ML17252A909
| ML17252A909 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/13/1974 |
| From: | Stephenson B Commonwealth Edison Co |
| To: | O'Leary J US Atomic Energy Commission (AEC) |
| References | |
| BBS Ltr. #339-74 | |
| Download: ML17252A909 (4) | |
Text
CommorAalth Edison One First rmnal Plaza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 BBS,Ltr.1339*74 Mr. J. F. O'Leary, Directo Directorate of Licensing U. s. Atomic Energy Couunission Washington, D. c..
20545 5o-Z49
SUBJECT:
LICENSE DPR-25 DRESDEN NUCLEAR POWER STATION UNIT I OF ABNORMAL OCCURRENCE PER SECTION 6.6.B.2.0F THE TECHNICAL SPECIFICATIONS.
FEEDWATER PRIMARY CONTAINMENT ISOLATION VALVE LEAKAGE.
References:
- 1) Notification of Region III of AEC Regulatory_ Operations
-Telephone: Mr. F. Maura, *1330 hours on May 6, 1974 Telegram: Mr *. J. G. K~ppler, 15()0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> on May 6, 1974
- 2) Dwgs: P&ID-M-347
- 3) Letter to Mr. A. Giambusso from Mr. W. P. Worden (WPW Ltr.
- 468*73). dated June 20, 1973.
4).Letter to Mr. J. F.O'Leary £ram Hr. :8. B. Stephenson
-. (BBS Ltr.#212-74) dated March.22, 1974.
Dear Mr. O'Leary:
This le-tter 18 to report' a. condition relating to Local Leak Rate Testing while the unit was shutdown for refueling.
The test was conducted on the day shift on May 6, 1974.
The test of the feedwater check valves, 3-220-588 and 3-220-628, determined that the leakage through each valve was in excess of the Technical Specification limit. This malfunction is contrary to Section 4. 7,,A.2.£, which specifies that the total leakage '.rate through any one isolation valve will not exceed 5% Lt0 (48).
In addition, this letter reports the conclusions of the on site review regarding the fix to the Unit 3 feedwater check valves.* This will satisfy 'the commitment for reporting review conclusions as made in a prior
. letter, reference 4, _reporting test failure of valves 3-220-5&\\ & 62A.
PROBLEM At the time of the deviation, the unit was shutdown for refueling and LLRT was being conducted.
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Mr *.. J. 'T. O'Leary
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- --- May 13, -1974 During testing of* the Uriit 3 "B" line cneck valves on May 6, -1974, excessive leakage was discovered from both tested volumes.
One of ~he tested volumes is. bounded by valves 220-S7B & 220-58B and the other is bounded by valves 220-57B & 220-62B.
The leakage through 220-58B was 1,207.9 scfh.
The leakage through 220-62B was 7,135.l scfh.
Both rates are in excess of si Lt0 (48), or 29.381 sfch, the maximum leakage allowed
- INVESTIGATION The 18" diameter.swing type check valves (220-58B & 220-62B) were disassembled.and inspected to determine the cause of the leakage. It was determined that the "O"ring which seals the valve seat to the valve oody-was no longer in its groove on either valve.
This is the same condition, as found,. on the "A" *line check valv~s in March, 1974 and reported in a letter dated March 22, 1974' (Reference 4).
Both the "A" and "B" line check valves were modified in June of
- 1973 (Ml2-3-73-112).
This modification replaced the j;lrig:f.nal stainless steel trim seal ring with a silicone "O"ring.
The silicone "O"ring is 3/1611 diameter by 16" l~D. and con.forms to MILR-5847 Class 2 Grade 70: Military Specification Rubber, Silicone,
- Low and High Temperature and Tear Resistance.
Class 2 has resistance to extreme high temperature (
425°F).
The absence of this "O"ring is the cause of the excessive leakage.
CORRECTIVE ACTION An on site review (74-66) to determine a fix* to the-Unit 3 feed-water check valves was completed on May 2, 1974.
After reviewing the recommendations made by CBCO's Engineering Department the review approved the use of a Viton "O"ring in place of the Silicone"O"ring. *The longevity of the Silicone: "O"ring was not acceptable for its environment.
The Vi ton* ring has good sealing characteristics, it will withstand radiation and should be better able to withstand environ-mental conditions.of the 350°F water. The Viton "O"rings were installed in the "A" and "B" line valves and were leak rate tested successfully.
Satisfactory longevity can only be assumed based on manufacturer's data -
until the next local leak rate test is conducted.
The success of the "O"ring modification and the anticipated
- success of Viton "O"ring are such that during the next refueling outage of Unit 2 the same modification will be made.
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May -13~- 1974 The retested data is listed below: - --
Valve 220-58A 220-62A 220-58B 220-62B EVALUATIONS 0.835 9.90 o.oo 1.108 scfh scfh scfh scfh An on site review_ (74-65) was completed -on April 4, 1974 regard-_
- ing the ~issing. "O"rings. A sample of the same material as the missing "O"ring was analyzed._ The. results of the analysis indicate that they_
contained no substances to cause stress corrosion cracking.
The material will break down under heat and radiation to form water, carbon dioxide
. and silica. The review concluded that-the loss of the rings could have no significant affect on iither present or future reactor operations.
- Considering the possibility of loss _of the newly installed Viton "O"rings, the results of such loss were* evaluated.
The disadvantage.of_
Viton, is that it contains flourides. According to DuPont, supplier of Viton, the ring contains 43 weight percent flourides.
The flQurides are tightly held within the.molecules by covalent bonding with*carbon.
Thus it is unlikely that any significant amount. of :flourides will be released.
, Assuming a catastrophic failure _releasing all flourides, the*
flouride content.of the reactor-pressure vessel water inven~ory will
- increase by 0.084 parts per million. Any flourides would soon be removed by the clean-up _system.
The modification (Ml2-3-74-87) w~ich effects the change to Vito~
addresses the fact that no probability of an occurrence or consequence of an accident important to safety as evaluated inthe FSAR is increased.
Concerning the leak4ng check valves, the o.ccurrence did not:
endanger the safety-of the public or of plant personnel. _
The parti~ular valves in question serve to prevent excessive release of reactor water (vapor) into the reactor or turbine building
- should the feedwater line break in ei~ber of these areas.
Should the highiy improbable b*reak have occurred~ the* release_ would have_ bee~ minor s'ince the leakage was. through a circuitous path by the seal ring. If the leakage was into the secondary.containment, the Standby Gas Treatment System offers a sufficient bar.rier to keep offsite do~~-s withi.n~\\10CFRlOO and station procedures protect plant personnel.
l_f the leakage was into
~he turbine bu.Uding, motor operated valves are. available to effectively isolate the leak, with the exception of two lengths of approximately 12 feet each between the MO valves in the turbine bui-lding and secondary containment.
The probability of a failure of this piping is so remote as to be considered non credible.
Should it have failed station emergency procedures would have been the only protection.
- -*.., - *--;;-4~ -
- May 13,-1974-- -
Cumulative experience* on'--:these -valves bas been poor regarding leak rate tests.
As mentioned above, the Unit 3 valves were modified to produce a better seal at the low te.st pressure of 48 1>>~ig and retai.n equally effective sealing at high differential pressures.
Now they.have been modified to change the "O"ring mat~rial _to one more suitable to the environment of the syseem.
BBS:JR:do
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Sincerely, B. B.
henson Superintendent
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