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**UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555-0001**

June 26, 1998

**Addressees**

All holders of operating licenses for nuclear power reactors except those who have permanently ceased operation and havecertified that fuel has been permanently removed from the reactor vessel.

**Purpose**

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform addressees about a designoversight that prevented operation of a safety-related system. It is expected that recipients will review the information forapplicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestionscontained in this information notice are not NRC requirements; therefore, no specific action or written response is required.

**Description of Circumstances**

On December 5, 1997, the licensee at the Hope Creek nuclear power plant, while restarting the reactor from a refuelingoutage, tested the RCIC turbine at 18 percent power and discovered that the controller had no effect on steam flow(Licensee Event Report (LER) 50-354/97-32, Accession Number 9801140220). The licensee's evaluation of the root causeof the failure concluded that the dominant reason was interference between the RCIC turbine governor valve's **Inconel�**stem and the carbon spacers that are interlayered with carbon steel washers along the axis of the stem. This arrangement isdesigned to allow stem movement while minimizing steam leakage. The coefficient of thermal expansion of the **Inconel�**stem is more than twice that for the carbon spacers. The licensee remedied the situation by boring out the carbon spacers,increasing the gap between the stem and spacers and making the carbon steel washers fit around the stem more loosely.Other potential reasons for governor valve inoperability involve overcompression of the stem spring and misalignment ofthe remote servo-governor lever.

On October 21, 1997, at the Perry nuclear power plant, during startup from a refueling outage, the RCIC turbine trippedwhen the licensee attempted to restart it after it had been accidentally tripped during a long run (NRC Inspection Report 50-440/97-16, Accession Number 9802230089). Previous cold surveillance starts had been successful. The licensee alsodetermined that binding had occurred because the carbon spacers fit too tightly on the **Inconel�**stem, which had beeninstalled in August 1997. The licensee replaced the **Inconel�**stem with a nitrided stem to gain a looser fit.

On October 9, 1997, at the Hatch Unit 1 nuclear power plant, during a surveillance test of the RCIC system from theremote shutdown panel, the licensee observed that sufficient flow and pressure could not be obtained due to lower-than-normal turbine speed (NRC Inspection Report 50-321/97-10, Accession Number 9712300190). The licensee determinedfrom a root-cause analysis that the restriction of governor valve movement was due to misaligned carbon spacers bindingon the governor valve stem in the open direction and that this misalignment was caused by scale accumulation in the valverather than by corrosion of the stem. At the time of the test, after realigning the system, the licensee successfully conductedthe same test from the control room. The licensee infers from this success that the binding must have been relieved duringthe realignment.

On March 20, 1998, Dresser-Rand Energy Systems Division (Dresser-Rand), Wellsville, New York, submitted an initialreport under 10 CFR Part 21 (Accession Number 9803300072). This company supplied the carbon spacers in the RCICturbine governor valve assembly discussed above for the Hope Creek event. On April 16, 1998, Dresser-Rand submitted afinal report under 10 CFR Part 21 (Accession Number 9804220222).

**Discussion**

In the final report, Dresser-Rand describes the defect as **Inconel�**718 material being used in place of 410 stainless steelfor the new spray coated valve stems. In the material selection process, engineers did not fully evaluate the coefficient ofthermal expansion of the different materials. The potential safety hazard is that if the cold clearance is not adequate toaccommodate the stem growth, control problems will result that may prevent the turbine or pump assembly fromperforming its intended function.

Dresser-Rand states that it is manufacturing a new carbon spacer, part number 800714-002, with an inside diameter largerby 0.0005 inch [0.01 mm] than the original spacer, part number 800714-001. This will return the running clearance atoperating temperature to the values of the original nitrided 410 stainless steel stems. The failure to adequately evaluate thepotential effects of the thermal expansion characteristic of the new material was a design oversight that occurred eventhough procedures for controlling the design process are currently in place.

In the final report, Dresser-Rand listed the affected plants as follows:

On April 27, 1998, Dresser-Rand added the Cook plant to this list (Accession Number 9806080110).

The **Terry�**Turbine Users Group discusses these matters in addition to other issues, such as linkage failure and checkvalve reliability, in its Spring 1998 newsletter.

**Related Generic Communications**

Similar interference problems were considered previously in IN 94-66, "Overspeed of Turbine-Driven Pumps Caused byGovernor Valve Stem Binding," on September 19, 1994, and in Supplement 1 issued on June 16, 1995. In 1995, the**Terry�**Turbine Users Group recommended using stem material that is not susceptible to corrosion, such as gas-nitridedsteel or **Inconel� .**

This information notice requires no specific action or written response. However, recipients are reminded that they arerequired by 10 CFR 50.65 to consider industry-wide operating experience (including information presented in NRCinformation notices) where practical, when setting goals and performing periodic evaluations. If you have any questionsabout the information in this notice, please contact one of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation project manager.

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