ML20246G393
| ML20246G393 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/03/1989 |
| From: | Haynes H, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RTR-REGGD-01.097, RTR-REGGD-1.097 MP-13039, NUDOCS 8905150289 | |
| Download: ML20246G393 (3) | |
Text
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J Docket No. 50-423 Re: 10CFR50.36 May 3, 1989 MP-13039 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Gentlemen:
Millstone Nuclear Power Station, Unit No. 3 Post Accident Samole System This event is being submitted as a Special Report since the event is considered to be of sufficient interest but there is no report required per the criteria of 10CFR50.73. The Post Accident Sample System is addressed by Plant Technical Specification 6.4.8.d:
Administrative Procedures and Programs.
On April 25, 1989 at 1115 hours0.0129 days <br />0.31 hours <br />0.00184 weeks <br />4.242575e-4 months <br />, with the plant in Mode 1, at 100% power, 2250 paia, and 586 degrees Fahrenheit, analysis of a gas sample drawn from the Post Accident Sample System (PASS) indicated that reactor coolant gases were not being removed from the liquid sample of the Reactor Coolant System (RCS).
The PASS can obtain liquid samples from the reactor coolant hot legs when RCS pressure is above 240 psig, or from the containment sump when the Containment Spray Recirculation System is operating.
Pressurized reactor conlant liquid samples are isolated in the liquid sample loop.
By then connecting the liquid sample loop to a gas sample loop through a four-way valve, the liquid sample expands and depressuri:es. A small stripping pump agitates the sample, " stripping" the gases for 'ollection in a gas sample chamber. The PASS can also obtain a sample of the containment atmosphere.
As directed by Regulatory Guide 1.97, Millstone 3 has a program to periodically verify PASS operability. The Millstone 3 program requires semi-annual surveillance be performed to verify that samples can successfully be drawn from the containment atmosphere, and the RCS. While not a surveillance requirement, the containment sump is sampled during the quarters between RCS samples, U
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, From March 3, 1988 to April 25, 1989, several RCS liquid samples were successfully obtained, but attempts to separate reactor coolant gas samples from the liquid samples were unsuccessful. PASS reactor coolant gas samples were last successfully drawn on August 15, 1988. PASS containment air samples were successful 3y drawn on March 10, 1989. A satisfactory liquid sample of the containment sump was drawn on October 10, 1988.
Gas chromatographic and isotopic analysis of the gas samples indicated that while activity and hydrogen were present, the acceptance criteria of the PASS surveillance were not met.
Gas samples were mostly nitrogen which is used to purge and fill the gas sample volume prior to sampling. These results indicated that gases were not being stripped from the reactor coolant liquid sample.
Throughout the period of March 3, 1989 to April 25, 1989 corrective maintenance was performed on the system and successive RCS samples drawn.
Two leaks on the service water side of the reactor coolant sample cooler were repaired, and the sample flowmeter calibration was checked.
Internal valve leakage on two sample isolation valves was corrected by replacing the valves. Problems were found with the valve actuator of the four-way valve between the liquid and gas loops. This may have prevented collection of the gas sample.
From April 12, 1989 to April 15, 1989, the plant was shutdown and depressurized, which prevented reactor coolant sampling from the PASS.
Another attempt to obtain a reactor coolant gas sample (on April 25, 1989) was unsuccessful Corrective actions include re-inspecting the liquid loop to gas loop four-way valve actuator, and verifying operation of the gas stripping pump, since pump failure will prevent gases from being stripped from the liquid sample. Root cause analysis of component failures will be conducted and the surveillance will be repeated to verify operability of the gas sample loop.
Additional corrective actions include reviewing surveillance procedures to identify improvements, increasing the surveillance frequency to enhance system reliability, evaluating possible design improvements, and sharing information with other plants with the same design PASS.
The PASS was supplied by General Dynamics Reactor Plant Services. A review of the system performance with General Dynamics was conducted in September 1987.
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' The licensee contact for this special report is Robert Conway, who may be contacted at (203).444-5642.
Very Truly Yours, NORTHEAST NUCLEAR ENERGY COMPANY For: Stephen E. Scace Station Superintendent Millstone Nuclear Power Station
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d By: Ha yF H ynes Station vices Su intendent Millstone Nuclear Power Station SES/RDC:dlr cc: W. T. Russell, Region I, Administration D. H. Jaffe, NRC Project Manager, Millstone Unit No. 3 W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos. 1, 2, and 3 m.
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