NUREG/CR-5037

BNL-NUREG-52106

FIRE ENVIRONMENT DETERMINATION IN THE

LASALLE NUCLEAR POWER PLANT CONTROL ROOM

J.L. Usher and J.L. Boccio

October 1987

DEPARTMENT

RELIABILITY & PHYSICAL ANALYSIS GROUP

OF NUCLEAR ENERGY, BROOKHAVEN NATIONAL LABORATORY

UPTON, NEW YORK 11973

Prepared for

United States Nuclear Regulatory Commission

Washington, D C 20555

NUREG/CR-5037

BNL-NUREG-52106

AN, R-7

FIRE ENVIRONMENT DETERMINATION IN THE

LASALLE NUCLEAR POWER PLANT CONTROL ROOM

J.L. Usher and J.L. Boccio

Manuscript Completed - March 1987

Date Published - October 1987

RELIABILITY & PHYSICAL ANALYSIS GROUP

DEPARTMENT OF NUCLEAR ENERGY

BROOKHAVEN NATIONAL LABORATORY

UPTON, N.Y. 11973

Prepared for

DIVISION OF ENGINEERING TECHNOLOGY, RES

OFFICE OF NUCLEAR REGULATORY RESEARCH

U.S. NUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 20555

UNDER CONTRACT NO. DE-ACO2-76CHOOO16

FIN A-3252
NOTICE

This report was prepared as an account of work sponsored by an agency of the United

States Government Neither the United States Government norany agency thereof. or any of their employees, makes any warranty, expressed or imphed, or assumes any

legal liability or responmbilty for any third party's use, or the results of such use, of

any information, apparatus, product or process disclosed in this report, or represents

that its use by such third party would not infringe privately owned rights

The views expressed in this report are not necessarily those of the U S. Nuclear

Regulatory Commission

. Available from

Superintendent of Documents

U.S. Government Printing Office

P 0. Box 37082

Washington, DC 20013-7982

and

National Technical Information Service

Spnngfield, Virginia 22161
-iiiABSTRACT

One of the objectives of the Fire Protection Research Program (FPRP) of

the U.S. NRC is to improve the modeling of environments caused by fires in typical nuclear power plant enclosures. A three-dimensional fluid dynamics computer code (PHOENICS) has been adapted as a field-model fire code (SAFFIRE)

for this purpose. The model has been applied to simulate two distinct fires

in the control room of the LaSalle County power plant. The environments

determined illustrate hazardous potential for both personnel and equipment.

CONTENTS

Page

ABSTR CT.CT .......... . .* se....................................... .* ............ * . * ** * * * cii

LIST OF FIGURES...o.... .................... . ................. ....... vi

LIST OF TABLES.........................................................vii

ACKNOWLEDGEMENTS..,..o..... .o.. oix ... ................................ 

I. INTRODUCTION .................................................... 1

A. Fire Protection Research ProgrIm............................... 1

B. Probabilistic Risk Assessment... .. *.... ... . ........... .**.. 2

1. Fire Hazard 2nlss.......................................

2

2. Fire PropagationAnalysis................................... 2

C. Control Room Habitability and Fire Safety Study (CR)........... 3

Do Summary .......................................... oe............. 4

II. PHOENICS/SAFFIRE COMPUTER MODELS.................................. 5

IlI. LASALLE CONTROL ROOM SIMULATIONS.................................. 9

A. Computational Model Parameters.... . ............................ 9

B. SimulationResults............................................. 11

IV. CONCLUSIONS/FUTURE DIRECTIONS....................o.............s..... 19

V. REFERENCES... *....... .... .......................................... 21
-viLIST OF FIGURES

Page

1. LaSalle control room - plan view....................................... 10

2. LaSalle control room - exhaust plenum - unit 2........................ 10

3. LaSalle control room - exhaust plenum - elevation ...................... 11

4. Cold flow velocity distribution - floor level .......................... 12

5. Cold flow velocity distribution - ceiling levelo........................ 12

6. Cold flow velocity distribution - transverse elevation................ 12

7. Velocity distribution fire case 1 - floor level........................ 13

8. Velocity distribution fire case 1 - longitudinal elevation*........... 13

9. Gas temperature at cabinet level - fire case 1 ........................ 14

10. 150%C isotherm- fire case 1........................................... 14

11. 50 0 C isotherm - fire case 1.. ......................................... 15

12. Velocity distribution - fire case 2 floor level ........................ 15

13. Velocity distribution - fire case 2 ceiling level...................... 15

14. Velocity distribution - fire case 2 transverse elevation............... 15

15. Gas temperature at cabinet level - fire case 2 ......................... 16

16. 1500C isotherm - fire case 2 .......................................... 16

17. 2000C isotherm - fire case 2........................................... 17
-viiLIST OF TABLES

Page

1, Exchange Coefficients (r 4 ) and Source Terms (S#) for Different

Vari , ... ble .... .... ... ... ... .... ... ... .... ... ... ... 6
It
-ixACKNOWLEDGEMENTS

The authors wish to thank Ashok Singhal and Luen Tam of CHAM of North

America, Inc., for their invaluable assistance with the computational aspects

of this work; and in particular, for performing the computer calculations. We

also thank Amar Datta of the NRC for his guidance and support. We especially

acknowledge the tireless efforts of Jeanne Danko, communications maven and

word-processing whiz, in the preparation and editing of this document.

1

I. INTRODUCTION

The primary objective of this report is to present the results of several

computer simulations of the fire-induced thermal environment within the control room of the LaSalle Nuclear Power Plant. These simulations were performed as part of a sub-task within the Control Room Habitability and Fire

Safety Study (CR) which is being performed as part of the overall Fire Protection Research Program (FPRP) for the U.S. NRC. A secondary objective is to

describe the development status of the SAFFIRE computer code somewhat in detail. This code, being developed as part of the FPRP, would be the first fire

environment model created with NRC fire safety issues in mind and has been

validated via comparison with fire tests conducted with nuclear power plant

concerns in mind.

Implementation of the NRC's safety goal and severe accident policy will

require that a reliable and credible technology, modeling and data base be

provided to answer the questions: What is the current and expected level of

safety of operational nuclear power plants, and what are cost effective ways

to either enhance or maintain acceptable levels of safety. The ability to

evaluate the risk contributions of important accident initiators involving

equipment malfunctions and human errors including common cause or dependent

failures has been improved to a point where useful select applications can be

made to assess conditional risks. Risk methodology for estimating risk contributions from external events, such as fires, floods and earthquakes, is

being developed. However, seismic risk analysis and seismic hazard analysis,

as compared to fire risk analysis and fire hazard analysis, is at a more detailed stage of model development. To assure consistency, accuracy, and

credibility in assessing the relative effects of the risk contributions from

external events requires that a concerted effort be expended to understand the

impacts of fires on the operational envelope of nuclear power plants. The

overall purpose of the FPRP was to enhance risk and reliability analysis from

a fire-induced-stress viewpoint in order to help inject consistency, accuracy

and credibility into the analysis of the impact of fires on the operational

safety of nuclear power plants. In addition, since risk-based analyses of inspection and enforcement issues, technical specifications and other licensing

issues can augment the safety of operating plants by identifying weaknesses in

design and operation, the FPRP was structured to address and resolve concerns

regarding implementation of fire-protection guidelines mandated in 10CFR50

Appendix R: "Fire Protection."

A. Fire Protection Research Program

The goal of the FPRP is to develop test data and analytical capabilities

to support the evaluation of:

1. the contribution of fires to the overall risk from nuclear power

plants,

2. the effects of fires on control room equipment and operations, and

3. the effects of actuation of fire suppression systems on safety

equipment.
2

B. Probabilistic Risk Assessment

NRC research needs in fire risk analysis have been outlined in previous

memoranda and reports .The recommendations in the area of external event

risks, such as fires, included the generation of information regarding equip-.

ment performance in accident environments, methods to predict variations in

environmental parameters during a fire, and data relating equipment failure

probabilities to environmental changes. Specifically, in the area of fire

risk, the Office of Nuclear Regulatory Research (RES) was urged to give attention to the aspects of interaction between fire protection features and safety

systems, the reliability of fire protection features, and the likelihood of

qualified equipment withstanding the effects of fire and fire suppression

activities.

1. Fire Hazard Analysis

Theoretically, the fire risk analyst should study the potential contribution to to risk of fires anywhere in the nuclear power plant. By screening

out unimportant locations, however, he can greatly reduce the amount of work

necessary without sacrificing significant confidence in the results. The purpose of the fire hazard analysis is to identify the locations that are important to the fire risk analysis.

For the purposes of initial analysis, fire locations are usually conýsidered to be coincident with the fire zones defined by the utility in its

Fire Protection Review. The fire zones consist of one or more compartments

and are separated from other fire zones by rated fire barriers. The spread of

fire between zones is considered unlikely, although possible. A more detailed

analysis of the fire zones may show that only limited areas within the fire

zones contain critical safety-related equipment, in which case a number of

fire locations may be defined within the particular fire zone.

The "importance" of a fire location is measured by its contribution to

the overall frequency of radionuclide release. Since this cannot be determined until it least the first iteration of the fire risk analysis has been

completed, more approximate measures are employed. The primary measures are

the type and quantity of fire-vulnerable safety equipment at the location of

interest. Other factors that may be used in the screening process are the

frequencies of fires, the types and amounts of combustible materials, and the

suppression systems available. Information on all of these factors can be

obtained in fire protection reviews.

To summarize, the step-by;-step procedure for fire hazard analysis consists of constructing a simple systems model of the plant, identifying the

locations of safety equipment, identifying critical fire-impact locations,

identifying locations adjacent to critical locations containing large quantities of combustibles, and determining the distributions for fire frequency for

each critical location.

2. Fire Propagation Analysis

The purpose of this analysis is to determine the likelihood and extent of

various levels of damage in a compartment given that a fire has occurred.
3

Several different approaches have been utilized to date: statistical modeling

based on past experience, multistage event-tree modeling, and a third requiring the construction of physical models to describe the relevant phenomena.

Each of these approaches utilizes data regarding the following elements of a

fire model: ignition, detection, suppression and propagation.

Regardless of the modeling approach chosen, the step-by-step procedure

for fire propagation analysis retains the same principal features: definition

of representative fire-growth scenarios for each location, determination of

distribution for growth time for each fire, determination of distribution for

suppression time for each scenario, and computation of the distribution for

frequency of growth.

C. Control Room Habitability and Fire Safety Study (CR)

In the control room there is a high density of electrical instrumentation

and control cables of the redundant trains in necessarily close proximity to

each other. Fire protection of the control room is complicated by the fact

that malfunctions of critical components may have cascading effects in spreading loss of control into areas remote from the control. room. The requirements

of operability for components in electrical cabinets in the control room,

therefore, becomes more stringent. A systematic study is needed of the control system and how faults may propagate in the event of a fire. A systems

approach, utilizing the knowledge and the methodologies of spatial separation,

should be used in such a study. The data base produced would be of value in

devising ways of ensuring a margin of safety.

The other concern in the control room is that existing requirements to

protect the occupants of the control room in accident situations may not be

adequate. NRR has responded to this concern with a program plan for a study

in control room habitability. One of the desired goals of such a study is

that limiting environmental conditions for operation in the control room

should be established and should consider human performance as well as equipment operation as the basis for selection of appropriate limits. The program

plan itself proposed environmental criteria for human performance. The need

is for a determination of whether the generic control room habitability system

is adequate for the maintenance of that minimal environment through a credible

fire accident. The effectiveness with which the habitability system, which

includes the UVAC system, isolates the control room and removes smoke and

toxic combustion products from within is to be studied, and possible remedial

actions are to be examined. The CR study addresses the issues by determining

the fire-generated environment and the purge system effectiveness.

The end products of the CR study will be:

1. a data base on a range of fire scenarios that could cause failure of

equipment and lead to conditions resulting in loss of shutdown and

safety functions;

2. the system-interactions affecting shutdown and safety functions for

the identified failures; and

3. an estimate of the smoke removal effectiveness of typical habitability systems.
4

D. Summary

In conclusion, the overall end products of the FPRP will be:

1. a user-interactive computer program applicable to a wide range of

geometries and internal partitioning for the purpose of predicting

fire environments in enclosures,

2. a data base of test results depicting fire environment for a range of

potential fires in nuclear power plant enclosures,

3. an integrated methodology whereby the environments created by a range

of fires in plant enclosures is determined, and in conjunction with

equipment damage thresholds is used to estimate the time-to-failure

of certain classes of equipment, and

4. a data base for development of fire PRA in nuclear power plant enclosures, including time-to-detection, time-to-suppression, and the

probable sequence of equipment failure in potential fire

environments.
5

II. PHOENICS/SAFFIRE COMPUTER MODELS

This chapter describes the mathematical and computational models derived

for the purpose of determining the fire environment within an enclosure typical of a nuclear power plant. The PHOENICS 2 , 3 code is a proprietary computational fluid dynamics model developed by CHAM, Inc. The model has had broad

utilization throughout the fluid dynamics community in various areas such as

aerodynamic flow modeling, combustion chamber modeling and fire environment

determination4 . The SAFFIRE computational model, being developed as part of

the FPRP, will be a self-contained, non-proprietary code dedicated solely to

the determination of the potential fire environments in nuclear power plant

enclosures. The SAFFIRE model will utilize a subset of the overall PlOENICS

model adapted specifically for this purpose.

The computational field model is based on the solution of the governing

partial-differential equations expressing the conservation of mass, momentum

and energy. Gas flow is treated as three-dimensional, transient and elliptic.

The fluid is assumed to be a perfect gas with constant physical properties

identically those of air. Density is calculated as a function of local temperature. Buoyancy effects are accounted for by using local densities in all

terms of the conservation equations, i.e., the Boussinesq approximation is not

used. Turbulence effects are accounted for by using the two-equation k-e

model of turbulence , with known refinements for buoyant flowsb-8.

Independent variables are three coordinates (x,y,z) of a cartesian coordinate system and time (t). Dependent variables include the three velocity

components (u,v,w), the pressure (p), the enthalpy (h), the turbulence kinetic

energy (k), and its dissipation rate (c). The conservation equations are

expressed in the following time-averaged form:

a ++

where f stands for a generic property (u,v,w,h,k, etc.) and p, u, Jp, Sf

are density, velocity vector, diffusive flux vector, and source term for

generic property f per unit volume, respectively. The diffusive flux is given

by:

J --r grad 4, (2)

where reff, ý is the effective exchange coefficient for the transport of

generic property f. The values of reff and S for.different X's are listed

in Table 1.
6

Table 1

Exchange Coefficients (rý) and Source Terms (S*) for Different f Variables

From the table:

Ueff 'it " lt

Ut = C U k 2 /p

(3)

(4)
7

au 2 av2 •2

Gk = 1t {2 [(t•) +--)+(-r-,) )

2 2 •2 (2

2 2

+ + ) , and

G It- g . (6)

The buoyancy production term, Gb, represents the generation/suppression of

turbulence due to buoyancy. In stable stratification (fire enclosures), ap/az

is negative; hence Gb becomes a sink term, and the turbulent mixing is

reduced. The turbulence model contains five empirical

C1 - 1.44 ,

C2 = 1.92 ,

Co W 0.09 ,

-k - 1.0, and

= 1.3.

Additionally the mathematical model may be apl~ied to determine smoke

concentration throughout the enclosure in question by utilizing a smoke mass

source term6 to replace the heat generation source term from Table 1, i.e.,

utilize S - If''' for * - f, the smoke concentration, in place of the

4''' and h terms.

The computational model consists of a finite difference solution of the

set of elliptic partial-differential equations expressing the conservation of

mass, momentum, energy and other fluid variables in three dimensions. The

code (SAFFIRE) generates local predictions of temperature, velocity, species

concentrations, and pressure. For finite differencing, the code utilizes a

modified version of the SIMPLE algorithm9 developed at Imperial College. The

SIMPLE procedure is as follows:

1. Guess the pressure field and the distribution of effective turbulent

eddy viscosity.

2. Using the guessed values of p and peff) solve the momentum equation

to obtain approximate velocity components.

3. Calculate the pressure corrections that enforce continuity.
8

4. Solve the k-c equations using the new values of velocity and

pressure.

5. Update the effective turbulent velocity.

6. Repeat from operation 1., until steady state is reached or convergence criteria are satisfied.

The SIMPLE algorithm is fully implicit, and finds a steady-state solution

at a designated point-in-time, but without having to march in time about the

designated point. An important advantage of SIMPLE is that for a complex

problem, where fine grids are essential for accuracy, computer time requirements are greatly reduced over algorithms not based on SIMPLE.

To date results from the computational model described above have been

compared to experimental data from two sets of fire tests conducted with NRC

needs in mindlo-11 for the purpose of preliminary bencbmarking of the model.

The results of these benchmark comparisons have been detailed previously3 and

will not be discussed here.
9

III. LASALLE CONTROL ROOM SIMULATIONS

As discussed previously, performance and evaluation of the FPRP is being

coordinated with work in progress on the Control Room Habitability Program and

the Risk Methods Integration and Evaluation Program (RMIEP). RMIEP research is

evaluating all risks associated with the LaSalle KPP. As a portion of this

coordinated research effort, an additional sub-project was initiated within the

FPRP: the Control Room Habitability and Fire Safety Study (CR). This study combines the methodologies of FSC, FED and FFT summarized above. This section presents a description of the geometry of the control room, including internal flow

obstacles and the distribution of forced ventilation inlets and outlets. The

modeling procedure is summarized and results of several simulation runs with and

without fires are presented.

A. Computational Model Parameters

The control room contains control and instrumentation cabinets and cables

for LaSalle NPP Units 1 and 2. The enclosure (Fig. 1) is 120 ft x 60 ft x 16.5

ft high with concrete walls generally two feet thick or more at the room boundary. Doors to the control room are fire-rated (3 hr) and are usually closed,

although there is a design leakage of 1500 cfm through these doors. Forced ventilation inlets are distributed throughout the room producing a total ventilation rate of 24020 cfm. Cabinets and control consoles are shown in Fig. 1.

There are a number of desks and tables located around the control room which are

not depicted in Fig. 1, but which are accounted for in the computational configuration. The exhaust configuration in the control room is unique in our experience: two L-shaped exhaust plena (Fig. 2), 40 ft. long x 10 ft. wide,'are

delineated by fronts of cabinets and consoles and further by steel valances extending to the enclosure ceiling as shown in Fig. 3. One exhaust vent is

located in each of these plena, and there are no ventilation sources in either

plenum. Air flow from the room proceeds into the exhaust plena through gratings

in the bottoms of the cabinets forming the L-shaped boundary. In addition to

the high cable loadings in the cabinets and consoles, horizontal cable trays,

shown in Fig. 3, are located above the cabinets throughout the plenum areas.

The cabinets are open both in the back and on top to the general plenum area.

The unique exhaust plenum configuration resulted in the simulation of two basic

fire types: one outside the plena in the control room working area and one inside an exhaust plenum behind the cabinets. The locations of these source fires

are indicated by "X" on Figs. I and 2.

Observation of the geometrical details outlined above together with the locations of the ventilation sources and the locations of internal flow obstacles,

guided the set-up of the three-dimensional (x,y,z) computational grid to be

.analyzed. The enclosure was divided into 4389 cells (x:33, y:19, z:7) of varying length, width and height. The spacing of the cells in the x and y directions is primarily due to the specific locations of flow obstacles in the control room, although consideration is also given to ventilation inlet locations

throughout the room. The height (z) of the control cells is determined by the

height of the control room benchboards and vertical cabinets (8 ft over 3 cells)

as well as the locations of cable trays, ventilation inlets and ducting. At the
I0

/

EZZZZZEJ

EII 7!7i IPHý

Q=3 M5

r- i,2 - - M n r- -

Figure 1. LaSalle control room - plan view

__ A

- --

'C

C

Figure 2. LaSalle control room - exhaust plenum - unit 2
11

Figure 3. LaSalle control room - exhaust plenum - elevation

present state of evolution the model requires the heat release rate of the

source fire as input to the code. The heat release rate used for nearly all of

the simulation runs was determined in a series of cabinet fire tests performed

previously for the NRC 1 2 . The peak heat release rate used in the simulations is

600 kW; the temporal variation approximates that determined in Ref. 12. The

design strengths of each ventilation source are also input to the code. Total

flow into the control room is distributed throughout the inlet system as per

design specifications. Design leakage through the control room doors is 1500

cfm; the remaining 22520 cfm exhausts through the vents located in each exhaust

plenum ceiling. Locations and porosities of all flow obstacles are simulation

input parameters.

B. Simulation Results

Each simulation run is preceded by a cold-flow case (without a source fire

present) to characterize the steady-state ambient flow environment. Sample flow

profiles from the cold-flow simulations are depicted in Figs. 4-6. Fig. 4

illustrates the flow at floor level. By comparison with Fig. I, it is possible

to see the pattern via which air flows into the L-shaped exhaust plena. It

should be noted that maximum velocity in this figure is 0.45 meters/second

(m/s). In Fig. 5 the air flow near ceiling level is shown, and the locations of

the two exhaust vents are clearly discernable. Maximum flow velocity in Fig. 5

is 1.5 m/s. Fig. 6 is an elevation view of the exhaust plenum showing both the

flow of air into the bottom of the exhaust plenum and the subsequent outflow

through the exhaust vent located near ceiling level. Maximum flow velocity in

this figure is 0.6 m/s.
12

* - fl

* - . ~ V

* . . U~t. t

. It,..

I,

* - ~. 

- - .. .. .. .1*1

.---... *1

* ~ * . I * S I ~ -

* .. I I I

I

Figure 4. Cold flow velocity distribution -floor level

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

Figure5.. ........................................ leve

Figure 5. Cold flow velocity distribution tranceilin elevelio

Two separate simulations involving source fires were performed as stated

above: one source fire located in the control room working area and one located

in the Unit 2 exhaust plenum as shown in Figs. 1 and 2. As mentioned above,

peak fire strength was 600 kW, while fire duration was 18 minutes. The 600 kW

heat release rate was distributed in and above the cabinet in question to a

flame height calculated from well-known flame-height correlations.

The first case to be examined was that of a fire in the main control room

area. The modified flow patterns produced by this fire are depicted in Figs. 7

and 8. Both of these snapshots were taken six minutes after source fire ignition. Fig. 7 shows the flow at floor level indicating the entrainment of air

into the fire plume as well as the flow into the L-shaped exhaust plena. Maximum

velocity for this figure is 0.65 m/s. Fig. 8 shows a horizontal elevation of

the control room sliced through the source fire. The location of the fire

stands out clearly. The flow of air through the bottoms of the cabinets and

consoles and out the exhaust vents is also discernable. Maximum flow velocity

is 4.2 m/s. The entrainment of air into the fire plume is shown most clearly in

this figure.
13

Fire

.• °* ° 8 S o ~

• "•• '• *.b *• . -0 . .. .b

Figure 7. Velocity distribution fire case I -floor level

Figure 8. Velocity distribution fire case 1 - :longitudinal elevation

Fig. 9 shows the temporal variation of gas temperature at a height roughly

equivalent to the tops of the cabinets (-8 ft) both at the fire location and

near the center of the control room. The temperature near room center is also

representative of the gas temperature at various other locations throughout the

control room. Gas temperature rose linearly in six minutes to 150*C in the corntrol room center at the 8 ft height. Gas temperature above the fire plume near

the ceiling rose to 240*C in 6 minutes. There was no appreciable gas temperature increase in the exhaust plena due to this fire. Fig. 10 shows an example

of perhaps the most valuable output from the simulations: an isothermal perspecwtive of the control room. The 150"C isotherm is shown at 2, 4 and 6 minutes

after fire ignition. The fire plume is clearly visible in the top view. The

spread of the isotherm around the exhaust plena can be seen in the remaining two

views. Notice that the 150%C isotherm only descends to the top of the cabinets

at the 6 minute mark. Fig. 11 depicts what is probably a more significant result for this case, The 50%C isotherm is shown in Fig. 11. The descent of this

isotherm to cabinet (and personnel) height occurs in one to two minutess,

The second case to be investigated produces an entirely different set of

results. For this case a source fire of the same strength is located wi~thin the

exhaust plenum of Unit 2 as indicated on Fig. 2. Recall that the backs and the

tops of these consoles/cabinets are open. Fig, 12 depicts the flow at floor

level six minutes after the ignition of the fire. Entrainment into the plume

can be readily observed. Maximum velocity is 0.75 m/s, Fig. 13 illustrates

flow near ceiling level. Maximum velocity is 1.6 m/s, Flow out of the fire

plume is observable as is flow into the exhaust vent. Note also the dead-end

swirling effect of--he flow at the top of the figure at the plenum boundary.

This phenomenon accounts for some of the gas temperature data presented subsequently. Fig. 14 shows an elevation view of the flow pattern located adjacent

to the fire. Maximum velocity is 6.0 m/s. This figure also illustrates both

flow into the exhaust vent itnd the swirling at the end of the plenum.
14

250-

0 200

ISOE 100-

I- Room Center

60-

0

O ' I * I I | -

0 60 120 180 240 300 360 420

Time - seconds

Figure 9. Gas temperature at cabinet level - fire case I

Figure 10. 150*C isotherm - fire case I
15

Figure 11. 500 C isotherm - fire case 1

* *..~d D* .V

Figure 12. Velocity distribution - fire case 2 floor level

*.o .-......... ......... . :. •'"". ...-...... :..:.: ... • .

•.5'............. *\... 

:.. .. . . . .: ..:- : 5I . . . ... •••I°.. . . .• •

Figure 13. Velocity distribution - fire case 2 ceiling level

* . . - - - ~ - - - - * *

S = - -

S

S S S S S S I

*........* S S S * * * *.

Figure 14. Velocity distribution - fire case 2 transverse elevation

In the case of a fire inside the exhaust plenum, temperature rise near the

cabinet tops was more pronounced than in the previous case. Gas temperature

rose to 200C near cabinet level in about two minutes, as shown in Fig. 15. The

three positions at which temperature is determined are indicated on Fig. 2.
16

Note that the gas temperature at position B at the plenum end is the most sensitive to the source fire. Mention must be made here that the gas temperature is

a measure of the convective heat flux only; no radiation effects are yet included in the model. Fig. 16 shows the temporal evolution of the 150*C isotherm. The fire plume is clearly visible as is the dead-end effect generated by

the plenum boundary and swirling flow pattern seen previously. Fig. 17 illustrates the evolution of the 200C isotherm. Gas temperature at cabinet level at

point B reaches 200%C about three minutes after ignition.

250-

B

200-

10-

E 100 -

0-

0 ~ •I I I I I

0 60 120 180 240 300 350 420

Time - seconds

Figure 15. Gas temperature at cabinet level - fire case 2

Figure 16. 150°C isotherm - fire case 2
17

Figure 17. 200*C isotherm - five case 2

A third case with a smaller source fire was also simulated. The location

of the fire was in the exhaust plenum as above. Total heat release rate for

this fire reached a peak value of 90 kW after 8 minutes, maintained this level

for 22 min,'and eventually burned out after 40 min. This fire was a comparison

with an actual cabinet fire observed in the experimental portion of the FPRP

conducted at SNL. 1 3 This fire was so small that no effect was seen outside in

the control room working area. Inside the exhaust plena, a peak gas temperature

of 70°C was reached at location B (ceiling level) 15 min after ignition. Temperatures near cabinet height were less than 60 0 C at all plenum locations. Flow

phenomena were similar to those observed in the cold-flow case described above.

Detailed graphical analysis of each of the simulation cases described above

is contained in a series of progress reports 1 4-17 prepared by CHAM of North

America, Inc., who performed the simulation calculations. These reports are

available from the authors at BNL.

19

IV. CONCLUSIONS, FUTURE DIRECTIONS

Conclusions were reached regarding the two separate fire simulation

examples, inside and outside the exhaust plenum. The fire in the control room

working area did not produce temperatures higher than 1500 C in the area of the

control cabinets/consoles over the time frame considered. These temperatures

are probably not sufficient to cause equipment damage in the time scales noted.

There is, however, concern in the area of habitability due to the fact that the

temperature in the control room working area at cabinet level rose above 50%C in

1.5 minutes. Smoke may well descend in a manner analogous to the 50°C isotherm

driven by the effects of room filling and the location of the exhaust gratings

at the bottoms of the cabinets. The control room may become uninhabitable in

this time frame. In the case of a fire in one of the exhaust plena, different

conclusions are reached. Temperatures rose above 200C at the cabinet level in

2 minutes, which may indicate when equipment or cable damage would begin to occur. Equipment in the dead-end area of the plenum may be most sensitive to this

potential damage from high gas temperatures. Conversely, the environmental effects outside the plenum in the working area are negligible for this fire scenario; only the plenum area environment becomes inhospitable. It is also important to recall that there is at present no radiative heat transfer model in

SAFFIRE; thus, thermal radiation damage effects on equipment/cables can not be

determined at present. There is also evidence that fires larger than 600 kW can

occur in cabinets/consoles,13 which would correspondingly increase the damage

potential of the fire. It was assumed in the course of these simulations that

no secondary fires occurred; this may not be the case in the plenum area in view

of the fact that cable trays pass through the upper portion of the fire plume

(Fig. 3). Any of these effects would exacerbate equipment/cable damage

potential.

A final series of aefinite conclusions regarding the specific effects of

these potential fire-induced environments on equipment can not be reached at

this time due to the need for specific values and parameters of damage criteria.

These criteria are being determined as part of the FPRP. Additional specific

conclusions concerning smoke and harmful combustion species also await the

determination of source term and propagation properties being measured as part

of experimental portions of the FPRP. The future direction of the FPRP as well

as the integration of the products of the FPRP with PRA methodology are indefinite at this time due to severe cutbacks in NRC research funding as initiated by

the Gramm-Rudman legislation. Nevertheless, we continue to recommend the extension of the modeling efforts of the FPRP as well as the efforts to integrate

SAFFIRE into PRA methodology and the more general areas of concern to both

Nuclear Reactor Regulation and Inspection and Enforcement.
0.
21

V. REFERENCES

1. Datta, A., "Nuclear Power Plant Fire Protection Research Program," U.S.

Nuclear Regulatory Commission Report. NUREG-1148, July 1985.

2. Spaulding, D.B., "A General Computer Program for Fluid Flow, Heat Transfer

and Chemical Reaction Processes," presented at the International FEMCongress, Baden-Baden, W. Germany, November 17-18, 1980.

3. Boccio, J.L. and Usher, J.L., "The Use of a Field Model to Assess Fire

Behavior in Complex Nuclear Power Plant Enclosures: Present Capabilities

and Future Prospects," U.S. NRC Report NUREG/CR-4479, December 1985.

4. Planning Research Corporation, "Solid Rocket Motor/Vehicle Assembly Building Inadvertent Ignition Effects Study," NASA KSC-DF-441, September 1981.

5. Launder, B.E. and Spaulding, D.B., Mathematical Models of Turbulence,

Academic Press, London, 1972.

6. Markatos, NC., Malin, M.R. and Cox, G., "Mathematical Models of Buoyancyinduced Smoke Flow in Enclosures," Int. J. Heat and Mass Transfer, Vol. 25,

No. 1, pp. 63-75, 1982.

7. Markatos, N.C. and Cox, G., "Turbulent Buoyant Heat Transfer in Enclosures

Containing a Fire Source," Seventh International Heat Transfer Conference,

Munchen, W. Germany, Vol. 6, p. 373, 1982.

8. Bagnaro, M., Lauuisset, M. and Lockwood, F.C., "Field Model Prediction of

Some Room Fires: Steady and Transient," The 21st National Heat Transfer

Conference, pp. 107-114, Seattle, July 1983.

9. Patankar, S.V. and Spaulding, D.B., "A Calculation Procedure for Heat, Mass

and Momentum Transfer in Three Dimensional Parabolic Flows," Int. J. Heat

and Mass Transfer, Vol. 15, pp. 1787-1806, 1972.

10. Hill, J.P., "Fire Tests in Ventilated Rooms - Extinguishment of Fires in

Grouped Cable Trays," EPRI Project RP 1165-1-1, Report Np-2660, prepared by

Factory Mutual Research Corporation, Norwood, MA.

11. Cline, D.D., Von Riesemann, W.A. and Chavez, J.M., "Investigation of

Twenty-foot Separation Distance as a Fire Protection Method as Specified in

10CFR5O, Appendix R," NUREG/CR-3192, October 1983.

12. Williamson, R.B., Mowrer, F.W. and Fisher, F.L., "Final Report: Fire Safety

of Electrical Cabinets," Lawrence Berkely Laboratory, Prepared for U.S.

NRC, January 1984.

13. Chavez, J.M. and Nowlen, S.P., "An Experimental Investigation of Internally

Ignited Fires in Nuclear Power Plant Control Cabinets, Part II - Room Effects Tests," SAND86-0336, Sandia National Laboratories, Albuquerque, 1986.
22

14. Singhal, A.K. and Tam, L.T., "Progress Report: Fire Modeling for Nuclear

Power Plant Enclosures - Three Dimensional Calculations," CHAM of North

America, Inc., Prepared for BNL, February 1985.

15. Singhal, A.K. and Tam, L.T., "Progress Report: Fire Modeling for Nuclear

Power Plant Enclosures - Three Dimensional Calculations," CRAM of North

America, Inc., Prepared for BNL, March 1985.

16. Singhal, A.K. and Tam, L.T., "Progress Report: Fire Modeling for Nuclear

Power Plant Enclosures - Three Dimensional Calculations," CHAM of North

America, Inc., Prepared for BNL, April 1985.

17. Singhal, A.K. and Tam, L.T., "Progress Report: Fire Modeling for Nuclear

Power Plant Enclosures - Three Dimensional Calculations," CHAM of North

America, Inc., Prepared for BNL, June 1985.
PIRC FORM 335 U S NUCLEAR REGULATORY COMMISSION I REPORT NUMBER (Au.9tOy A TIDC add V140 SO d aVJ

NACM 1102 NUREG/CR- 5037 1 32 BIBLIOGRAPHIC DATA SHEET BNL-NUREG- 5 2106 SEE INSTRUCTIONS ON THE REVERSE

3 TITLE ANO SUBTITLE 3 LEAVE BLANK

FIRE ENVIRONMENT DETERMINATION IN THE LASALLE

NUCLEAR POWER PLANT CONTROL ROOM 4 DATE REPORT COMPLETED

MONTH YEAR

• AUTHOR(S) March 1987

S DATE REPORT ISSUED

JOHN L. USHER AND J.L. USHER MONTH - YEAR

October 1987

7 PERFORMING ORGANIZATION NAME AND MAILING ADDRESS (1'KCIZ' code) B PROJECTITASKIYORK UNIT NUMBER

BROOKHAVEN NATIONAL LABORATORY 9 FIN OR GRANT NUMBER

UPTON, NEW YORK 11973

FIN A-3252

10 SPONSORING ORGANIZATION NAME ANO MAILING ADDRESS linclud. Z' Cadel Ila TYPE OF REPORT

DIVISION OF ENGINEERING TECHNOLOGY, RES

OFFICE OF NUCLEAR REGULATORY RESEARCH

U.S. NUCLEAR REGULATORY COMMISSION b PERIOD COVERED IM-M,w darn)

WASHINGTON, D.C. 20555

12 SUPPLEMENTARY NOTES

13 ABSTRACT f2 0wga' 0, an/

One of the objectives of the Fire Protection Research Program (FPRP) of the U.S.

NRC is to improve the modeling of environments caused by fires in typical nuclear

power plant enclosures. A three-dimensional fluid dynamics computer code (PHOENICS)

has been adapted as a field-model fire code (SAFFIRE) for this purpose. The model

has been applied to simulate two distinct fires in the control room of the LaSalle

County power plant. The environments determined illustrate hazardous potential for

both personnel and equipment.

14 DOCUMENT ANALYSIS -'a KEYWOROS/IESCRIPTORS IS AVAILABILITY

fire protection cable fires complex geometry STATEMENT

computer codes pool fires Unlimited

control rooms field models

nuclear power plants cabinet fires ,SU,, ICO

a IDETIIERSIYOEN ENDED TERMS forced ventlatonUnclassified

(T,. rfflow

Unclassified

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18 PRICE