ML20003B055
| ML20003B055 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 01/22/1981 |
| From: | Tramm T COMMONWEALTH EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| NUDOCS 8102100278 | |
| Download: ML20003B055 (3) | |
Text
Commonwe:lth Edison One Fas' Nat+cral Plaza Chicago. linois Address Reply to Post Off.ce Box 767 Chicaro. Ilhnois 60690 January 22, 1981 Mr. James G.
Keppler, Director Directorate of Inspection and Enforcement - Region III U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, IL 60137 Suoject:
Zion Units 1 and 2 Steam Generator Snubbers NRC Docket Nos. 50-295 and 50-304 References (a):
O ctober 15, 1980 letter from J. S. Abel to J. G. Keppler (b):
November 20, 1980 letter from J. G.
Keppler
- o C. Reed
Dear Mr. Keppler:
This is to provide additional information regarding the testing of Zion's steam generator snubbers which was reporteo in re ference (a).
Attatncent A to this letter addresses the comments contained in reference (b).
Please contact this office if there are any further questions.
Very truly yours, T. R.
Tramm Nuclear Licensing Administrator Pressurized Water Reactors Attachment cc:
Zion Resident Of fice 06/
J
/ f 9946A 8102100 FEB 0 31981
Attachment A Additional Information Requested by NRC Regarding Zion Steam Generator Snubbers The NRC, Region III, has reviewed the report of Unit 2 Steam Generator Snubber testing performed in May, 1980.
The NRC considers tnis report factual, however, several comments were made by the NRC which require clarification.
These comments are summarized as follows:
Item 1)
Provide more detail descricing the stiff spring modification to the valve control block.
i Item 2a) Evaluate whether or not a long term system improvement is warranted in lieu of the current control valve block design.
Item 26) Evaluate the hydraulic fluid " boiling phenomenon" and corrosion ef fects observed during extended LOCA environmental testing.
Item 2c) Consider external and internal filteting of hydraulic fluid in the steam generator snubber to preclude plugging of the control valve block bleed orifice.
Dis cus sion Item 1 Testing of the modified steam generator snubbers indicated that bleed rates were consistently low due to control valve bleed port pressure compensators' inadequate spring constant.
New springs of like quality with _ a higher spring constant were installed in all Unit 1 and 2 control valve blocks.
The new springs allowed the i
. compensator spool to position and reset consistently, thus maintaining the bleed rate within the snubber's allowable _ range of 0.116 to 0.6 in/ min.
Recent-static functional testing has proven that the modified control valve block will provide the required bleed rate af ter lockup under rated design load.
i Item 2a Further investigation of long term system improvements to the control valve block is not warranted.
This is due to the consistent satisf actory performance of _ the modified ' Unit 2 snobbers to perform their intended function' within the tolerances established oy the archite ct-engineer.
In the future, all seal materials installed will be ethylene-propylene material, which has been demonstrated to be an acceptable substitute for molded polyurethane.
This may be considered a long term improvement.
Item 2b Silicone fluids are stable from -1220F to +4820F, therefore Ge Silicone fluid (SF-ll54), which is used in all of our hydraulic snubbers, will not boil at 2710F, which is well within the stability range.
Silicone is also resistant to oxidation, high temperature, and radiation.
The " boiling phenomenon" occurred af ter the 10,000 second soak at accident environmental conditions of 2710F and approximately 15 psig, and af ter several design load functional tests.
In other words, the snubber had been subjected to transients beyond actual accident requirements.
At this point, a flange seal failed.
When the flange seal failled, autoclave steam pressurized the snuober system internals through the flange seal break, and caused a release of the steam via the reservoir and vent to atmosphere.
Any corrosion of the control valve internals was due to steam impingement after the flange seal break.
Grade AISI 4140 and 4340 steels, which are the materials used in the S/G Snubbers, are chrome molybdenum, and nickel chrome molybdenum steels.
They exhibit high strength, toughness, and provide excellent corrosion resistance under severe service conditions.
Corrosion of the snubbers during accident ~ environmental testing was deemed to be minimal, and not of a magnitude to inhibit the normal operation of the units during accident conditions.
This f act was demonstrated by the actual testing resultc.
Item 2c The obstruction in the bleed port of #21 snubber, which causea bleed rate to decay to zero, was attributed to metal chasings from the new test fixturing and was introduced during initial fitup.
Adequate quality control practices in the future should preclude the additon 'of any foreign particles into the snubber fluid system, thus insuring proper functioning of the control valve block.
9946A