ML20084S946
| ML20084S946 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 05/10/1974 |
| From: | Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084S948 | List: |
| References | |
| AO-02-74, AO-2-74, NUDOCS 8306200303 | |
| Download: ML20084S946 (3) | |
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Mr. John'F. O' Leary, Director Re: Docket 50-25 Directorate of Licensing License DPR-20 US Atomic Energy Commission Palisades Plant Washington, DC 20545
Dear Mr. O' Leary:
Attached is a copy of an abnormal occurrence report (A-02-74) for the Palisades Plant.
This is the first written report submitted to the Directorate of Licensing concerning this abnormal occurrence even though it oc-curred on April 7, 1974. A similar report with the exception of the detailed'information present in Item 8 vaa submitted by TWX to the Directorate of Regulatory Operations, Region III, on April 15, 1974.
At that time, Mr. R. Cook of DRO, Region III, inforned us that we could delay submitting a written report until the detailed information concerning the chemical decomposition was available. This information is, included in this report.
Yours very truly, Ralph B. Sewell (Signed)
RBS/ce Ralph.B. Sewell Nuclear Licensing Administrator CC: JGKeppler, USAEC
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ABNORMAL OCCURRENCE REPORT Palisades Plant 1.
Report Number:
AO-2-Th, Docket 50-255 2a.
Date: May 10, 1974 2b.
Occurrence Date: April T, 1974 3.
Facility: Palisades Plant 4.
Identification of Occurrence: Plexiglas Dropped Into Reactor Cavity 5
Conditions Prior to Occurrence: Refueling in Progress 6.
Description of Occurrence: While inserting fuel assemblies into the reactor, the underwater lights are normally adjusted to better illuminate the field of view of the refueling machine TV camera.
One of the lights which is used is positioned through a viewing port on the deck of the refueling machine trolley. The viewing port has standard 3" x 1" deck grating which rests over a piece of plexiglas.
The grating provides support for personnel standing in the vicinity and the plexiglas is provided to prevent objects from falling through the grating into the reactor cavity.
During the insertion of the underwater light, a piece of the plexi-glas (estimated to be 3" vide and 18" long and 1/3 6" thick) broke off the large piece and fell into the reactor cavity. A thorough search of the reactor vessel, reactor cavity and tilt pit revealed that the plexiglas piece had come to rest on the top of the core shroud former plate at the northeast side of the reactor. While attempting to retrieve the plexiglas, it subsequently fell through the annulus between the shroud former plate and the core support barrel.
7 Designation of Apparent Cause of the Occurrence:
Inadequate Design of the Viewing Port 8.
Analysis of Occurrence: The 3" x 15" x 1/16" piece of plexiglas, polymethyl methacrylate, is apparently located in a compartment or void bounded by the bolted core shroud plates, core shroud formers and a portion of the core barrel. All components are vrought Type 304 stainless steel. No component is furnace sensitized. The core barrel veld heat affected zones are remote from the location of the plexiglas sheet. In this location, the plexiglas sheet is effec-tively trapped and cannot adversely perturb core hydraulics nor can it be retrieved. The probability of the plexiglas exiting the void prior to decomposition is very low.
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A literature r3 view indicates that thermal decomposition occurs at about 200*F and the major by-product of polymethyl methacrylate is acrylic acid. This by-product is mildly corrosive toward stainless steels with general corrosion rates being of the order of 2 mils per year for acid concentrations greater than 30 veight percent. A sample piece of the plexiglas, which was obtained from a remaining piece of the original, was exposed at 600 F in an autoclave. In contact vrought and wrought /velded 304 stainless steels exhibited no localized corrosion. Following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> at 600 F, 90 percent of the plexiglas had dissolved. By-product liquid residues contained 1.1 ppm chloride and 0.05 ppm fluoride. The plexiglas to water volume ratio in the autoclave was 540 times that in the primary system. The 10 percent gel-like residue is expected to contain halide concentrations equivalent to that detectable in the as-received material, viz,100 ppm chloride and no fluoride.
9 Corrective Action:
a.
A screen vill be used to replace the plexiglas so that it is not likely to fall off and, even if it does fall off, it will be easier to retrieve.
b.
Although no chemical attack was detected in the test described in 8 above, care vill be exercised during the next heatup to minimize the oxygen concentrations. This will minimize the possibility of halide induced attack during start-up. If either the chloride and/or fluoride concentrations are deter-mined to be greater than Technical Specifications limits, the primary coolant system vill not be heated further until the concentrations are reduced below the limits.
c.
After the plant is heated to the hot standby condition, it will be held there for two days. This will ensure thermal decompo-sition of the plexiglas and contaminant removal via the puri-fication system prior to resuming reactor operations.
10.
Failure Data: No Previous Similar Experiences
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