ML12305A258

Safety Guide 20, Vibration Measurements on Reactor Internals.

ML12305A258
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Issue date:	12/29/1971
From:	Office of Nuclear Regulatory Research
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References
Safety Guide 20 RG-1.020
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12/29/71 SAFETY GUIDE 20-VIBRATION MEASUREMENTS ON REACTOR INTERNALS A. Introduction The analytical and empirical techniques which provide the initial basis for the evaluation General Design. Criterion 1 requires that of the effects of vibration need verification by structures, systems and components important measurement. Because of the lack of experience to safety, be designed, fabricated, erected, and with vibration characteristics of various reactor tested to quality standards commensurate with configurations, and the limitations of the the importance of the safety functions to be analytical and empirical techniques used to date, performed. This guide presents an acceptable a program of vibration analysis, measurement, method for implementing this criterion with and inspection, is needed for each prototype regard to preoperational vibration testing of design.' The extent of this program is reactor internals (structural components inside dependent on the adequacy of analytical and the reactor vessel) important to safety to empirical data available for a given design, as demonstrate that flow-induced vibrations similar may be. derived from scale tests or other in nature to those expected during operation prototype tests.

will not cause damage. Subsequent inservice inspections to verify that these components have For reactors whose internals are similar in not been subjected to structuraldegradation as a design of that of the vibration-tested reactor result of vibration during normal reactor considered as the prototype, either an inspection operation are not covered by this guide. of the reactor internals following preoperational functional testing, or the use of appropriate B. Discussion vibration-measuring instrumentation to detect the predominant vibratory responses observed in Reactor internals that are important to safety the prototype reactor, provides a basis for are designed to withstand the predicted cyclic confirmation that the vibrational characteristics loads due to vibration in combination with the and their effects are not unlike that of the other loads encountered during their service life. prototype reactor.

The dynamic conditions generated by the flow of the reactor coolant within the reactor vessel C. Regulatory Position for Prototype Reactor and reactor coolant system components are Internals' predicted analytically and in conjunction with data derived from laboratory and full-scale test 1. A vibration analysis and test program programs. should be developed. The test program The purpose of these calculations and tests is should be submitted for review by the to estimate the input forcing functions which Commission prior to the performance of cause vibrations and to verify the vibrational the scheduled preoperational functional response (frequency and amplitude) of the tests.

reactor internal components predicted for the The vibration testing should be prototype design. However, the analytical conducted with the fuel elements in the techniques and limited test data available, at core structure of the reactor internals (or present, are not yet adequate to. predict and with dummy elements which provide confirm the significant sources and levels of the equivalent mass and flow characteristics).

input forcing functions and the associated responses of the internal components without A prototype design of reactor internals is the first verification by measurement.

design respresentative of a group of reactors of At several nuclear power plants, the dynamic substantially the same design, size and configuration.

forces associated with the flow of reactor This group of reactors may include all those in which the coolant have resulted in excessive vibration of variations in the parameters of operation pressure, some components of the reactor internals. The temperature, flow conditions, coolant velocities, and

• vibration has been sufficient to weaken (fatigue) pressure losses for the range of operating conditions can the components and, in some cases, has resulted be demonstrated as negligible with respect to their in their failure. influence upon the input vibratory functions.

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,Testing .may also be conducte4d with functional testing program to measure the the core structure not loaded with fuel response2 of the reactor internals and, elements provided such conditions can be where appropriate, the values of those demonstrated., to , result in vibrational parameters which will define the input characteristic which, for the purposes of forcing !functions for the more critical the test, will yield conservativeresults. modes of reactor operation. The data The test program should include: obtained by these measurements on

a. a brief description of the vibration test reactor internals should be sufficient to program, including instrumentation verify, that the cyclic stresses in the types and diagrams of their, location, components, as determined by analyses of which will be used for measurement of these data, are within the acceptable vibration responses and those design stress limits set forth in the design parameters which. define the input specifications and applicable code forcing functions, requirements and that the results meet the

b. the planned duration of the test for acceptance criteria of the vibration test normal operating modes to assure that program.

all critical components are subjected to at least 10'. cycles of vibration, 3. The extent of the measurements should

c. the additional test duration for other be determined, for each individual case, than normal operating modes to assure on the basis of the design and that the number of cycles imposed on configuration of those structural elements the critical components is sufficient to of the reactor internals important to analyze their adequacy to withstand safety and their predicted behavior as vibrations under these operating determined from the vibration analyses modes, used in their design. The type of vibration

d. the description of different flow test instrumentation used, the number of modes of operation and transients to measurements taken, and the distribution which the internals will be subjected of measuring devices within the reactor during the test, should be adequate to detect the presence

e. the predominant response mode shapes of lateral, vertical, and torsional and the estimated range of numerical amplitudes of vibration (e.g., beam, values of the response of the major column, and shell modes of vibrations,'as components of the reactor internals in applicable to the geometry of the terms of amplitudes and, where internals) and at sufficient locations to appropriate, the anticipated values of determine the points of predominant the paramaters which may influence maximum vibratory oscillations.

the input forcing function, under those flow modes of reactor operation which 4. After the reactor internals have been are shown by the analyses to be the subjected to the significant flo,-' modes most critical, expected during service lifetme under

f. the test acceptance criteria and the normal reactor operatior, and other permissible deviations from these modes of reactor operation, visual and criteria, and the bases upon which nondestructive surface examinations of these criteria were established, reactor internals should be conducted to

g. a description of the inspection detect any evidence of the effects of program which will be followed after vibrations. These examinations should be the completion of the vibration tests, conducted preferably following removal including the areas of reactor internals of the internals from the reactor vessel.

subject to examination, the method of Where removal is not feasible, the examinations should be performed by examination, the design access provisions in the reactor internals and means of examination equipment appropriate for in situ examination. The the specialized equipment to be areas examined should include all major employed for performing such examinations.

2. A vibration' test program should be implemented during the preoperational 2

Frequency'and amplitudes of vibration, in terms of velocities, accelerations and displacements or strains.

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load-bearing :elements ' of the' reactor D. Regulatory Position for Reactor Internals internalswhich are relied upon to retain Similar to the Prototype Design the! core structure in place, the lateral, vertical, and torsional -restraints provided -1. The reactor internals important to safety within the reactor vessel, those locking should be subjected during the and bolting devices whose failure could preoperational functional testing program adversely affect the structural integrity of to all significant flow modes of normal the internals, and those critical locations reactor operation and under the same test o-n ' reactor internal components as conditions imposed on the prototype identified from the vibration analyses. design whose vibration analysis and tests have been accepted and approved.

5. In the event either the inspections of The test duration should be at least as reactor internals reveal unacceptable long as that conducted on the prototype defects or the results of the vibration test design.

program fail to meet the specified acceptance criteria, a report should be 2. Following completion of the prepared and submitted to the preoperational functional tests, the Commission for review, which includes an reactor internals should be removed from evaluation and a description of the the reactor vessel and visual and corrective, actions planned in order to nondestructive examination of the reactor justify the adequacy of the reactor internals should be conducted. The areas internals design to withstand the examined should include:

vibrations expected in service.

a. all major load bearing elements of the

6. If the test and examination program is reactor internals relied upon to retain acceptable, a summary of the results the core structure in place, obtained from the vibration tests and inspection should be submitted to the b. the lateral, vertical, and torsional Commission after completion of the tests. restraints provided within the vessel, The summary should include: c. those locking and bolting devices

a. a description of any differences from whose failure could adversely affect the specified vibration tests program, the structural integrity of the internals, instrumentation reading anomalies and instrument failures.

d. those other locations on the reactor

b. a comparision between the measured internal components which were values of vibration responses including examined on the prototype design, the parameters3 from which input forcing functions are determined and

e. the interior of the reactor vessel for the predi*cted values from the analysis.

evidence of loose parts or foreign This comparison should be made for material.

those components of the reactor internals for which the acceptance

3. In lieu of the visual and surface criteria under C.l.f. have been examinations of the removed reactor established with respect to the internals of 2. above, a vibration test different modes of vibration, program may be implemented during the

c. an evaluation of measurements that preoperational functional testing program exceeded acceptable limits or of by using sufficient and appropriate observations that were unanticipated, vibration-measuring instrumentation to and the disposition of such deviations.

detect the predominant vibratory responses observed in the approved and accepted prototype design.

'Where mleasurements to determine forcing The predominant vibratory responses functions cannot be obtained practically in all areas by to be measured should be those which, means of pressure transducers (or other instruments). from the results of the prototype test, such values may be estimated from measured responses identify the principal characteristics and and from analytical and empirical results. modes of vibration of the reactor internal 20.3

components, and which will permit material.

comparison of measured responses to 4. A summary of the inspection of D.Z.

confirm the substantially similar above, or the results from the vibration vibrational behavior, between the tested test program of D.3. above, should be internals and its prototype unit, within submitted to the Commission- after .

the limits of the test acceptance criteria of completion of the inspection and tests, in the prototype design. the form of summary discussed under C.5.

In the event significant dissimilarity of above, to confirm that the observed responses are obsered for specific vibrational characteristics are similar to components, visual examinations should those of the prototype design. The report be performed of these components by should include an evaluation of any means of appropriate examination observed dissimilarity of responses equipment which permits insitu between the tested internals and its inspection. In all cases, the interior of the prototype and the corrective actions reactor vessel should be visually checked taken to confirm the acceptance of the for evidence of loose parts and foreign test results.

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