iea-r1 primary and secondary coolant piping systems ... · development of the primary and secondary...

13
2013 International Nuclear Atlantic Conference - INAC 2013 Recife, PE, Brazil, November 24-29, 2013 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-05-2 IEA-R1 PRIMARY AND SECONDARY COOLANT PIPING SYSTEMS COUPLED STRESS ANALYSIS Gerson Fainer 1 , Altair A. Faloppa 1 , Carlos A. Oliveira 1 and Miguel Mattar Neto 1 1 Instituto de Pesquisas Energéticas e Nucleares - IPEN / CNEN - SP Av. Professor Lineu Prestes, 2242 05508-000, São Paulo, SP, Brazil [email protected]; [email protected]; [email protected]; [email protected] ABSTRACT The aim of this work is to perform the stress analysis of a coupled primary and secondary piping system of the IEA-R1 based on tridimensional model, taking into account the as built conditions. The nuclear research reactor IEA-R1 is a pool type reactor projected by Babcox-Willcox, which is operated by IPEN since 1957. The operation to 5 MW power limit was only possible after the conduction of life management and modernization programs in the last two decades. In these programs the components of the coolant systems, which are responsible for the water circulation into the reactor core to remove the heat generated inside it, were almost totally refurbished. The changes in the primary and secondary systems, mainly the replacement of pump and heat-exchanger, implied in piping layout modifications, and, therefore, the stress condition of the piping systems had to be reanalyzed. In this paper the structural stress assessment of the coupled primary and secondary piping systems is presented and the final results are discussed. 1. INTRODUCTION IEA-R1 reactor is a pool type, light water moderated and graphite reflected research reactor. Its first operation was in 1957 in the ancient Institute of Atomic Energy, currently named IPEN (Nuclear and Energy Research Institute), in Sao Paulo. The original design was developed by the American company Babcock & Wilcox, and the reactor started with 2 MW power [1]. Since its start-up in 1957, the IEA-R1 has been modified for several reasons such as replacement of aged structures and components, upgrading of systems, and adequacy to safety codes and standards that have changed during the years. The main modifications up to 2012 are listed bellow: [2], [3] 1971: - Changes in reactor building ventilation system. 1974: - Duplication of the primary coolant system to redundancy; - Introduction of flywheels on the primary centrifugal pumps; - Installation of a 16 N decay tank to reduce operational dose. 1976: - Replacement of original instrumentation and control operation console; - Replacement of the original control drive mechanism; - Changes in the pneumatic system.

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Page 1: IEA-R1 PRIMARY AND SECONDARY COOLANT PIPING SYSTEMS ... · development of the primary and secondary piping structural model, processing and post-processing of results, and analysis

2013 International Nuclear Atlantic Conference - INAC 2013

Recife, PE, Brazil, November 24-29, 2013 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN

ISBN: 978-85-99141-05-2

IEA-R1 PRIMARY AND SECONDARY COOLANT PIPING SYSTEMS

COUPLED STRESS ANALYSIS

Gerson Fainer1, Altair A. Faloppa

1, Carlos A. Oliveira

1 and Miguel Mattar Neto

1

1 Instituto de Pesquisas Energéticas e Nucleares - IPEN / CNEN - SP

Av. Professor Lineu Prestes, 2242

05508-000, São Paulo, SP, Brazil

[email protected]; [email protected]; [email protected]; [email protected]

ABSTRACT

The aim of this work is to perform the stress analysis of a coupled primary and secondary piping system of the

IEA-R1 based on tridimensional model, taking into account the as built conditions. The nuclear research reactor

IEA-R1 is a pool type reactor projected by Babcox-Willcox, which is operated by IPEN since 1957. The

operation to 5 MW power limit was only possible after the conduction of life management and modernization

programs in the last two decades. In these programs the components of the coolant systems, which are

responsible for the water circulation into the reactor core to remove the heat generated inside it, were almost

totally refurbished. The changes in the primary and secondary systems, mainly the replacement of pump and

heat-exchanger, implied in piping layout modifications, and, therefore, the stress condition of the piping systems

had to be reanalyzed. In this paper the structural stress assessment of the coupled primary and secondary piping

systems is presented and the final results are discussed.

1. INTRODUCTION

IEA-R1 reactor is a pool type, light water moderated and graphite reflected research reactor.

Its first operation was in 1957 in the ancient Institute of Atomic Energy, currently named

IPEN (Nuclear and Energy Research Institute), in Sao Paulo. The original design was

developed by the American company Babcock & Wilcox, and the reactor started with 2 MW

power [1].

Since its start-up in 1957, the IEA-R1 has been modified for several reasons such as

replacement of aged structures and components, upgrading of systems, and adequacy to

safety codes and standards that have changed during the years. The main modifications up to

2012 are listed bellow: [2], [3]

1971: - Changes in reactor building ventilation system.

1974: - Duplication of the primary coolant system to redundancy;

- Introduction of flywheels on the primary centrifugal pumps;

- Installation of a 16

N decay tank to reduce operational dose.

1976: - Replacement of original instrumentation and control operation console;

- Replacement of the original control drive mechanism;

- Changes in the pneumatic system.

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INAC 2013, Recife, PE, Brazil.

1978: - Replacement of the original ceramic liner of the pool walls by steel liner;

- Installation of an auxiliary bypass system for emergency water supply.

1987: - Separation of the reactor building area into radiological hot and cold rooms;

- Introduction of access chambers;

- Introduction of vertical duct for irradiated material transfer;

- Installation of a new cooling tower;

- Main maintenance of the emergency generators.

1991: - Construction of a radiation shielding for the resins columns in the pool water

purification and treatment system.

1995: - Power upgrade from 2 MW to 5 MW.

2001: - Main maintenance of the cooling towers.

2002: - Main maintenance of primary pumps;

- Installation of beryllium reflectors.

2005: - Replacement of a heat exchanger (TC1A).

2007 - Installation of a new pneumatic system

2012: - Withdrawal of check valves of the secondary system;

- Replacement of secondary pumps.

The modifications indicated by these processes: “duplication of primary coolant system to

redundancy”, “installation of decay tank” and “replacement of a heat exchanger” in the

Primary Circuit, and “installation of a new cooling tower”, “withdrawal of check valves” and

“Replacement of secondary pumps” in the Secondary Circuit caused changes in piping

layout.

This paper is the outcome of the structural analysis of the IEA-R1 coupled Primary and

Secondary Circuits piping after these modifications. In order to develop this work it was

carried out the following schedule:

assessment of piping documents;

verification of the as-built condition of the primary and secondary piping systems;

construction of a 3D solid model of the primary and secondary piping systems;

preparation of the isometric drawings for stress calculation;

development of the primary and secondary piping structural model, processing and post-

processing of results, and analysis of the obtained results.

The piping analysis was performed by using the program CAESAR II [4], a very well know

piping system analysis software, which has become the standard for piping stress analysis.

The stress analysis was performed as follow: the Primary Circuit Piping was classified as

nuclear safety class 2, according to the ASME code, section III, subsection NC [5] and the

Secondary Circuit Piping was classified as non nuclear, according to the ASME code B31.1

[6].

2. PRIMARY AND SECONDARY CIRCUIT DESCRIPTION

The figure 1 shows a simplified flowchart of the Primary and Secondary Systems of the IEA-

R1 reactor.

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INAC 2013, Recife, PE, Brazil.

The primary circuit provides the water to cool the reactor core. It is an open circuit, since the

refrigeration is provided by the own pool water in the reactor. In this system, the water passes

through the plates of the reactor core and the header located at the bottom of the pool, coming

out of the pool through the piping nozzle. Then, passes through a decay tank of 16

N and it is

pumped by pumps B1A and/or B1B, to the respective heat exchanger TC1-A and/or TC1-B,

where it's cooled, returning, then, to the pool through a diffuser plugged in the piping nozzle.

The system has redundant pumps, heat exchangers and valves.

The secondary circuit provides the water to cool the heat exchanger TC1-A and/or TC1-B. It

is also an open circuit, since the refrigeration is provided by cooling towers TR1-A and/or

TR1-B. The returning water is pumped by B102-A and/or B102-B to the respective heat

exchanger TC1-A and/or TC1-B.

Figure 1. Simplified flow chart of the IEA-R1 Primary & Secondary Circuit

To better analyze the system, in a comprehensive manner, a three-dimensional solid model of

the complete primary and secondary circuit was built using the program "SOLIDWORKS"

[7]. This work was initiated with the preparation of a complete isometric drawing of all

components of the primary and secondary circuits based on the as-built condition. Then, with

the objective to show the whole system, to recheck the dimensions to guarantee that the as-

built is correct, and to allow the preparation of the isometric for stress calculation, a 3D solid

model was done. The resultant 3D solid model is shown in the figure 2.

Decay

Tank CP-VGV-04

Pump B1-A

CP-VGV-03

CP-VGV-02

Pump B1-B

diffuser

core POOL

CP-VRT-01

CP-VRT-02

CP-VGV-06

CP-VRT-05

CS-VGV-04

Pump B102-B

CS-VGV-07

CS-VGV-02

Pump B102-A

CS-VGV-06

CP-VIS-02

CP-VIS-01

Heat

Exch.

TC1A

CP-VGV-01

CP-VGV-08

CP-VGV-07

Heat

Exch.

TC1B CP-VIS-03

CP-VIS-04

CP-VGV-09

CS

-VG

V-1

4

CS

-VG

V-1

1

CS

-VG

V-1

5

CS-VGV-10

CS-VGV-03

Cooling

Tower

TR-1B

Cooling

Tower

TR-1A

Primary

Circuit

Secondary

Circuit

CS-VGV-01

CS-VGV-05

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INAC 2013, Recife, PE, Brazil.

Figure 2. 3D Model of the IEA-R1 Primary & Secondary Circuit

Cooling Tower

Decay Tank

Heat Exchanger

Primary Pump

Secondary Pump

Pool

Core

Suspension Frame

- Primary Circuit Piping

- Secondary Circuit Piping

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INAC 2013, Recife, PE, Brazil.

3. PIPING MODEL DESCRIPTION

For piping analysis purpose, the primary and secondary circuits of the reactor IEA-R1, as

described in item 2, were modeled as a whole, encompassing piping and equipment coupled

together. The program CAESAR II [4] was used for the analysis. Calculation model was

developed and nodes and elements are shown in the isometric for stress calculation presented

in figures 3 and 4.

The following theoretical premises were adopted:

The Primary Circuit Piping was considered as Nuclear Safety Class 2, according to the

ASME code, section III, subsection NC [5], and the Secondary Circuit Piping as non

nuclear, according to ASME B31.1 [6];

To build the model, straight pipe and bend elements were used, with three DOF (Degrees

Of Freedom) for translation and three DOF for rotation;

The valves were modeled as rigid elements;

The components were modeled as equivalent beams;

The piping supports were modeled by adopting a restraint stiffness of 1 x 105 N/mm to

the restrained direction;

The inlet and outlet pool nozzles, the heat exchangers nozzles, the decay tank nozzles, the

cooling towel nozzles, and the suction and discharge pump nozzles were modeled by

adopting a restraint stiffness of the 1 x 107 N/mm for the translational DOF’s and 1 x 10

12

Nmm/rad for rotational DOF’s;

Components stress-intensification factor’s (SIF), were modeled as follows: “tees” were

modeled as “welding tee” and “reductions” were modeled according to their geometry.

The Calculation Model will be valid whether the following premises were true:

The piping, valves, tees, flanges and reductions must be without defects, it means: there is

no denting, no pitting, no misalignments, no out of roundness and nor any corroded points

on external or internal surface of the piping or fittings;

The attachments, welded or threaded, that connects piping to piping, piping to equipment

and piping to fittings (valves, tees, flanges, reductions) must be without defects, it means:

there is no denting, no pitting, no misalignments, no out of roundness and nor any

corroded points on external or internal surface of the fittings;

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INAC 2013, Recife, PE, Brazil.

1780

980

2110

3030

6501

300

386

1690

15

46

1760

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360

41°V

400

1838

93

0

2710

985

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0

1800

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Po

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ank

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Exchanger

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Exchanger

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Figure 3. Isometric drawing for stress calculation of the IEA-R1 Primary Circuit

Page 7: IEA-R1 PRIMARY AND SECONDARY COOLANT PIPING SYSTEMS ... · development of the primary and secondary piping structural model, processing and post-processing of results, and analysis

INAC 2013, Recife, PE, Brazil.

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DN

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3530

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3280

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2020

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Figure 4. Isometric drawing for stress calculation of the IEA-R1 Secondary Circuit

Page 8: IEA-R1 PRIMARY AND SECONDARY COOLANT PIPING SYSTEMS ... · development of the primary and secondary piping structural model, processing and post-processing of results, and analysis

INAC 2013, Recife, PE, Brazil.

3.1. General Data

The materials used in the analysis are: a stainless steel for the Primary Circuit Piping and

carbon steel for the Secondary Circuit Piping. The physical and mechanical properties of the

piping materials are shown in table 1 and the geometric properties of the piping in table 2.

Table 1: Materials Properties ([6], [8])

Material Thermal Expansion

(mm/mmºC)

Modulus of Elasticity

(N/mm2)

Stress (N/mm2)

Allowable Yield

SA-358 TP304

(stainless steel) 15.6x10

-6 195100 137.0 206.0

A 671 C65

(carbon steel) 11.8x10

-6 201000 112.5 241.5

Table 2: Piping Cross Sections Properties (mm)

Primary Circuit Secondary Circuit

DN Outlet diameter Thickness DN Outlet diameter Thickness

250 274.64 3.175 200 219.07 8.18

300 311.15 3.175 250 273.05 9.27

350 355.60 3.960 300 323.85 9.52

400 410.37 3.581 400 406.04 9.52

450 457.20 9.52

The operation modes of the IEA-R1 primary and secondary circuits are shown in table 3.

Table 4 lists the process data for pressure and temperature applied in the analysis.

Table 3: Operation Modes

Primary Circuit Secondary Circuit

Operation Pump Heat Exchanger Pump Cooling Towel

Mode B1A B1B TC1A TC1B B102A B102B TR1A TR1B

#1 On Off On Off On Off On Off

#2 Off On Off On Off On Off On

#3 On On On On On On On On

Table 4: Process condition [2]

Primary Circuit Secondary Circuit

Pressure (N/mm2) 0.69 0.518

Temperature (ºC) 43.9 37.3

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INAC 2013, Recife, PE, Brazil.

3.2. Load cases

In order to perform the piping stress analysis, the following load cases were defined:

DW - (Dead Weight) - Pipe, fluid, flanges and valves weight,

PD - (Design Pressure) - Maximum pressure applied to the lines (see table 4),

Th - (Thermal Expansion) - Three Thermal load cases (see table 3):

Th1 Operation Mode #1;

Th2 Operation Mode #2;

Th3 Operation Mode #3.

3.3. Stress analysis

Piping stress analysis was performed according to ASME code. As stated before, the primary

circuit piping was classified as nuclear safety class 2 and analyzed by section III subsection

NC [5], and the secondary circuit piping was classified as non-nuclear and analyzed by B31.1

[6].

The ASME code provides the criteria for the stress evaluation of components and piping

based on two categories of loading. Such categories are related to non-self-limiting and self-

limiting stresses.

A non-self-limiting stress is produced by the mechanical load that causes primary stresses,

which are responsible for the equilibrium of the system. When they exceed the material’s

yield strength it could result in failure or gross distortion. Pressure and weight are typical

mechanical loads.

A self-limiting stress is generated by restraining the deformation of the system and, generally,

produces secondary stresses that can lead to ratcheting. Thermal expansion is a typical

example of this load.

Table 5 shows ASME code equations according to plant condition, failure mode and category

of the loads.

Table 5: ASME code Equations

Condition Failure Mode

Equation

Stress categorization NC B31.1

Design plastic collapse 8 11B Primary

Service ratcheting 10 13A Secondary

To prevent gross rupture of the system, the general and local membrane stress criteria must

be satisfied. This is accomplished by meeting equation (8) of NC-3652 of the ASME code [5]

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INAC 2013, Recife, PE, Brazil.

and equation (11B) of 104.8.1 of the ASME B31.1 [6]. These equations require that primary

stress intensity resulting from design pressure; weight and other sustained loads meet the

stress limit for the design condition.

To prevent ratcheting, the secondary stress criteria must be satisfied. This is accomplished by

meeting equation (10) of NC-3653.2 of the ASME code [5] and equation (13A) of 104.8.3 of

the ASME B31.1 [6]. These equations require that secondary stress intensity resulting from

thermal expansion meet a level A and B service limits.

The equations for design and service conditions for ASME – NC and ASME – B31.1 are

summarized in tables 6 and 7.

Table 6: Equations of ASME Code Section III subsection NC [5]

CONDITION: Design CONDITION: Thermal Expansion

(Equation 8) ha

n

oS

Z

MB

t

PDB 5.1

221 (Equation 10) A

c SZ

Mi

where:

B1, B2 → primary stress indices;

oD → outside diameter of pipe;

tn → nominal wall thickness;

P → internal design pressure;

Ma → resultant moment loading on cross

section due to weight and other sustained

loads;

Z → section modulus of pipe;

Sh → basic material allowable stress at design

temperature.

where:

i → stress intensification factor;

cM → range of resultant moments due to

thermal expansion;

SA → tensão admissível p/ cargas cíclicas:

hcA SSfS 25.025.1 ;

Sc → basic material allowable stress at room

temperature (20º C);

f → stress range reduction factor for cyclic

loads

f = 1 (N ≤ 7000 cycles).

Table 7: Equations of ASME Code - B31.1 [6]

CONDITION: Design CONDITION: Thermal Expansion

(Equation 11B) ha

n

oS

Z

Mxi

t

PD 0.1)75.0

4( (Equation 13A) A

c SZ

Mi

where:

i → primary stress intensification factor;

oD → outside diameter of pipe;

tn → nominal wall thickness;

P → internal design pressure;

Ma → resultant moment loading on cross section

due to weight and other sustained loads;

Z → section modulus of pipe;

Sh → basic material allowable stress at design

temperature.

where:

i → stress intensification factor;

cM → range of resultant moments due to

thermal expansion;

SA → allowable stress range for expansion

stresses:

hcA SSfS 25.025.1 ;

Sc → basic material allowable stress at room

temperature (20º C)

f → stress range reduction factor for cyclic

loads

f = 1 (N ≤ 7000 cycles).

diffuser

Pump B1-B

Decay Tank

Pump B1-A

CP-VGV-02

CP-VGV-03

Heat Exchanger

TC1B

Heat Exchanger

TC1A

CP-VGV-04 CP-VRT-01

CP-VRT-02

CP-VGV-06

CP-VGV-05

CP-VIS-02

CP-VIS-01

CP-VGV-01

CP-VGV-08

CP-VGV-07

CP-VIS-03

CP-VIS-04

CP-VGV-09

POOL core

diffuser

Pump B1-B

Decay Tank

Pump B1-A

CP-VGV-02

CP-VGV-03

Heat Exchanger

TC1B

Heat Exchanger

TC1A

CP-VGV-04 CP-VRT-01

CP-VRT-02

CP-VGV-06

CP-VGV-05

CP-VIS-02

CP-VIS-01

CP-VGV-01

CP-VGV-08

CP-VGV-07

CP-VIS-03

CP-VIS-04

CP-VGV-09

POOL core

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INAC 2013, Recife, PE, Brazil.

4. STRESS ANALYSIS RESULTS

The piping calculation model, built in accordance with the routing of the lines presented in

isometric drawings of the figures 3 and 4, was simulated with the computer program

CAESAR II [4], taking into consideration the load cases described in item 3.2 and performing

the stress analysis of piping according to:

The Primary Circuit Piping – nuclear safety class 2 (ASME III, subsection NC [5]);

The Secondary Circuit Piping – non- nuclear (ASME B31.1 [6]).

The maximum stress values calculated in the simulation do not exceed the limits set by

ASME code. These results were obtained considering the:

primary stresses, defined by equation (8) [5] for the Primary Circuit Nuclear Piping and

equation (11B) [6] for the Secondary Circuit Non-Nuclear Piping;

secondary stresses, defined by equation (10) [5] for the Primary Circuit Nuclear Piping

and equation (13A) [6] for the Secondary Circuit Non-Nuclear Piping.

The 3 highest values of stress, obtained from the computing simulation, in all load cases for

both conditions, are presented in the table 8.

Table 8: Stress Results Summary

Condition Equation Node stress (N/mm

2)

Ratio Nodal Allowable

Primary

Circuit

Design

1000 70,7 0,34

8 898 63,4 205,5 0,31

780 47,4 0,23

Thermal

Expansion

340 115,0 0,56

10 129 101,0 205,5 0,49

99 83,0 0,41

Secondary

Circuit

Design

3010 79,1 0,70

11B 3410 50,3 112,5 0,45

3480 42,1 0,37

Thermal

Expansion

2160 79,4 0,47

13A 2470 70,2 168,7 0,42

2100 53,3 0,32

The resulting stresses shown in table 8 are all bellow the limits of the ASME code.

Page 12: IEA-R1 PRIMARY AND SECONDARY COOLANT PIPING SYSTEMS ... · development of the primary and secondary piping structural model, processing and post-processing of results, and analysis

INAC 2013, Recife, PE, Brazil.

5. CONCLUSIONS

The modifications in the IEA-R1 Primary Circuit Piping caused by:

“duplication of primary coolant system to redundancy”;

“installation of decay tank”;

“replacement of the heat exchanger”

The modifications in the IEA-R1 Secondary Circuit Piping caused by:

“installation of a new cooling tower”

“withdrawal of check valves”

“Replacement of secondary pumps”

This paper is the outcome of the structural analysis of the IEA-R1 coupled Primary and

Secondary Circuits piping after these modifications and changes in the layout. The structural

analysis developed in this paper is valid and can be considered correct, if the piping systems

are according to the following:

The piping, valves, tees, flanges and reductions must be without defects, it means: there is

no denting, no pitting, no misalignments, no out of roundness and nor any corroded points

on external or internal surface of the piping or fittings;

The attachments, welded or threaded, that connects piping to piping, piping to equipment

and piping to fittings (valves, tees, flanges, reductions) must be without defects, it means:

there is no denting, no pitting, no misalignments, no out of roundness and nor any

corroded points on external or internal surface of the fittings;

For the analysis purpose, the primary and secondary circuit of the reactor IEA-R1 was

modeled as a whole, encompassing piping and equipment coupled together. The Primary

Circuit Piping was classified as Nuclear Safety Class 2 (ASME III - subsection NC [5]) and

the Secondary Circuit Piping was classified as non nuclear (ASME - B31.1 [6]). Piping

calculation model was developed and the stress analysis was performed with the program

CAESAR II [4] considering the load cases presented below:

“DW” - Dead Weight; “PD” - Design Pressure; “Th1/ Th2/ Th3” - Thermal Expansion.

The values of the stresses calculated to the primary and secondary circuit piping do not

exceed the limits set by ASME code.

To sum up, the modifications made in the piping routing of the primary circuit for the

replacement of the heat exchanger, duplication of primary coolant system, installation of

decay tank and installation of a new cooling tower, replacement of secondary pumps and

withdrawal of check valves in the secondary circuit are guaranteed.

Page 13: IEA-R1 PRIMARY AND SECONDARY COOLANT PIPING SYSTEMS ... · development of the primary and secondary piping structural model, processing and post-processing of results, and analysis

INAC 2013, Recife, PE, Brazil.

ACKNOWLEDGMENTS

We acknowledge the help of colleagues in doing this work, particularly the IEA-R1 staff,

which have facilitated the documents assessment and/or guided us into internal areas of the

IEA-R1 reactor building.

REFERENCES

1. “The Babcock & Wilcox Co., “Open-Pool Research Reactor – Instituto de Energia

Atômica”, Instruction Book – Vol. 1, 1957.

2. Maiorino, J. R. et al, “The conversion and power upgrade of the IEA-R1”, “The

International Reduced Enrichment for Test Reactor Conference” 1998, SP Brasil

3. Faloppa, A. A. and Ting, D. K. S, “Safety of research reactors: IEA-R1 Ageing

management”, AIEA – Projeto Arcal LXVIII “Seguridad de Reactores de Investigacion”

2002, Lima - Peru

4. CAESAR II, Structural Analysis Guide & Theory Reference Manual

5. ASME Boiler & Pressure Vessel Code, “Section III, Division 1, Subsection NC – Class 2

Components”, ASME, 2007.

6. ASME Boiler & Pressure Vessel Code, “B31.1 – Power Piping”, ASME Code for Pressure

Piping B31, 2007.

7. SOLIDWORKS Premium 2010 SP4.0, Dassault Systems.

8. ASME Boiler & Pressure Vessel Code, “Section II, Part D – Properties (Materials)”,

ASME, 2007.