WS RC-TR-95-028 6 CONF-73?787--88.

Comparison Testing of Mound Calorimeter and a SRS Calorimeter

by L. A. ReFab Westinghouse Savannah River Company Savannah River Site Aiken, South Carolina 29808 L A Foster Los Alamos National Laboratory NM

A document prepared for INSTITUTE OF NUCLEAR MATERIALS MANAGEMENT CONFERENCE MEETING at Palm Desert from 07/09/95 - 0711 3/95.

DOE Contract No. DE-AC09-89SR18035

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COMPARISON TESTING OF A MOUND CALORIMETER AND A SAVANNAH RIVER SITE CALORIMETER

Lee A. ReFalo Westinghouse Savannah River Company

Savannah River Technology Center Aiken, South Carolina, 29803, USA

Lynn A. Foster Nuclear Materials Management and Accountability, Group NMT-4 Los Alamos National Laboratory, Los Alamos, NM, 87545, USA

ABSTRACT This paper describes the paired comparison

testing of a Savannah River Site (SRS) calorimeter and a Mound calorimeter. Prior to this test, no offsite testing had been performed on an SRS calorimeter. The testing was performed at the Plutonium Facility of Los Alamos National Laboratory (LAW) , The SRS calorimeter was designed, fabricated and delivered to LANL. The Mound calorimeter chosen for comparison was similar in well dimensions and located in the same room as the SRS calorimeter. There were three series of tests performed. First, twenty radiometric standard measurements were compIeted using two different standards. The second series of tests were dedicated to heat distribution measurements and the third series focused on measuring typical process samples.

INTRODUCTION Calorimetry is the most accurate method

used for nuclear materials accountability. Calorimeters measure the emitted thermal power from radioactive decay. The measured thermal power is converted to mass through accepted watts per gram constants.

Mound began making radiometric calorimeters for other DOE sites in 1949 and has built more than 200 calorimeters since then. The types of calorimeters vary both in size and configuration. Sizes have ranged from 1.0 to 17 inches in height and 0.25 to 12.5 inches in diameter. Mound built its first twin resistance bridge in 1948 and subsequently three different configurations of it: the full twin, the over/ under, and the gradient gap. Each of these configurations has been used in a variety of systems including glove boxes, automatic loadingfunloading, and sealed chambers for measurement of standards1.

The Equipment Engineering Section (EES) of the SRS delivered its first calorimeter in 1987. EES began building calorimeters to support high accuracy measurements without using water. The first calorimeter was a 'heat removal down a rod' design utilizing a power replacement technique. It was used with success in SRS's tritium area and was the design basis for several other calorimeters. Sizes have ranged from 2.5 to 7.3 inches in diameter and 8 to 18 inches in height. Other design bases have been developed over the past few years including air and water convection calorimetry.

EES was requested to build a calorimeter and submit it for independent, comparison testing. An agreement was established with LANL to conduct the testing. The test protocol was developed and the calorimeter delivered to LANL.

MOUND CALORIMETER The Mound calorimeter chosen for

comparison was a water jacket, overlunder system with a measurement well 7 inches in diameter and 12 inches deep. The calorimeter was a resistance bridge calorimeter which has two resistance thermometers. The first resistance thermometer is wrapped around the sample's thermel. Beneath the sample thermel is a thermel wrapped with the second resistance thermometer which serves as a reference. Each resistance thermometer is connected to a Wheatstone bridge. Constant current is supplied to the bridge and voltage measured. The water jacket provides a constant temperature for the calorimeter to operate against. When a heat producing source is placed in the measurement well, heat will flow from the source to the water jacket producing a voltage differential across the bridge. The voltage is measured and equated to watts through calibration constants.

SRS CALORIMETER The SRS calorimeter was designed similar in

both measurement well size and overall size as the Mound calorimeter. The design intent was to fabricate a medium range and complexity system. The SRS calorimeter operates on a power replacement technique. A unique configuration of active and passive heat shields keeps heat flow, other than through a power metering rod, to a very low and constant value. To achieve the power replacement technique, an electrical heater is attached to the base of the thermal well. A high conductivity power metering rod is also attached to the base of the thermal well. The other end of the power metering rod is connected to a heat removal device. The electrical heater supplies power to maintain a thermistor at the hot end of the power metering rod at a fixed temperature. The heat removal device removes power and holds the cold end thermistor at a fixed temperature. The constant temperature difference across the power metering rod establishes a fixed and constant heat flow. Thus, any power added by a sample in the thermal well is measured by a corresponding decrease in power to the electrical heater.

TEST PROTOCOL The comparison testing included three series

of tests. First, ten measurements of a 2.97 watt plutonium-238 heat source were made on each calorimeter alternating with a 7.26 watt plutonium-238 heat source. .Second, the 2.97 watt source was used to conduct heat distribution measurements. Five measurements were taken on each calorimeter with varying source locations. The third series of tests provided for typical process samples.

Data analysis for the first series included baseline repeatability, sample measurement repeatability, and measurement timing. The heat distribution measurements were analyzed for sample measurement repeatability and the typical process samples were analyzed for their measurement timing.

The coefficient of variation (CVAR) of the theoretical (T), or standard's, power divided by the actual (A), or measured, power was used for comparison of sample measurement repeatability. The coefficient of variation of the baseline power value was used for baseline repeatability comparison and average times were used for measurement time comparison.

Following are the two equations used to compute the coefficient of variation.

Standard Deviation (STD):

i=l J (n-1)

Coefficient of Variation (CVAR%):

CVAR'Yo = [STD(T/A's)]* 100Yo

TEST RESULTS The Mound calorimeter was operated in the

replacement mode (not in the servo-controlled mode) and inserts were used. The SRS Calorimeter was operated using its power replacement technique. Measurements were conducted during the same time frame with sources alternating between calorimeters. Timing information from the Mound calorimeter was taken from computer generated data sheets and on the SRS calorimeter from the computer screen. Mound certified radiometric heat sources were used in all test series. Typical process sam les used in the third series of tests included 2 p 9 ~ metals, oxides, and residues.

Tables I - VI present a summary of the test results. Tables I and I1 show the coefficient of variation in percent and wattage. The wattage values in Table I were obtained by multiplying the percentage times the source value (2.97 watts and 7.26 watts). The wattage values in Table I1 are the standard deviations of the baselines. Table I11 is the average assay time of the first twenty standard measurements and Table IV is the average baseline measurement time for the first twenty baselines. The heat distribution, coefficient of variation is shown in Table V and reflects measurements from the upper portion of the well to the lower portion. Table VI shows the average of ten process sample measurements.

Table I I Series 1. SamDle Measurement CVAR% I

Mound

Table I1 1 Series 1. Baseline Measurement CVAR% I

B B H 0.248% 2.89 mW 0.0182% 1.89 mW

Table 111 Series 1, Sample Measurement Time AVG

Mound II SRS

1 - - ~ - ~~~

354 minutes r 368 minutes

Table IV I Series 1, Baseline Measurement Time AVG I

341 minutes 267 minutes

Table V , Series 2, Heat Distribution WAR%

Mound I I SRS

I II .014% .057% I Table VI

-1 ~ - ~ -~

Series 3, Typical Process Sample Measurement Times AVG

I 474 minutes II 434 minutes I

CONCLUSION The test was an overall success. The

calorimeter was moved to LANL and performed at least as well as the Mound calorimeter. No significant damage occurred to the system both on delivery and return. The calorimeter is now operational at the SRS.

Full cooperation was received from LANL. throughout the delivery, testing, and return of the SRS calorimeter.

REFERENCES 1. J.R Wetzel, M.F. Duff, "Mound Calorimeter Instrumentation", Proceedings Of The International Workshop on Calorimetry , 36-38, 1992.

* The information contained in this article was developed during work under Contract No. DE- AC09-89SR18035 with the U. S. Department of Energy.