ML11186A728
| ML11186A728 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 03/21/2011 |
| From: | Cavey E Detroit Edison |
| To: | Office of Nuclear Reactor Regulation |
| Bedi G | |
| Shared Package | |
| ML11186A384 | List: |
| References | |
| TAC ME1150, NUREG-1482 | |
| Download: ML11186A728 (2) | |
Text
4.2.1 Stroke-Time Testing for Power-Operated Valves In the ASME OM Code, Subsection ISTC 5113 specifies that active POVs shall have their stroke times measured when exercised in accordance with the nominal 3-month schedule specified in Subsection ISTC 3500. Stroke-time testing may indicate degradation in the performance of POVs. NRC requirements and guidance for supplementing the ASME Code provisions for stroke-time testing are discussed later in this document.
The ASME Code includes provisions for establishing reference values and limiting values for POV stroke times. Subsection ISTC 3300 states that reference values shall be determined from the results of preservice testing or inservice testing. Subsections ISTC 5113, 5121, 5131, 5141, and 5151 also state that limiting values for stroke time for various types of POVs shall be specified by the owner. In addition, Subsections ISTC 5114, 5122, 5132;, 5142, and 5152 include a set of acceptance criteria for the reference value of the stroke time for POVs, and specify various corrective actions to be taken if those criteria are not satisfied. If the limiting value of stroke time is exceeded, Subsections ISTC 5115, 5123, 5133, 5143, and 5153 state that the POV shall be immediately declared inoperable.
The Code does not specify provisions for establishing the limiting value for stroke times, and it does not identify the relationship that should exist between those limits and the reference values for stroke time or any limits identified in the plant Technical Specifications (TS) or safety analysis. In Position 5 of GL 89-04, the NRC staff provided guidance for establishing' limiting values of stroke times.
NRC Recommendation The limiting value of full-stroke time should be based on the reference (or average) stroke time of a POV when it is known to be in good condition and operating properly. The limiting value should be a reasonable deviation from this reference stroke time, based on the size and type of the valve and power actuator. The deviation should not be so restrictive that it results in a POV being declared inoperable as a result of reasonable stroke time variations. However, - the deviation used to establish the limiting value should be such that corrective action would be taken to provide assurance that the POV would remain capable of performing its safety function.
The limiting value for stroke time of a POV should be that point at which the licensee seriously questions continued operability. It is expected to be a value that is determined to be reasonable for the individual POV based on its characteristics and past performance, but not to exceed any safety analysis requirements. The value should not be based solely on the system requirements or values specified in safety analyses for system performance. When the identified limiting value is exceeded, the licensee shall declare the component inoperable and shall enter any applicable TS limiting condition for operation (LCO). After declaring the valve inoperable, the licensee should perform an analysis to identify the cause of the problem with the POV. If this analysis clearly demonstrates that the POV remains capable of performing its safety function, the analysis might constitute the corrective-action required by the Code. The analysis must be documented.
Licensees should establish reference values that reflect the stroke time of the specific POV when in good condition and operating under applicable conditions. A licensee may establish additional sets of reference values as discussed in Subsection ISTC 3320, such as reference values that reflect alternate test conditions of fluid pressure or flow in the system.
Licensees may use a quantitative multiplier on a reference time as a means of establishing a limiting value for stroke time. The licensee should document the justification for its selection of reference values for the stroke time of each POV, and should have this justification available at the plant site for review by NRC personnel.
Basis for Recommendation The purpose of the limiting value of full-stroke time for a POV is to establish a value for taking corrective action on a degraded POV before it reaches the point where there is a high likelihood of failure to perform its safety function. While the TSs provide assurance that important plant systems are capable of performing their safety functions in a timely manner during selected plant accidents, the provisions of the ASME OM Code are intended to ensure the continued operability of particular plant components. The distinct bases for these two documents (i.e., TSs and ASME Code) lead to criteria that may differ significantly. Nonetheless, the TSs and ASME Code are both needed to provide confidence that the nuclear power plant can be operated safely.
Therefore, licensees must follow the more restrictive criteria of the two documents, even though this might result in a component or system being declared inoperable.
For example, if the TS or safety analysis limit for a POV is less than the IST value established using the above guidelines, the TS or safety analysis limit should be used as the limiting value of full stroke time. When the TS or safety analysis limit for a POV is greater than the IST value established using the above guidelines, the limiting value of full-stroke time should be based on the above guidelines instead of the TS or safety analysis limit. The TS and safety analysis limits are useful for analyzing data when a POV has indicated degraded performance and been declared inoperable. In accordance with Subsections ISTC 5115, 5123, 5133, 5143, and 5153 [4.2.9] the data may be analyzed to verify that the new stroke time represents acceptable POV operation.