Issue Date: 07/14/86 - 1 - 61706

NRC INSPECTION MANUAL DI

INSPECTION PROCEDURE 61706

CORE THERMAL POWER EVALUATION

PROGRAM APPLICABILITY: 2515 (SUPPLEMENTAL), 2525

61706-01 INSPECTION OBJECTIVE

To verify that the calculation of core thermal power is correct and

that the procedure used is technically adequate.

61706-02 INSPECTION REQUIREMENTS

02.01 Review the licensee's core thermal power evaluation

procedure for boiling-water reactors (BWRs), pressurized-water

reactors (PWRs), and high-temperature gas-cooled reactor (HTGR) at

>50% power for the following:

a. Examine the "Core Performance Evaluation" data sheet, or

equivalent, and verify that data are reasonable, consistent

with previous data, and properly recorded.

b. Review the procedure for initial conditions and prerequisites.

c. Verify that the test and plant instruments used to obtain data

are properly calibrated.

d. Review the licensee's core thermal power calculations to

verify that they are correct.

e. Verify that the power range nuclear instruments are properly

adjusted to agree with the results of the heat balance.

f. Verify that the procedure specifies the condition of the steam

generator blowdown system during the core thermal power

evaluation (PWR only).

02.02 Verify, by a 1-month sample, that the frequency of

evaluations is as prescribed by the Plant's Technical Specifications

(TS).

02.03 Independently calculate the core thermal power using the

licensee's procedure for manual calculations or an NRC-developed

calculation such as TPDWR1.
61706 - 2 - Issue Date: 07/14/86

02.04 Verify that the core thermal power evaluation results were

reviewed, approved, and documented in accordance with the licensee's

administrative control procedures.
Issue Date: 07/14/86 - 3 - 61706

61706-03 INSPECTION GUIDANCE

General Guidance. The thermal power of the BWR, PWR, and the HTGR

is determined by a heat balance on the reactor system using

operating data. Under steady-state conditions, the reactor heat

output is obtained as the difference between the total heat removed

from the reactor system and the total heat added in the flow streams

returning to the reactor. A core heat balance in the power range

is made to ensure that the core is operated at all times within the

required thermal limits and/or fuel warranty requirements. Thermal

power calculation is performed either by the plant's computer or by

a manual method. The latter is normally required when the computer

program is not working or to double check results obtained from the

computer.

03.01 Specific Guidance

a. Inspection Requirement 02.01b. Typical initial conditions and

prerequisites for a core thermal power determination are as

follows:

1. At the desired power level, the plant is operated for a

sufficient length of time to show that steady-state

operating conditions have been attained.

2. Feedwater flow, water levels, and all controllable

temperatures and pressures are maintained as nearly as

possible, unchanged throughout the data acquisition

period.

b. Inspection Requirement 02.01c. Although some of the instruments and most of the computer points may not be safety

related, they must be calibrated in a traceable manner if they

are used to verify operation within the licensed power limit.

In many situations, problems with input data are far more

common findings than findings of inadequate heat balance

equations or poor arithmetic.

c. Inspection Requirement 02.01d. The thermal power is equal to

the rate of heat transfer to the steam system plus certain

heat losses, less the power contributed by the main coolant

pumps (recirculating pumps in BWRs). The heat transfer to the

system is equal to the enthalpy difference between the

feedwater and the steam, multiplied by the mass flow of the

feedwater. For PWRs this quantity must be calculated for each

steam generator and summed. The minor heat losses are added.

These include heat losses through the thermal insulation and

the net loss between the letdown and the makeup to and from

the reactor water cleanup system (or gas cleanup system for

gas cooled reactors). The loss from steam generator blowdown

is also added, if this is present. The heat added by the

large reactor coolant pumps is subtracted.

d. Inspection Requirement 02.01e. For BWRs the gain of each

average power range monitor (APRM) amplifier should be

adjusted so that each APRM, following determination of the

heat balance, is adjusted or verified to read the APRM value
61706 - 4 - Issue Date: 07/14/86

required by plant procedures and/or TS. Likewise, for PWRs

and HTGRs, the power range instruments are adjusted to the

reactor power indicated by the heat balance.

Core thermal power evaluation is performed on a daily basis

for both PWRs and BWRs. The specific requirements can be

found in the plant's TS although the plant may follow more

stringent guidelines as recommended by the manufacturer.

Refer to Inspection Procedure 61705, "Calibration of Nuclear

Instrumentation Systems," if calibration is required. In

addition, the inspector should check that the average power

level over any 8-hour shift did not exceed the "full

steady-state licensed power level" (and similarly worded

terms). The exact 8-hour periods defined as "shifts" are up

to the plant, but should not be varied from day to day (the

easiest definition is a normal shift manned by a particular

"crew").

It is permissible to briefly exceed the "full, steady-state

licensed power level" by as much as 2% for as long as 15

minutes. In no case should 102% power be exceeded, but lesser

power "excursions" for longer periods should be allowed, with

the above as guidance. For example, 1% excess for 30 minutes

and 1/2% for 1 hour should be allowed. There are no limits

on the number of times these "excursions" may occur, or the

time interval that must separate such "excursions." The above

requirement regarding the 8-hour average power will prevent

abuse of this allowance.

e. Inspection Requirement 02.01f. The steam generator blowdown

system is designed to remove dissolved solids and other

impurities from the steam generator. If the blowdown is in

progress during the core thermal power evaluation,

consideration of the mass flow and enthalpy of this blowdown

should be based on a review of the licensee's calculations and

assumptions.

f. Inspection Requirement 02.03. Manual calculation is intended

as a backup for the computer-calculated thermal power in case

the computer is not operating. Manual calculation is

inherently not as accurate as the computer-calculated thermal

power. However, despite its accuracy limitations, the manual

calculation should agree within ±5% of the computer-calculated

thermal power (MWe). Even though the ±5% tolerance is not a

requirement, a difference of >5% between the computer

calculation and manual calculation indicates in all likelihood

that an error in either the computer calculation or the manual

calculation has been made. Most manual calculations performed

utilizing data from the computer are within 1% of the

computer-calculated thermal power.

An NRC program for Westinghouse PWRs entitled "TPDWR2:

Thermal Power Determination for Westinghouse Reactors, Version

2", is available from the Engineering and Generic

Communications Branch for use on the IBM PC. Users of this

program should refer to the user's guide, NUREG-1167. A

similar program for use on Combustion Engineering's reactors
Issue Date: 07/14/86 - 5 - 61706

entitled "TPDCER2: Thermal Power Determination for Combustion

Engineering Reactors, Version 2", and the users guide for this

program is also available from the Generic Communications

Branch.

END