ML17054B661
| ML17054B661 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 05/15/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17054B660 | List: |
| References | |
| NUDOCS 8505290756 | |
| Download: ML17054B661 (8) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALAUTION BY THE OFFICE OF NUCL A REA OR REGULA ION RELATED.TO RELIEF FROM HE ASME BOILER AND PRESSURE VESSEL CODE SECTION XI RUL S OR NSERVICE INSP CTION OF NUCL AR POWER PLANT COMPONENTS - DIVISION I
'NINE MILE POINT NUCLEAR ON N
1 DOC NO. 50-220
- 1. 0 INTRODUCTION On May 7, 1985, leakage was observed in the water box to tubesheet weld of containment spray heat exchanger 8111 while performing a surveillance test in accordance with Section 4.3.7.c of the Technical Specifications.
The heat exchanger was declared functionally operable but administratively inoperable.
On May 8, 1985, similar leakage was found while performing surveillance testing on heat exchanger 8122.
It was also declared functionally operable but administratively inoperable.
With two heat exchangers out of service, the Technical Specifications, Section 3.3.7.c require the components to be returned to the operable status within 7 days.
In addition, crack indications on the remaining two heat exchangers weve found on May 8 and 9, 1985.
- However, no leakage was observed.
Section 3.2.6.a. 1 of the Technical Specifications requires quality group A, B, and C components to satisfy the requirements of Section XI of the ASME Boiler Pressure Vessel Code as applied to Class 1, 2, and 3 equipment in order to be considered
- operable, except where relief has been granted by the Commission pursuant to 10 CFR 50, Section 50.55 a(g)(6)(i).
The con-tainment spray heat exchangers are classified as quality group B.
Section XI, paragraph IWA-4120 requires that repairs shall be performed in accordance with the original design specification and construction code of the component or system.
The original code of construction for these heat exchangers is ASME,Section III, Class B and Section VIII.
In a letter dated May 13,
- 1985, Niagara Mohawk Power Corporation requested relief from the ASME Boiler and Pressure Vessel
- Code,Section XI, Paragraph IWA-4120 requirements in accordance with 10 CFR 50.55a(g)(6)(i).
The licensee provided supplemental information in a letter dated May 14, 1985.
Section 50.55a(g)(6)(i) allows the Commission to determine that compliance with Code requirements are impractical and to grant relief from those requirements, to impose alternative requirements as authorized that will not endanger the public health and safety, and to ascertain if relief is in the public interest by not imposing the burden of, complying with code requirements on the 8505290756 8505i5 PDR
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The licensee requested the relief since a permanent repair in accordance with Section XI was impractical considering the complexity of the heat exchanger weldment.
- 2. 0 EVALUATION Since the tubesheet material (aluminum bronze SB-161, alloy 614) is very difficult to weld and replacement equipment is not available, the licensee performed a temporary repair involving only the steel shell of the heat exchangers
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This consisted of welding str aps between the water boxes and shel,l.
This welding was performed in accordance with ASME Section III.
The repair was performed to preclude the potential for gross structural failure of the heat exchangers by using the straps to carry the design loads.
A stress analysis of the welded straps was performed by the licensee to ensure the structural integrity of the heat exchanger.
In the licensee's
- analysis, the straps are considered as linear type supports.
The analysis conservatively assumed that the potential cracked welds between the shell and the tubesheet carried no load.
The result of the licensee's analysis showed that the stress level in the straps under the maximum operating pressure loading condition (210 psi) is within the ASME Code Section III, Subsection NF allowables.
The licensee stated that loads due to seismic,
- thermal, and deadweight were also considered and were found to be negligible.
Based on a review of the information provided by the licensee, we have determined that the licensee's analysis provided a reasonable assurance that the design of the welded straps is capable of maintaining the structural integrity for the interim period until a permanent fix is implemented.
The licensee has performed complete visual examinations of the shell side to tubesheet and tubesheet to water box welds.
In addition, liquid penetrant examinations have been performed on all tubesheet to -water box welds as well as both shell side to tubesheet welds, in the areas not covered by the repair straps, on heat exchanger ¹lll. All crack like indications are located on the water box side of the heat exchangers.
Multiple indications have been found in each water box to tubesheet welds; however, only one long crack (maximum of 10 inches in length) has been identified on each of the two leaking heat exchangers.
The licensee's estimate of leakage has been based on a crack extending the whole length between the repair straps (about 14 inches),
considering the crack opening at this location, the maximum estimated leakage for the thru-wall flaw is estimated to be between 15 and 25 gpm.
E Considering the repair straps and the fact that the heat exchangers will be tested
- monthly, we conclude that increases in leakage from the current rate of a few drops per minute, to those identified from the leakage analysis would be readily apparent and the estimated maximum leakage rates appear reasonable.
- 2. 2
~Sstems The licensee has indicated that the leakage through the welds consists solely of uncontaminated raw water used as the coolant on the tube side of the heat exchanger.
The torus water is pumped through the shells which are not degraded.
The licensee has indicated to the staff that the primary functions of the heat exchangers, namely containment spray and suppresion pool cooling, would only be very slightly affected by a leak of 30 gpm (1X of the design flow, by a leak of 30 gpm of raw water from a given heat exchanger.)
There are four containment spray heat exchangers.
Each has 100X capacity.
The licensee stated the only effect of the postulated leakage on postulated post accident operation would be to slightly lengthen the overall operating times for the spray.
In the previous section, the staff has agreed that the maximum postulated leakage estimate appears reasonable.
The staff has reviewed the proposed increase in surveillance frequency from quarterly to monthly, and finds it acceptable.
The licensee has proposed a
leakage limit of 30 gpm to consider a heat exchanger operable.
The staff requires and the licensee has agreed that any leakage of raw water be limited to 7 1/2 gpm for a heat exchanger.
Me feel this.limit would be representative of degradation of the heat exchanger to point where it should be declared inoperable.
This represents a margin of approximately 2 to 3 times to the case that was analyzed.
The licensee has verified that the floor drains located in the vicinity could accommodate the postulated leakage.
The removal of water is limited by pumping capacity of 60 gpm.
This is well in excess of the postulated leakage.
The staff finds the proposed surveillance program for the heat exchangers acceptable and conclude that containment spray/suppression pool cooling system operability would not be significantly impaired in postulated post accident functions.
- 3. 0 CONCLUSIONS We have concluded that relief from the ASME Boiler and Pressure Vessel
- Code,Section XI, Paragraph IWA-4120, requirement (that repairs shall be performed in accordance with the Owner's Design Specification and Construction Code of the component or system) is justifiable.
The interim repairs to ensure structural integrity have been in accordance with the design allowables for Section NF of Section III of the ASME Boiler and Pressure Vessel Code.
The increase in surveillance testing and leakage limit of 7 1/2 gpm for each heat exchanger coupled with the interim repairs performed and the supporting analyses provide reasonable assurance that the system would be able to perform its intended design function in a post accident condition.
- Further, the licensee has committed to replace the heat exchangers during the Spring 1986 refueling outage.
- Further, should unacceptable degradation occur in the interim or replacement not be possible at the outage because of delivery, the licensee has committed to develop and qualify a suitable procedure for replacement of the defective welds.
Therefore, relief may be granted pursuant to paragraph 10 CFR 50.55a(g)(6)(i) based on our finding that certain requirements of Section XI of the ASME Boiler and Pressure Vessel Code are impractical.
The staff concluded, based on the considerations above, that the granting of this relief is authorized by law and will not endanger life or proper ty or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that results if the requirements were imposed on the facility.
This relief is effective through the Spring 1986 refueling outage.
Principal Contributors:
R.
Hermann J.
Lane R.
Li D. Smith G.
Thomas Dated:
May 15, 1985
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