NUREG/CR-2486

UCRL-53036

R-4

Final Results of the Hydrogen

Igniter Experimental Program

Manuscript Completed: November 1981

Date Published: February 1982

Prepared by

.W. E. Lowry (Principal Investigator), B. R. Bowman, LLNL,

B. W. Davis, Northern Arizona University

Lawrence Livermore National Laboratory

7000 East Avenue

Livermore, CA 94550

Prepared for

Office of Nuclear Reactor Regulation

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555

NRC FIN No. A0418
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FINAL RESULTS OF THE HYDROGEN

IGNITER EXPERIMENTAL PROGRAM

ABSTRACT

Thermal igniters proposed by the Tennessee Valley Authority for

intentional ignition of hydrogen in nuclear reactor containments have been

tested in mixtures of air, hydrogen, and steam. The igniters, conventional

diesel engine glow plugs, were tested in a 10.6 ft 3 pressure vessel with dry

hydrogen concentrations from 4% to 29% hydrogen, and in steam fractions of up

to 50%. Dry tests indicated complete combustion between 8% and 9% H2 , and

no combustion for concentrations below 5%. Steam tests were done with

hydrogen volume fractions of 8%, 10%, and 12%. Steam concentrations of up to

30% consistently resulted in ignition. Most of the 40% steam fraction tests

resulted in combustion. In a few isolated cases the 50% steam fraction tests

indicated a pressure rise. Circulation of the mixture improved combustion in

both the dry and the steam tests, most notably at low H2 concentrations. An

analysis of the high steam fraction test data showed a high probability for

the presence of small, suspended, water droplets in the test mixture. The

suppressive influence of this condensation-generated fog on combustion is

evaluated.

iii-iv

CONTENTS

Abstract . . . . .. . ... . ... .. . .

List of Illustrations ........ .....

List of Tables

Foreword . . . . . . . . . . . . . . . . . .

Executive Summary .. ................

Chapter 1: Introduction ...............

TMI-2 and the Hydrogen Problem.

NRC and Industry Response....

Previous Research.. ..........

The LLNL Program ............

iii

vi

viii

ix

1

3

3

4

5

8

Chapter 2:

Chapter 3:

Chapter 4:

Experimental Design . . . ........ . ........... .......

Mechanical System. ..... .......... ........ . .....

Instrumentation ..... .............................

Test Procedures .... .... .....................

Results ......... . ...................... .......

Dry Tests ............ ............... . ......... ..

Standard Steam Tests ......... ...... ............. .

Condensation Tests ......... ......................

Conclusions . . . . .......... ..................

10

10

13

19

21

22

28

32

38

41-

43

47

References .. ........ . ........

Appendix A. Pre- and Post-Test Calculations .

. I . . . . . . . . . .

. . . . . . . . . .. .

Appendix B. Scoping Analysis of Condensation Test Conditions

v
LIST OF ILLUSTRATIONS

1. The Sequoyan Unit 2 containment vessel encloses

approximately 1 million cuoic feet of free volume.

Forty-five igniters are spaced throughout that volume . 6. 

2. TVA chose tne GM AC-7G glow plug as the thermal

ignition source in their Interim Distributed Ignition

System (IDIS). The heating element is tne l-in.-long

by 3/16-in.-diameter rod on the left ...... . ......... 7

5. The LLNL igniter tests were conducted *in a modified

compressed air storage vessel. The fluid and mechanical

syscems are shown in schematic form .I........ .......... 10

4. Tne glow plug holder could place the plug at vafious

elevations in the center of the vessel . . . 12

5. Primary measurement locations are shown. Thermocouples

are indicated by T's................. ..... . .. .. 14

6. (a) Vessel mixture temperatures were detected witn

thermocoupies inserted through pressure fittings

(o) Pressure transducers were .offset by 6-in. tubes to

protect them from thermal transients. . . ... . .... 16

7. A Chromel-Alumel (type K) thermocouple was spot welded

to the glow plug surface for dynamic temperature recording 17

8. The experimental assembly was mounted on a trailer and

located on a firing taole at the Site 300 hign

explosives test facility.... .................... . . 18

9. Pressure rise is snown as a function of hydrogen

concentration for dry H2 /air tests ................. 24

10. To compare with results of other test programs,

normalized pressure (zAP/P init) is plotted as a

function of H2 concentration.. . .................. ... 25

11. Burn completion is depicted as percentage of original

H2 consumed for dry tests. . ............ 26

12. Glow plug temperature traces are snown• for 14.4 VAC

and 12.0 VAC voltage levels.............. 27

13. Pressure rise is shown as a function of H2 concentration

for steam tests ................. 30

vi
LIST OF ILLUSTRATIONS (Continued)

14. Burn completion plotted vs. percentage of H2 for

standard steam tests. . ....... . . . .... .. 31

15. A Storz lens in conjunction with a lowlight level

television camera was used to film the condensation tests . 34

16. This sequence of pictures was taken from a video tape of

test #52. Note that the "fog" is clear four minutes

into the test, but no burn was noticed....... ..... . . . 35

vii
LIST OF TABLES

1. instrumentation specifications for hydrogen igniter tests . . 13

2. H2 igniter dry test series. .................. . ...... . . 23

3. H2 igniter standard steam test series ..... .. ..... 29

4. Condensation test series....... ....... ....... . 33

viii
FOREWORD

This document reports the final experimental results of the LLNL Hydrogen

Igniter Test Program. The project was undertaken at the request of the

Nuclear Regulatory Commission to provide technical assistance in the licensing

process for the Tennessee Valley Authority's Sequoyah Unit 1 nuclear power,

plant. The program was funded and directed by the Containment Systems Branch

(Division of Systems Integration) of the NRC Office of Nuclear Reactor

Regulation. Its purpose was to independently test thermal igniters, proposed

by TVA, as combustion initiators in environments containing known

concentrations of hydrogen, air, and steam.

The test program was administered by the Reactor Safety Program of the

LLNL Nuclear Systems Safety Program. Experimental design and project

management were supplied by the Thermo Fluid Mechanics Group of the Nuclear

Test Engineering Division.

Design, fabrication, and conducting the first phase of the tests was to be

completed in three months. The ability of this program to produce

experimental results in such a short time was due to the excellent support

provided by various organizations at LLNL. The authors would like to

acknowledge the contributions of the following people:

* Bill Comfort and Dick Martin who provided conceptual design and

subsequent technical assistance;

* Bill Shay and John Holm, who provided instrumentation support;

0 Del Eckels and Gary Power, who provided mechanical support;

* Rex Blocker and John Mellor who were responsible for program

coordination; and

0 Bob Kaster, Fred Sator, and Hal Vyverberg, who carried out the

Site 300 bunker operation.

Additional appreciation is extended to US NRC contacts, Charles Tinkler and

Walt Butler, for their patience and cooperation.

ix

EXECUTIVE SUMMARY ',

The US Nuclear Regulatory Commission (NRC) has engaged the Lawrence

Livermore National Laboratory (LLNL) to evaluate the capability of glow plugs

to function as ignition sources in hydrogen/air/steam environments. The-glow

plugs are the active components of a hydrogen mitigation system, proposed by

the Tennessee Valley Authority, used to control hydrogen released into the

containment from a loss of coolant accident involving core degradation.

Tests were conducted in a 10.6 ft3 insulated pressure vessel. Primary

data recorded included temperature, pressure, and gas concentration

measurements. Dry hydrogen/air tests were conducted with hydrogen

concentrations as high as 29% by volume, and steam tests with 8% to 12%

hydrogen concentrations and steam fractions as high 'as 50%..

Dry tests showed the glow plug to be capable of at least partially

igniting hydrogen/air mixtures as low as 6% H2 , and down to 5% H2 if the

mixture was circulated. As the hydrogen concentration approached 9%, a jump

to relatively complete combustion took place. Stoichiometric hydrogen/air

tests (29% H2 ) produced no detonation pressures with either the glow plug or

a one-Joule spark source.

Steam tests with H fractions from 8% to 12% and steam fractions of 10%

to 30% consistently produced burns. Three 40% steam tests did not combust, as

would be indicated with discrete pressure/temperature rises. With a few

exceptions, no 50% steam fraction test ignited. In most steam tests,

circulation of the mixture increased the degree of burn completeness.

In order to explore more severe, but less likely, conditions under which

glow plugs must function, several condensation-type tests were conducted in

which the vessel was charged up to a 50% steam, 10% H2 condition. The steam

was then allowed to condense slowly while the glow plug remained activated.

Frequently, the steam would condense enough so the bulk vessel conditions

appeared to be similar to previous tests in which the mixture combusted.

Rarely was any discrete pressure rise noted, although hydrogen had been

consumed as indicated by the gas analysis. Subsequent examination of the data

had indicated a high probability of enough suspended water droplets in the

vessel mixture to suppress combustion. It was clear that thermal

1
recombination was taking place in the longer tests. Another effect noted was

the possibility of a fuel-lean zone around the glow plug due to the

evaporation of. local suspended water droplets, which would increase the local

steam fraction.

Throughout the test series no-deterioration was noted in the glow plug's

heat-up characteristics.

2
CHAPTER 1: INTRODUCTION

TMI-2 AND THE'HYDROGEN PROBLEM

During the Three Mile Island Unit 2 accident in March 1979,. gaseous

hydrogen produced in the reactor vessel was released into the containment

building and combusted to produce-a substantial pressure rise of 28 psi. The

fact that hydrogen was produced was not unexpected, since reactors are

equipped with thermal recombiners designed to assimilate hydrogen from

radiolytic decomposition of water in a design-basis loss-of-coolant accident

(LOCA). However, the TMI-2 event was not a design-basis LOCA; the open relief

valve and subsequent operator errors closely represented a small LOCA

compounded by Emergency Core Cooling System override. This led to a gross

uncovering of the core fuel assemblies for a.significant length of time,

releasing excessive hydrogen as a result of the interaction of steam with'the

zirconium fuel cladding. The conventional thermal recombiners were not

capable of handling the high rate of hydrogen produced from this degraded-core

metal-water reaction.

It is suspected that most of the hydrogen was released into the

containment atmosphere during the first four hours of the accident. Steam

generator pressure transducers sensed a rapid 28 psi pressure rise, and

temperature sensors noted a 500F increase approximately ten hours after the

accident. Varied opinions exist regarding both the amount of hydrogen present

and the probable source of ignition. It is generally agreed that the pressure

rise was a result of a hydrogen burn. Post accident analyses have estimated

that approximately 45% of the fuel cladding had reacted (thedesign basis

assumes only 5% of the fuel cladding would react). Subsequent entrances into

the containment building have produced confirming evidence, in the form of

charred equipment and overpressure damage, that a burn did occur.

3
NRC AND INDUSTRY RESPONSE

'The observed 28-psi pressure spike was well below the TMI-2 design

pressure of 55 psig; however, this event was clearly not one included in

design basis accident scenarios. The containment building at TMI-2 is

classified as a "large dry" containment. This means that its net free volume

is about two to three million cubic feet. Containment buildings classified as

"intermediate" have volumes of 1.2 to 1.5 million cubic feet (with

corresponding design pressures of 12 to 15 psig); those classified as "small"

containments have volumes of approximately 0.3 million cubic feet (45 to 62

psig design pressures).

The vulnerability of a containment building to hydrogen combustion is a

function of several variables. Included among these are: 1) quantity and

rate of hydrogen combustion; 2) volume of the containment; and 3) pressure

capability of the containment. Examination of the design of light water

reactor containments reveals that the pressure suppression containments are

more vulnerable because of their smaller volume or lower pressure capacity.

The- pressure suppression containments include the small Mark I and II boiling

water reactor (BWR) containments, the intermediate-sized Mark III BWR, and the

ice condenser PWR containments.

The NRC has determined that small containments (BWR Mk I & II) might fail

if 6 to 9% of the fuel cladding reacted with steam and subsequent combustion

of the hydrogen produced an adiabatic pressure rise (Ref. 1). Consequently,

an interim rule, posted October 1980, required that the atmospheres of these

units be made inert by purging the containment with nitrogen. Most Mark I and

II BWR's already operate in this manner so this ruling only affected new

plants and two existing plants. The large PWR dry containments, by virtue of

their large volume (2-3 million ft 3 )and higher design pressures (50-60

psig), are capable of withstanding pressures resulting from combustion of

hydrogen produced by the reaction of 100.% of the fuel cladding.

Consequently, for these structures no near-term mitigation measures were

required.

4
Similar calculations indicate that the intermediate containments may fail

if 25% of the fuel-cladding were to react and the resulting hydrogen released

into the containment to ignite instantaneously. These plants have not been

purged with an inert gas in the past because frequent entry is required for

maintenance and inspection. Consequently, the NRC has required, pending a

rulemaking on degraded core accidents, that owners of intermediate

containments provide additional control capability to accommodate hydrogen

produced by'a 75% reaction of the cladding.

The first utility to address the issue of degraded-core hydrogen control

was the Tennessee Valley Authority (TVA) in the process of licensing the

Sequoyah Unit 1 plant, an ice condenser unit (see Fig. 1). TVA has proposed

to use an array of 45 thermal igniters, called the Interim Distributed

Ignition. System (IDIS). These igniters are conventional diesel-engine glow

plugs (shown in Fig. 2), which are to be spaced throughout the containment

volume and activated at the start of an accident sequence. The purpose of the

IDIS is to ignite the gas mixture at lower concentrations of hydrogen,

preventing the accumulation of a mixture which could threaten the integrity of

the containment structure. Each igniter is mounted on a metal housing powered

by a 120 Volts ac (VAC) to 14 VAC step-down transformer.

TVA received its license to operate Sequoyah Unit 1 in'September 1980.

For operation of the plant beyond January 31, 1982, the NRC must confirm that

the hydrogen control measures installed will provide adequate safety margins.

At the time of this writing, TVA was in the process of developing the

permanent hydrogen mitigation system. The permanent system is envisioned to

represent an improvement of the IDIS while retaining the concept of locating

thermal igniters throughout the containment.

PREVIOUS RESEARCH

Although hydrogen combustion has been studied for years, information

applicable to the utilization of thermal ignition sources in containment

environments is not plentiful. Most ignition sources studied have been either

5
condenser.

1!50'

Accumulator

FIG. 1. The Sequoyah Unit 2 containment vessel encloses approximately 1

million cuoic feet of free volume. Forty-five igniters are spaced throughout

that volume.

6
-~

F

FIG. 2. TVA chose the GM AC-7G glow plug as the tnermal ignition source in

their Interim Distributed Ignition System (IDIS). The heating element is the

1-in.-long by 3/16-in.-diameter rod on tne left.

of the spark or pyrofuse type, capable of imparting large amounts of energy to

a small volume in a short time. The TVA glow plugs, however, are of low power

density and require a heat-up period of 12 to 20 seconds before reaching the

hydrogen ignition temperature. At that temperature, they emit from-150 to 220

W/in. over a surface area-of 0.6 in., 2 depending on the input voltage

(which varied from 12.0-to 14.4 VAC in the LLNL tests). An area of concern is

whether the igniters will function as intended in the post LOCA containment

environments. Typically, the post-LOCA atmosphere will contain some fraction

of steam and suspended water droplets. These water droplets may be created by

the expulsion of water from a break in the reactor coolant system,

condensation of steam in the atmosphere, or by operation of the containment

spray system.

Previous research has generally applied to dry hydrogen-air mixtures

ignited in small volumes. Extensive examination of dry hydrogen combustion in

7
enclosed spaces has been Conducted by the United States Bureau of Mines (Refs.

2 and 3). They have emphasized the identification of flammability and

detonation limits. In the last several years the nuclear power industry has

directed more attention to hydrogen management safety issues. Canadian

researchers (Ref. 4) have studied the effects of steam on hydrogen combustion

near the lower flammability limit and the effect of initial temperature on

burn velocities. Utility-sponsored experiments at Atomics International

(Ref. 4) utilized a shock tubeto'study flame and detonation initiation and

propagation in hydrogen-air mixtures, which included an assessment of spray

system effects. Work sponsored by General Electric (Ref. 6) assessed

characteristics of lower-explosion limit hydrogen-air mixtures with a variety

of ignition sources. More recently, TVA has sponsored a program to evaluate

the operational characteristics of the glow plugs installed in the Sequoyah

plant (Ref. 7). This study will include an evaluation in both dry and steam

environments.

At this time, both the Electric Power Research Institute and Sandia

National Laboratory (Albuquerque) are in the midst of extensive analytical and

experimental programs dealing with the hydrogen mitigation issue. The breadth

of involvement by various research institutes in the US and abroad was

realized when over 40 papers on hydrogen control were presented at the

workshop on the Impact of Hydrogen on Water Reactor Safety, sponsored by

Sandia at Albuquerque in January 1981.

THE LLNL PROGRAM

In July 1980 the NRC Office of Nuclear Reactor.Regulation requested.that

Lawrence Livermore National Laboratory conduct a short-term test program to

evaluate the use of the glow plugs selected by TVA in environments containing

known concentrations of hydrogen, air, and steam. The experiment, initiated

on August 1, 1980, was designed, constructed, and completed within three

months, as reported in Ref. 8. A follow-on series of tests was conducted from

February through June 1981, bringing the total number of tests to 100.

The specific objective of-the LLNL test program was to evaluate the

capability of the glow plugs proposed by TVA to ignite various mixtures.

Conditions and parameters studied included:

0 Dry hydrogen-air mixtures ranging from 4% to 16% hydrogen, with some

stoichiometric (29% hydrogen) tests;

8
* Standard steam tests with steam fractions from 10% up through 50%

with various hydrogen concentrations;

* Condensation tests with bulk conditions starting at 50% steam and 10%

hydrogen. The steam fraction was allowed to drop (via condensation)

to as low as 25% while ,the glow plug was activated continuously or

intermittently; and

* Circulation studies to assess the influence of fan-induced

circulation on ignition and'flame propagation.

9
,CHAPTER 2: EXPERIMENTAL DESIGN

MECHANICAL SYSTEM DESCRIPTION

Due to the short term nature of the program, it was necessary to use

available hardware and to design the equipment with emphasis on simplicity,

versatility to accommodate change, and rapid turnaround between tests. Major

components at the facility included the insulated and instrumented test

vessel, gas and air supplies, a commercial boiler, and the control/

instrumentation system. The experimental assembly was mounted on a flat bed

trailer and set on a firing table at the LLNL high explosives test facility.

All operations were conducted remotely from a firing bunker, once

instrumentation and the hydrogen supply were prepared. This procedure assured

personnel safety without requiring qualification of equipment for hydrogen

combustion pressures and temperatures.

A schematic of the igniter test facility is provided in Fig. 3. The burns

were contained in a 20-in.-diameter by 60-in.-long compressed air storage tank

with 3/16-in. thick walls, a working pressure of 200 psi, and a free volume of

10.6 ft 3 . The vessel was modified by the addition of two 8-in. ID ports and

Gas Glow plug conductor H2 fill bottle

vent a

Compressed air supply

10.6 ft 3

pressure vessel

Steam

bypass

AM

Condensate

drain

FIG. 3. The LLNL igniter tests were conducted in a modified compressed air

storage vessel. The fluid and mechanical systems are snown in schematic form.

10
one 4-in. port, several threaded penetrations for plumbing and instrument

connection, and R-11 fiberglass insulation on the exterior. Saturated steam

was supplied by a 300 lb/hr boiler at approximately 75 psi. The vessel was

equipped with both a gas vent and a condensate drain valve. Filtered

compressed air provided purging and pressurization. The contents were mixed

by a fan placed at one end of the chamber. Glow plug positioning and power

supply were provided by the assembly shown in Fig. 4.

Several mechanical changes were made after the first phase of testing

(tests #1 through #43). These are described below.

Glow Plug Location and Voltage. In the first test series, the glow plug

was located three inches above the bottom of the vessel. Later tests

positioned the plug at the bottom, center, and top of the vessel. Glow plug

voltage throughout the first series was 14.4 VAC, producing 130 Watts. For

some of the later tests, this was dropped to 12.0 VAC, producing 90 Watts.

Hydrogen Fill. Hydrogen was injected into the test vessel from a small

bottle mounted on the vessel. During the first series of experiments, the

bottle was filled to a pre-determined pressure and allowed to empty its

contents into the test vessel to achieve the desired hydrogen concentration.

Later experiments were conducted by slowly releasing hydrogen into the test

vessel until a desired overpressure was detected. This allowed several tests

to be made before the fill bottle had to be recharged.

Post-Test Vessel Purging. An additional change during the second test

series was'in the vessel purging procedure. Originally, a vacuum pump was

used to reduce vessel pressure to about one-half an atmosphere; then the

vessel was refilled with filtered compressed air. This process was repeated

several times before the vessel was prepared for the next test. In some

cases, the post-burn mixture had a high moisture content which caused

operating problems for the vacuum pump. The purging procedure was then

changed to circulate dry-filtered compressed air through the vessel for five

minutes after a test.

Circulating Fan. An air-powered fan was used in the first test series to

mix the vessel contents at various times during the test. This was changed to

an electric-induction type AC fan (4-in. diameter) and later to a variable

11
Copper

conductor

Insulator

P ower

supply

lead

/- Ground wire

1" flange

Modified Conax

pressure fitting

Support and

ground

Copper

cond uctortElectrical pressure

penetration

Glow plug i -"SS tube,

(GMA7 machined

3/16"D bybent

Chromel-Alumel

thermocouple spot

welded to glow

plug

FIG. 4. The glow plug holder could place the plug at various elevations in

tne center of the vessel.

12
speed DC motor/fan combination (6-in. diameter) for the second series. Both

of these later fans produced air speeds at the glow plug of approximately one

ft/sec.

INSTRUMENTATION

Primary data fdr the igniter tests included temperature, pressure, and gas

concentration measurements. Table 1 lists the instrument type and

application, and Fig. 5 shows the transducer locations.

Most temperature measurements were made with Chromel-Constantan (Type E)

thermocouples. These thermocouples were placed at five locations to sense the

TABLE 1. Instrumentation specifications for the hydrogen igniter tests.

Measurement Instrument Quantity Recorder

Vessel internal Kulite #XTM-I-190 2 recessed, 2-channel strip chart,

peak and static Strain guage type 1 flush mounted magnetic tape,

pressure transducer oscillograph, digital

read-out

Vessel mixture Chromel-Constantan 5 Magnetic tape,

temperature (Type E) thermocouple oscillograph,

digital read-out

Vessel outer Chromel-Constantan 2 Point plotter,

surface thermocouple magnetic tape

temperature

Ambient air Chromel-Constantan 1 Point plotter

temperature thermocouple

Glow plug Chromel-Alumel 1 Magnetic tape,

temperature (Type K) thermocouple oscillograph,

X-Y recorder

Glow plug Shunts 1 ea. X-Y recorder

voltage,

current

13
gage pressure transducers

-8" I D ports T (glow plug)

4" port

Sample bottle flange: T -

(6) 75 cc bottles

mounted concentrically

- 113.5"

18"l 31.5"

FIG. 5. Primary measurement locations are shown.- Thermocouples are indicated by T's.
mixture temperature inside the vessel. Two indicated the vessel outer wall

temperature, and an external thermocouple measured-the ambient air temperature

at. the facility. A typical installation for measurement of the mixture

temperature is shown in Fig. 6a.

Pressure measurements were made using two strain-gage pressure transducers

located on the top flange next to the glow plug penetration and at the 4-in.

port at the end of the vessel. These were offset with 1/8-in, pipe for

thermal protection (see Fig. 6b). Two additional pressure transducers were

added later. A low range sensor was added to assist in the hydrogen injection

operation, and another (identical to the two original transducers) was mounted

flush with the inner wall of the vessel.

Glow plug dynamic performance data included measurements of surface

temperature, input voltage, and input current. One Chromel-Alumel (type K)

thermocouple was spot-welded directly to the glow plug surface as shown in

Fig. 7.

Pressures and most temperatures were recorded on high-speed frequencymodulated magnetic tape at 20,000 samples per second. This data was then

digitized and transferred to computer tape for filtering, reduction, and

plotting on the LLNL CDC7600 computers. Other recorders used included an X-Y

plotter, a point plotter, a two-channel strip-chart recorder, and a multiple

channel osciliograph (see Table 1).

Gas sampling was accomplished by a six location sampling system. Samples

taken were later analyzed by mass spectrometer. The-six sampling stations

were located concentrically on the test vessel's side flange (see Fig. 5).

The 75 cm3 sample bottles were set up to provide "pull-through' samples. A

vacuum pump was used to pull a rough vacuum on the bottle for three to five - .

seconds. The vessel mixture was then pulled through the bottle for two

seconds before the bottle was sealed. One sample was taken before each glow

plug activation, and-another after'a burn had been Andicated by an increase in

the test vessel pressure. The fan was used to circulate the mixture in the

vessel before each sample was taken. Mass spectrometer analysis provided mole

fractions of all gases in. the bottle with the exception of water vapor. Water

vapor content was determined by the calculational procedure outlined in

Appendix A.

The final trailer-mounted assembly is shown in Fig. 8.

15
Chromel-Constantan

thermocouple assembly

Conax pressure fitting

vessel

wall

0. 125" outer sheath

*Pressure transducer

(strain gage)-k

II

6" " "

II

1/8" sch. 40

SS pipe

1" flange

0.020" SS sheath

0.003" thermocouple leads

(grounded junction)-

Brazed over tip

(cutaway view)

(a) (b)

FIG. 6. (a) Vessel mixture temperatures were detected with thermocouples inserted through pressure-fittings. (o) Pressure transducers were offset by

6-in. tubes to protect them from thermal transients.

16
8 -

4- , ./

. -,- - . .- -

-. - -- - -4

Type-K thermocouple

:spot welded to plug

FIG. 7. A Chromel-Alumel (type K) thermocouple was spot welded to the glow

plug surface for dynamic temperature recording.

17
H2 fill bottle SSteam geni

FIG. 8. The experimental assembly was mounted on a'trailer, and located on a

firing table at.the Site 300 high'explosives test facility.
TEST PROCEDURES

The tests conducted can be grouped into three generic types: 1) dry

air/H2 ; 2) standard steam; and 3) condensation tests. In all cases before a

test was started, the vessel was purged of combustion products or steam from a

previous test, any remaining water was drained, and the vessel was vented to

the atmosphere. Sampling-bottles were prepared, and the hydrogen fill bottle

was recharged. After this, the experiment was operated remotely from the

bunker.

The vessel was sealed and hydrogen injected to achieve the desired

concentration. To assure a homogeneous mixture, thecirculating fan was

operated for three to five minutes, then a pre-test gas sample was taken.

This procedure was the same for all tests. Details specific to each type of

test are described in the following.

Dry Air/H 2Tests.

1. If the mixture was to be in a quiescent state at firing, the

circulating fan was turned off for one. minute before activating

the glow plug. Otherwise, the fan was left on for the

circulating mixture tests. The approximate mixture velocity at

the glow plug was 1 ft/sec.

2. The glow plug was energized for 1 to 1-1/2 minutes.

3. The vessel contents were remixed for 3 to 5 minutes, and a

post-burn sample taken.

Standard Steam Tests.

These tests were similar to the dry tests with the exception of thesteam injection. Mixing and sampling of the contents before firing

was done in the same manner as for the dry tests. The detailed

procedure was as follows:

1. After the pre-burn sample was taken, steam was injected until

the pressure was well above that required to yield the

appropriate steam fraction. Appendix A contains a description

of the calculational method used to determine the appropriate

pressure at the moment of mixture ignition. The vessel was not

externally heated, so the steam concentration was reduced by

19
condensation, which resulted in a drop in the mixture

temperature and pressure. By repeatedly charging the vessel

with steam at the beginning of each test, the vessel walls were

pre-heated and the condensation rate reduced to a relatively

slow process. Glow plug energizing was timed so that the glow

plug would reach ignition temperature at a vessel pressure which

represented the desired steam fraction. Typically, the plug Was

energized for 1 to 1-1/2 minutes.

2. After the plug was deactivated, the vessel contents were remixed

for 3 to 5 minutes and a post-burn sample was taken.

Condensation Tests.

These tests were performed to iconfirm the results of earlier research

of combustion in the presence of high steam fractions (Ref. 9). Test

procedures were similar to those for the standard steam tests, except

that the intended initial steam fraction was uniformly high

(typically 50% with a hydrogen fraction of 10%). In addition, the

duration of these tests was long, at times 30 minutes. The glow plug

was either left on continually or fired for one minute at steam

fraction intervals of 5% (i.e., 50%, 45%, 40%...). During some of

these tests the steam fraction fell as low as 25%. Post-burn gas

sampling and vessel venting and purging were done in the normal

fashion.

20
CHAPTER 3:' RESULTS

Forty-three tests were made in the first phase of the program (Ref. 2).

This report presents results from the complete program.

At the completion of the first series of tests, pressure rise.and burn

completion data showed that the igniters were capable of igniting dry mixtures

with hydrogen concentrations as low as 7% and steam mixtures with 30% to 40%

steam with hydrogen concentrations as low as 8% (these were the lowest

hydrogen concentrations tested in the first series). A clear transition to

complete burns occurred in the dry tests between 8% and 9% hydrogen. This

transition was not as well defined in the steam tests, but occurred at

hydrogen concentrations of approximately 10 to 12%. It was clear that the

peak pressures were lowered for the steam tests, at times yielding half the

pressure of a dry test for the same hydrogen concentration. It was also noted

that circulation of the mixture increased combustion, particularly for low

hydrogen concentrations. Further, the glow plug performed consistently

throughout all tests and showed no signs of deterioration (at 14.4 VAC).

Two tests of the first series, tests #34 and #43, surfaced as anomalies.

In both cases initial assessment of the bulk test vessel conditions indicated

that combustion of the mixture should take place. In neither of these cases

was the mixture ignited as evidenced by pressure and temperature

measurements. These were "condensation" tests, in which the vessel was

charged to approximately 50% steam and 10% hydrogen. The steam was allowed to

condense slowly, while the glow plug was activated continuously in test #34,

and at 5% steam fraction intervals in test #43. In test #43, a significant

fraction of hydrogen (30%) was consumed with no indicated pressure increase.

It was not possible to convincingly explain the cause of these anomalies;

however, they caused enough concern to warrant further examination. The most

promising explanation of this anomalous behavior is that enough condensation

fog was present (as a result of repeated steam charge-up of the vessel) to

suppress flame initiation or propagation. In subsequent similar tests, fog

was observed at the start of the experiment but seemed to dissipate as the

steam fraction dropped to between 40% and 30%. These results are presented in

the subsection, Condensation Tests.

The second test series was begun with the following objectives:

0 To re-create the conditions of the two anomalous tests to determine

their inconsistent behavior;

21
" To examine-the influence of a circulating mixture on burn

characteristics, particularly at lower hydrogen fractions;

" To conduct more tests at steam fractions less than 30%;

* To determine if the glow plug voltage and vertical location

significantly alters the glow plug performance;

" To determine whether the no-burn anomalies were a function of igniter

characteristics by using a spark igniter as an alternate ignition

source in the condensation tests;

* To determine if the igniter could initiate a detonation by executing

several tests with stoichiometric hydrogen and air.

Results of the dry, standard steam, and condensation type tests are discussed

separately below.

DRY TESTS

Hydrogen concentrations from 4 to 16% and stoichiometric (29%) mixtures

were tested without steam under-quiescent conditions. For hydrogen

concentrations up to 8%, comparison tests were made with the fan circulating

the mixture at 1 ft/sec past the glow plug. The purpose of these tests was to

understand the flammability characteristics of dry hydrogen and air mixtures

with a glow plug ignition source.

Results of these tests are listed in Table 2. Initial pressure and

temperature conditions, gas concentrations, glow plug location and voltage,

fan on/off data, burn temperature and pressure rise data, and post experiment

concentrations are provided. Burn completeness data indicated by "% of

Original H2 Consumed" is calculated using gas analysis information. These

calculations are detailed in Appendix A.

Pressure rise for the dry tests is plotted as a function of hydrogen

concentration in Fig. 9. For all tests, the pressure of the vessel was

approximately 14.2 psia, ambient atmospheric, before hydrogen was injected.

Consequently, the initial pressure in the vessel when the glow plug was

activated was not the same for all cases, but increased as the H2

concentration increased. The corresponding maximum adiabatic pressure-rise

calculated with the CECS code (Ref. 10) for these initial conditions is also

indicated.

The results for both quiescent and circulating tests are shown. No

pressure rise was observed in either type of test, until the hydrogen

22
TABLE 2. H2 igniter dry test series.

Wall Glow Plug Data Burn Conditions

Percent H2 Initial Cond.b Temp. Temp.c Time To Peak AP Tmaxe % H2

Test # Expected Actuala Fan? T(oF) P(psig) (OF) (OF) Volts Loc.d (sec) (psi) (OF) Consumed

62

63

64

65

31

66

67

68

69

70

17

71

72

7677

7873 N.)

74

75

4

4

4

4,

6

6

6

6

6

6

8

8

8

8

8

8

8

8

8

4.27

4.05

3.34

4.02

7.30

5.61

5.89

5.96

6.'11

5.78

8.00

9.18

8.17

7.94

8.19

7.59

7.97

7.95

Off.

Off

On

On

Off

Off

Off

Off

On

On

Off

Off

Off

Off

Off

Off

On

On

On

70.0 0.44

71.2 0.43

70.9 0.48

74.1 0.48

72

72

74

75

14.4 Center

14.4 Center

14.4 Center

14.4 Center

67.0

77.2

81.7

87.4

88.0

90.3.,

81.0

60.4

67.6

80.2

79.5

80.1

70.0

74.7

76.6

1.8

0.76

0.78

0.79

0.90

0.97

1.2

1.1

1.2

1.1

1.1

1.3

1.2

1.2

1.1

75

80

87

90

91

64

70

82

83

82

70

75

80

1350

1300

1300

1300

1330

1310

1310

1300

1300

1300

1300

1300

1310

1330

1320

14.4

14.4

14.4

12.0

12.0

12.0

14.4

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

Bottom

Center

Center

Center

Center

Center

Bottom

Center

Center

Center

Center

Center

Center

Center

Top

3.5

3.0

3.0

3.0

0.2

0.2

5.0

0.15

0.5

0.5

0.2

0.3

0.1

0.1

0.1

None

None

None

None

2.5

0.1

0.2

0.2

16.0

13.5

3;5

37.0

1.2

0.6

3.0

2.4

32.0

33.0

32.0

37.0

38.0

42.0

.428

Same

Same

Same

475

450

545

975

190

Same 550

470

770

850

850

48

31f

3 3 f

20

61

53

55

100

43

63

44

49

97

99

99

Same <2

Same <2

Same' <2

Same <2

20 9 8.80

23 10 9.20

32 10 9.10

21 11 10.4

19 12 12.3

22 14 13.3

24 16 15.1

Off 46.0 1.5

Off

Off

77.0 1.6

75.0 1.7

--- 1310 14.4 Bottom

--- 1330 14.4 Bottom --- 1330 14.4 Bottom

1360 14.4 Bottom

2.0

1.6

0.8

968 100

1010

986

98

100

Off 54.0 1.8

Off 90.0 2.0 --- 1360 14.4 Bottom

0.5 45.0

0.4 62.0

Off 64.0 2.3 0.3 68.0

Off 82.0 2.5

1330 14.4 Bottom

1360 14.4 Bottom

932 100

965 100

1130 `100

1260 100

1540 100 (est.)

1660 100 (est.)

1850 .100 (est.)

98

99

100

29

29

29

'-29.0

32.9

28.0

Off 183

Off 180

Off 183

6.0

6.0

6.1

190

190

190

1440

1440

Spark

13.0 Center

13*0 Center

--- Center

0.3

0.2

0.2 0.15

87.0

105.0

110.0

120.0

a

b

c

d

e

f

Determined by gas analysis.

Average temperature in vessel. Atmospheric pressure was 14.2 psia.

Temperature of glow plug at ignition.

Location of plug in vessel: bottom--3 in. above bottom of vessel; center--center of vessel; top--3 in. from top.

Measured at T-2, adjacent to top flange of vessel. "Same" implies no rise in temperature noted at T.-2.

During tests 66 and 67, a second, more vigorous burn was experienced after the plug was turned off and the fan switched on to circulate the mixture before post-burn gas sampling. Burn could have been initiated by spark from fan; glow plug temperature was typically

500 - 7000 F at this time. ,,% H2' Consumed" value reflects second burn also.
90

80 -0 Quiescent test

X Circulating mixture test

70

60 

.

Adiabatic pressure rise

i5 (CECS, Tn =800 F)Y 0

50 -- ini

I.0

.0 0-

40

30 a.

201

10

4 6 8 10 12 14 16

Initial hydrogen fraction(%

FIG. 9. Pressure rise is shown as a function of hydrogen concentration for

dry H2/air tests.

concentration reached 5 to 6%. A~t-these concentrations the quiescent tests

began to show pressure rises of less than 1 psi, while the circulated tests

resulted in substantially higher pressures more closely paralleling the

calculated adiabatic curve. Under quiescent conditions a stepwise jump to

nearly complete burns was noted at hyd rogen concentrations between 8 and 9%.

This is consistent with other experimental data taken for similar tests.

To compare these results with those obtained by others at different

initial pressures, the ratio of the pressure rise to the absolute initial

pressure (AP/P init ) is plotted in Fig. 10. Normalized LLNL test results

are combined with previous work by the US Bureau of Mines (USBM), Fenwall Labs

(sponsored by TVA), and Sandia National Laboratory (Refs. 3, 7, and 11). The

USBM tests were conducted in a 905-ft3 spherical vessel, initiated by a

3

24
6 I II

0 LLN L, fan off

0 5 LLNL, fan on Adiabatic

io -Sandia, fan off pressure rise

: Sandia,.fan on (CECS, Tn 800 F)

_ A Fenwall, no fan

Of 4 0 USBOM, no fan

0~0

3 0

09

3) . ... "•-

.00

(2

0O•

0.0

N

0

z

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Initial hydrogen fraction(%)

FIG. 10. To compare with results of other test programs, normalized pressure

(AP/Pinit) is plotted as a function of H2 concentration.

spark source. Fenwall results utilized the TVA glow plug igniter in a

134-ft 3 spherical test chamber. The Sandia program uses an -108-ft 3

cylindrical vessel oriented vertically with the glow plug igniter at either

the center or in the lower portion of the vessel.

Burn completeness as a function of hydrogen concentration is shown in

Fig. ll. This plot also illustrates the transition to complete combustion at

H2 concentrations between 8 and 9%.

In general, the dry test results compare well with both the older USBM

data and that of current programs. The differences indicated in Fig. 10 could

be attributed to the difference in geometries of the test vessels. The Sandia

test vessel, for example, presents a greater fraction of the vessel volume to

the upward-propagating flame front characteristic of low H2 concentrations.

The LLNL tests and those performed in spherical vessels present less of the

25
~' I I ' I I I I V, . I

100 C) 0

80 F-

-o

E

60

0

-.-

C0-

o 40

0

0

0

0

0

o

F20 0

0 Quiescent mixture

0 N 0 Circulated mixture

II ,I ,I , I, I

4 6 8 .10 12 14 16

Initial hydrogen fraction (%)

FIG. 11. Burn completion is depicted .as percentage of original .H2 consumed

for dry tests.

26
total volume to the flame under similar conditions, which may explain the more

vigorous burns achieved at Sandia at low H2 concentrations..

.Variations in glow plug position and voltage produced no detectable

deviations from the trends seen in other data. Decreasing the glow plug

voltage to 12 VAC increased the time required for the plug to reach combustion

temperature (1300 - 14000 F) by 6 to 8 seconds (see Fig. 12).

The last three tests of the series (#98-#100) were stoichiometric burns,

with a hydrogen concentration of 29%6. The purpose of these tests was to

determine the capability of the glow plug to initiate a detonation. Tests #98

and #99 used a glow plug source. Test #100 involved an exploding-bridge-wire

spark source which produced approximately 1 Joule of energy. The calculated

pressure rise under these test conditions is 114 psi for simple adiabatic

combustion, and 290 psi for a Chapman-Jouget detonation. The pressures listed

in Table 2 (105, 110, and 120 psi) are close to the adiabatic combustion

pressure rise. Some uncertainty in the pressure measurements at this rapid

rate of pressure rise and at this magnitude was indicated by a significant

difference in the readings of the three pressure transducers. The listed

pressure was recorded by the transducer located at the end of the vessel.

This transducer was recessed by a 6-in. tube. The transducer directly above

2000

1750

-- 1500

• 1250

0.

1000

" 750

0

&500

250

0 10 20 30 40 50

Time (sec)

FIG. 12. Glow plug temperature traces are shown

voltage levels.

60 70 80 90

for 14.4 VAC and 12.0 VAC

27
the glow plug, also recessed, typically gave higher readings, and the

flush-mounted transducer located on the sidewall halfway between the center.

and end of the vessel typically gave lower readings. The spark source was

placed at the same central location as the glow plug for these tests. The

magnitudes of the pulses are listed below:

Flush-mounted, Recessed, Recessed,

Test # sidewall top flange end of vessel

98 70 psi rise 115 psi rise 105 psi rise

99 78 128 110

100 (spark) 100 150 120

This scatter in pressure readings was evident only for high hydrogen

concentrations. Because of the geometry differences between the recessed

transducers and the flush-mounted transducer, a difference in recorded

pressure is expected. It is conceivable that the small confined volume of the

offset tubes produced a higher pressure pulse than would be expected in an

unconfined case. The flush-mounted transducer eliminated the influence of the

confining volume, but was subject to a severe temperature transient which

could affect the reading. These measurements indicate uncertainty; however,

they probably bound the actual pressure rise in the bulk mixture. The spark

source produced. the highest pressure rise, while none of the tests indicated

detonations.

STANDARD STEAM TESTS

Steam concentrations between 10 and 50% were tested in the standard steam

tests. Results.of these tests are listed in Table 3, and plotted in Figs. 13

and 14.

Steam fractions were calculated assuming saturation conditions using the

procedure in Appendix A. The likelihood that suspended water droplets were

present in the vessel mixture during the tests may account for some of the

scatter in the data. The presence of very small amounts of condensed water,

as low as 0.05% by volume, can have pronounced suppressive effects on the

pressure rise (Ref. 12). Visual observations of steam tests indicated the

..presence of water in the form of a.condensation fog, which eventually

28
TABLE 3. H2 igniter standard steam test series.

Expected Actual Initial Cond.b Vessel Glow Plug Data Time to Burn Conditions

Concentrations Concentrationsa T P Wall Temp. Temp.C Peak AP TmaxL %H2 Test # % H2 % Steam. % H2 % Steam Fan? (OF) (psig) (OF) (OF) Volts Loc.d Press (psi) (OF) Consumed

(sec.)

82 8 10 8.4- 10 On 135 3.5 145 1450 12.0 Center 0.1 31.0 670 100

83 8 10 8.4 .9.7 Off 143 3.1 143 1400 12.0 Center 0.5 0.8 160 38

84 10 10 9.5 10 On 136 3.5 138 1440 12.0 Center 0.2 36.0 470 100

85, 10 10 11.1 9.6 Off 144 3.0 145 1400 12.0 Center 0.1 38.0 880 100

86 8 20 7.8 24 On 175 7.8 175 1480 12.0 Center 0.1 21.0 470 64

87 8 20 7.4 22 Off 177 7.3 175 1450 12.0 Center 0.5 0.2 .177 18

88 10 20 11.3 22 On 175 7.0 177 1480 12.0 Center 0.15 38.0 670 100

89 10 20 10.1 21- Off 178 7.2 178 1430 12.0 Center 0.3 1.2 200 50

25 8 30 7.5 30 off: 188 15.0 --- 14.4 Bottom --- 0.5 194 38

33,. 8 30 7.1 32 Off,, 178 13.0 --- 1400 14.4 Bottom 5.0 2.0 185 81

35 8 30 7.6 32- . Off 181 15.0 1440 14.4 Bottom 4.0 2.5 338 46

26 10 30 7.7 32 Off 184 11.0 1490 14.4 Bottom 3.0 5.5 536 36

36;" 10 30 9.6 30 Off 185 11.0 --- 1390 14.4 Bottom 4.0 4.5 500 53

277,. 12 30 11.9 33 Off 184 12.0 1470 14.4 Bottom 3.5 32.0 887 99

37 12 30 10.1 31 Off 180 11.0 1430 14.4 Bottom 4.5 22.0 1000 96

28 14 30 11.1 32 Off 176 11.0 - 1480 14.4 Bottom 4.0 24.0 968 91

29 14 30 14.9 32 Off 190 11.8 1440 14.4 Bottom 1.0 50.0 896 100

38 8 40 7.8 41 0ff 194 14.5 --- 1450 14.4 Bottom 2.0 1.5 293 41

90 8 40 8.4 41 Off'ý 208 17.0 208 1420 12.0 Center 0.5 0.2 215 20

91 8 40 9.3 44 On 215 17.4 218 12.0 Center --- None Same 0

39 10. 40 10.0 41 Off 198 15.5 --- 1450 14.4 Bottom 5.0 9.5 716 57

92 10 40 11.2 42 Off 219 17.6 218 12.0 Center --- None Same 1--

93(a)f 10 40 12.8 41 On 218 17.6 220 12.0 Center --- None Same 0

93(b) -- - 13.7 37 On --- 14.5 --- 12.0 Center --- 24.0 Same 45

40 12 40 11.9 42 Off 208 18.0 --- 1450 14.4 Bottom 4.0 36.0 1000 98

94 10. 50 11.2 52.0 Off 253 27.0 255 12.0 Center --- None Same '0

95 10 50 9.9 52.0 Off 243 27.0 245 14.4 Center --- None Same --- 96 10 50 13.0 53.0 Off 255 27.0 255 Spark --- Center --- None Same 0

97 10 50 13.8 53.0 Off 249 27.0 245 Spark --- Center --- None Same 0

a Steam fraction is calculated (Appendix A), H2 fraction from gas analysis.

b Temperature is average of measurements inside vessel. Atmospheric pressure was 14.2 psia. c Temperature of glow plug at ignition.

d:•Location of plug in vessel: center--center of vessel; bottom--3 in. above bottom of vessel. e -Measured at T-2, adjacent to top flange of vessel. "Same", implies no rise in temperature at T-2

f 'Test 93 showed no burn at first glow plug activation. Pressure was then allowed to drop to 14.5

indicated.

location.

psig and plug activated again. Burn was
60 I I i. I

X denotes circulating mixture

test

I

50--

Zt 10% Steam fraction

0 20% Steam fraction

'0 30% Steam fraction

o 40% Steam fraction

o 50% Steam fraction

40 HIn

D.

In

S.-

a,

I...

InIn

a,

1~

0~

0

30V20 I10- 0

0 00 0--

6 7 8 9 10 11

Initial hydrogen fraction (%

12 13 14 15

FIG. 13. Pressure rise is shown as a function of H2 concentration for steam

tests.

dissipated. Because of the uncertainty in the suspended water droplet sizes

and concentration in the vessel mixture, it is difficult to identify the

precise relationship between steam fractionrand pressure rise or between steam

fraction and burn completion. However, it is possible to see general trends

in the data.

The 50% standard steam fraction tests never ignited. As discussed later,

however, some of the condensation tests showed very slight pressure rises at

the beginning of the test when concentrations were 10% hydrogen, 50%,steam.

At the 40% steam fraction, almost all of the tests ignited but produced less

than 10 psi pressure rises. Tests at all steam fractions less than 40%

indicated some pressure rise, with the magnitude varying with the hydrogen

fraction. With the exception of two 40% steam tests, all of the circulated

mixture tests ignited and produced substantial pressure rises. The 10%, 20%,

30
= - I B

A 10% Steam fraction

o 20% Steam fraction

0 30% Steam fraction

0 40% Steam'fraction

o 50% Steam fraction

i .ý.I'

X denotes circulating mixture

test

I - I

100 .v~ %/

-~ 0

~0

CU

0

C.,

0

8-0

80F

60H. 0

0

401- 0

20 0 0

.0

6

FIG. 14.

tests.

0 0p

7 8 9 10 11

Initial hydrogen fraction (%

12 .1 13 -- 14 15

Burn completion plotted vs. percentage of H2 for standard steam

and 30%'steam tests consistently indicated combustion and more closely

resemoled dry tests than did the higher steam fraction tests.

The nature of the test procedure led to a higher amount of condensed water

droplets in the tests for which the steam fraction was greater than the 30%.

Condensation rates in the vessel were relatively rapid in the 40 and 50% steam

tests, but became progressively slower as the steam fraction dropped.

31
Consequently, the lower steam fraction tests were probably influenced less by

the presence of suspended water.

CONDENSATION TESTS

A total of 14 tests was executed in an attempt to explain the two

anomalous tests of the first LLNL experimental series. The results of these

tests are tabulated in Table 4. At the completion of the second series, there

was still no clear explanation for the anomalies. The following, however, was

known with some certainty:

0 In all of the.tests the glow plug temperature was higher than that

required for ignition.

* The location of the plug in tests #34 and #43, 3 in. above the pool

of condensate in the vessel bottom, had no measurable influence on

the inability to initiate combustion. Most of the second series

tests were conducted with the plug at the center of the vessel.

" Observations of the tests verified that the plug was not submerged in

condensate.,

* The inability to initiate combustion was not a repeatable phenomena,

based on our understanding at the time.

" Combustion was not indicated (by discrete pressure rises) in most of

the tests executed with the glow plug continuously activated. The

majority of these tests, however, showed a marked decrease (40-50%)

in hydrogen within the test vessel. This may be a result of thermal

recombination or limited combustion.

* Intermittent firing of the glow plug at 5% steam fraction intervals

would periodically produce pressure rises, although not at every

firing.

. Instrumentation failure or experimental error was ruled out, because

of the number of tests conducted which showed the anomalous behavior.

It is our opinion that the cause of these "anomalies", is the presence of

condensation water droplets in the vessel mixture. The high steam fraction

tests provide favorable conditions for the formation of this fog, because

repeated recharging of the vessel was required to heat it up and reduce the

condensation rate. This process tends to generate fog, and the saturated or

slightly super-saturated state of the vessel mixture does not readily

revaporize the droplets.

32
TABLE 4. Condensation Test Series'

Glow Plug Data 2

Test # Test Conditions Firing Voltage Location Time on Fan? Burn? Consumed Comments

(min.)

34 12% H2 53% steam, Cont. 14.4 'bottom 23 off ..no

to 23% steam

43 12% H2 49% steam, Interm. 14.4 bottom 3.3 off no

to 32% steam

45 9.'3% H2 52% steam Cant. 14.4 bottom 1.5 off yes 44% 2 psi ourn occurred when

plug reached 15000 F

46 9.4% H2 60%-steam, Cant. 14.4 bottom 17 off no ' 7%

to 37% steam

47 9% H2 57% steam, Cant. 14.4 bottom 25 off no

to 40% steam

50 9.6% H2 52% steam, Cant. 14.4 bottom 13 off yes 55% 1 psi rise when plug

to 34% steam reached 15000 F

51 9.3% H2 52% steam, Interm. 14.4 bottom 5 off yes 57% 1 to 2,psi rise noted

to 25% steam 4 out of 6 firings

52 10% H2 53%'steam, Cant. 14.4 center 20 off no 57%

to 26%, steam

53 9.5% H2 52% steam, -Interm. 14.4 center 3.3 off yes 51% 1 psi rises noted 4

to 26% steam ' '"out of 6 firings

55 11.9% H2 50% steam Cont. 14.4 center 1 on yes 100% 65 psi rise noted.

56 13.5% H2 52.8% steam Cant. 14.4 center 6 on no

-to 43% steam

57 11.3% H2 52% steam Cant. 14.4 center 12 on no

to 42%.steam

58 10.8% H2 51% steam Cant. 14.4 center 24 on no 40%

to 34%"steam -

59 9.2% H2 49% steam Cant. 14.4 center 2.5 on yes 18% 14 psi pressure rise

60 8.6% H2 53% steam - Cant. 14.4 center -. 26 on no 43%

to 39% steam

61 9.6% H2 ,53% steam Cant. 14.4 center 25 on no 33%

to 40% steam
Several of the tests in the second series were video-taped through a Storz

lens.' The lens is a long, small diameter tube (24.0-in.-long by

0.25-in.-diameter) containing specialized optics that allow a 600 angle of

view from one end. The lens was inserted into the vessel through a pressure

fitting attached to a Lexan flange, and coupled to a low-light-level

television camera outside the vessel. A floodlight shining through the Lexan

flange provided illumination (see.Fig. 15). The camera view included the glow

plug, the gas sampling flange, and the top flange of the vessel through which

the glow plug holder and conductor passed.

Figure 16 is a sequence of images taken from the television monitor during

*test #52. The first image represents the point at which steam has been

injected into the vessel, the conditions have reached the desired state of 53%

steam and 10% hydrogen, and the glow plug has been activated. The glow plug

is just noticeable through the swirling cloud of water droplets. As time

progresses the fog slowly clears, and the glow plug is seen as a glaring

FIG. 15. A Storz lens in conjunction with'a low light level television camera

was used to film the condensation tests.

34
(a) t = 0 min. (plug activated)

p =.:27 psig

fs = 53% fH2 = 10%

(b) t, = 1 min.

p = 25 psig

fs = 51%

(c) - t = 2 min..

p = 23 psig

f = 49%

FIG. 16. This sequence of pictures was taken from a video tape of test #52.

Note that the "fog" is clear four minutes into the test, but no Ourn was

noticed.

35
(d) t = 3 min. (e) t = 4

p = 21.5 psig p = 20 psig

fs = 47% fs = 45%

(f) t = 24

p = 10.5

f= 27%

FIG. 16. (Cont'd.)

36
'bright spot. The vessel atmosphere soon becomes completely clear, and the

condensate puddle on the bottom is visible. During this.20'minute test, no

pressure rise was'detected, although the Igas'analysis indicated that 57% of

the original hydrogen was consumed.

A scoping study was conducted to analyze the conditions during these tests

in an attempt to explain the anomalous results. Basic thermodynamic

principles were utilized to evaluate condensate formation and the influence of

suspended water droplets on the combustion process. A, summary of this

analysis is provided in Appendix B. The significant results are identified

below:

* The total condensation rate inside the vessel can be accurately

calculated using pressure histories.

-o It is possible to estimate the amount of condensate present in the

vessel atmosphere. This cannot be determined as accurately as the

total condensation rate. A calculation for test #58 indicates that

as much as 1.8 lbs of water could be suspended in the mixture at the

start of the test.

0 A very small amount of suspended liquid water will suppress the

adiabatic flame ;temperature enough to prevent propagation of the%

flame front. Calculations estimate that as little as .05% by volume

or .32 lbs of suspended liquid in the LLNL vessel is sufficient for

this range of hydrogen fractions.

0 If water droplets are.present in the bulk mixture, a fuel lean zone

around the glow plug may ,occur as a result of vaporization of the

liquid water which increases the local steam fraction.

This scoping analysis only treated a few tests of the total igniter test

program. A more extensive effort is required to refinecthe models used and to

evaluate all of the condensation tests.--

37
CHAPTER 4: CONCLUSIONS

This program evaluated the capability of thermal ignitersto initiate

combustion in a variety of hydrogen-air-steam environments to better

understand the performance of the TVA Interim Distributed Ignition System.

The conclusions drawn from these results are based on the current

understanding of the data. An in-depth analytical program would improve the

understanding of the influence of the steam environment on the igniter's

performance characteristics. The following statements can be made with

confidence:

* The glow plugs are capable of igniting any dry hydrogen-air mixture

if the hydrogen concentration is greater than 6%. Concentrations of

5% hydrogen can be ignited if the mixture is circulated in a fashion

similar to the LLNL tests. Complete combustion occurs in dry

mixtures with hydrogen concentrations between 8 and 9%. This is

consistent with other experimental results.

* The glow plug was not capable of. initiating detonations in a

stoichiometric hydrogen/air mixture.

• With the exception of three tests, combustion occurred consistently

in mixtures with steam fractions as high as 40%. Mixtures with steam

concentrations of 50% rarely could be ignited. It appears that

failure of the mixture to ignite at these higher steam fractions was

the result of.the presence of suspended water droplets.

" Circulation of the mixture at approximately 1 ft/sec past the glow

plug improved combustion in both the dry and steam tests.

* The glow plug consistently ignited the mixture at surface

temperatures between 1300°F and 15000 F, with the higher

temperatures required in steam environments. Decreasing the glow

plug voltage from 14.4 VAC to 12.0 VAC had no discernible influence

on the tests other than increasing the time to reach ignition

temperature. Throughout the series of tests, the glow plug showed no

appreciable deterioration in heat-up characteristics.

" The condensation tests showed that suspended water has a marked

suppressive influence on combustion. A scoping study of the data

indicated the possibility of enough suspended water to prevent

combustion in some cases. Another effect noted from the scoping

38
study was that-a local fuel lean-zone might exist aroundthe glow

plug when condensation droplets are present in the vessel mixture.'

An extended analyticaleffort is recommended to-..characterize the

conditions in the vessel mixture during steam tests., This effort should. be

..,.particularly directed to analyzing the effects of the presence of

condensation-generated suspended water droplets. The models used in the

scoping study require refinements to more accurately predict actual amounts of

suspended water. Once the models are refined, they should be applied to the

LLNL steam tests. An additional effort should concentrate on identifying the

conditions expected during a Loss of Coolant Accident (LOCA) with respect to

the presence of condensation fog.

39

References.,

1. W. R. Butler, C. G. Tinkler, L. S. Rubenstein, "Regulatory Perspective on

H...Hydrogen -: Control . for,.LWR Plants-, "published in the Proceedings of the

Workshop on the .Impact of Hydrogen on*"Water Reactor Safety, Volume I,

Sandia National Laboratories report NUREG/CR-2017, SAND81-0661,- August

1981.

2. , H. F. Coward,..- W. Jones, "Limits:-of Flammability of Gases and Vapors,"

U.S. Bureau of.Mines, Bulletin 503,. 1952.

3. .A., L. Furno,,-E. B. Cook, J. M. Kuchta, D. S.. Burgess, "Some Observations

on Near Limit Flames," Thirteenth Symposium.(International) on

Combustion, The Combustion Institute, p.. 593.

4. D. S. Liu, et al., "Canadian Hydrogen Combustion Studies Related to

Nuclear Reactor Safety- Assessment," AECL-6994, 1980.

5. L. W. Carlson, R. M. Knight, J. 0. Henrie, "Flame and Detonation

Initiation and Propagation in Various Hydrogen-Air Mixtures, With and

Without Water Spray," Atomics International, AI-73-29, 1973.

6. H. R. Cutler, E. A. Omotoso, I"Explosion Characteristics of Near LEL

Hydrogen-Air Mixtures," Fenwall Incorporated, Ashland,, Mass., (work

sponsored by General Electric).

7. Tennessee Valley Authority Sequoyah Nuclear Plant Core Degradation

Program, Vol. 2, Report on the Safety Evaluation of the Interim

Distributed Ignition System, Dec. 15, 1980.

8. W. E. Lowry, "Preliminary Results of Thermal Igniter Experiments inil

H2 -Air-Steam Environments," Lawrence Livermore National Laboratory,

UCRL-84167, Rev. 1, January 1981.

41
9. M. G. Zabetakis, "Flammability Characteristics of Combustible Gases and

Vapors," U.S. Bureau of Mines Bulletin 627, 1965.

10. S. Gordon, et al., "Computer Program for Calculation of Complex Chemical

Equilibrium Compositions, Rocket Performance, Incident and Reflected

Shocks, and Chapman-Jouguet Detonations," NASA SP-273, 1971.

11. M. Berman, et al., "Light Water Reactor Safety Research Program Quarterly

Report, January-March 1981," Sandia National Laboratory, NUREG/CR-2163/1

of 4, SAND81-1216/1 of 4, July 1981.

12. M. Berman, et al., "Analysis of Hydrogen Mitigation for Degraded Core

Accidents in the Sequoyah Nuclear Power Plant," Sandia National

Laboratories, NUREG/CR-1762, SAND 80-2714, March 1981.

42
APPENDIX A

Pre- and Post-Test Calculations

'Steam Fraction Determinations

Because the mass spectrometer can only analyze the,gaseous water whose

vapor pressure equals the operating pressure of the spectrometer sample

chamber (which is very low), water concentrations obtained in the analysis'are

discarded and the remaining results for non-condensible gases'normalized to

represent a "dry". mixture. Consequently, steam fractions must be calculated

as a function of both temperature and pressure to specify the conditions in

the vessel at a given instant. This was done twice: first to predict the

vessel pressure, after steam injection, at which the glow plug was fired, and

again after the tests to verify the actual conditions from pressure andtemperature data. If saturation conditions are assumed, it is possible to

predict the.steam fraction with a partial pressure calculation; by the

following procedure:

a) The total number of moles of gas in the vessel before steam

injection, n gas' is known from the previous fill bottle pressure

calculation or can be inferred from the pressure and temperature

inside the test.vessel after hydrogen injection.

b) A temperature Tbulk is selected (iteratively) which provides a

partial pressure ratio corresponding to the appropriate steam

fraction. -The gas partial pressure P is first calculated as:

/• .... gas

=ntot R "Tbulk

n R

gas V

c) The steam saturation pressure-. Ps at Tbulk is obtained from

the steam tables.

d) The steam fraction f steamis calculated from the partial pressure

ratios:

f s a P sat

fsteam Pgas + Psat

43
e) Once the correct Tbulk is found so conditions yield the appropriate

steam fraction, the total pressure (Psat + Pgas ) is the pressure

at which the glow plug should be fired.

After the test is completed, conditions are reconstructed to determine how

close to the desired state was the actual experiment. In the data table of

the standard steam test'results, the gas partial pressure (P" ) is first

gas

calculated using the listed temperature at ignition (this is the average

temperature measured by the thermocouples in the vessel). The steam-fraction

is then calculated from the ratio of P to the measured total pressure:

gas

fPgas (calc.)

steam (meas.)

%H2 Consumed

Mass spectrometer analysis provides mole fraction figures for the

non-condensible gases in the samples. Of primary interest, and comprising

usually at least 99% of the sample, are the concentrations of hydrogen,

nitrogen, and oxygen. The degree of combustion, or "%H consumed", 2

calculation is detailed below, using the following notation:

pre-burn H2 and N2 mole fractions

H2 fN obtained from gas analysis

f' post-burn H2 and N2 mole fractions,

fH2' fN2 also from gas analysis

n H n pre-burn number of moles H2 and

H- 2 1-nN2 N2 in vessel

post-burn number of moles'of H and nH nN N in vessel 2

2 2 2

n ntotal number of moles of dry gas in

ntot, ntot vessel before and after ignition

44
The following equations identify the total number of moles of each constituent

inside the vessel.

Pre-burn

fH2 "n = niH2 f "N tot nN

2 t2

Post-burn

' n' -n' H2 tot H 2 2'

f N2 * 2 ntot = nN22

The valuefor "%H2 Consumed"' is defined as:

%H2 Consumed = 1

nlH2 'n H 2

This can be expanded, using the previous equations, to give:

%H2 Consumed = 1

H2 ntot

fH ntot .2

(1)

For this combustion process it is reasonable to assume that the number of

moles of nitrogen remains constant throughout the experiment. So,

f n -n _ N2 2 tot t N 2 2 = 2 2il = fNN2 tot

The left and right hand sides of this equation can be combined to yield:

fN2 ntot.

N ntot

2

The '"%H2 Consumed" figure can be written in terms of only pre- and post-burn

hydrogen and nitrogen concentrations by substituting this last equality into

equation (1):

45
%H Consumed = 1 H2 * f, N2

fH2 . N2

The same equation can be applied to the oxygen fraction. Knowing the "%

of original" consumed for both oxygen and hydrogen, the actual amount (number

of moles) of each consumed by the reaction can be determined. This provides

one way of checking the reliability of the gas sampling system: if the ratio

of H2 moles consumed to 02 moles is two to one, the gas analysis data

tends to be believable. In most cases the ratio was what would be expected;

if the ratio was obviously bad, the data was discarded.

46
APPENDIX.B

Scoping Analysis of Condensation Test Conditions

Introduction

The "condensation" tests conducted in the LLNL Hydrogen Igniter Test

Program produced results which could not be explained by first examination of

the data. It had been suspected that the presence of small suspended water

droplets from. the steam condensation process inhibited the capability of the

glow plug to initiate'a self-propagating flame. Observations of these tests

showed that a fog did indeed exist in the vessel during the early period of

the test, but that this visible "cloud" dissipated as'the pressure and

temperature in the vessel dropped. Since the glow plug was still energized at

this time, the presence of a visible fog did not appear to' be the sole cause

for this inability to ignite the mixture. The presence of very small amounts

of condensed'water:suspended in the mixture might:prevent.-.combustion of the

test vessel mixture. This conclusion was drawn from analysis of the data.

This brief summary treats two aspects of the -LLNL analytical effort.

First is the characterization of the fog formation rates during the Livermore

tests, and the second is the influence of this condensation rate on glow plug

performance.

Condensation Rate Determination'and Fog Formation

The LLNL steam-type tests were executed in an unheated vessel.

Consequently, after steam was injected into the vessel, the mixture pressure

and. temperature dropped as steam condensed. This condensation rate was

controlled to some degree by preheating the vessel with repeated steam

injections before the actualtest sequence was started.

The total condensation rate in the vessel can be calculated very

accurately (+ 5%) using pressure decay data. Dalton's Law, the Ideal'Gas

47
Model, and Clapeyron's Equation can be combined to yield an expression for the

total mass condensation rate in the mixture of steam, air, and hydrogen:

• 18 V Pi P /T dP t

mct R T 1 C1 + C2 + (hfg/Tvfg) dT (1)

where:

mct total mass condensation rate

V = vessel volume

T = mixture temperature--

R = universal gas constant

P t = total vessel pressure

T =time

hfg = enthalpy of evaporated steam

Vfg = specific volume of steam.

n = number of moles of specified gas (air or H2 )

Cl ! ( •R\H2 ) .. .. .

C2 = V Air

.A sampling of the LLNL test data indicates a possible correlation-between

this calculated condensation rate and burn/no-burn results. Two tests at

initial conditions of approximately 10% H2 and 30% steam (#33 and #25), and

two at 10% H2 and 50% steam (#58 and #59) are compared below. These

condensation rates are calculated at the time the glow plug was energized.

Test # % H2 % Steam AP (psi) mct(lbm/s)

33 10.5 32.2 2.0 0.53 x 1073

25 10.7 30.2 0.5 0.82 x 10-3

58 10.8 51.0 0 0.99 x 10-3

59 9.2 49.0 14.0 0.57 x 10-3

48
In both comparisons-,-he testwith the-highest' total'condensation rate

(mct) yielded the lowest pressure rise.

Whi e these condensation rates do not appear to be large, if one-were to

scale up to the volume of the Sequoyah containment, test #58 would represent"

807 gallons-of total condensate being formed per minute.

The condensation rate which affects the glow plug is that fraction of the

total condensatlhn which-takes place in the mixture, producing fog.

Condensation fog is formed by cooling of the-bulk steam/air/H mixture.

This cooling is dominated ,by'two mechanisms: radiation-between the mixture

and the walls, and natural. convection cooling of the bulk mixture.; It is

possible to derive- an, equation.for the droplet formation rate by combining the

First Law of Thermodynamics and Clapeyron's Equationto'ýyield:

, . [ . 1 d t (2) fg 2 ' mvcv C 2

TY fg

where:

mcd droplet mass formation rate*

q(H 2o) = heat transfer rate between H20 vapor and walls

(all other variables same as Eq. (U))

The large uncertainty.,in this model is due in part toLthe difficulty in

determining the heat transfer from the vessel mixture, to.the walls... However,

a preliminary calculation for test #58 indicates that.two thirds .of the total

condensation could.be occurring in the mixture itself to form fog.

It is also possible to determine the total instantaneous mass.of condensed

droplets suspended in the mixture by using the First Law. This calculationis

subject.to the same limitations on heat transfer rates from the mixture to the

walls. A crude calculation for test #58 indicates that 1.79 lbs of water

could be suspended in the vessel mixture at the time of glow plug activation.

49
Influence of Suspended Liquid Water,:on Flame Propagation

We have known for some time that the presence of suspended water droplets

inhibits flame propagation. Adiabatic calculations yielding flame

temperatures provide a useful means to determine whether a flame will

propagate through a mixture-of known constituents. If the calculations

produce a flame temperature which is lower than the auto-ignition temperature

required to initiate hydrogen combustion (which under these conditions is

about 8500 K), then the flame is not expected to propagate. Calculations

show that while the presence of steam has relatively little influence on the

adiabatic flame temperature, suspended liquid water has a dramatic effect.

Consider three cases below:

Case I. Dry 120 mole fraction H2

Tf = adiabatic flame temperature = 12850 K >> 8500 K

Case II. 12% H2 , 33% steam

Tf = 12280 K, still much greater than 8500 K

(both Case I and Case II would be expected to burn well)

Case III. 12% H2 , no steam, but a mass of liquid water suspended equal

to the mass of steam in the previous case (0.24 lbm)

Tf = 7700 K < 8500 K

(a flame would not be self-sustaining in this case)-

Consequently, it takes very little liquid water to prevent flame

propagation. The above calculation shows that as little as 0.24 lbm in the

LLNL test vessel could inhibit combustion. The calculation for test #58

presented earlier yielded 1.79 lbm present in liquid form, a substantial

amount by these standards.

This discussion has addressed only the capability of the flame to

propagate through mixtures of steam, air, H2 , and suspended liquid water.

The ability of the glow plug to locally initiate a flame is also of interest.

A locally fuel-lean environment can exist around the glow plug if water

droplets are suspended in the mixture. This is best described by an example.

A 10% H2 , 50% steam mixture theoretically can combust. If, however,

0.5 lbm of suspended water is distributed throughout the LLNL test chamber, a

non-combustible environment will be sustained around the glow plug even though

there are no locally suspended water droplets (they would be vaporized by the

50
heat flux from the plug). Consider the local-environment to be a-swirling

mixture flowing past-the glow plug. As water droplets pass close to the plug,

they will evaporate to increase the local steam fraction. For each mole ofH2 passing the plug,ý:"5 moles of steam and 4-moles of air will accompany it.

As the field approaches the plug, however, another 5 moles of steam can join

the mixture via evaporation of the water droplets. This yields a local

mixture of 6.7% H2 , 66.7% steam, and 26.7% airi which is theoretically

non-combustible.

Conclusions

These results are preliminary and require further in-depth analysis to

yield quantitative conclusions with high confidence levels. However, the

following can be stated at this point:

1) Steam does not inhibit H2 combustion enough to be the sole source

of "anomalous" results in the LLNL tests. Suspended condensed water

droplets, on-the other hand, can effectively inhibit combustion.

2) An accurate model for total condensation rates has been developed.

Preliminary results show a'correlation between total condensation

rates and burn/no-burn cases, as well as indicating that a

significant quantity of suspended water droplets were present in the

LLNL tests.

3) The analysis showed that a fuel-lean zone can engulf the ignition

zone of the glow plug if suspended water droplets are present in the

bulk mixture.

HL/jp .LLNL* 1981/12

51

I-jRC FORM 335 -1. REPORT NUMBER (Assigneaby DOC

(7.77) U.S. NUCLEAR REGULATORY COMMISSION NJRXG/CR-2486ý

BIBLIOGRAPHIC DATA SHEET UCRL-53036

4: TITLE AND SUBTITLE (Add Volume No., if appropriate) 2. (Leave blank)

Final Results of the Hydrogen Igniter. Experimental Program

3. RECIPIENT'S ACCESSION NO.

7. AUTHOR(S) 5. DATE REPORT COMPLETED

W.E. Lowry, B.R. Bowman, : and B.W. Davis Nvea0•r M - I8 9f

9. PERFORMING ORGANIZATIONNAME AND MAILING ADDRESS (Include Zip Code) DATE REPORT ISSUED

Lawrence Livermnre National Laboratory MONTH j YFAR

P.O. Box 808 February 1982

Livermore, CA 94550 6. (Leave blank)

S8. tLeave blank)

12. SPONSORING ORGANIZATION NAME AND MAILING ADDRESS (Include Zip Code)

Division of Systems Integration 10. PROJECT/TASK/WORK UNIT NO.

Office of Nuclear ReactOr Regulation

U.S. Nuclear Regulatory Ctmmission

Washington, D.C. 20555 FIN No. A0418

13. TYPE OF REPORT PERIOD COVERED (Inclusive dates)

Technical

15. SUPPLEMENTARY NOTES 14. (Leave blank)

16. ABSTRACT (200 words or less)

Thermal igniters proposed by the Tennessee Valley Authority for intentional

ignition of hydrogen in nuclear reactor containments have been tested in mixtures

of air, hydrogen, and steam. The igniters, conventional diesel engine glow plugs,

were tested in a 10.6 ft. 3 pressure vessel with dry hydrogen concentrations from 4%

to 29% hydrogen, and in steam fractions of up to 50%. Dry tests indicated complete

,combustion between 8% and 9% H2 , and no combustion for concentrations below 5%. Steam

tests were done with hydrogen volume fractions of 8%, 10%, and 12%. Steam concentratioi

of up to 30% consistently resulted in ignition. Most of the 40% steam fraction tests

resulted in combustion. In a few isolated cases the 50% steam fraction tests indicated

a pressure rise. Circulation of the mixture improved combustion in both the dry and

the steam tests, most notably at low H2 concentrations. An analysis of the high

steam fraction test data showed a high probability for the presence of small, suspended

water droplets in the test mixture. The suppressive influence of this condensationgenerated fog on combustion is evaluated.

17. KEY WORDSAND DOCUMENT ANALYSIS 17a. DESCRIPTORS

17b. IDENTIFIERS/OPEN-ENDED TERMS

18. AVAILABILITY STATEMENT 19. SECURITY CLASS (Thisreport) 21. NO. OF PAGES

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