanded to assure that adequate monitoring exists to assure no leakage of radioactive material in the other direction - into the service water and thus to the environment.
Information for this assessment was gathered from plant personnel during the safe shutdown review site visit in June 1978 and from related telephone convenations. Information was also taken from the Big Rock Point Techni-cal Specifications and the Big Rock Point Final Hazards Sumary Report.
Tr.e bases for the review of these cooling systems on today's plants include: (1) the NRC's Standard Review Plan (SRP)9.2.1,whichrequires that the service water system include the capability for detection and control of radioactive leakagt into and out of the system and prevention of accidental releases to the environment; (2) SRP 9.2.2, which requires that auxiliary cooling water systems (such as the shutdown cooling system) include provisions for det*ction, collection and control t,f system '
leakage and means to detect leakage of activity from one system to another and preclude its release to the environment; and (3) SRP 5.2.3, which
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discusses compatibility of materials with reactor coolant and requirss sonitoring and sampling of the primary coolant system. These Standard Review Plans were used only in the comparison of Big Rock Point against today's criteria and were not used as licensing requirements which must be met, especially if the plant incorporates other equally viable means of accomplishing the stated goals.
Because the Shutdown Cooling System (SCS) heat exchangers (2) are on the suction side of the shutdown cooling pumps, the primary (reactor coolant) side of the heat exchangers may be at a pressure as low as 11.5 psig.
The secondary side of these heat exchangers is the Reactor Cooling Nter (aCW) system, which operates at a maximum nominal pressure of 70 psig. Thus,
,1f there were tube failure (s) inf eakage of RCil into the primary system would occur. There has been no inservice code-approved hydrostatic test of the SCS heat exchanger tubes, although what serves e a quasi-hydrostatic test is performed during each SCS startup, according to plant sources. This occurs because the systemis typically initiated when primary pressure is in the range of 150-280 psig,' auch greater than the normal pressure noted above. Additicnally, ' requirement for hydrostatic testing will be imposed as part of %1e inservice inspection program in connection with the staff's ger. M c 10 CFR 50.55a(g) review. Although the new inservice inspection program requirements were originally scheduled to begin with the 40-month interval com.encing September 1,1978, the staff has approved a delay until February 1979 to more closely coincide with a planned refueling 00tage.
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, As protection against undetected leakage into the primary system, the Big Rock Point RCW syrtem water tank incorporates a low level alarm which will alert the plant operators to leakage through the SCS heat exchangers Tor any of the other components cooled by the RCW system). In addttton, although of no need with regard to the SCS heat exchanger (unless* RCW is shut down), the RCW system incorporates a radiation detector and alarm, as does the service water system, which cools the RCW heat exchangers and is thus the ultimate heat sink.
The RCW system pressure at the two RCW heat exchangers varies from a few 3
inches of water vacuum to a few psig. Because the service water pressure attheseheatexchangersvariesfremapproximatelf20to45PSIG,thepossibility exists for inleakage of contaminants from Lake Michigan into the RCW system.
As noted above, such inleakage could find its way into the primary coolant system during SCS operation because of the differantial pressures across the SCS heat exchanger. Although this scenario presumes failures of tubing in r
a combination of the SCS and RCW heat exchangers, such a combination, with resultant primary system contaminat' ion, cannot be ruled out, given that no inservice inspection of heat exchanger tubes has been perfomed and that differential pressures would aid such leakage.
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4 Big Rock Point procedures require the twice weekly analysis of the RCW system, testing for chr6 mates (a compound of which is used in the RCW system as a corrosion inhibitor), chloride, and conductivity. These tests w'.11 adequa*ely detect any inleakage from the SW system, but added defense and early warning could be obtained by the incorporation of a high level alam in the RCW system water tank. Presently only the low level alam exists as protection in addition to be twice weekly sazpling.
The staff will examine this further during the integrated asressment at,the end of Design Basis Event review.
As defens2 against primary system contamination during power operation.
8,ig Rock Point Technical Specification 4.1.2(b) requires daily primary coolant sampling., which includes chtorides and conductivity. Ttis should be expa.ded to include sa g ling during shutdown when the SCS is in operation and thus when leakage into the primary system is most likely.
As noted above, the recocrnendations for improvements will be reviewed as pa-t of th-integrated assessment. No action on the part of the licensee is necessary at this time.
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