ML20058K540
| ML20058K540 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 06/10/1974 |
| From: | Wachter L NORTHERN STATES POWER CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| IEB-74-04, IEB-74-4, NUDOCS 9102120448 | |
| Download: ML20058K540 (3) | |
Text
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NORTHERN STATES POWER COMPANY MIN N E A POLI S. MIN N E GOTA SS401 June 10, 1974 Mr J G Keppler, Regional Director r
Directorate of Regulatory Operations g
,rq Region III
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799 Roosevelt Road
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Glen Ellyn, Illinois 60173 go g
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0 Dear Mr Keppler-
-6 MONTICELLO NUCLEAR GENERATING PLANT gg i
Docket No. 50-263 License No. DPR-22
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In accordance with Item B.3 of Directorate of Regulatory Operati s
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Bulletin 74-4 the following information is submitted-f The temporary second stage piston stem locking nut modifications a.
described in the bulletin were completed on April 24, 1974.
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b.
The attached table summarizes other Target Rock relief valve modifications which have been completed on the eight valves presently installed.
It is our understanding that there are
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no other recommended modifications.
Yours very truly, Y
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L J nachter, Vice President Power Production 6 System Operation LJW/ma ec:
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, Directorate of Licensing p/
F Minnesota Pollution Control Agency
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Attn: E A Pryzina
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REGULATORY DOCKET FILE COPY - 5262 i
Summary of Modifications Made to the Original Design of Target Rock Safety / Relief Valves at the Monticello Nuclear Generating Plant Summary of Change References l'
1.
Increased the size of the orifice in the second stage piston from Monticello Semi-Annual O.016 inch diameter to 0.035 inch diameter and increased the size Operating Report No. 2, of the orifice in the main valve piston from 0.0625 inch diameter
- p. VII-4 to 0.076 inch diameter.
This modification decreases the closing time of the valves and reduces the pressure reset band.
2.
The set-pressure adjusting springs were replaced with springs Monticello Semi-Annual manufactured from A-286 alloy.
Operating Report No. 3,
- p. VII-7.
This change was made to preclude drif ting of valve setpoint due to relazation of the adjusting spring.
3.
New main discs were installed.
The new discs were manufactured Monticello Semi-Annual with stellite coated stems making them more resistant to galling.
Operating Report No. 3,
- p. VII-4.
This change was initiated following a reset failure of one valve due to severe galling of the main disc stem.
4.
The bellows leakage detection pressure switches were replaced with Monticello Semi-Annual switches having adjustable settings.
Operating Report No. 4, p.
IV-2.
This change was initiated to correct a design deficiency in the bellows leakage detection system.
This deficiency would have Letter from L 0 Mayer, prevented a small, but significant, leak from being detected NSP, to A Giambusso, and result in an alteration of the valve trip setting.
USAEC-DL, dated July 28, 1972.
5.
The stainless steel pilot stems were replaced with monel stems.
The pilot stems were replaced to produce valve lift pressures essentially the same with both nitrogen and steam.
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7-Summary of Change Neferences 6.
The piston rings on both stages were replaced with rings of greater
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hardness and the diameter of the main pistons were reduced.
The piston rings were replaced and the main piston diameters reduced to increase piston ring life.
7.
Milled 2 circular grooves in the main piston hub assembly, drilled a drain passage through the main piston hub assembly and through the Letter from L 0 Mayer, NSP, to J F O' Leary, valve body on the inlet side, doweled the main piston hub assembly to USAEC-DL, dated August 1, the valve body and removed the filter assembly from the first stage
- 1973, pilot sensing line.
These modifications prevent delays in valve opening due to steam condensation in the area above the main operating piston or in the sensing line.
8.
The stainless steel air operator glands were replaced with silicone bronze glands.
i This modification was made to increase the operational reliability of the air operator.
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