ML20035A920
| ML20035A920 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 03/23/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20035A912 | List: |
| References | |
| NUDOCS 9303300235 | |
| Download: ML20035A920 (3) | |
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3....s SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE COPROSION MONITORING SYSTEM FOR THE RESIDUAL HEAT REMOVAL HEAT EXCHANGER - RELIEF RE0 VEST RR-16 LIMERICK GENERATING STATION UNIT 1 PHILADELPHIA ELECTRIC COMPANY DOCKET NO. 50-352
1.0 INTRODUCTION
Pitting corrosion was discovered by eddy current testing on the inside diameter of tubes in the residual heat removal (RHR) heat exchanger in Train B-of Unit I at the Limerick Generating Station.
The inside' diameter of the AISI Type 304L Stainless Steel (304L) tubes was exposed to service water from the spray pond.
The root cause of the pitting was attributed to the deposition of manganese caused by an oxidizing environment and the presence of microbes.
Sodium hypochlorite used as a biocide contributed to the pitting because of the oxidizing nature of sodium hypochlorite.
The licensee initiated a number of actions to reduce the probability that pitting would reduce the wall thickness of any of the tubes in the Unit 1, Train B RHR heat exchanger below the allowable limit.
Deposits inside of the tubes have been removed by hydrolazing. The use of sodium hypochlorite has been discontinued and the use of a non-oxidizing'bircide has been implemented.
Also, the licensee has increased the frequency of monitoring and controlling the spray pond chemistry.
Finally, the licensee has installed a corrosion monitoring system that simulates the actual heat exchanger conditions.
The corrosion monitoring system will permit frequent checks on the corrosion rate, determina if the administrative corrosion limit has been established, and confirm the corrosion allowance assumptions. The corrosion monitoring system i
was started on July 9, 1992, and will be removed after the current refueling cycle.
2.0 CODE CONSIDERATIONS i
The licensee has requested relief from the American Society of Mechanical Engineers (ASME) Code,Section XI, Subparagraph IWA-7210a requirements for the RHR service water system modification that added a corrosion monitoring-system.
ASME Code,Section XI, IWA-7210a, 1986 Edition requires that-replacements, repairs, or modifications meet the requirements of the edition of the code in effect at the time of construction. The Unit 1, Train B, RHR service water system was constructed to ASME Code,Section III, Class 3 for pipe, valves and pumps.
The corrosion monitoring system was designed and constructed in a short period of time and nuclear grade materials conforming to ASME Code,Section III, Class 3 requirements were not available for all components of the corrosion monitoring system.
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! l 3.0 EVALUATION The licensee has stated that materials used for portions nf the inlet and I
outlet piping of the corrosion monitoring system, from the-RHR service water system up to single valves capable of automatic closure, was' constructed from t
material conforming to ASME Code Section III, Class 3.
A second valve conforming to ASME Code Section III, Class 3 was not available for the inlet and outlet valves. The inlet isolation-valves will automatically close when the pressure inside the monitoring system exceeds a predetermined value based on a postulated RHR heat exchanger tube rupture, or on loss of air and/or power to the valve operators.
The outlet lines are provided with check valves 3
which will close as a result of reverse differential pressure between the corrosion monitoring system and the RHR heat exchanger. However, these check valves are not Class IE qualified and the licensee can not take credit for the check valves.
The licensee has stated that these check valves are not safety i
related and that manual isolation valves are available for isolation between i
high and low pressure piping classes.
g The remainder of the corrosion monitoring system with the exception of the specimen holder (which is code material designed to ASME Code,Section III) are constructed from commercial grade material and components. This portion of the corrosion monitoring system has been designed to American National Standard Institute (ANSI) Standard B31.1. Chemical and hardness tests have been performed on all commercial grade material and Certificates of Compliance j
have been prepared to the appropriate American Society for Testing and Materials (ASTM) material specification.
Tensile tests have been conducted-where practical and Certified Material Test Reports have been prepared for materials subjected to tensile tests.
The commercial grade portion of the l
corrosion monitoring system is designed to be isolated from the RHR service l
water system in the event a loss of coolant accident (LOCA) occurs.
The j
licensee at Limerick has determined that isolation of the corrosion monitoring system is not required since the amount of flow through the corrosion monitoring system is small and the operation of the RHR heat exchanger will-not be degraded.
The RHR heat exchanger will operate within the plant Technical Specifications even if the corrosion monitoring system cannot be isolated.
All field welds connected to the RHR service water system meet the ASME Code,Section III, Class 3 requirements including non-destructive examination and.
the use of qualified filler weld metal. Also, all components in the RHR service water system are subjected to hydrostatic testing following the requirements of ASME Code,Section III, Class 3. Further, all of the s
components of the corrosion monitoring system connected to the RHR service l
water system are required to meet the ASME Code requirements for Seismic Category I piping. Thus, the modification and the materials and components used will provide an acceptable level of quality and safety.
4.0 CONCLUSION
Based on our review of the information provided by the licensee, the staff has concluded that the approach taken by the licensee is an acceptable alternative i
to the requirements of ASME Code,Section III, Class 3, as specified in' 1
i
sSection XI, Subparagraph IWA-7210a. requirements, for the use of commercial grade material in the corrosion monitoring system.
This use will not affect the safety of the RHR service water system and will provide an acceptable level of quality and safety.
The staff concludes pursuant to 10 CFR 50.55a(a)(3)(i), that permitting the use of the proposed alternative until the end of the current fuel cycle will provide an acceptable level of quality and safety. Accordingly, the alternative to the ASME Code,Section XI, Subparagraph IWA-7210a requirements for the RHR service water system modifications is hereby authorized.
Principal Contributor:
J. A. Davis Date: March 23, 1993 t
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