ML20082K277

Informs NRC of Intent to Elimate Dynamic Effects Associated W/High Energy Pipe Ruptures in RCS Piping from Licensing & Design Bases of Units 2 & 3,by Application of leak-before- Break Technology

ML20082K277
Person / Time
Site:	San Onofre
Issue date:	04/17/1995
From:	Marsh W SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9504190195
Download: ML20082K277 (9)

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t e 4 Southem Califomia Edison Campany 23 PARKER STREET BRVINE, CALIFORNIA 92718 f

WALTER C. MARSH April 17,1995 m - ~E MANAGER OF NUCLE. AR REGULATORY AFF AIRS (714)454-440"3 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:

Subject:

Docket No. 50-361 and 50-362 Application of Leak-Before-Break Technology to Reactor Coolant System Piping San Onofre Nuclear Generating Station i Units 2 and 3 The purpose of this letter is to inform the NRC of Southern California Edison's (Edison's) intent to eliminate the dynamic effects associated with high energy pipe ruptures in the Reactor Coolant System (RCS) piping from the licensing and desig(n Leak-Before-Break bases LBB) of San This technology. Onofre changeUnitsto2the and 3 by application of the licensin bases is permitted by revised General Design Criterion 4 (GDC-4)g and design of Appendix A to 10 CFR 50. By this letter NRC approval is requested by the end of 1995 to allow Edison to start using LBB technology during the Unit-2 C outage to 1) remove pipe whip restraints from the RCS loop,eliminate 2)ycle 9.jet refueling impingement loads from the RCS piping and branch lines connected to the RCS, and 3) relax the in-service testing criteria for the Reactor Coolant Pump snubbers'and Steam Generator hydraulic snubbers.

On October 30, 1990, the NRC staff, in its Safety Evaluation for Topical Report CEN-367, " Leak-Before-Break Evaluation of Primary Loop Piping in Combustion Engineering Designed Nuclear Steam Supply Systems," accepted referencing CEN-367 as a technical tasis for applying LBB technology to primary loop piping. The acceptd version of the topical report was issued as CEN-367-A in February 1991, fa a condition of referencing CEN-367 the NRC requires licensees, as stated in Section 3.0 of the NRC Safety Evaluation, to

" submit information to demonstrate that leakage detection systems installed at the specific facility are consistent with Regulatory Guide 1.45," which is titled " Reactor Coolant System Pressure Boundary Leakage Detection Systems."

Edison evaluated the existing radiation monitoring and RCS leakage detection systems at San Onofre Units 2 and 3 and concluded the installed leakage detection' systems are consistent with Regulatory Guide (RG) 1.45. Specific details are provided in the enclosure to this letter which includes a summary of Edison's compliance with the RG 1.45 positions. Additionally, a Design Change Package is in progress to replace the existing gas channel monitor with a state-of-the-art, more responsive design. It is Edison's intent to implement this design change by the end of 1996.

T ". C " ' q 9504190195 950417 i PDR ADOCK 05000361 .

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Do'cument Control Desk If you have any questions regarding this submittal, please let me know.

t Very truly yours, h0 i

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cc: L. J. Callan ~, Regional Administrator, NRC RegionLIV i A. B. Beach, Director, Division of Reactor. Projects, Region IV K. E. Perkins, Jr., Director, Walnut Creek. Field Office, NRC Region IV l; J. A. Sloan, NRC Senior Resident' Inspector, San Onofre Units 2 and 3 M. B. Fields, NRC. Project Manager, San Onofre Units 2 and 3 ,

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,. Enclosure APPLICATION OF LEAK-BEFORE-BREAK (LBB) TECHNOLOGY TO SAN ONOFRE UNITS 2 AND 3

'I . Background The October 30, 1990 NRC Safety Evaluation Report (SER) approving CEN-367, " Leak-Before-Break Evaluation of Primary Loop Piping in Combustion Engineering Designed Nuclear Steam Supply Systems," states "The revised GDC-4 is based on the development of advanced fracture mechanics techno'ogy using the LBB concept. On October 27, 1987, a final rule was published (52 B 41228), effective November 27, 1987, amending GOC-4 to 10 CFR 50. The revised GDC-4 allows the use of analyses to eliminate from the design bases the dynamic effects of postulated pipe ruptures in high energy piping in nuclear power units.

The new technology reflects an engineering advancement which allows simultaneously u, increase in safety, reduced worker radiation exposures, and loser construction and maintenance costs. Implementation permits the reinoval of pipe whip restraints and jet impingement barriers as well as other related changes in operating power plants, plants under construction, and future plant designs. Although functional and performance requirements for containments, emergency core cooling systems, and environmental qualification of equipment remain unchanged, local dynamic effects uniquely associated with postulated ruptures in piping which qualified for LBB may be excluded from the design basis (53 8 11311)."

The Combustion Engineering Owners Group (CE0G) submitted CEN-367 for NRC review on November 20, 1987. Edison was a participating member of the CE0G and San Onofre Units 2 and 3 were included in the bounding analyses of CEN-367. On October 30, 1990, the NRL accepted CEN-367. The Safety Evaluation Report (SER) accepting CEN-367 concluded that the subject CE0G primary loop piping complies with revised GDC-4 according to the criteria in NUREG-1061, Volume 3, " Report of the U. S. Nuclear Regulatory Commission Piping Review Committee, Evaluation for Potential for Pipe Breaks," November 1984. Thus, the probability or likelihood of large pipe breaks occurring in the primary coolant system loops of the subject CE0G plants is sufficiently low such that the dynamic effects associated with postulated pipe breaks need not be included in the l design basis. However, when referencing CE0G Topical Report CEN-367-A as a technical basis for applying LBB to primary loop piping licensees l must submit information which demonstrates that leakage detection systems installed at specific facility are consistent with Regulatory Guide (RG) 1.45, " Reactor Coolant System Pressure Boundary Leakage i Detection Systems."

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. l I I.. Evaluation of the Leakaae Detection Systems A. Purpose The purpose San Onofre of this Units evaluation 2 and 3 Reactor is to analym Coolant the Boundary Pressure capabilityRCPB)

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leak detection systems to meet Regulatory Guide (RG) 1.45,

" Reactor Coolant System Pressure Boundary Leakage Detection Systems."

8. Background A limited amount of leakage is expected from pressure-containing '

components forming the RCPB which consists of the reactor coolant system (RCS) and associated components. Components subject to leakage include valves, pump shaft seals, valve stem packing,  :

flanges, and gaskets. RG 1.45 requires this type of leakage, to j the extent practical, be monitored, limited, and isolated from containment by routing, collecting, and monitoring in closed systems, such as tanks or sumps. This type of leakage is termed

" identified leakage," and is separated from any other type of ,

leakage which is termed " unidentified leakage." Unidentified '

leakage, which includes steam generator or tube sheet and intersystem leakage, etc., is monitored by several methods / devices as required by RG 1.45. The leakage detection system is-designed I to identify changes in unidentified leakage.

RG 1.45 requires three methods for monitoring RCPB leakage into -

containment. Two methods which are specified by RG 1.45 are 1) containment sump level / inlet flow rate and 2) containment airborne ,

particulate radioactivity. The third method was left for the licensee to choose from either one of the two methods given in RG 1.45. The third method chosen by Edison for monitoring RCPB leakage was containment airborne gaseous activity.

C. Consistency with Regulatory Guide 1.45 The Technical Specifications (TSs) provide part of the technical basis for the San Onofre Units 2 and 3 operating licenses.

Section 3/4.4.5.1 of the TSs Bases states:

"The RCS leakage detection systems required by this specification are provided to monitor and detect leakage from the Reactor Coolant Pressure Boundary. These detection systems are consistent with the recommendations of Regulatory Guide 1.45, ' Reactor Coolant System Pressure Boundary Leakage Detection Systems,' May 1973."

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The RCS leakage detection systems are also described in the San Onofre Units 2 and 3 Updated Final Safety Analysis Report (UFSAR) i Section 5.2.5 which states in part: J

...For leaks of 1 gal / min or greater, other than controlled l leakage sources, the RCPB leak detection systen is capable l

of detecting leakage and of determining the leakage rate as l required by NRC General Design Criterion 30."

"The RCPB leak detection system provides means for identifying the source for reactor coolant leakage to the '

extent practicable as required by NRC General Design Criterion 30." i "The RCPB leak detection system is consistent with the recommendations of NRC Regulatory Guide 1.45."

The design of the San Onofre leakage detection systems was ,

evaluated and accepted by the NRC as documented in NUREG-0712, ,

" Safety Evaluation Report related to the operation of San Onofre Nuclear Generating Station Units 2 and 3," dated February 1981.

Section 5.2.5 of this Safety Evaluation Report states in part:

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...The RCPB leakage detection systems are diverse and the applicants' design conforms to the requirements of Regulatory Guide 1.45 as noted above." ,

' l "We conclude that the San Onofre 2 and 3 design provides i reasonable assurance that primary system leakage will be i detected as required by General Design Criterion 30 and is  !

acceptable."

D. San Onofre Compliance with Regulatory Guide 1.45 The intent of the Regulatory Positions in RG 1.45 are met by the San Onofre Units 2 and 3 leakage detection systems. Table 1 summarizes the method of Edison's compliance to RG 1.45.

Regulatory Positions C.1, C.2, C.3, C.4, C.6, C.8, and C.9 are met without exceptions. Regulatory Positions C.5 and C.7 are met by i

alternative methods of compliance which are justified and )

discussed below: 4 o Regulatory Position C.5 requires the sensitivity and response time of each detection system for unidentified leakage to be adequate to detect a leakage rate, or its equivalent, of 1 gpm in one hour or less. For San Onofre Units 2 and 3, the particulate channel and sump level / flow methods of detection have the capability of detecting 1 gpm in liquid leakage within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Compared to the

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. . particulate channel, the gas channel method of leakage detection is less responsive due to the long half-life (5.3 days) of the predominant noble gas isotope (133Xe) in the reactor coolant. The existing gas channel response time has been estimated to range from 10 to 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> depending on i

length of operation, percent failed fuel, and the background l noble gas concentrations inside containment.

l l However, the gas channel is more responsive to leakage from l the pressurizer steam space due to noble gas concentrations i in the pressurizer steam space reaching concentrations up to i 25 times that in the liquid coolant. The gas channel is l capable of detecting pressurizer steam space leakage rates as low as 1 gpm within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.

The shortcomings of the gas channel method of leakage i

detection had been acknowledged by the NRC staff in a l memorandum dated June 5, 1978, from P. Gurney (Reactor Systems Branch) to T. Novak, Chief (Reactor Systems Branch),

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Subject:

" Radiation Monitor Response for Reactor Coolant 1 Pressure Boundary Leakage Detection." The memorandum l recognizes that factors exist which "...by themselves or in the right combination can render the radiation monitors ,

useless as leak detectors." These factors include RCS activity, background radiation levels, isotope plateout, and alarm setpoints.

The Instrumentation Society of America (ISA) in Standard ISA-S67.03, " Standard for Light Water Reactor Coolant Pressure Boundary Leak Detection," 1982, Section 2, also acknowledges the shortcomings of leak detection systems and states "... It is recognized that some systems other'than sump monitoring may not be capable of meeting the requirements during certain plant operating conditions. In these cases, these systems shall be designed for leakage sensitivity as high as reasonably achievable."

The existing Units 2 and 3 leakage detection systems are designed for leakage sensitivity as high as reasonably achievable which meets the intent of RG 1.45, Position C.5.

Additionally, a Design Change Package is in progress to replace the existing gas channel monitor with a state-of-the-art, more responsive design. It is Edison's intent to implement this design change by the end of 1996.

o Regulatory Position C.7 requires that indicators and alarms for each leakage detection system should be provided in the

main control room, procedures for converting various indicators to a common leakage equivalent should be available to operators, and calibration of these indicators should account for needed independent variables.

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The intent of Regulatory Position C.7 related to procedural requirements is met by a justifiable alternative.

Converting radiation monitor channel readings to a " common leakage equivalent," does not exist in procedures because alarms for leakage detection are provided by systems other than the leakage detection systems themselves. The results of Edison engineering calculation A-92-J-002 indicate that the relationship between changes in gas or particulate radiation monitor readings and changes in Reactor Coolant System (RCS) leakage depend on a number of factors which are subject to change with time. Radiation monitor reading changes do not have a direct correlation with RCS changes.

Radiation monitor indications of increases in RCS leakage are used to initiate specific actions but not for quantifying RCS leakage. This is due to the dependence of the indications / readings on a number of plant operating conditions and the general uncertainty of the results from the conversion of these readings to equivalent leakage.

As an alternative method, upon activation of a high activity alarm or operator knowledge of a trend indicative of increasing RCS leakage, San Onofre Units 2 and 3 procedures direct and provide operators the methods for locating and quantifying the leakage system by system (e.g , RCS, Chemical & Volume Control, or Steam Generator). The procedure additionally requires that a liquid inventory balance be performed.

The Regulatory Position C.7 alarm requirement for leakage detection is met by transmitting alarm signals provided by other systems to the annunciator and computer systems. The alarms in these other systems have their own design bases requirements distinct from the leakage detection systems.

As such, these alarms are not seismically qualified for the purpose of leak detection, but the leak detection monitors and their meters and recorders are seismically qualified as required by Regulatory Position C.6. Therefore, indications of changes in containment sump level and particulate / gas channel readings would be available to the operators following a seismic event. The operating procedures for a seismic event require immediate action to perform a RCPB leakage evaluation which does not depend on leak detection system alarms. Activation of any specific set of {

alarms / indications on the Seismic Instrument panel L-167 I requires surveillances for identifying and quantifying any increase in RCPB leakage. If the seismic indication / alarm involves an operating basis earthquake (0BE) or greater, procedures require a thorough inspec'c ion of the RCS, steam generators, reactor coolant pumps, and all RCS piping. <

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. The Regulatory Position C.7 requirement to account for i

needed independent variables in the calibration of the indicators is met without exception.

E. Conclusions The requirements for the leakage detection systems are included in the Technical Specifications for San Onofre Units 2 and 3. The ,

leakage detection systems were evaluated by the NRC during the original plant licensing and were determined to meet the '

guidelines of Regulatory Guide 1.45. Since San Onofre Units 2 and 3 are bounded by the CE0G analyses and the leakage detection systems are capable of detecting the specified leakage rate, the dynamic effects associated with postulated pipe breaks in the primary coolant system piping can be excluded from the licensing and design basis for the San Onofre units.

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TABLE 1

• • SU M RY OF THE REGULATORY GUIDE 1.45 COMPLIANCE San Onofre Units 2 and 3 REGULATORY RG 1.45 POSITION COMPLIANCE METHOD OF COMPLIANCE REFERENCES C.1 Yes. No RCS liquid inventory control; UFSAR Sections exception. Containment sump flow rate 5.2.5.1.5 and and level. 5.2.5.1.3 C.2 Yes. No Containment atmosphere UFSAR Sections exception. radiation indicators; 5.2.5.2.1 and Containment area sump and 5.2.5.4 level instrumentation.

C.3 Yes. No Containment sump and flow UFSAR Sections exception monitoring; airborne gaseous 5.2.5.1 and and particulate radioactivity 5.2.5.2 monitoring.  ?

C.4 Yes. No Decreasing Volume Control UFSAR Section exception. Tank level; increasing 5.2.5.1.11 charging flow rate; t increasing Component Cooling Water radioactivity.

l C.5 Intent met. Monitor sensitivity and NRC Interoffice

[ Alternative response time met NRC memorandum dated

! justified, expectations. A design 6/5/78, Edison improvement is in process. Calculation l

A-92-J-002 C.6 Yes. No Leak detection systems and San Onofre Units exception. their indications are 2/3 Consolidated seismically qualified and Control Data will perform their intended Base Instrument functions regardless of Index 90010A operating conditions of any ,

associated alarm features. l C.7 Intent met. Procedures direct and provide UFSAR Section Alternative operators methods to locate 5.2.5 justified, and quantify RCS leakage and to perform a reactor coolant i inventory balance. Alarm i requirement is met by l transmittal of alarm signals l provided by other systems to l the annunciator and computer i systems.

C.8 Yes. No Surveillance testing TSs 4.4.5.1, l exception requirements. 4.4.5.2.1 and i

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, C.9 Yes. No TechnicalSpecifications(TS) TSs 3.4.5.1 and l exception, in compliance with RG 1.45. 3.4.5.2 j Page 7 of 7 l

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