ML20206B884
| ML20206B884 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 04/08/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20205N261 | List: |
| References | |
| NUDOCS 8704100073 | |
| Download: ML20206B884 (4) | |
Text
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UNITED STATES 8"
7 NUCLEAR REGULATORY COMMISSION o
gE WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AN EXEMPTION FROM CERTAIN REQUIREMENTS OF APPENDIX J TO 10 CFR PART 50 IOWA ELECTRIC LIGHT AND POWER COMPANY CENTRAL IOWA POWER COOPERATIVE CORN BELT POWER COOPERATIVE DUANE ARNOLD ENERGY CENTER DOCKET NO. 50-331
1.0 INTRODUCTION
On August 7, 1975, the NRC requested the licensee (Iowa Electric Light and Power Co.) to review its containment leakage test program for Duane Arnold Energy Center (DAEC) for compliance with the requirements of 10 CFR 50, Appendix J.
In a letter dated October 13, 1975, the licensee identified several areas in the current Technical Specifications (TS) which deviated from the requirements of Appendix J.
Subsequently, through submittals and telephone discussions, the licensee requested that certain test methodology, components and penetrations be exempted from Appendix J requirements. The NRC staff with its consultant, the Franklin Research Center (FRC), reviewed these submittals and prepared a Safety Evaluation Report (SER). The SER was forwarded to the licensee by letter dated January 17, 1984.
By letter dated October 29, 1984, as supplemented December 7,1984 and April 22 and July 12, 1985, the licensee requested an exemption from the Type C testing requirements for containment spray isolation valves.
In the December 7,1984 letter, the licensee submitted a summary status of Appendix J issues resulting from the previous staff review:
Torus Drain Line and RCIC stean supply line modifications to allow testing in accordance with Appendix J requirements are to be completed by the cycle 7/8 refueling outage.
Valves M0-4423, M0-2238, M0-2400 are now leak testable in accordance with Appendix J.
The Technical Specifications will be revised accordingly, and requested the following exemptions from Appendix J:
Exemptions from Appendix J testing requirements for containment spray isolation valves and torus drain line flanges.
The following evaluation addresses the acceptability of the licensee's Appendix J exemption requests.
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. 2.0 EVALUATION 2.1 Containment Spray Isolation Valves The licensee requested an exemption from the requirements of Type C testing for containment spray isolation valves, MOV-1902, 1933, 2000 and 2006.
The containment spray subsystem, which delivers water to the spray headers through low pressure coolant injection (LPCI) loops, is an integral part of the residual heat removal (RHR) system. The subsystem consists of two 10" diameter lines to the spray headers in the drywell and two 4" diameter lines to the spray headers on top of the suppression pool.
Each line has two isolation valves outside containment that are normally closed. The subject valves, M0V-1902, 2000, are the inboard valves which isolate the lines to the drywell spray headers and MOV-1933, 2006 are the inboard valves which isolate the lines to the torus spray headers. These valves are manually opened following a LOCA to divert the LPCI pump flow from the reactor vessel to the spray headers after core cooling requirements have been satisfied.
FRC has previously reviewed these valves and found that, if any of them leak through the packing or body-to-bonnet seals, the leakage will cause containment air to reach the outside atmosphere. Consequently, Appendix J requires that these inboard valves be Type C tested. However, since the packing and body-to-bonnet seals are the only potential sources of leakage, the testing may be limited to these potential areas.
The containment spray isolation valves do not receive containment isolation signals, are required to remain closed for the duratic.i of the accident when sprays are not required and are single active failurs. protected.
In a letter dated July 12, 1985, the licensee explained that tN existing configuration of the valves and the associated piping allows no practical means of testing these inboard valve seals. These inboard valves are located outside the drywell and the torus. There is no flange or other valve between the valve and the spray header.
To pressurize the inboard valve from~the containment side would require an additional inboard valve inside containment and a test connection. Due to limited space in the drywell, modifying the containment spray piping is undesirable. The licensee has proposed the following alternate testing of these valves in lieu of Type C testing:
(1) performing a soap bubble test on the valve body-to-bonnet seals during Type A testing and initiate corrective actions if leakage is detected.
(2) pressurizing between the inboard and outboard valves at the same frequency required for Type C tests to indicate the general condition of the valves.
The staff has reviewed the licensee's submittals and finds Type C testing of these valves to detect potential body-to-bonnet leakage is necessary.
However, because of the difficulty in modifying the system due to limited space in the drywell, the staff considered the alternative test methods in lieu of Type C testing. Through the submittals and telephone conversations
em.
. with the licensee, the staff realizes that these inboard valves are designed at zero-leakage in the body-to-bonnet seals.
If any leak through valve packing or seals is detected during Type A testing, the deteriorated packing and seal materials will be replaced.
Furthermore, the piping around the valves is normally filled with water and water will flow into the contain-ment to the spray header during accident conditions. Consequently, the possibility of containment air leakage through the body-to-bonnet seals would be minimized because of the water seal in the valve. Based on the above discussion, the staff concludes that the licensee requested exemption from Type C testing requirements for the inboard valve body-to-bonnet seals and its proposed alternative test methods summarized above and as detailed in the submittals are acceptable.
2.2. Penetrations N-231A and B The licensee also requested an exemption from Type B testing requirements for flanges connecting the torus and torus drain line (penetrations N-231A and B).
The ' torus drain line is connected to the torus at two locations with flanges sealed with FLEXITALLIC spiral wound (inorganic) gaskets. The torus drain connections afford no mechanism for performing Type B testing. To perform Type B testing would require replacing the existing flanges and gaskets with flanges designed for double 0-ring (organic) gaskets. The licensee stated that such a design modification would downgrade the integrity of the containment and requested an exemption from Type B testing with the following justification:
(1) The gasket and flange assemblies will be exposed to the Appendix J required Type A Containment Integrated Leak Rate Test (CILRT) pressure.
Leakage through flanges could be identified and correcteo.
(2) A constant pressure of approximately 5 psi (torus water head) would detect gross leakage of the gaskets.
(3) The flanges are rarely disassembled for maintenance or access. The probability of leakage through the flanges would not increase.
(4) The torus water provides a water seal for the submerged torus drain line.
If the existing flanges should leak, the leakage rate would not be sufficient to expose the connection to the containment atmosphere within 30 days following a postulated accident.
The staff has reviewed the licensee's submittals and finds the torus drain line is below the torus water level and is water sealed. Since the licensee stated that the water seal will be maintained for 30 days folloving a postulated accident, there is no potential air leakage from containment through the falanges. Consequently, no Type B testing on the flanges is required and no exemption from Appendix J is required.
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3.0 CONCLUSION
S From its review of the licensee's submittals, the staff concludes the following:
(1) The licensee's proposals to exempt containment spray isolation valves from Type C testing and to use the alternative testing methods described above are acceptable.
(2) The licensee's proposed exemption from Type B testing for the flanges connected to the torus drain line is not required since the system is water sealed.
Principal Contributors:
J. Guo Dated: April 8,1987
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