ML12305A254

Safety Guide 14, Reactor Coolant Pump Flywheel Integrity

ML12305A254
Person / Time
Issue date:	10/27/1971
From:	Office of Nuclear Regulatory Research
To:
References
Safety Guide 14 RG-1.014
Download: ML12305A254 (2)

Text

10/27/71 SAFETY GUIDE 14-REACTOR COOLANT PUMP FLYWHEEL INTEGRITY A. Introduction General Design Criterion 4 requires that structures, systems, and components of nuclear power plants important to safety be protected against the effects of missiles that might result from equipment failures. This guide describes an acceptable method of implementing this requirement with regard to the flywheels of reactor coolant pump motors in water cooled power reactors.

B. Discussion The flywheels on reactor coolant pump motors provide inertia to assure a slow decrease in coolant flow in order to prevent fuel damage as a result of a loss of power to the pump motors. Because they have large masses and rotate at speeds of 900 rpm or 1200 rpm during normal reactor operation, a loss of flywheel integrity could result in high energy missiles and cessive vibration of the reactor coolant pump embly. The safety consequences could be gnificant because of possible damage to the reactor coolant system, the containment, or the engineered safety features.

Reactor coolant pump flywheels are of a simple geometric shape, and normally are made of a ductile material. Their quality can be closely controlled, and their service conditions are not severe; therefore, the use of suitable material, and adequate design and inservice inspection can provide a sufficiently small probability of a flywheel failure that the consequences of failure need not be protected against.

C. Regulatory Position I. The flywheel material should be produced by a process that minimizes flaws in the material and improves its fracture toughness properties, such as the vacuum-melt and degassing. process. The material should be examined and tested to meet the following criteria:

a. The nil-ductility transition (NDT) temperature of the flywheel material, as obtained from the dropweight tests (DWT) performed in accordance with the specification ASTM E-208, should be no higher than 10' F.

b. The Charpy V-notch (Cv) upper-shelf energy level in the "weak" direction (WR orientation in plates) of the flywheel material should be at least 50 ft-lb.

A minimum of three Cv specimens should be tested from each plate or forging, in accordance with the specification ASTM A-370.

c. The minimum fracture toughness of the material at the normal operating temperature of the flywheel should be

'equivalent to a dynamic stress intensity factor (KIc dynamic) of at least 100 ksi in. Compliance can be demonstrated by any of the following:

(I)Testing of the actual material of the flywheel to establish the KIc (dynamic) value at the normal operating temperature.

(2)Testing of the actual material of the flywheel by means of Cv specimens oriented with respect to the "weak" direction (WR orientation in plates). The Cv impact tests should be conducted to define the Cv test curve up to at least 50 ft-lb fracture energy value. The Cv curve should then be adjusted for the NDT temperature and size effect, as described in the proposed AEC

Fracture Toughness Requirements", 10 CFR Part 50 § 50.55a, Appendix G,Section III B.

The adjusted fracture energy, as read from the adjusted Cv curve at the normal operating temperature of the

flywheel, should be demonstrated to be equivalent to a KIc (dynamic) value of at least 100 ksi in by using appropriate correlation data. The test data and the correlations used should be submitted to the regulatory staff for review.

(3)Use of a lower bound fracture toughness curve obtained from tests on the same type of material. Such 14.1

a curve should be translated along the temperature coordinate until the KIc (dynamic) value of 45 ksi in is indicated at the NDT

• temperature of the material, as obtained from the DWT tests. The proposed lower bound fracture toughness curve should be submitted to the regulatory staff for review.

d. Each finished flywheel should be subjected to a

100%, volumetric ultrasonic examination using procedures and acceptance critiera equivalent to. those specified for Class I vessels in the ASME Boiler and Pressure Vessel

Code, Section III-Nuclear Power Plant Components.

e. If the flywheel is flame cut from a plate or forging, at least 1/2 inch of stock should be left on the outer and bore radii for machining to final dimensions.

f. Finish machined bores, keyways and drilled holes should be subjected to magnetic particle or liquid penetrant examination.

2. The flywheel should be designed to withstand normal conditions, anticipated transients, the design basis loss of coolant accident, and the design basis earthquake without loss of structural integrity. The design of the pump flywheel should meet the following'criteria:

a. The combined primary. 'stresses at the normal operating

speed, due to centrifugal forces and the interference fit of the wheel on the. shaft, should not exceed 1/3 of the minimum specified yield strength, or 1/3 of the measured yield strength in the weak direction of the material if appropriate tensile tests have been performed on the actual material of the flywheel.

b. The design overspeed of a flywheel should be at least 10 percent above the highest anticipated overspeed.

The anticipated overspeed should include consideration of the maximum rotational speed of the flywheel if a break occurs in the reactor coola piping in either the suction discharge side of the pump. The basq, for the assumed design overspeed should be submitted to the regulatory

c. staff for review.

c. The combined primary stresses at the design overspeed, due to. centrifugal forces and the interference fit, should not exceed 2/3 of the minimum specified yield strength, or 2/3 of the measured yield strength in the weak direction if appropriate tensile tests have been performed on the actual material of the flywheel.

d. The shaft and the bearings supporting the flywheel should be able to withstand any combination of the normal operating loads, anticipated transients, the design basis loss of coolant. accident and the design basis earthquake loads.

3. Each flywheel assembly should be tested at the design overspeed of the flywheel.

4. The inservice in-spection program for each flywheel should include.the following:

a. An. in-place ultrasonic volumetd examination of. the areas of highl stress, concentration. at the bore and, keyway at approximately

3. year intervals, during the refueling or maintenance shutdown coinciding with the inservice inspection schedule as required -by the ASME Boiler and b ' Pressure Vessel Code Section XI.

b.surface examination of all exposed surfaces and complete ultrasonic volumetric examination at approximately 10 year intervals, during the plant shutdown coinciding with the inservice inspection schedule as required by the ASME Boiler and Pressure Vessel Code -Section XI.

Removal of the flywheel is not required to perform these examinations.

c. Examination procedure, and acceptance' criteria in conformance

-with the requirements specified in C.1.d.

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