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NRC INSPECTION MANUAL DI

INSPECTION PROCEDURE 61710

CONTROL ROD WORTH MEASUREMENTS FOR PRESSURIZED WATER REACTORS

PROGRAM APPLICABILITY: 2515 (SUPPLEMENTAL)

61710-01 INSPECTION OBJECTIVES

The objectives of this procedure are:

01.01 To verify that control rod worth measurement procedures

follow license commitments (e.g., ANSI Standards and core reload

analysis reports),

01.02 To verify that control rod bank worth measurements are

conducted in accordance with licensee procedures,

01.03 To verify that control rod bank worth measurement

calculations are correct, and

01.04 To verify that control rod bank reactivity worth values

are within their acceptance criteria.

61710-02 INSPECTION REQUIREMENTS

02.01 Review the licensee's procedure for measuring differential

and integral rod worth. Determine the adequacy of this procedure

by comparing it to the license commitment documents of 01.01, above.

02.02 Review the retained records for recent control rod bank

worth measurements. If possible, observe actual measurements as

they are conducted. Verify that:

a. Prerequisites and initial conditions were met.

b. Precautions and limitations were observed.

c. Plant conditions were maintained as specified in the procedure. Changes or relaxations of plant conditions were

approved by the appropriate licensee personnel (e.g., chief

test engineer) and any other procedural deviations were

similarly approved.
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d. Reactor coolant and pressurizer boron concentration samples

were taken at periodic intervals (typically 30-minute sampling

frequencies).
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e. Calculations of control rod bank reactivity worths are

correct. This includes the application of necessary correction factors.

f. Values obtained for control rod bank worths are within the

acceptance criteria generated from analytical prediction of

core reactivity and control rod neutron absorption characteristics.

g. The licensee has properly resolved any discrepancies between

actual measurements and predicted reactivity worths.

61710-03 INSPECTION GUIDANCE

General Guidance

a. Measurement Purposes. The purposes of measuring control rod

bank reactivity worths are to verify they are in accordance

with design predictions and assist in the verification of

adequate shutdown margin (the determination of shutdown margin

is a Technical Specification requirement).

b. Reactor Conditions. The reactivity worth of each control rod

bank (or group) is typically measured with the reactor

maintained critical at hot zero power. An attempt is made to

maintain reactor coolant temperature and pressure constant

throughout each test. The test procedure should call for

periodic recording of reactor parameters such as reactor

neutron level, reactor coolant system temperature, pressure

and boron concentration, and pressurizer boron concentration.

c. Control Rod Reactivity Worth Measurement Methods. Two control

rod reactivity worth measurement methods are typically used.

1. Boron Exchange Method. Boron concentration is changed in

a continuous manner. One control rod bank is

incrementally moved over its full travel in response to

the changing boron concentration. Differential control

rod bank reactivity worth values (/h) are calculated

using the reactivity computer. Differential control rod

bank reactivity worth curves are then plotted versus bank

height (/h vs. h). The inspector should verify that

the licensee's method of conversion from reactivity

measured per unit time to reactivity per unit rod length

is correct and reasonable. Corrections must be included

for changes in reactor coolant system parameters during

the test. An integral control rod bank reactivity worth

curve (vs. h) is produced directly from the

differential curve for that bank.

2. Rod Swap Method. Prior to this test, the control rod

bank reactivity worth curve for a reference control rod

bank must be determined using the boron exchange method

of 03.01c1 above. The reference control rod bank is

withdrawn from its fully inserted position while

inserting the test control rod bank from its fully
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withdrawn position. A critical condition is established

with the test control rod bank fully inserted. The

position of the reference control rod bank is recorded.

The integral control rod bank reactivity worth of the

test bank is determined from the integral control rod

reactivity worth curve for the reference bank.

Corrections are made for changes in reactor coolant

system parameters during the test.

d. Control Rod Bank Sequence for Boron Exchange Method. Typically, the reactivity worths of the control rod banks are

measured during dilution in the normal order in which the

banks are inserted into the core, but without overlap (each

bank is fully inserted before moving the next bank). The

reactivity worths of the banks are then measured a second time

during boration while a normal overlap withdrawal sequence is

followed.

e. Because residents are generalists and do not have extensive

experience and technical expertise in the core physics field,

this inspection procedure should be performed by regional

inspectors during the startup physics testing sequence for

each refueling outage.

03.01 Specific Guidance

a. Inspection Requirement 02.02a. Typical prerequisites and

initial conditions for these measurements are as follows:

1. Operational alignment of the neutron monitoring system

has been satisfactorily completed.

2. The reactivity computer is installed and operational.

The reactivity computer is usually connected to an upper

detector of one excore detector string and to a lower

detector of an adjacent detector string to obtain a more

representative flux profile of the core.

3. Chemistry support is available to sample the reactor

coolant system and pressurizer for boron concentration at

the required intervals.

4. The reactor is critical at hot zero power. Reactor

neutron flux is at the level prescribed in the licensee

procedure.

5. Control rod banks are in their specified positions. The

control rod mode switch is in the position specified in

the licensee procedure (e.g., MANUAL or AUT0).

b. Inspection Requirement 02.02b. Typical precautions and

limitations for these measurements are as follows:

1. A limitation on the maximum startup rate and boron

dilution rate allowed during the procedure.
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2. Control bands to be observed for reactor coolant system

temperature and pressure.

3. A maximum neutron flux level and/or reactor power limit.

4. The maintenance of proper overlap or no overlap

conditions during specific steps of the procedure.

5. Positive adherence to unrelaxed core parameter

requirements such as hot channel factor or radial or

axial flux peaking limits.

6. Awareness and understanding of applicable Technical

Specification requirements (e.g., rod group height and

rod insertion limits).

61710-04 REFERENCES

Technical Specifications

Core Reload Analysis Report

Applicable Fuel Vendor Reports

ANS-19.6.1, "American National Standard Reload Startup Physics Tests

for Pressurized Water Reactors," (To be published Fall 1985).

END