* Minimum inspection program.

Issue Date: 10/11/85 - 1 - 61707

NRC INSPECTION MANUAL DI

INSPECTION PROCEDURE 61707

DETERMINATION OF REACTOR SHUTDOWN MARGIN

PROGRAM APPLICABILITY: 2515 (MINIMUM, SUPPLEMENTAL), 2525

61707-01 INSPECTION OBJECTIVES

01.01 To determine that the licensee is ensuring adequate

shutdown margin throughout the operating cycle.

*01.02 To verify that changes in shutdown margin due to

inoperable control rods have been properly addressed.

61707-02 INSPECTION REQUIREMENTS

02.01 PWR Inspection Requirements

a. Review the licensee's shutdown margin determination procedure

for technical adequacy.

b. Determine that shutdown margin calculations have been

performed at the frequency specified in the plant's technical

specifications (TS) since the last refueling outage.

c. Verify the following for shutdown margin determinations made

since the last refueling outage, or made in the last 6 months

while in the applicable TS mode, whichever is less:

*1. The most recent critical conditions prior to the shutdown

were accurately recorded.

*2. The calculations to assess the reactivity contributions

to the total core reactivity change were correctly

performed for the following parameters:

(a) boron concentration

(b) full-length control rod bank worth changes as a

result of position, boration, etc.
61707 - 2 - Issue Date: 10/11/85

(c) shutdown bank rods

(d) part-length rods (if in use, verify that their operational status was reflected in the shutdown margin

allowance)

(e) temperature

(f) power level

(g) xenon concentration

(h) samarium and other fission product concentrations

(i) fuel burnup and burnable poison depletion

*3. The results of the shutdown margin calculation met the

conditions prescribed by the TS.

*4. Changes made in boron concentration as a consequence of

the shutdown margin calculation were properly verified by

chemical analysis.

*d. Evaluate the licensee's analysis of a condition where the

shutdown margin could not be met and evaluate the adequacy of

corrective actions that were taken.

e. Review the results of the licensee's procedure for demonstrating agreement between the overall core reactivity balance and

the predicted values for surveillance tests performed since

the last refueling or in the last 6 months while in the

applicable TS mode, whichever is less.

1. Verify that the determination was made at the periodicity

required by TS.

2. Verify that the determination was made using the parameters required by TS.

3. Verify that the normalization of the predicted reactivity

values was accomplished within the timeframe required by

TS.

f. Verify that the licensee has reviewed all data supplied by the

fuel vendor that is used in the shutdown margin determination.

02.02 BWR and HTGR Inspection Requirements

a. Review the licensee's shutdown margin procedure for technical

adequacy.

b. Examine the shutdown margin determination made at the

beginning of the current operating cycle to determine if

results are in agreement with TS requirements.
Issue Date: 10/11/85 - 3 - 61707

c. Verify the correctness of the calculations made to determine

the amount of control rod withdrawal required to correspond

to the specified shutdown margin.

d. Verify that the licensee has reviewed all data supplied by the

fuel vendor that is used in the shutdown margin determination.

*e. Verify that a shutdown margin determination was performed

after any recent incidence of the inability of a control rod

to insert and that the results met the conditions prescribed

by TS.

*f. Examine the licensee's analysis of a condition where the

shutdown margin could not be met and evaluate the adequacy of

corrective actions that were taken.

g. Review the results of the licensee's procedure for demonstrating agreement between the overall core reactivity balance and

the predicted values (reactivity anomaly surveillance) for

tests performed since the last refueling or in the last 6

months while in the applicable TS mode, whichever is less.

1. Verify that the determination was made at the periodicity

required by TS.

2. Verify that the determination was made using the parameters required by TS.

3. Verify that the normalization of the predicted reactivity

values was accomplished within the timeframe required by

TS.

61707-03 INSPECTION GUIDANCE

General Guidance. Because residents are generalists and do not have

extensive experience and technical expertise in the core physics

field, the majority of this inspection procedure should be performed

by regional inspectors during the startup physics testing sequence

for each refueling outage. Residents should, however, be called

upon to conduct the asterisked inspection requirements to ensure TS

compliance in the event of an inoperable control rod. Residents are

best able to perform these inspection requirements because they can

readily respond due to their location onsite, and TS compliance can

easily be determined without a detailed core physics background.

03.01 Specific Guidance

a. Inspection Requirement 02.01c2. The basic computation

performed to determine the reactivity change associated with

each parameter is to multiply the reactivity coefficient of

each parameter by the parameter's change in going from the

most recent critical condition to the shutdown condition. The

inspector should be aware that the "most recent critical"

condition may not truly be what these words imply. For

instance, occasionally a startup following an outage is made

in which criticality is reached and maintained for a brief
61707 - 4 - Issue Date: 10/11/85

period of time followed by a shutdown. Although this would

truly represent the "most recent critical" condition, it would

be incorrect to assess this as representative of core

reactivity conditions. Rather, the equilibrium condition for

the extended pre-outage power history would be most representative of core conditions and, therefore, should be used as

the "most recent critical" condition for deriving data for the

determination of shutdown margin.

Reactivity coefficients (or reactivity values) for the various

parameters are normally obtained from curves found in the

plant's technical data book. The inspector should verify that

the curves used for obtaining the reactivity values are the

most current and up-to-date and that the values observed were

applied correctly in the shutdown margin determination. In

addition, the inspector should verify that the curves were

approved by the onsite review committee and plant manager.

Ensure that the curves are controlled and so marked. The

inspector should verify that the sign convention for reactivity used in the licensee's calculations is consistent

throughout.

b. Inspection Requirement 02.01c4. If the available shutdown

margin resulting from the total reactivity change is insufficient to meet TS requirements, an additional amount of

negative reactivity in the form of boration of the reactor

coolant system must be added. A calculation of the boron

concentration needed to meet the required shutdown margin must

be performed. Some procedures require these calculations to

be independently checked. Should this be the case, the

inspector should verify that the calculational check was

accomplished pursuant to this requirement.

c. Inspection Requirement 02.02a. Historically BWRs have used

two types of shutdown margin tests to demonstrate compliance

with TS requirements. One type involves withdrawing the

strongest control rod plus additional rod(s) with a calculated

worth equal to or greater than the required margin. The other

type (most common) is performed by pulling the strongest

control rod plus additional rods until criticality is

achieved. This method, recommended by GE, is termed the

In-sequence Critical Demonstration. This involves pulling

rods in the normal startup sequence. Table 11-1 in GE Station

Nuclear Engineering Manual (NEDO-24810A, Volume 1) provides

a worksheet for making calculations using this method.

d. Inspection Requirement 02.02b. Shutdown margin must be

demonstrated at the beginning of cycle (BOC). For BWRs, if

the core reactivity exhibits an increase with exposure

(defined as the R-value) due to burnable poisons, the

inspector should verify that an additional increment of

shutdown margin equal to this increase was demonstrated at

BOC.

e. Inspection Requirements 02.01f. and 02.02d. Data provided by

the fuel vendor normally includes new core loading pattern,

location of highest-worth control rod, rod worth curves, and
Issue Date: 10/11/85 - 5 - 61707

increase in core reactivity with exposure for BWRs (R-value).

If rod worth curves, boron worth curves, or xenon values

supplied by the fuel vendor have been adjusted by the

licensee, the inspector should determine the reason for and

validity of this adjustment.

f. Inspection Requirements 02.01d. and 02.02f. Under circumstances where the shutdown margin cannot be met, the following

items, which could cause the anomolous conditions, should be

checked:

1. rod drifting

2. fuel assembly positions

3. water temperature

4. water chemistry (boron carbide tubes in BWRs may have

ruptured, or water coolant tube rupture in HTGRs may

introduce water into the helium coolant system and

graphite moderator)

5. manufacturing (manufacturing records should be matched

against actual fuel)

Specific action on the part of the licensee is prescribed by the

plant's TS. The inspector should verify that the required action

was taken.

END