B12195, Forwards Reviews for Isap Topic 1.27, Compliance W/10CFR50.46 & Isap Topic 1.28, Reactor Coolant Pump Trip. Review Includes Discussion of Safety Objective & Evaluation of Plant Design for Issue Addressed

Forwards Reviews for Isap Topic 1.27, Compliance W/10CFR50.46 & Isap Topic 1.28, Reactor Coolant Pump Trip. Review Includes Discussion of Safety Objective & Evaluation of Plant Design for Issue Addressed

ML20210Q368
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	09/18/1986
From:	Opeka J, Sears C CONNECTICUT YANKEE ATOMIC POWER CO.
To:	Charemagne Grimes Office of Nuclear Reactor Regulation
References
B12195, NUDOCS 8610060934
Download: ML20210Q368 (8)

Text

.- s CONNECTICUT YANKEE ATOMIC POWER COMPANY B E R LI N. CONNECTICUT P O Box 270 HARTFORD. CONNECTICUT 06141-0270 T ELE PHONE 203-66s-5000 September 18,1986 Docket No. 50-213 B12195 Offic.e of Nuclear Reactor Regulation Attn: Mr. Christopher I. Grimes, Director Integrated Safety Assessment Project Directorate Division of PWR Licensing - B U.S. Nuclear Regulatory Commission Washington, D.C. 20555

References:

(1) 3. F. Opeka letter to C. I. Grimes, dated May 17,1985.

(2) H. L. Thompson letter to J. F. Opeka, dated July 31,1985.

Gentlemen:

Haddam Neck Plant

. Integrated Safety Assessment Program in Reference (1), Connecticut Yankee Atomic Power Company (CYAPCO) provided a proposed scope for the Integrated Safety Assessment Program (ISAP) review of the Haddam Neck Plant. In Reference (2), the Staff formally issued the results of the ISAP screening review process, establishing the scope of ISAP for Haddam Neck and initiating issue-specific evaluations. Reference (1) also indicated that for each issue or topic included in ISAP, CYAPCO would provide a discussion of the safety objective and an evaluation of the plant design with respect to the issue being addressed to identify specific items to be considered in the integrated assessment. In accordance with this commitmeit, reviews for the following ISAP topics are attached:

1) ISAP Topic No.1.27 " Compliance with 10CFR50.46"

2) ISAP Topic No.1.28 "RCP Trip" If you have any questions concerning the attached reviews, please contact us.

Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY J. F. Opeka '

Senior Vice President gtA"183M St83$A3 &c By: C. F. Sears 1

Vice President

Docket No. 50-213 B12195 Haddam Neck ISAP Topic No.1.27 Compliance with 10CFR50.46 September 1986

Haddam Neck ISAP Topic No.1.27 Compilance with 10CFR50.46 I. Introduction Small break loss of coolant accidents (LOCAs) are one of several categories of events which, if not successfully mitigated, could lead to core melt. To ensure that each plant has the capability to provide coolant after a small break LOCA, redundant high pressure injection pumps must be provided as part of the plant's emergency core cooling system (ECCS).

Haddam Neck has two diverse means of providing make-up.after a small break LOCA. Two 360 gpm centrifugal charging pumps are part of the chemical and volume control system (CVCS). One of these pumps is contiriually running during normal operation and the standby pump will start on a safety injection (SI) signal. Two high pressure safety injection (HPSI) pumps which are part of the Haddam Neck ECCS are also available for high pressure cooling injection. These pumps automatically start on an SI signal.

To ensure that these redundant and diverse means of high pressure injection are adequate to provide sufficient make-up for all small break LOCAs in all locations, extensive analysis was undertaken by CYAPCO for the Haddam Neck Plant.

II. Review Criteria

1. 10CFR50.46

2. NUREG-0737, II.K.3.31 Ill. Related Topics / Interfaces ISAP Topic No.1.18 "RCP Seal Cooling Modifications" ISAP Topic No.1.23 " Reactor Coolant Pump Trip" ISAP Topic No. 2.15 - "Long-Term Small Break LOCA and ECCS Modifications" IV. Evaluation Federal Regulation 10CFR50.46 requires each light-water reactor to be equipped with an ECCS which can provide cooling for all postulated small break LOCAs in the reactor coolant system (RCS). This project is an engineering evaluation of the Haddam Neck ECCS to ensure that all small break LOCAs can be successfully mitigated, thus demonstrating compliance with 10CFR50.46.

CYAPCO has performed plant-specific calculations which show that the Haddam Neck ECCS is in compliance with 10CFR50.46 and is capable of mitigating all small break LOCAs in the injection phase (Reference 1).

These calculations only credited the HPSI pumps and did not include the charging pumps. The best estimate LOCA analysis for Haddam Neck (Reference 2) showed that one HPSI or one charging pump is adequate for all small break LOCAs for both the injection and recirculation phases except for a certain range of break sizes (0.02 to 0.045 f t.2) n the RCS loop 2 cold leg and for breaks of less than 0.038 f t.2 in the charging line.

For these breaks the ECCS was not capable of providing adequate core cooling in the high pressure recirculation mode. At the time the Haddam Neck Probabilistic Safety Study (PSS) was performed, only the charging pumps were able to provide high pressure recirculation and the only injection path was via the loop 2 cold leg. Since that time procedural modifications have been made to enable the HPSI pumps to provide high pressure recirculation in the event that the charging pumps are unavailable or inadequate (i.e., the small break LOCA occurs in the loop 2 cold leg).

These modifications allow the operator to align the HPSI pumps to take suction from the residual heat removal (RHR) pumps during the recirculation mode and inject coolant into the unfaulted cold legs. This method of recirculation is not single-failure proof, however. A temporary exemptior. request has been granted for Cycle 14 operation. See Reference 8.

With respect to meeting the plant-specific small break LOCA calculations required by 10CFR50.46, CYAPCO has performed these calculations for the injection phase of the small break LOCA using procedural and analytical methods which conform to the criteria set forth in 10CFR50.46.

The Haddam Neck best estimate analysis shows that the ECCS is adequate for all small break LOCAs in the recirculation phase except for the limited range of breaks previously described. This analysis used the same methods and computer code which were employed in the analysis documented in Reference I with some minor changes. These changes only affect the analysis of the injection phase. Because of the large flow capacity of the HPSI pumps, the conclusion based on the best estimate analysis would not differ from that based on the licensing analysis which was performed to meet the criteria specified in 10CFR50.46 for the small break LOCA response during the recirculation mode.

V. Conclusions Based on the aforementioned, CYAPCO has determined that further analyses of the recirculation mode for small break LOCAs to show compliance with 10CFR50.46 are unwarranted. Plant modifications resulting from this small break LOCA analysis are being evaluated  !

separately as ISAP Topic No. 2.15. These modifications will address ECCS l performance considering the single failure criterion. Therefore, CYAPCO l considers this ISAP topic closed, recognizing that additional actions will be taken under the scope of ISAP Topic No. 2.15. l VI. References 1

1. W. G. Counsil letter to W. A. Paulson, " Calculative Methods for the ,

Northeast Utilities Small treak LOCA ECCS Evaluation Model '

(Proprietary)," dated August 23,1984.

2. " Connecticut Yankee Best Estimate LOCA Analysis," LOCA Analysis Section/ Safety Analysis Branch, NUSCO, NUSCO-150, February 1986.

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3. W. G. Counsil letter to D. M. Crutchfield, "Haddam Neck Plant - TMI Item II.K.3.30 - Revised Small Break LOCA Analysis," dated April 14, 1983.

4. W. G. Counsil letter to D. M. Crutchfield, "Haddam Neck Plant - TMI Item II.K.3.30 - Revised Small Break LOCA Analysis," dated December 12,1983.

5. W. G. Counsil letter to D. M. Crutchfield, "Haddam Neck Plant, TMI Action Item II.K.3.30 - Response to Questions on Small Break LOCA Evaluation," dated June 19,1984.

6. W. G. Counsil letter to 3. A. Zwolinski, "Haddam Neck Plant Small Break LOCA Topical Report, TMI Action Plan Items II.K.3.5, II.K.3.30 and II.K.3.31," dated December 20,1984.

7. 3. F. Opeka letter to C. I. Grimes, "Haddam Neck Plant -

Probabilistic Safety Study LOCA Analyses," dated April 10,1986.

8. F. 3. Miraglia letter to 3. F. Opeka, " Exemption From Single Failure Criterion (GDC 35)- Haddam Neck Plant", dated April 28,1986.

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Docket No. 50-213 B12195 Haddam Neck ISAP Topic No.1.28 Reactor Coolant Pump Trip 1

l l

September 1986

( . .

Haddam Neck ISAP Topic No.1.28 Reactor Coolant Pump Trip I. Introduction Small break loss of coolant accidents (LOCAs) are one of several categories of events which, if not successfully mitigated, could lead to core melt. Generic evaluations made by the PWR vendors have shown that either delayed trip or continuous operation of the reactor coolant pumps (RCPs) during a small break LOCA may result in insufficient core cooling.

Subsequent NRC review of these evaluations have resulted in the same conclusion. See Reference 1.

II. Review Criteria

1) 10CFR50.46 " Acceptance Criteria for ECCS for LWR's"

2) Generic Letter 86-06 " Implementation of TMI Action Item II.K.3.5,

' Automatic Trip of Reactor Coolant Pumps'"

3) NUREG-0737 Item II.K.3.5 III. Related Topics / Interfaces

1) ISAP Topic No.1.27 " Compliance with 10 CFR 50.46"

2) ISAP Topic No.1.18 "RCP Seal Cooling Modifications" IV. Evaluation The proposed project is the design and installation of circuitry which would automatically trip all four RCPs on detection of a small break LOCA.

In 1984 CYAPCO submitted a topical report (Reference 2) to the NRC which documented a small break LOCA analysis for Haddam Neck. The conclusion of this analysis was that with or without the RCPs runmng the HPSI pumps are capable of providing sufficient injection flow for all small break LOCAs. This analysis did not evaluate the charging pumps as a means for mitigating small break LOCAs. The charging pumps will automatically start on a safety injection signalif offsite power is available and can be manually started af ter a loss of offsite power.

Additional analyses were also performed to assess the operation of the RCPs on small break LOCA performance with only charging available.

This analysis demonstrated that for break sizes 0.02 to 0.01 f t.4, the RCPs '

must be tripped no later than one minute following a Safety Injection Actuation Signal (SIAS). Break sizes greater than 0.02 ft.Z result in unacceptable consequence regardless of the status of the operation of the RCPs. While there will be a range of smaller breaks below 0.01 f t.2 that will produce acceptable results with the RCPs running, the analysis to identify this smaller range of breaks was not pursued. Thus, in general it can be concluded that for the case where only the charging pumps are available, the RCPs should be tripped following an SIAS to assure acceptable small break LOCA performance.

F .. .

Two of the four RCPs at Haddam Neck automatically trip on a LOCA. The Westinghouse Owners' Group Emergency Response Guidelines are currently in place and provide improved discrimination between LOCA and non-LOCA Events. This directs the operator to allow two RCPs to trip either automatically or manually, while allowing the other two to continue operation. This will remain the practice pending NRC review of our small break LOCA analysis, which concluded that there is no significant impact on the peak clad temperature whether the RCPs are tripped during a LOCA or not.

V. Conclusions CYAPCO has determined that with or without the RCPs running, the HPSI pumps are capable of assuring acceptable ECCS performance for all small break LOCA's. However, in the highly unlikely event that only the charging system is available, the RCPs must be tripped on an SAIS following a small break LOCA to assure acceptable ECCS performance.

The preceding analysis constitutes the closure of this ISAP topic, pending NRC review of CYAPCO's Small Break LOCA Analysis.

VI. References

1. " Generic Assessment of Delayed Reactor Coolant Pump Trip during Small Break Loss of Coolant Accidents in Pressurized Water Reactors," NUREG-0623, November 1979.

2. W. G. Counsil letter to W. A. Paulson, "Haddam Neck Small Break LOCA Topical Reports", Bil231, dated August 23,1984.

3. 3. F. Opeka letter to C. I. Grimes, "Haddam Neck Probabilistic Safety Study - Summary Report and Results", B12020, dated March 31,1986.

4. W. G. Counsil letter to 3. A. Zwolinski, "Haddam Neck Plant - Small Break LOCA Topical Report - TMI Action Plan Items II.K.3.5, II.K.3.30, and II.K.3.31," dated December 20,1984.

5. 3. F. Opeka letter to C. I. Grimes, "Haddam Neck Plant, Probabilistic Safety Study - Summary Report and Results," dated March 31,1986.

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