eri/nrc 09-203, 'comparison of blast pressures and effects ...explosion energy for different...

ERI/NRC 09-203

COMPARISON OF BLAST PRESSURES AND EFFECTS METHODOLOGIES

WITH APPLICATION TO SOUTH TEXAS UNITS 3 & 4

Work Performed under the Auspices of: U.S. Nuclear Regulatory Commission

Office of New Reactors (NRO) Washington, D.C. 20555

Under Contract Number NRC 42-07-483

Rockville, Maryland 20847 P. O. Box 2034

February 2009

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ERI/NRC 09-203

COMPARISON OF BLAST PRESSURES AND EFFECTS METHODOLOGIES

WITH APPLICATION TO SOUTH TEXAS UNITS 3 & 4

February 2009

Final Report

Edward A. Rodriguez, P.E.1 and Wayne Schofield2

Energy Research Inc. 6167 & 6189 Executive Blvd. Rockville, Maryland 20852

Work performed under the auspices of United States Nuclear Regulatory Commission

Washington, D.C. Under Contract Number NRC 42-07-483 (Task Order 13)

1 Global Nuclear Network Analysis, LLC 2 Dade Moeller & Associates, Inc.

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EXECUTIVE SUMMARY The Nuclear Regulatory Commission queried the South Texas Project (STP) Units 3 & 4 engineering on the Final Safety Analysis Report (FSA) regarding Regulatory Guide 1.91 computations to determine safe distance from an explosion source. STP provided answers to the NRC’s Request for Additional Information (RAI), which was further reviewed by subject matter experts for Energy Research, Inc. The results of the technical independent review show that STP engineering appropriately and correctly applied substance-specific thermodynamic data, under specified conditions, to obtain the heats-of-combustion in calculating the TNT-equivalent explosion energy for different fuels/oxidizer mixtures. As such, it should be understood that specific thermodynamic parameters and atmospheric conditions applicable to the event of interest must be well founded to yield conservative safe distances. This report is intended to provide background information and comparison of engineering methods, which are currently applied elsewhere in industry, to determine effects of combustions, explosions, and detonations, and normalize these methods to utilize common TNT-equivalent blast curves. Secondly, in reviewing Regulatory Guide 1.91, it has become evident that misuse or misapplication of technical information within Regulatory Guide 1.91 may result in inappropriate safe distance calculations for nearby explosions.

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TABLE OF CONTENTS

EXECUTIVE SUMMARY ..................................................................................................................................v LIST OF TABLES........................................................................................................................................... viii LIST OF FIGURES ........................................................................................................................................ viii 1. INTRODUCTION.....................................................................................................................................1 2. METHODOLOGIES USED BY OTHER UTILITIES................................................................................3

2.1 Bellefonte Nuclear Plant, Units 3 & 4 ........................................................................................... 3 2.2 Levy Nuclear Plant, Units 1 & 2 ................................................................................................... 3 2.3 Shearon Harris Nuclear Plant, Units 2 & 3................................................................................... 3 2.4 William States Lee III Nuclear Plant, Units 1 & 2 ......................................................................... 4 2.5 V. C. Summer Nuclear Plant, Units 2 & 3 .................................................................................... 4 2.6 South Texas Project Nuclear Plant, Units 3 & 4 .......................................................................... 4

3. BACKGROUND ......................................................................................................................................5 4. DOD HIGH EXPLOSIVES CURVES ......................................................................................................7 5. REGULATORY GUIDE 1.91 METHODOLOGY ...................................................................................11 6. THERMODYNAMICS FUNDAMENTALS.............................................................................................15

6.1 Thermophysics ........................................................................................................................... 15 6.2 Thermochemistry........................................................................................................................ 15

6.2.1 Heat-of-Reaction........................................................................................................ 16 6.2.2 Heat-of-Combustion................................................................................................... 16 6.2.3 Heat-of-Detonation..................................................................................................... 17

6.3 Adiabatic Isentropic Gaseous Expansion................................................................................... 17 7. NUREG-1805 AND FM DATA SHEETS COMPARISON OF METHODOLOGIES ..............................21

7.1 NUREG-1805 (Confined Explosion-Leaking Flammable Gas) .................................................. 21 7.2 Factory Mutual Data Sheets....................................................................................................... 22

7.2.1 Gas Releases............................................................................................................. 22 7.2.2 Liquid Releases.......................................................................................................... 23 7.2.3 Calculation of Initial Flash Fraction............................................................................ 23 7.2.4 Calculation of Liquid Pool Size .................................................................................. 24 7.2.5 Calculating of Evaporation from a Liquid Pool........................................................... 24 7.2.6 Calculation of Total amount of Vapor in a Cloud ....................................................... 25 7.2.7 Calculating TNT Equivalency..................................................................................... 26

8. BOUNDING METHODOLOGIES..........................................................................................................27

8.1 Solid Materials............................................................................................................................ 27 8.2 Liquids ........................................................................................................................................ 27 8.3 Vapor Clouds.............................................................................................................................. 27

8.3.1 Theory and Principle .................................................................................................. 28 8.3.2 Materials not Conducive to VCEs .............................................................................. 29

8.3.2.1 Liquefied Natural Gas (LNG) and Natural Gas (NG) (methane) ............... 29 8.3.2.2 Ammonia Gas ............................................................................................ 29 8.3.2.3 Gaseous Hydrogen.................................................................................... 29 8.3.2.4 Miscellaneous Flammable or Combustible Gases .................................... 30

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8.3.2.5 Flammable Liquids or Gases processed above their Auto-ignition Temperature .............................................................................................. 30

8.3.2.6 Flammable Liquids (High Viscosity) .......................................................... 30 8.3.2.7 Mixtures ..................................................................................................... 30 8.3.2.8 Hybrid Mixtures.......................................................................................... 30

8.3.3 VCE Methodologies ................................................................................................... 30 8.4 Additional Literature ................................................................................................................... 31

9. CONCLUSIONS....................................................................................................................................33 10. RECOMMENDATIONS.........................................................................................................................35 11. REFERENCES......................................................................................................................................37 APPENDIX: CONFIRMATORY CALCULATIONS.........................................................................................39

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LIST OF TABLES

Table 1 TNT Equivalence ...................................................................................................... 6 Table 2 Combustion Parameters for Stoichiometric Gasoline and Oxygen ........................ 18 Table 3 Comparison of Calculated Safe Distances (ERI versus STP)................................ 34

LIST OF FIGURES

Figure 1 Blast parameters for HE charges [3] ........................................................................ 7 Figure 2 Peak “incident” and “reflected” pressures [3]............................................................ 8 Figure 3 Zoom view of incident and reflected pressures near 1-psi. ...................................... 9 Figure 4 Pressure-time history for free-air burst [3] ................................................................ 9 Figure 5 Exposure distance calculation [1] ........................................................................... 11 Figure 6 Radial distance to peak incident pressure of 1-psi [1] ............................................ 11 Figure 7 Radial distance from blast source for 1-psi incident overpressure......................... 13

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1. INTRODUCTION In accordance with US Nuclear Regulatory Commission (NRC) Regulatory Guide 1.91 [1], postulated accident analyses on routes near nuclear power plants must be addressed for all known combustible or detonable fuels. However, Regulatory Guide 1.91 addresses only solid explosives and hydrocarbons liquefied under pressure, and air blasts on highway, rail, and water routes. The regulatory guide does not address liquids (pressurized or non-pressurized), cryogenically liquefied hydrocarbons (LNG, CNG, propane), vapor clouds (confined or unconfined), fixed facilities, pipelines, etc. Since Regulatory Guide 1.91 does not include methodologies that can be used to address these additional scenarios it was important to review the different methodologies utilized by other utilities as a basis for their FSAR Chapter 2, section 2.2.3, “Evaluation of Potential Accidents”. A summary of some available evaluations follow in Section 2. Finally, a note on engineering units utilized in this report. Wherever possible, Systems International (SI) units are used, except in certain figures and equations, which were derived from existing DOD documents. In some instances, both English and SI units will be included as appropriate, however a thorough unified convention was used, where possible, herein.

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2. METHODOLOGIES USED BY OTHER UTILITIES Prior to evaluating the methodologies presented in Regulatory Guide 1.91 and other industry guidance, it was important to determine what methodologies other utilities have used in their submittal of Combined Operating License (COL) Application FSAR section 2.2.3, in order to accommodate scenarios not encompassed by Regulatory Guide 1.91. A search was performed in ADAMS on the NRC website to locate FSAR Chapter 2, section 2.2.3 for several utilities who have recently submitted their COL Applications for NRC review. These included:

Bellefonte Nuclear Plant, Units 3 & 4 Levy Nuclear Plant, Units 1 & 2 Shearon Harris Nuclear Plant, Units 2 & 3 William States Lee III Nuclear Plant, Units 1 & 2 V. C. Summer Nuclear Plant, Units 2 & 3 South Texas Project Nuclear Plant, Units 3 & 4

These sections were reviewed and a summary discussion follows. 2.1 Bellefonte Nuclear Plant, Units 3 & 4 For solid fuels transported by truck, rail, or barge, the methodologies presented in Regulatory Guide 1.91 were used to determine the safe standoff distance from a detonation/deflagration from a mass equivalent of TNT. For methodologies used as the basis for determining the effects and safe stand off distance from Confined and unconfined VCEs at nearby facilities, only summary information was presented in the FSAR and further review of the associated calculation package would be necessary to determine what methodologies were used. For flammable vapor clouds (delayed ignition), the ALOHA code [2] was used to evaluate the dispersion and detonation/deflagration of the vapor clouds. 2.2 Levy Nuclear Plant, Units 1 & 2 For solid fuels transported by truck, the methodologies presented in Regulatory Guide 1.91 were used to determine the safe standoff distance from a detonation from a mass equivalent of TNT. It is stated in the FSAR section that unconfined VCEs from the rupture of natural gas transport pipeline were not considered a credible event, as previously determined in NRC licensing actions, and were not considered further in the document. Regulatory Guide 1.194 was used to calculate concentrations via plume rise and dispersion of a vapor cloud. For confined VCEs, it was determined that no credible mechanism existed to trap a natural gas leak that would lead to a detonation/deflagration. 2.3 Shearon Harris Nuclear Plant, Units 2 & 3 For solid fuels transported by truck or rail, the methodologies presented in Regulatory Guide 1.91 were used to determine the safe standoff distance from a detonation/deflagration from a mass equivalent of TNT.

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For the rupture of a nearby LPG pipeline and analysis of the effects from a fire and explosion, the scenario was previously analyzed in the HNP FSAR and the results extrapolated for the new facilities. 2.4 William States Lee III Nuclear Plant, Units 1 & 2 For solid fuels transported by truck or rail, the methodologies presented in Regulatory Guide 1.91 were used to determine the safe standoff distance from a detonation/deflagration from a mass equivalent of TNT. Unconfined VCEs from the rupture of natural gas transport pipeline were not considered a credible event, as previously determined in NRC licensing actions and not considered further in the document. For methodologies used as the basis for determining the effects and safe standoff distance from Confined VCEs at nearby facilities, only summary information was presented in the FSAR and further review of the associated calculation package would be necessary to determine what methodologies were used. For Flammable vapor clouds (delayed ignition), the ALOHA code [2] was used to evaluate the dispersion and detonation/deflagration of the vapor clouds. 2.5 V. C. Summer Nuclear Plant, Units 2 & 3 For solid fuels transported by truck or rail, the methodologies presented in Regulatory Guide 1.91 were used to determine the safe standoff distance from a detonation/deflagration from a mass equivalent of TNT. NUREG 1805 was used as the basis for determining the volume of vapor at the upper flammability limit capable of occupying the largest vessel considered available for combustion. Regulatory Guide 1.91 was used to determine the safe standoff distance. For Flammable vapor clouds (delayed ignition), the ALOHA code [2] was used to evaluate the dispersion and detonation/deflagration of the vapor clouds. 2.6 South Texas Project Nuclear Plant, Units 3 & 4 For solid fuels transported by truck, rail, or barge, the methodologies presented in Regulatory Guide 1.91 were used to determine the safe standoff distance from a detonation/deflagration from a mass equivalent of TNT. For atmospheric liquids and gases, the South Texas Project used guidance obtained from both NUREG-1805 and the Factory Mutual Data sheets to account for the limited applicability of Regulatory Guide 1.91. For Flammable vapor clouds (delayed ignition), the ALOHA code [2] was used to evaluate the dispersion and detonation/deflagration of the vapor clouds.

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3. BACKGROUND Basis for guidance provided in Regulatory Guide 1.91 [1] stems from the US Department of Defense (DOD) laboratories, which conducted blast effects starting in the 1940’s, utilizing solid state high-explosives (HE). The DOD developed these curves for all known solid explosives, yet normalized the detonation parameters to TNT-equivalence. The equivalence method is quite elementary, but effective, such that a multitude of different high explosives have been correlated with great precision to TNT. A US military tri-services manual titled, Structures to Resist the Effects of Accidental Explosions [3], commonly referred to as “TM 5-1300,” has been used in blast engineering design by DOD since the early 1960’s. The US Department of Energy (DOE) developed a similar, yet site-specific manual titled, A Manual for the Prediction of Blast and Fragment Loading on Structures [4], for design against accidental explosions primarily in HE facilities, with much the same information and guidance as TM 5-1300. TM5-1300 and Lawrence Livermore National Laboratory’s (LLNL) methodology for TNT-

equivalence provide similar results because they both use the heat-of-detonation oDetH in

scaling, but the former is based on scaling weight (or mass) while the latter is based on energy-per-unit-density. Further discussions on heats-of-detonation are expanded in Section 6.2. As such, the slight difference in TNT-equivalence is due to the density ratio, and for all practical purposes, the two methods are identical. Theoretical density of TNT is set at 654.1 g/cm3, which is typically

used with the LLNL [5] methodology. The TM5-1300 Method [3]:

oDet

E EoTNT

HW W

H

xp

(1)

oDet

o Exp

oTNT

o TNT

H

H

Or, the LLNL Method [5]:

0.2107oDet

o Exp

H

(2)

Table 1 shows sample computations with both methods in determining the TNT-equivalence for common high explosives utilized by DOD and DOE.

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Table 1 TNT Equivalence

TNT Equivalence High Explosive

TM5-1300 LLNL

TNT 1.00 1.00

HMX 1.26 1.27

PBX-9501 1.16 1.17

PBX-9502 0.84 0.85

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4. DOD HIGH EXPLOSIVES CURVES The two blast effects manuals from DOD [3] and DOE [4] previously mentioned, contain the current technical philosophy for determining blast overpressures and analyzing blast effects on structures. Figure 1 shows the TM 5-1300 blast curve(s) as a function of scaled distance, Z is defined in Equation 1. As stated previously, these curves were developed by the US Department of Defense (DOD) laboratories, which conducted blast effects starting in the 1940’s, utilizing solid-state high explosives. The DOD developed these curves for all known solid explosives, yet normalized the detonation parameters to TNT-equivalence.

1/3

RZ

W

(3)

Where: R Distance from explosive to target, (ft) W Weight of Explosive, (lb) The scaled distance equation, or the “one-third” scaling law, is commonly called the Hopkinson-Crantz scaling law, as described by Baker [6].

Scaled Distance Z = R/W^(1/3)0.1 0.2 0.3 0.50.7 1 2 3 4 5 67 10 20 30 50 70100

0.0050.010.02

0.050.10.2

0.512

51020

50100200

50010002000

50001000020000

50000100000

Pr, psiPso, psiIr, psi-ms/lb^(1/3)Is, psi-ms/lb^(1/3)ta, ms/lb^(1/3)to, ms/lb^(1/3)U, ft/msLw, ft/lb^(1/3)

Figure 1 Blast parameters for HE charges [3]

Primarily, Figure 1 curves provide blast parameters such as peak incident pressure (or, side-on

pressure) soP , reflected pressure , incident impulserP soI , reflected impulse rI , and time of arrival

as well as pulse period . Additional parameters included in Figure 1 are the shock front

velocity,U , and the positive phase wavelength, . As stated previously, these curves are

normalized to TNT-equivalent energy and therefore utilize the heat-of-detonation method

described in section 2.0 of this report. Figure 2 clearly shows the incident and reflected pressure

at ot

wLdExpH

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as a function of scaled distance, where at 1-psi incident positive overpressure, and the scaled distance, Z , is approximately 36-ft/lb1/3.

Scaled Distance Z = R/W^(1/3)

Pre

ssu

re,

(psi

)

0.1 0.2 0.3 0.50.7 1 2 3 4 5 67 10 20 30 50 701000.20.2

0.5

1

2

5

10

20

50

100

200

500

1000

2000

5000

10000

20000

50000

100000

PrPso

Figure 2 Peak “incident” and “reflected” pressures [3]

Figure 3 present a close-up view of the incident and reflected pressure scale near the low-pressure regime. Here, one clearly sees the scaled distance of ~36 ft/lb1/3 for attaining a 1-psi incident positive overpressure, while the reflected pressure is a factor of 2 higher, i.e., 2-psi. Figure 4 provides a typical pressure-time history of a blast wave, showing both the incident and reflected pressure waves. The blast pressure moving away from the HE source and towards a target surface is termed the

incident pressure, soP , and is also the pressure magnitude immediately before impacting on a

hard (reflecting) surface. Reflected pressure, , is the magnitude of blast pressure that is

subsequently amplified after striking a hard surface. It is the reflected peak pressure and its associated impulse that causes damage to structures.

rP

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Scaled Distance Z = R/W^(1/3)

Pre

ssu

re,

(ps

i)

10 20 30 40 50 60 70 80 1000.20.2

0.3

0.4

0.50.60.7

1

2

3

4

567

10

PrPso

Figure 3 Zoom view of incident and reflected pressures near 1-psi.

Figure 4 Pressure-time history for free-air burst [3]

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5. REGULATORY GUIDE 1.91 METHODOLOGY NRC Regulatory Guide 1.91 utilizes the methodology discussed in Section 4.0 for determining the safe distance from an explosion source to a facility or critical location. Figure 5 shows the Regulatory Guide exposure distance along a roadway, which potentially is accessed by vehicles carrying hazardous and/or detonable materials. The radial distance, R , measured from a facility, is based on the scaled distance, Z , of 45 ft/lb1/3. This difference from the TM 5-1300 methodology will be discussed in some detail later, showing there is a rationale for the increase.

Figure 5 Exposure distance calculation [1]

Figure 6 shows the Regulatory Guide 1.91 design curve for radial distance to TNT weight, based on peak incident overpressure of 1-psi. It is interesting to note that the examples noted on the graphical plot imply these are TNT weights for solid materials, yet there is no indication of how to arrive at these weights for other substances or mixtures (i.e., gaseous or liquid).

Figure 6 Radial distance to peak incident pressure of 1-psi [1]

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Herein, provided is a comparison of the different methods to evaluate their conservative or non-conservative nature. The methodologies presented in Regulatory Guide 1.91 and TM 5-1300 are illustrated in Equations 4 and 5 and are compared to show the differences between them. English Units

1/345RGR W Regulatory Guide 1.91 (4)

1/35 36.225TMR W

TM 5-1300 (5)

Where:

RGR Radial distance, (ft)

W Charge weight, (lb) SI Units

1/317.85RGR W Regulatory Guide 1.91 (4a)

1/35 14.37TMR W

TM 5-1300 (5a)

Where:

RGR Radial distance, (m)

W Charge mass, (kg) For a given radial safe distance, the differential on HE mass to reach 1-psi incident (i.e., side-on) positive overpressure is:

1/3 1/3545 36.225RG TMW W

W (6)

5 1.92TM RGW (7)

For a given HE mass, the differential on radial distance to reach 1-psi incident positive overpressure is:

5

45 36.225RG TMR R

(8)

51.24RG TMR R (9)

Graphically, these differences represent a conservative factor of safety for applications of design conditions under Regulatory Guide rules. Figure 7 shows the Regulatory Guide 1.91 and TM 5-1300 design curves for 1-psi incident positive overpressure. Not having any knowledge of the NRC’s original effort on developing Regulatory Guide 1.91, it appears from the plot that the TM 5-1300 scaled distance factor was utilized and increased by 25%, if one uses whole numbers for the scaled distance;

451.25

36f

(10)

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100

1000

104

100 1000 104 105 106 107

Comparison of Reg Guide and TM 5-1300

Reg Guide 1.91TM 5-1300

Dis

tanc

e "

R"

fro

m E

xplo

sion

(ft

)

TNT Equivalent Weight, "W" (lb)

R = 24%

W = 92%

Figure 7 Radial distance from blast source for 1-psi incident overpressure

It should be emphasized, and as previously described in Section 1.0, that Regulatory Guide 1.91 addresses only solid explosives, hydrocarbons liquefied under pressure, and air blasts on highway, rail, and water routes. The regulatory guide does not address cryogenically liquefied hydrocarbons (LNG), fixed facilities and pipelines. Proper treatment for other hazardous and detonable mediums requires fundamental knowledge of the system thermodynamics, and specifically thermo chemistry of mixtures.

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6. THERMODYNAMICS FUNDAMENTALS As has already been discussed, the Regulatory Guide does not address other types of detonable fuels except for solid HE and hydrocarbons liquefied under pressure. However, for hydrocarbons liquefied under pressure, the Regulatory Guide utilizes a factor of 240% increase in mass that account for the differences with TNT. Although this might be acceptable for some hydrocarbons, it is by no means a conservative assumption, as will be seen later. Furthermore, it would not be prudent, nor technically correct, to assume that a given mass (or weight) of a fuel is energetically equivalent to the same mass (or weight) of TNT. In order to determine heat energy from different substances, it becomes necessary to approach the problem from fundamentals of thermodynamics. Herein we will briefly discuss applications of thermodynamics to chemically reacting mixtures, such as gases or other liquid fuels. 6.1 Thermophysics Changes in physical states, such as temperature and pressure, involve changes in internal

energy and enthalpy of the system [ U H 7]. The heat capacity of a substance defines the

quantity of heat energy required that a given amount of a substance must absorb to raise its internal temperature 1-degree. Therefore, the amount of heat required to raise the temperature of a substance, such as gas or liquid, in a closed (i.e., constant) volume is:

v

dUc

dT

(11)

This implies that all the heat goes into increasing the gas, or liquid’s, internal energy, U ,

where:

H U PV (12)

On the other hand, if the gas or liquid is allowed to expand during heating process, then some of

the heat will increase the internal energy U and some utilized as “work” involved in expansion:

p

dHc

dT

(13)

Thus, the above implies that:

pdH c dT , or pd U PV c dT

6.2 Thermochemistry Having described the internal energy and enthalpy from the standpoint of heat capacities of a substance, we will briefly describe the changes in the chemical state of a mixture. That is, chemical changes of a substance, or changes in the composition of molecules, also involves changes in internal energy and enthalpy of system [7]. The foundations of a chemically reacting mixture is a balanced reaction, where mass is always conserved while maintaining the number of atoms equal between the reactants and products.

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6.2.1 Heat-of-Reaction

The heat-of-reaction is the change in enthalpy between the starting and ending chemical

states of a substance or mixture. Heats-of-formation

orH

ofH are merely the heats-of-reaction, or

changes in enthalpies, involved in forming a particular compound from its elements, where these elements and final compound are at a standard-state, i.e., standard temperature and pressure (STP). The standard-state is chosen arbitrarily as 1-atm pressure and 298.15K temperature, however, it is also for consistency and because it is generally easier to determine chemical states at room temperature and pressure. These states are known as heats-of-formation. For example,

if the starting state for hydrogen 2H and oxygen 2O is a gaseous mixture at constant

pressure, and we burn the mixture, the chemical balance becomes:

2 2 22 2H O H O (14)

Implying that upon burning 2 molecules of 2H with one molecule of 2O , we obtain water

vapor . If the heat-of-reaction occurs at constant pressure, the energy balance can be

written between enthalpies of formation of gaseous reaction products and reactants (i.e., fuels and oxidizers):

2H O

0

products reactants o or f fH H H

(15)

Thus, the substance’s heat-of-reaction from using heat-of-formation data for the reactants and reaction products of the H2-O2 mixture is,

2 2

02 2 o o

r f f 2HH O OH H H (16)

No matter what terminology is used, heat-of-combustion, heat-of-detonation, or heat-of-explosion, these terms all imply the same phenomena. That is, it implies the enthalpy difference between reaction products and reactants at STP. 6.2.2 Heat-of-Combustion

Heat-of-combustion ocH of a substance, or mixture, is the heat-of-reaction for a complete

combustion (or burning) with molecular oxygen, to its most oxidized state. For the majority of substances in gaseous, liquid, or solid form, these tests have been conducted and reference values of heats-of-combustion may be found in most standard reference books [8 - 9]. Where heats-of-combustion for unusual substances cannot be found, then it becomes necessary to calculate heats-of-formation for both reactants and reaction products. Heats-of-formation for many substances are found in the CRC Handbook [10], Cooper [7], Glassman [11], and the most comprehensive are contained in the tri-services sponsored compendium titled, JANAF Thermochemical Tables [12].

0

products reactants o oc f fH H H

(17)

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6.2.3 Heat-of-Detonation Heat-of-detonation is yet another special case of heats-of-reaction associated primarily with propellants or solid explosives that release heat through the process of detonation. Again, the same process is applied in determining the heat-of-detonation as was accomplished for the heat-of-reaction or heat-of-combustion. However, in this case, heats-of-formation for the actual explosive compound and reaction products must be obtained utilizing a chemical balance.

0

detonation products explosive o od f fH H H

(18)

Section 7 provides examples of these calculations for typical fuels. Alternatively, there are a number of thermochemical kinetics, or thermal equilibrium, codes available to solve the thermodynamic parameters, as well shock and detonation conditions. STANJAN [13], CHEMKIN [14], CEA [15], and CHEETAH [16] are a few codes capable of evaluating the chemical species and heats-of-formation. 6.3 Adiabatic Isentropic Gaseous Expansion As an initial approximation to the explosive fuels, assume that the energy of explosion is an adiabatic isentropic expansion of detonation gases [17] to atmospheric conditions, per Equation 19. That is, in this particular case, the assumption is that the contents of the reactions products in the vessel will expand from the Chapman-Jouguet (C-J) pressure (i.e., ideal peak detonation pressure) to ambient conditions through an adiabatic isentropic process. The energy, or work,

accomplished by the expansion of a gas at an initial volume, , and pressure , into an

external atmosphere at pressure, ;

oV oP

eP

e

eoE P P dV (19)

kVP

E oo

1

(20)

11

111o

e

o

e

o

e

P

P

P

P

P

Pk (21)

Where: E = Energy (kJ or MJ)

eP = External (atmospheric) pressure

oP = Detonation peak pressure

oV = Initial volume

= Isentropic expansion coefficient p

v

c

c

k = Proportion of available gas energy converted to kinetic energy

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Once the energy of explosion is determined, it becomes necessary to convert this energy to a TNT equivalent energy for utilizing the scaled distance curves of TM 5-1300 [3] or Regulatory Guide 1.91 [1]. For simplicity, the energy of explosion per unit volume (kJ/m3) will be considered, such that:

1

o

o

E Pk

V

(22)

or 1 1

1 1 11

o e e e

o o o

E P P P P

V P P P

o

(23)

In his seminal text, Baker [6] utilizes a slightly modified form for the blast energy assuming

isentropic gas expansion from a closed initial volume, , to external atmospheric pressure, : oV eP

1

exp 1e o o e

e o

PV P PE

P P

(24)

In comparison to Baum [17], Baker’s [6] results are higher for a given gas-mixture and associated isentropic expansion coefficient. The expansion energy for a given volume of gas, can equated to a TNT-equivalent weight by:

exp GasTNT o

d TNT

EW

H

Where:

exp GasE = Energy of expansion (kJ or MJ)

od TNT

H = Heat-of-detonation (kJ/kg or MJ/kg)

Table 2 shows thermodynamic parameters, as derived from the NASA CEA code [15], for typical hydrocarbon, i.e., gasoline (C8H18), combustion in air. Therefore, 1-mole of gasoline plus 12.5-moles of oxygen makes this a balanced stoichiometric reaction.

8 18 2 2 212.5 8 9C H O CO H O (25)

Table 2 Combustion Parameters for Stoichiometric Gasoline and Oxygen

Gas Composition Thermodynamic Parameters

%C8H18 (moles)

%O2 (moles)

MW (g/mol)

p

v

c

c oc

(m/s)

8 18

0f C H

H

(kJ/mole)

2 2

of CO H O

H

(kJ/kg)

1 12.5 114 1.111 1103 -213 -5722

Note: Initial pressure @ 1.0132 bar (1-atm).

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mol

Calculating the heat-of-combustion from the difference of heat-of-formation of products and reactants, as shown in Eq. 17:

5722 ( 213)ocH

(26)

5509 /ocH kJ

(27)

Where:

oc Sonic velocity of unburned gas ocH Heat-of-combustion ofH Heat-of-formation

MW Molecular weight (g/mol) The total heat-of-combustion is:

5509 /

114 /oc

kJ molH

g mol

(28)

48.3 /ocH k J g

g

Comparing this to the heat-of-detonation for TNT: , it becomes clear that

the ratio of heats-of-reaction is about a factor of 10. The TNT-equivalent weight would be:

4.65 /odH kJ

oc

TNT Eq ExpoTNT

HW W

H

(29)

48.310.4

4.65TNT Eq Exp ExpW W

W

With actual heat-of-combustion for gasoline as calculated above, the safe distance to reach 1-psi incident positive overpressure may be determined using Regulatory Guide curve as,

1/345RGR W , provided that the yield fraction, , associated with the vapor-phase is

determined. It is important to note that hydrocarbons stored at atmospheric conditions, or below their boiling point, will combust only that portion within the vapor phase between the LFL and UFL. Thus, the fraction available for immediate combustion is generally about 1/20th of the total mass. Also, according to NPFA 325, the atmospheric boiling point for gasoline lies between 100 -400°F (311-478K) depending on the grade of gasoline. Thus, it is incumbent upon the analyst to ensure that flash point limits, boiling points, and other relevant thermodynamic data are taken into consideration in the calculation of safe distances. For boiling points below atmospheric conditions, flashing vapor quantity must be considered in the analysis. See Section 7.2 for additional guidance in utilizing these parameters based on the FM Global Datasheets, and calculations provided in the attached Appendix for gasoline combustion.

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7. NUREG-1805 AND FM DATA SHEETS COMPARISON OF METHODOLOGIES Section 6 briefly described and detailed the fundamentals of calculating the enthalpies of reactants and reaction products, to achieve the heat-of-combustion of a mixture. NUREG-1805 [18] and Factory Mutual Data sheets [19] utilize this philosophy throughout in calculating the TNT-equivalent energy of combustion/detonation. Calculating the mass of a flammable gas or the mass of evaporative vapors from a liquid spill is not encompassed in the guidance provided by Regulatory Guide 1.91. Several utilities have used the methodologies presented in NUREG-1805 and/or that which is presented in the Factory Mutual Data Sheets to calculate the mass of vapor in a cloud. Presented below is a comparison of the methodologies: 7.1 NUREG-1805 (Confined Explosion-Leaking Flammable Gas) One typical explosion in an enclosure is caused by flammable gas leaking, which mixes with air in the enclosure and subsequently ignites to cause an explosion. The energy released by expansion of compressed gas upon rupture of a pressurized enclosure may be estimated using the following equation.

oc fE H M (30)

Where: E = Explosive energy released (kJ) = Yield (i.e., the fraction of available combustion energy participating in blast wave

generation) ocH = theoretical net heat-of-combustion (kJ/kg)

fM = mass of flammable vapor release (kg)

The yield, , is typically in the range of 1 percent (0.01) for unconfined vapor releases, to 100 percent (1.0) for confined vapor releases. One of the most common methods used to estimate the effects of an explosion is to relate the exploding fuel to trinitrotoluene (TNT). This method converts the energy contained in the flammable cloud into an equivalent mass of TNT, primarily because blast effects of TNT have been extensively studied as a function of TNT weight and distance from the source. Hence, the blast effects of an explosion can be inferred by relating an explosion to an “equivalent” explosion of TNT. To do so, we relate a given fuel type and quantity to an equivalent TNT charge weight, as follows:

4500TNT

EW (31)

Where:

TNTW = Weight of TNT (kg)

E = Explosive energy released (kJ) Blast effects can also be related to the equivalent weight of TNT using by the relationship between the distance from the source, the charge weight, and the overpressure caused by the blast wave, including the reflected shock wave. Scaled distance is the distance at which the overpressure is calculated divided by the cube root of the TNT charge weight.

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3/1TNTW

DDsc

(32) Where: Dsc = Scaled distance [m/(kg)1/3] D = Distance at which the overpressure is calculated (m) WTNT = Weight of TNT (kg) 7.2 Factory Mutual Data Sheets The Factory Mutual Data Sheets (formerly Data Sheet 7-0S) [19] provides technical guidance to evaluate the physical property damage consequences to buildings and process structures from explosion overpressures and ensuing fires, caused by the outdoor release and delayed ignition of a flammable vapor cloud. The FMDS uses a TNT equivalency methodology to evaluate approximate effects of a worst credible case VCE. Other refined VCE prediction or estimation methods, while briefly discussed, are beyond the scope of the data sheets. The techniques and procedures described in the guidelines are a simplified approach to a complex problem. Application is not appropriate for non-chemical plants that may have storage or use of hazardous materials, or for smaller chemical plants that lack the congestion or confined layout needed to produce outdoor VCEs. Loss history supports that VCEs have occurred primarily in large petrochemical or refinery facilities and/or as a result of transportation incidents and that, they have occurred on a very low frequency as compared to other major events. 7.2.1 Gas Releases If the material exists in the system as a gas, the following equation can be used to estimate the

mass of gas released, gW , from a break.

2g d r l dW KC A t P (33)

Where:

gW = Mass of gas released (kg)

rA = Area of release opening (m2)

dC = Discharge coefficient (use 1.0)

1P = Process or reservoir pressure (Pa)

aP = Ambient pressure (Pa) (absolute) (@ sea level =1.014×105 pa) aP

l = Vapor density at process conditions (kg/m3)

t = Discharge duration (sec) (use 600) K = Gas Constant. usually falls in the range 0.63 to 0.73. An average value of

may be used with little error when calculating vapor or gas flow rates for most materials.

K0.68K

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dP = Use actual process or reservoir pressure 1 whe 1P is in excess of 20 psi (135

kPa) (sonic flow). For pressures less than this subsonic flow, a

P n

1dP P P (Pressure- Pa

absolute). 7.2.2 Liquid Releases

If the material exists in a system as a liquid, the mass of the liquid released , assuming

gravity and/or vessel pressure as the driving force with no vaporization (two-phase flow) in the orifice, can calculated by Equation 32:

lW

122a

l d l rl

P PW C A t gh

(34)

Where:

lW = Mass of liquid released (kg)

rA = Area of release opening (sq m)

dC = Discharge coefficient (use 0.62)

g = Gravitational constant (9.81 m/s2)

h = Height of liquid in tank above discharge point (m)

aP = Ambient pressure (Pa absolute)

1P = Process or reservoir pressure (Pa absolute)

l = Density of Liquid (kg/m3) @ process temperature 1T

T = Discharge Duration (sec) (Use 600) 7.2.3 Calculation of Initial Flash Fraction The pressurized liquid will flash once it has escaped and is at atmospheric pressure. The heat required for vaporization is taken from the liquid itself so that any liquid which is left will have

been cooled to its atmospheric boiling point. The initial flash fraction of liquid is given by: vapF

1 1

b

P bvap

vap

C T TF

H

(35)

Where:

vapF = Fraction of liquid flashed to vapor

1PC = Specific heat of liquid at constant pressure (J/kg° K) averaged between process

temperature and atmospheric BP. If range figures not available, use 1T1PC at boiling

point to be conservative.

bvapH = Heat of vaporization (J/kg) at boiling point

bT = Atmospheric Boiling point (°K or °C)

1T = Temperature of liquid in vessel (°K or °C)

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As suggested in the FM Global Guidelines, is doubled to account for aerosol mist in the

cloud. Therefore if the initial flash fraction is 50% or greater, the entire liquid contents can be

assumed to vaporize, and equals W and then Equation 37 can be used in conjunction with

to solve for the mass of equivalent TNT.

vapF

vapF

vlW

vW

If is less than 50%, then that portion of that is not vaporized will rainout into a ground

pool. The next step, Equation 34, can be used to calculate the amount of this ground pool that is subsequently vaporized due to thermal and atmospheric effects. For example, if the initial flash

fraction, , is calculated to 15% and is doubled to 30% to account for aerosol mist, then 70%

of the initial liquid release, , will rain out into the liquid pool.

vapF lW

vapF

lW For a more accurate prediction of initial flash fraction, a source term computer model can be used. 7.2.4 Calculation of Liquid Pool Size The size of the liquid pool will be a factor in the evaporation rate. The extent of an unconfined spill on a relatively non-porous surface can be calculated as follows:

oA t gV (36)

Where: A = Spill area (m2) g = Gravitational constant (use 9.81 m/s2)

t = Time (Use 600 even if discharge duration is less) (Sec)

oV = Volume spilled (m3)

For unconfined spills on essentially flat surfaces, the area of the spill should be limited so that the pool depth is not less than 6 mm (1⁄4 in.). For a confined spill, such as inside a diked or curbed area, use the ground surface as well as vertical surfaces of walls up to the maximum level of liquid. When a dike or process area has drainage, the pool calculation becomes difficult. While drainage is favorable and required for controlling pool fires, it may be of little help in limiting vapor formation. The hot liquid can continue to vaporize within the drainage system, often more rapidly due to standing water and vapor can be released to the process area environment through the drainage system openings. The presence of drainage within a dike or curbed area should generally be ignored and the full amount spilled should be used for vaporization calculations. However, for very large capacity drainage systems designed specifically to both rapidly remove spilled material to a safe remote location and to retard vapor formation to the atmosphere, credit can be given after using considerable engineering judgment. 7.2.5 Calculating of Evaporation from a Liquid Pool Any material discharged as a liquid, if not initially flash vaporized or carried into the cloud as aerosol droplets, will form a pool on the ground and vaporization of the boiling pool may occur. If the atmospheric boiling temperature of the discharged liquid is below the ambient temperature, the liquid will continue boiling after it is spilled on the ground. The heat necessary for boiling is supplied by conduction heat transfer from the ground.

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The amount of liquid evaporated boilW by ground heat transfer is calculated using Equation 35.

1/2

2

b

boil a bvap

B tW T

H

T A (37)

Where:

boilW = Amount of liquid (kg) evaporated, not to exceed the amount of liquid spilled

B = Thermal property of spill surface (Table 3, Section 7-42, Page 21 of the FMDS) t = Time (Sec) (use 600 even if discharge duration is less) A = Area of the spill (m2) in contact with solid surface.

aT = Ambient temperature (°K or °C) (Use actual summer high for ambient temperature)

bT = Atmospheric Boiling point of liquid (°K or °C)

bvapH = Heat of vaporization (J/Kg) at atmospheric boiling point

If the liquid boiling point is above ambient, this equation is no longer applicable. According to NFPA 325, gasoline has a boiling point between 100-400°F (311-478K)*, depending on the grade of gasoline. For example; assume gasoline, whose boiling point is at the lower-limit of 100°F, is stored in a hot summer day with air temperatures at, or below, 100°F, no amount of liquid evaporation will take place, and Equation (37) is invalid. Ambient atmospheric temperatures would need to exceed the boiling point in order to achieve evaporation. In this situation, diffusional evaporation is the controlling factor. Equations to determine this rate are highly subject to atmospheric conditions, particularly wind speed. Since wind speed is not known, this factor is excluded from this simplified approach. A computer model must be used to predict the release under this type of conditions. 7.2.6 Calculation of Total amount of Vapor in a Cloud The amount of material used to solve the TNT equivalency equation (Equation 37), should be

either gW (contents initially gas) or (contents initially liquid or mixed liquid vapor). can be

calculated by adding the amount of released liquid (Equation 32) to that which flashes

(Equation 33) and the amount evaporated from the liquid pool (Equation 35).

vW vW

lW

boilW

2v vap l boilW F W W (38)

Note that the initial flash fraction is doubled to account for aerosolization. Doubling the

cannot exceed unity (1.0) and W cannot exceed the total mass of material initially released from

the vessel.

vapF

v

vapF

* Note: For gasoline types, whose boiling point ranges vary between 70-400°F, the amount of evaporation

would be significant on a hot summer day. For conservatism, the highest temperature difference ba TT ,

i.e., the lowest boiling point of chemical bT and highest ambient temperature aT may be used.

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7.2.7 Calculating TNT Equivalency The energy released in an explosion of a vapor cloud is expressed as a TNT equivalent. This methodology is often called the Ideal Blast Wave method. Based on an approximate energy of decomposition for TNT of 2000 Btu/lb, the following may be used to calculate a TNT equivalent

for a vapor cloud containing a known weight of flammable gas gW or vapor in SI Units: vW

61.11 10

oc

e

H fW W

x

(39)

Where:

eW = Mass of Equivalent TNT Energy Yield (t)

W = Mass of vapor in cloud (kg) of gas (Wg) or vapor (Wv) ocH = Heat of combustion of material (Kcal/kg)

f = Explosive yield (efficiency) factor (Section 3.4.3, Section 7-42, Page 22 of the FMDS)

The regulatory Guide 1.91 guidance is dated and requires revision to encompass the differing scenarios that need to be addressed by the utilities. The FMDS appear to be the best resource for those scenarios not captured in Regulatory Guide 1.91 and the guidance needs to be revised to reflect the additional augmenting methodologies.

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8. BOUNDING METHODOLOGIES The NRC has posed the following question:

“What methodologies could be used by utilities, for detonable solids, liquids and gases, that would provide bounding safe distance values for those materials that are being transported or stored in close proximity to a Nuclear Power station such that the associated peak positive incident overpressure from the detonation never exceeds 1 psi at the critical facility being analyzed.”

Provided in this section is a discussion regarding the difficulties in calculating universal bounding values for every scenario and type of detonable material analyzed. 8.1 Solid Materials For solid materials and hydrocarbons liquefied under pressure, the methodologies and maximum probable quantity of hazardous cargo transported, as presented in Regulatory Guide 1.91, would provide bounding safe standoff values. The maximum probable quantity of hazardous cargo transported or stored is dependent on the transportation mode, the transportation vehicle used, or the storage method. As suggested in Regulatory Guide 1.91, the maximum probable hazardous solid cargo for a single highway truck is 50,000 pounds (23,000 kg). Similarly, the maximum explosive cargo in a single railroad boxcar is approximately 132,000 pounds (60,000 kg). The largest probable quantity of explosive material transported by ship is approximately 10,000,000 pounds (4,500,000 kg). When shipments are made in connected vehicles such as railroad cars or barge trains, an investigation of the possibility of explosion of the contents of more than one vehicle is necessary. However, it must be understood that heat-of-reaction for each of these different hazardous material quantities are correlated to TNT-equivalence. Regulatory Guide 1.91 does provide some rudimentary bounding information regarding Vapor Clouds and as stated in the guide, “A reasonable upper bound to the blast energy potentially available based on experimental detonations of confined vapor clouds is a mass equivalence of 240 percent.” 8.2 Liquids If the material in the vessel exists as a liquid, the amount discharged into a confined or unconfined area, and the fraction that will flash vaporize and evaporate can be estimated using the methodologies illustrated in section 7.2. Calculating one bounding scenario that would comfortably encompass most is very difficult based on the all the variables discussed in section 7.2. For example, the results of the calculations in section 7.2 depend heavily on the assumptions used which include; amount released, discharge coefficient, release duration, density of the discharged liquid, fraction of the liquid that flashes to vapor, spill area, thermal property of the spill surface, ambient temperature, heat of vaporization, heat of combustion, and explosive yield factor. 8.3 Vapor Clouds A vapor cloud explosion is defined as an explosion occurring outdoors which produces damaging overpressure. It is initiated by the unplanned release of a large quantity of flammable vaporizing liquid or high-pressure gas from a storage tank or system, process vessel, pipeline, or transportation vessel.

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8.3.1 Theory and Principle Generally speaking, for a VCE with damaging overpressure development to occur, several factors must be present. First, the material released must be flammable and processed or held under suitable conditions of pressure or temperature. Examples of such materials are liquefied gases under pressure (e.g., propane, butane,); ordinary flammable liquids at high temperatures and/or pressures (e.g., cyclohexane, naptha) and non-liquefied reactive flammable gases (e.g., ethylene, acetylene). Second, a cloud of substantial size and concentration also must form prior to ignition. With most common flammable materials, should ignition occur instantly with release of the material, a large vapor cloud fire may occur, causing extensive localized heat radiation damage; however, significant blast pressures causing widespread damage will likely not occur. (Exception: some highly reactive materials, such as ethylene oxide under some conditions, might produce overpressures even with immediate ignition.) Should the cloud be allowed to form over a period of time within a confined process area and subsequently ignite, blast overpressures away from the cloud center can equal or even exceed those developed from detonation of high explosives and result in extensive damage over a wide area. Ignition delays of from one to five minutes are considered most probable, although major incidents with ignition delays as low as a few seconds and higher than 60 minutes have occurred. Third, a sufficient amount of the cloud must be within the flammable range of the material to cause extensive overpressure. The percent of the vapor cloud in each region varies, depending upon many factors including type and amount of the material released, pressure at release, size of release opening, direction of release, degree of outdoor confinement of the cloud, and wind speed, atmospheric stability and other environmental effects. The cloud will move over time, changing the flammable regions. For example, a continuous release over a long period of time will generally have a rich region near the source, a lean region at the cloud leading edge, and a flammable region in between. A puff release (essentially instantaneous release) will usually have a rich region at the leading edge with flammable regions following. Important factors that must be present for an ignited vapor cloud to produce overpressure are outdoor confinement and turbulence generation. Research testing, incident investigation, and computer modeling have demonstrated that the greater the horizontal and vertical confinement and the more turbulence in the gas cloud, the greater the potential for overpressure development. Turbulence can be caused by two primary mechanisms. First, repeated obstacles in the center of a cloud can accelerate gas mixing (due to eddy and shear layer effects), which in turn can increase flame speeds within the cloud. This highly influences pressure development due to flame instabilities. Second, turbulence can be directly initiated from a high-pressure release. Because obstacles cause turbulence, obstacles between the material and the plant play a principal role in the ability of a released vapor cloud to burn as a flash fire with only radiant heat effects or transit to an explosion with overpressure effects as well as radiant heat effects. The amount of congestion, confinement, the horizontal and vertical spatial arrangement of obstacles in the flow path of a cloud, are all important in determining if an ignited cloud of vapor will transit from a fire to an explosion. Wide-open spaces between the released material and the critical structure do not easily promote VCE events unless the area presents unusual conditions of confinement (such as long, narrow ravines) or repeated obstacles (such as dense forests or large railroad staging yards). However, a cloud released in an open area may be of sufficient size and winds may be of suitable velocity and direction to disperse the cloud into a congested process area at great distances from the actual release. While the ignition of the cloud could occur anywhere in the cloud (even in the

29 ERI/NRC 09-203

open space, for example, by a vehicle), the apparent explosion epicenter will be the area where the cloud is confined and where obstacles exist that can cause transition from a cloud fire to a cloud explosion. Remaining portions of the cloud outside the congested area will not contribute to blast effects, although radiant heat effects will occur. 8.3.2 Materials not Conducive to VCEs Throughout the industry, it is generally accepted that the following materials do not present a significant or credible outdoor VCE exposure. These exclusions are based on many factors such as heats of combustion, fundamental burning velocities, research testing, ease of dispersal, other experts’ opinions and loss history. 8.3.2.1 Liquefied Natural Gas (LNG) and Natural Gas (NG) (methane) LNG or NG, when the ethane component is less than 15% by volume. If LNG or NG has an ethane component in excess of 15%, it may be susceptible to VCE with overpressure development. However, with 85% or greater methane concentration, an explosion outdoors with damaging overpressures is not considered likely. Normal NG or LNG for fuel use is composed of 92–94% methane, 3–4% ethane and other hydrocarbons, and 3% nitrogen. While this varies by region, supplier and time of year, rarely would ethane content exceed 5% due to cost and value of ethane for other uses. The only condition where LNG or NG might have high ethane content would be where it is used as a pure feedstock in chemical processing. For all practical purposes, the ethane content of NG and LNG in pipelines and storage systems will never exceed 5%, and will normally be much lower. The validity of excluding LNG or NG is supported by testing by the Institution of Gas Engineers (Great Britain) in small- and full-scale obstacle arrays simulating natural gas processing units. While it was concluded that NG with high methane content could produce moderate overpressures if released into process arrays of extremely close packed obstacles, it was further stated that the tests “demonstrated that both the probability of a vapor cloud explosion occurring and its consequences will be lower for natural gas than with other common hydrocarbons.” Further, there have been no reported VCEs involving LNG or NG with high methane content, even though numerous ignited vapor releases resulting in flash fires without overpressures have occurred worldwide. Coupling testing and loss history with the low reactivity, the lightness of the vapor, and the relatively low flame speeds of LNG or NG, a VCE involving these materials is considered beyond the scope of a worst credible case scenario. 8.3.2.2 Ammonia Gas Ammonia Gas can and has exploded when substantially confined inside equipment or buildings. There is no indication, based on loss history, testing or combustion features, that ammonia will produce overpressures if released and ignited outdoors. 8.3.2.3 Gaseous Hydrogen Hydrogen gas such as in tube trailers, in a pipeline, or in a process, regardless of system pressure, should not be considered to present an outdoor VCE potential. Only one outdoor explosion incident involving hydrogen is widely reported. This involved a small release of high-pressure gaseous hydrogen during an acoustical test at the US Department of Energy Nevada Test Site. The extremely turbulent aerial cloud ignited, probably due to static energy caused by the turbulence of release. The overpressures were low and caused minimal damage to test equipment and structures. According to large users of gaseous hydrogen, aerial clouds are occasionally released from hydrogenation units and other processes with slightly delayed ignition. However, these so called ‘‘aerial detonations’’ have not caused significant far-field overpressures and have resulted in localized damage. For this reason, gaseous hydrogen is not deemed an unusually severe or credible VCE exposure.

30 ERI/NRC 09-203

8.3.2.4 Miscellaneous Flammable or Combustible Gases Such as ammonia synthesis gas (a hydrogen/carbon monoxide mix), coal and blast furnace gases, methylene chloride, and trichloroethylene are excluded from this document, because of low flame speeds and heats of combustion and lack of loss history. 8.3.2.5 Flammable Liquids or Gases processed above their Auto-ignition Temperature Flammable liquids or gases processed above their auto-ignition temperature will immediately ignite on contact with air. A severe flash fire may result, but delayed cloud ignition, necessary for development of significant overpressure, will not occur with these materials. 8.3.2.6 Flammable Liquids (High Viscosity) Flammable liquids having a high viscosity (greater than 1×105 centipoises) will likely not present normal vapor formation and will form pools of non-vaporizing liquid rapidly. 8.3.2.7 Mixtures Mixtures of two or more liquid or gaseous materials in a process system may occur, creating difficulty in choosing a material class, calculating release, etc. There is no easy solution for calculating mixtures, even with advanced computer models. Considerable judgment must be used. Generally, the more hazardous material should be selected as if it were the entire volume. If equal amounts exist, several calculations may be necessary to determine a worst credible event. If the actual heat of combustion of the mixture is known, it may be used in energy equations. 8.3.2.8 Hybrid Mixtures Hybrid Mixtures are a mixture of dust in a flammable gas medium. VCEs have occurred in hybrid systems, notably at polyolefin manufacturing facilities. Some VCE researchers feel suspended polymer dust in a gas cloud might contribute to overpressure development. While possible, there is no calculation procedure or model known to accurately factor in hybrid mixtures. 8.3.3 VCE Methodologies The conditions necessary to produce a VCE are fairly well understood, and a number of calculation methods are available to convert the VCE scenario into an assessment of damage effects. Most calculation techniques include methods for determining amount of material released, cloud size and energy release upon ignition. The energy of the material released is often converted into TNT equivalency (following principles of the so-called Ideal Blast Wave methodology), by assigning an explosion efficiency number. Also referred to as explosive yield, explosion efficiency is an estimation of the explosive effect of the mass in the cloud relative to an equivalent mass of TNT. Once a TNT equivalency is determined, published test data is used to calculate blast overpressures. Other methods have been developed and published to evaluate VCE overpressure effects. Section 7.2 abstracts several of the more well-known methods, including the TNT equivalency method. Calculating one bounding scenario that would comfortably encompass most is very difficult based on all the variables discussed in this section. Calculation of vapor cloud releases and consequences can either be performed in a spread sheet or be estimated by using one of many computer models available (for example ALOHA [2]). The primary feature of the more sophisticated modeling codes is their ability to more accurately calculate source term release,

31 ERI/NRC 09-203

cloud dispersion and drift, primarily because they factor in wind speed and atmospheric stability conditions. Many, however, apply a TNT Equivalency method for determining energy release, which requires the practitioner to determine a credible release scenario and assign variables such as explosion efficiency and blast epicenter. 8.4 Additional Literature The Center for Chemical Process Safety (CCPS) of the American Institute of Chemical Engineers (AIChE) has devoted a tremendous amount of effort into development of guidance to assess vapor-cloud explosions, flash fires, and BLEVES. General engineering solutions to these phenomena are provided along with detailed analyses of specific hazardous release conditions. The CCPS has two volumes that are widely used in the process industry to assess these phenomena through much of the same philosophy as described in the body of this report:

(1) “Guidelines for Evaluating the Characteristics of vapor Cloud Explosions, Flash Fires, and BLEVES,” [20] and

(2) “Guidelines for Use of Vapor Cloud Dispersion Models” [21].

These two volumes were a collaborative effort between the AIChE and TNO Prins Maurits Laboratory in the Netherlands.

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9. CONCLUSIONS As stated in the introduction section of this document, according to the Regulatory Guide 1.91, postulated accident analyses on routes near nuclear power plants must be addressed for all known combustible or detonable fuels utilizing the methodologies presented in the guide. However, Regulatory Guide 1.91 addresses only solid detonable materials, hydrocarbons liquefied under pressure, and air blasts on highway, rail, and water routes. The regulatory guide does not address liquids (pressurized or non-pressurized), cryogenically liquefied hydrocarbons (LNG, CNG, propane), vapor clouds (confined or unconfined), fixed facilities, pipelines and other scenarios. Figure 6 shows the Regulatory Guide 1.91 design curve for radial distance to TNT weight, based on peak incident overpressure of 1-psi. It is interesting to note that the examples noted on the graphical plot imply these are TNT weights for solid materials, yet there is no indication of how to arrive at these weights for other substances or mixtures (i.e., gaseous or liquid). Proper treatment for other hazardous and detonable mediums requires fundamental knowledge of the system thermodynamics, and specifically thermochemistry of mixtures. The Regulatory Guide 1.91 guidance is dated and requires revision as it is applicable to only solid explosives and hydrocarbons liquefied under pressure. Since Regulatory Guide 1.91 does not address other scenarios utilities are forced to utilize the methodologies inherent in the regulatory guide for the various bounding scenarios or seek out other sanctioned industry guidance to address these additional scenarios. The South Texas Project, lacking sufficient guidance in Regulatory Guide 1.91, sought out other sanctioned industry guidance to address these additional scenarios in order to provide a bounding analysis to the NRC in their FSAR COLA submittal. Their submittal resulted in an RAI, which is summarized in the following text:

“The minimum safe distance values shown in Table 2.2S-9 are said to be based on TNT equivalency method using Regulatory Guide (RG) 1.91 methodologies. But they seem smaller than generally expected. Please explain the methodology in detail.”

The South Texas Project, in response to the RAI, provided a detailed description of the methods utilized for different sources of explosion phenomena such as, atmospheric liquids, liquefied gases, and gases. The South Texas Project described the methodologies and approach to ascribing minimum safe-distances from explosion sources, utilizing methods in NUREG-1805 and the Factory Mutual Data Sheets. ERI utilized the methodologies presented in this document to evaluate a few of the more detonable materials selected by STP in their analysis. The attached Appendix contains a comparison of ERI calculated safe distances versus STP calculated safe distances for those detonable materials. The results are presented in Table 3 below. It is concluded, based on this technical independent review, that the South Texas Project engineering staff appropriately and correctly applied substance-specific thermodynamic data to obtain the heats-of-combustion in calculating the TNT-equivalent explosion energy for different fuels/oxidizer mixtures.

34 ERI/NRC 09-203

Table 3 Comparison of Calculated Safe Distances (ERI versus STP)

Detonable Material ERI Calculated Value

(m) ERI Calculated Value

(ft) STP Calculated

Value (ft)

Gasoline 72 235 266

Hydrogen 326 1070 1047

Hydrazine 13 42 86

Ethylene 2293 7537 7575

Acetic Acid 230 754 814

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10. RECOMMENDATIONS It is recommended that the Regulatory Guide 1.91 guidance be updated as it only addresses solids or hydrocarbons liquefied under pressure. Furthermore, it is recommended that Regulatory Guide 1.91 be revised to either provide a tangible link to those sanctioned industry methodologies that encompass scenarios not included in the guidance provided by Regulatory Guide 1.91, or incorporate the guidance provided in NUREG-1805, Factory Mutual Data Sheets, or other acceptable methodologies approved by the NRC (e.g. modeling codes, AIChE recommendations, international standards/methodologies, etc.).

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11. REFERENCES 1. “Evaluation of Explosions Postulated to Occur on Transportation Routes Near Nuclear Power

Plants,” Nuclear Regulatory Commission, Regulatory Guide 1.91, Washington, D.C., February 1978.

2. "ALOHA User's Manual: Aerial Locations and Hazardous Atmospheres," Version 5.4.1, US

Environmental Protection Agency (EPA), Office of Environmental Management, Washington, D.C. and U.S. National Oceanic and Atmospheric Administration (NOAA), Emergency Response Division, Seattle, Washington, 2007.

3. “Structures to Resist the Effects of Accidental Explosions,” U.S. Army, Navy, and Air Force,

U.S. Department of Defense, TM 5-1300, Revision 1, Washington, D.C., 1990. 4. “A Manual for the Prediction of Blast and Fragment Loadings on Structures,” U.S.

Department of Energy, DOE/TIC-11268, Albuquerque Operations Office, Amarillo Area Office, Pantex Plant, Albuquerque, New Mexico, 1980.

5. B. Dobratz, “LLNL Explosives Handbook: Properties of Chemical Explosives and Explosive

Simulants,” Lawrence Livermore National Laboratory, University of California, UCRL-52997, Livermore, California, 1981.

6. E. E. Baker, Explosions in Air, Wilfred Baker Engineering, San Antonio, Texas, 1973. 7. P. W. Cooper, Explosives Engineering, VCH Publishers, Inc., New York, 1996. 8. SFPE Handbook of Fire Protection Engineering, Society of Fire Protection Engineers,

National Fire Protection Association, Quincy, Massachusetts, 2002. 9. V. Brabauskas, Ignition Handbook, Society of Fire Protection Engineers, Fire Science

Publishers, Issaquah, 2003. 10. Robert C. Weast (Ed.), Handbook of Chemistry and Physics, 55th Edition, CRC Press,

Cleveland, Ohio, 1975. 11. I. Glassman, Combustion, 3rd Edition, Academic Press, New York, New York 1996. 12. David Lide. s.l (Ed), JANAF Thermochemical Tables, American Chemical Society and

American Institute of Physics for the National Bureau of Standards, Journal of Physical and Chemical Reference Data, 1985..

13. W. C. Reynolds, “STANJAN Thermochemical Code,” Department of Mechanical Engineering,

Stanford University. Stanford, California, 1987. 14. “CHEMKIN,” Reaction Design, Inc., San Diego, CA, 2008. 15. S. Gordon, B. McBride, “Computer Program for Calculation of Complex Chemical Equilibrium

Compositions and Applications,” National Aeronautic and Space Administration (NASA), NASA Reference Publication RP-1311, May 2004.

16. L. Fried, L., C. Souers, M. Howard, “CHEETAH: A Next Generation Thermochemical Code,”

Ver. 2.0. Lawrence Livermore National Laboratory University of California, UCRL-ID-117240, Livermore, California, 1994.

38 ERI/NRC 09-203

17. M. R. Baum, S. J. Brown [Ed.], “The Velocity of Missiles Generated by the Disintegration of Gas Pressurized Vessels and Pipes,” American Society of Mechanical Engineers, 1984 Pressure Vessels and Piping Conference and Exhibition, PVP-Vol. 82, pp. 67-83, San Antonio, Texas, 1984.

18. “Fire Dynamics Tools (FDT's): Quantitative Fire Hazard Analysis Methods for the US Nuclear

regulatory Commission Fire Inspection Protection Program,” Nuclear Regulatory Commission, NUREG-1805, Washington, D.C., 2004.

19. “Guidelines for Evaluating the Effects of vapor Cloud Explosions Using a TNT Equivalency

Method,” Factory Mutual Global, Property Loss Prevention Data Sheet 7-42, Boston, Massachusetts, 2006.

20. “Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and

BLEVES,” American Institute of Chemical Engineers, Center for Chemical Process Safety, Park Ave., New York, New York.

21. “Guidelines for Use of Vapor Cloud Dispersion Models,” American Institute of Chemical

Engineers, Center for Chemical Process Safety, Park Ave., New York, New York.

22. “Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids,” National Fire Protection Association, NFPA 325, Quincy, Massachusetts, 2001.

39 ERI/NRC 09-203

APPENDIX: CONFIRMATORY CALCULATIONS

ERI/NRC 09-203 40

GASOLINE (Liquid) ΔHc (Kcal/kg) - Gasoline 10,437.60 From the internet

f - Explosive Yield Factor (Class I Materials FMDS)

0.05

Explosion efficiencies listed in paragraph 3.4.3 of the FMDS (page 22) are based on historical evidence and on literature classification of materials by several different sources, including Dave J. Lewis of ICI (England), Unconfined Vapor Cloud Explosion—Historical Perspective and Predictive method Based on Incident Records, (1980) Prog. Energy Comb. Sci., VC, pp 151-165.

Vapor density of gasoline (lbs/ft3) 0.2516 Density of air (0.074 lb/ft3) x Specific Gravity of Gasoline (3.4)

Material at Risk Amount of Liquid Released Units

Mass in Vapor Cloud

(kg) Assumptions

Gasoline 9000 Gal 137.3

9,000 gallons of gasoline leaks from confinement and spills to surrounding asphalt. The liquid is assumed to flash once it has escaped confinement and is vaporized and concentrations in the vapor are between the LFL and the UFL. The vapor remains confined in a cloud and is not dispersed and detonates.

Equation 7 from FMDS

Where:

We Mass of Equivalent TNT Energy Yield (Tonnes)

W Mass of vapor in cloud (kg)

ΔHc Heat of combustion of material (Kcal/kg) for gasoline

f Explosive yield (efficiency) factor (section 3.4.3 of FMDS)

61.11 10

oc

e

H fW W

x

ERI/NRC 09-203 41

GASOLINE (Liquid)

Tonnes kg

Then We = 0.065 64.6

From Regulatory Guide 1.91

Where:

RRG Radial Distance (m) where pressure wave is less than 7 KPa (1 psi)

W Charge mass, (kg)

ERI Calc. (m) ERI Calc.

(ft) STP Calc. (ft)

Then RRG = 71.5 234.5 266

1/317.85RGR W

ERI/NRC 09-203 42

HYDROGEN (GAS)

ΔHc (BTU/lb) - H2 51,600.00 Taken from Table 1 - FM Datasheets

Vapor density of H2 (lbs/ft3) 0.005254 Density of air (0.074 lb/ft3) x Specific Gravity of H2 (0.071)

Material at Risk Amount of Hydrogen Released Units

Mass in Vapor Cloud

(lb) Assumptions

Hydrogen gas 100,200 ft3 526.5 100,200 ft3 of hydrogen escapes confinement and is immediately mixed with air. The gas remains confined in a vapor cloud and is not dispersed.

From ERI TER lb

Where:

We Mass of Equivalent TNT Energy Yield (lbs)


ΔHc Heat of combustion of material (BTU/lb) for H2

lbs kg

Then We = 13582.431 6162.6 From Regulatory Guide 1.91

Where:

oc

e of TNT

HW W

H

1/317.85RGR W

ERI/NRC 09-203 43

HYDROGEN (GAS)


W Charge mass, (kg)


(ft) STP Calc. (ft)

Then RRG = 326.3 1070.3 1047

ERI/NRC 09-203 44

Hydrazine (Liquid) ΔHc (Kcal/kg) - Hydrazine 4,000.00 From the internet

f - Explosive Yield Factor (Class III Materials FMDS)

0.15


Vapor density of Hydrazine (lbs/ft3) 0.074 Density of air (0.074 lb/ft3) x Specific Gravity of Hydrazine (1.0)

Density of Hydrazine (lbs/ft3) 62.93


Mass in Vapor Cloud

(kg) Assumptions

Hydrazine 1260 lbs 0.7

Approximately 150 gallons of Hydrazine leaks from confinement and spills to surrounding asphalt. The liquid is assumed to flash once it has escaped confinement and is vaporized and concentrations in the vapor are between the LFL and the UFL. The vapor remains confined in a cloud and is not dispersed and detonates.


Where:



ΔHc Heat of combustion of material (Kcal/kg) for Hydrazine

61.11 10

oc

e

H fW W

x

ERI/NRC 09-203 45

Hydrazine (Liquid)


Tonnes kg

Then We = 3.63E-04 3.63E-01 From Regulatory Guide 1.91

Where:


W Charge mass, (kg)


(ft) STP Calc. (ft)

Then RRG = 12.7 41.8 86

1/317.85RGR W

ERI/NRC 09-203 46

Ethylene (Gas) ΔHc (BTU/lb) - Ethylene 20,300.00 Taken from Table 1 - FM Datasheets

Vapor density of Ethylene (lbs/ft3) 0.0932 Density of air (0.074 lb/ft3) x Specific Gravity of Ethylene (1.26)

Material at Risk Amount of Ethylene Released Units

Mass in Vapor Cloud

(lb) Assumptions

Ethylene gas 470,000 lbs 4.70E+05 470,000 lbs of Ethylene gas escapes confinement and is immediately mixed with air. The gas remains confined in a vapor cloud and is not dispersed.

From ERI TER

Where:

We Mass of Equivalent TNT Energy Yield (lbs)


ΔHc Heat of combustion of material (BTU/lb) for Ethylene

lbs kg

Then We = 4.77E+06 2.16E+06 From Regulatory Guide 1.91

Where:

oc

e of TNT

HW W

H

1/317.85RGR W

ERI/NRC 09-203 47

Ethylene (Gas)


W Charge mass, (kg)


(ft) STP Calc. (ft)

Then RRG = 2297.8 7536.8 7575

ERI/NRC 09-203 48

Acetic Acid (Liquid)

ΔHc (Kcal/kg) - Acetic Acid 3,137.00 From the internet

f - Explosive Yield Factor (Class II Materials FMDS)

0.1


Vapor density of Acetic Acid (lbs/ft3) 0.078 Density of air (0.074 lb/ft3) x Specific Gravity of Acetic Acid (1.05)


Mass in Vapor Cloud

(kg) Assumptions

Acetic Acid 500,000 Gal 7628.2

500,000 gallons of acetic acid leaks from confinement and spills to surrounding asphalt. The liquid is assumed to flash once it has escaped confinement and is vaporized and concentrations in the vapor are between the LFL and the UFL. The vapor remains confined in a cloud and is not dispersed and detonates.


Where:



ΔHc Heat of combustion of material (Kcal/kg) for acetic acid

61.11 10

oc

e

H fW W

x

ERI/NRC 09-203 49

Acetic Acid (Liquid)


Tonnes kg

Then We = 2.156 2155.8 From Regulatory Guide 1.91

Where:

RRG

Radial Distance (m) where pressure wave is less than 7 KPa (1 psi)

W Charge mass, (kg)


(ft) STP Calc. (ft)

Then RRG = 230.0 754.4 814

1/317.85RGR W

ERI/NRC 09-203 50


eri/nrc 09-203, 'comparison of blast pressures and effects ...explosion energy for different...

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