development of instrument transmitter protecting device against

Research ArticleDevelopment of Instrument Transmitter Protecting Deviceagainst High-Temperature Condition during Severe Accidents

Min Yoo, Sung Min Shin, and Hyun Gook Kang

Nuclear Plant Reliability & Man-Machine Interface Design Laboratory, Korea Advanced Institute of Science and Technology,Daehak-ro 291, Yuseong-Gu, Daejeon 305-701, Republic of Korea

Correspondence should be addressed to Hyun Gook Kang; [email protected]

Received 9 March 2014; Accepted 3 May 2014; Published 17 June 2014

Academic Editor: Inn Seock Kim

Copyright © 2014 Min Yoo et al.This is an open access article distributed under the Creative Commons Attribution License, whichpermits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Reliable information through instrumentation systems is essential inmitigating severe accidents such as the one that occurred at theFukushima Daiichi nuclear power plant. There are five elements which might pose a potential threat to the reliability of parameterdetection at nuclear power plants during a severe accident: high temperature, high pressure, high humidity, high radiation, andmissiles generated during the evolution of a severe accident. Of these, high temperature apparently poses the most serious threat,since thin shielding can get rid of pressure, humidity, radiation (specifically, alpha and beta radiations), and missile effects. In viewof this fact, our study focused on designing an instrument transmitter protecting device that can eliminate the high-temperatureeffect on transmitters to maintain their functional integrity. We present herein a novel concept for designing such a device in termsof heat transfer model that takes into account various heat transfer mechanisms associated with the device.

1. Introduction

On March 11, 2011, one of the most serious accidents innuclear power history took place at the Fukushima Daiichinuclear power plant as a result of the extreme natural disastercaused by an earthquake and subsequent tsunami [1–3].The emergency response manuals for severe accidents atthe Tokyo Electric Power Company (TEPCO) were devel-oped based on the assumption that the monitoring systemswould be normally operating during the severe accidents.However, during the actual accidents at Fukushima they lostdetectors and monitoring equipment, so that “the decisionsand responses to the accident had to be made on the spotby operational staff at the site, with absent valid tools andmanuals” [4]. Without the information on the plant opera-tion,monitoring the process parameters such as temperature,pressure, water level, or radiation was extremely difficult.

There are some detectors that are needed in mitigatingsevere accidents. For instance, the following are referred toas requisite detectors in the severe accident managementguidance (SAMG) for a pressurized water reactor (PWR):core exit thermocouple (CET), heated junction thermocouple(HJTC), resistance temperature detector (RTD), pressurizer

manometer, safety injection flow meter, auxiliary feedwa-ter flow meter, steam generator water level gauges, waterlevel gauges for in-containment refueling water storage tank(IRWST), hydrogen sensor, radiation sensor, containmentpressure sensor, containment temperature sensor, and con-tainment spray flow meter [5]. Among requisite detectors,thermocouple, RTD, pressure sensor, and radiation sensorare exposed to high temperature. Thermocouple (TC) andRTD sensor do not need to be protected once the temperatureis below melting point. TC, RTD, and radiation sensor areexpected to lose their accuracy if they are protected by thedevice. Pressure sensor transmitter includes pressure sensingfunction. Pressure is directly put to the transmitter fromthe place where it should be measured through pipe; thentransmitter produces electric signal. Thus the study aims toprotect the transmitter (pressure sensor and RTD) from hightemperature.

A transmitter in an instrumentation system convertsanalog signals from a sensor to a few mA electronic signals.Then, those signals can be transferred over long distancewith little noise. Among the requisite detectors, manometer,flow meter, and water level gauges have a transmitter. Ina severe accident, transmitters may be out of control in

Hindawi Publishing CorporationScience and Technology of Nuclear InstallationsVolume 2014, Article ID 345729, 7 pageshttp://dx.doi.org/10.1155/2014/345729

2 Science and Technology of Nuclear Installations

harsh environment. They are not manufactured so that theycan endure in harsh environmental conditions. One of thetransmitters that supports pressure detectors endures (a) 1hour at 157.8∘C and 4.826 bar; (b) 7 hours at 150.5∘C and 3.819bar; and (c) 42 hours at 110∘C and 0.414 bar steam exposure,with an accuracy within ±0.75% [6]. In the case of othertransmitters, the long-term limitation of temperature over afew tens of hours is 80∘C with some safety margin.

Based on the severe accident analysis for Shin Kori Units3 and 4 PWRs, the temperature and pressure around thetransmitters during severe accidents are too high to endure.One of the most harsh compartment temperatures reaches600∘C right after the accident occurrence and then decreasesto 180∘C during the first 10 minutes remaining aroundthis temperature afterwards. Under this harsh environmen-tal condition associated with high temperature, pressure,humidity, or radiation, the transmitters are not likely toperform their intended functions. In addition, they also maybe subject to missiles generated during a severe accident.Each of these five elements poses a potential threat to thereliability of parameter detection at nuclear power plants.

Therefore, in order that instrument transmitters canproperly send signals during a severe accident, they must beprotected against such harsh environment asmight be causedduring the evolution of such an accident. Of the aforemen-tioned five elements, this research focuses on protection oftransmitters from high temperature.The reason for this focusis that high temperature is the most serious threat, since thinshielding can get rid of pressure, humidity, radiation (alphaand beta), and missile effects.

This research is specially aimed at maintaining the tem-perature of instrument transmitters below the long-termlimitation temperature mentioned above, that is, 80∘C, forat least 72 hours in the harsh environmental conditions. Theduration of 72 hours is in line with a typical assumption that ifthe accident condition is managed for 72 hours, core damageis not likely to occur in a nuclear power plant [7, 8].

In the sequel, we present a novel concept to designa protecting device for instrument transmitters in high-temperature environmental condition. The structural designscheme of a cooler is first discussed along with the theoreticalheat transfer model. Cooling methods are then describedtaking into account various factors affecting the protectorperformance, such as the protector thickness, material, size,environmental pressure, inside heat generation from thetransmitter, and environmental temperature.

2. Design Concept for Instrument TransmitterProtecting Device

According to a study performed forAPR1400 byKoreaHydroand Nuclear Power Company (KHNP), the temperaturein some compartments at the APR1400 plant for accidentscenarios such as loss of feedwater flow (LOFW), loss ofcoolant accident (LOCA), or station blackout (SBO) reachesas high as 600∘C for 10 seconds into the initiating event, dropsto around 180∘C in 600 seconds, and then remains at 180∘C[5].Therefore, in order to protect the integrity of transmitters,

Cooler

Transmitter

Ti(t)

qc

Tm(t)

Outer protectorTo

Inner protector

Sk2A2L2

{Tm(t) − To}

k1A1L1

{Tm(t) − Ti(t)}

Figure 1: Instrument transmitter protecting device.

we envision that the critical transmitters should be protectedby a box-shaped protecting device for insulation.

2.1. Cooler and Cooling Method. Figure 1 shows a schematicof the protecting device. The protection system consists ofinner and outer protectors in the form of a double-boxshape. Transmitters are placed in the interior of the innerprotector surrounded by air. The space between the outerprotector and the inner protector is filled with water. Theouter protector shields heat from the outside, and the innerprotector releases heat from inside heat source. The watercontained between the two protectors stores heat from boththe inside and the outside. A cooler is optionally installed.We derive an equation for the inner temperature from heattransfer relations with an aim to determine appropriateprotector properties, sizes, amount of water, and so on.

𝑇𝑖(𝑡) and𝑇

𝑚(𝑡) represent the temperature inside the inner

protector and the intermediate water temperature, respec-tively. 𝑆 is heat generation from the inside (i.e., transmitter),and (𝑘𝐴/𝐿)Δ𝑇 represents the heat transfer by conductiondue to temperature difference between the inside and theoutside protectors. 𝑞

𝑐represents heat removal by the cooler.

Subscripts 1 and 2 refer to the inner and the outer protector,respectively.

There are a few coolingmethods available based on use ofheat conduction, refrigerant, vortex tube, and thermoelectriccooler (TEC). However, spatial limitation and harsh environ-mental condition should be taken into account in designingthe instrument transmitter protecting device. Furthermore,the cooling method that will be applied to such devices oughtto have high reliability. In consideration of these variousconstraints, only TEC was judged to be a feasible method inthis research. The TEC is based on Peltier effect which is athermoelectric phenomenon where current flows at junctionof two different conductors; one side is heated and the otherside is cooled. Figure 2 is a general structure of single stageTEC [9]. It consists of insulators (ceramics plates), soldering,semiconductors (pellets), and electric conductors [9, 10].

Science and Technology of Nuclear Installations 3

Cold side Ceramics plate

Soldering

Hot sidePelletsElectric conductors

Terminal wires

Ceramics plate

(+)

(−)

Figure 2: Structure of TEC.

The heat pumped at cold surface of the TEC can beexpressed as

𝑞𝑐= 2𝑁[𝛼𝐼𝑇

𝑐− (

𝐼2

𝜌

(2𝐺)

) − 𝑘𝑐(𝑇ℎ− 𝑇𝑐) 𝐺] , (1)

where 𝑁 is the number of thermocouples, 𝛼 is Seebeckcoefficient, 𝑇

𝑐and 𝑇

ℎare cold and hot side temperatures, 𝐼 is

current,𝐺 is the area divided by the length of the element, and𝑘𝑐is thermal conductivity. 𝛼, 𝐺, and 𝑘

𝑐are constants related

to the TEC material properties [11].In this study, the inner temperature of the protector

system is derived based on the following assumptions.

(1) Convections are ignorable and, as a result, the surfacetemperature of the protector is assumed to equal thetemperature of the fluid that it faces. Only conductiveheat transfer works through the wall. That is, the heattransfer rate equals (𝑘𝐴/𝐿)Δ𝑇.

(2) It is reasonable to assume that the ambient temper-ature 𝑇

𝑜is constant. The initial thermal shock has a

negligible impact on 𝑇𝑖(𝑡).

(3) The initial temperature of all materials andmedium is𝑇(0) = 20∘C.

(4) The temperature of the protector wall changes linearlyalong the wall thickness. 𝑇(0, 𝑡) is the outer surfacetemperature of the wall at time 𝑡, and 𝑇(𝐿, 𝑡) is innersurface temperature of thewall at time 𝑡.𝐿 is thicknessof the wall, and with wall temperature along thickness𝑥 and time 𝑡, 𝑇(𝑥, 𝑡) equals ((𝑇(𝐿, 𝑡) − 𝑇(0, 𝑡))/𝐿)𝑥 +𝑇(0, 𝑡).

(5) The outside size of the inner protector is assumed tobe 𝑙11× 𝑙12× 𝑙13= 0.3 × 0.3 × 0.4m3.

(6) The width, length, and height of outer protector are𝑙21

= 𝑙11+ 𝑙, 𝑙22

= 𝑙12+ 𝑙, and 𝑙

23= 𝑙13+ 𝑙, where

𝑙 is length difference between the inner and outerprotector edges.

(7) The temperature of the protector wall is a volumetricaverage temperature of 𝑇(0, 𝑡) and 𝑇(𝐿, 𝑡). It meansthat average temperature is

𝑇avg

=

∫𝑇 (𝑥, 𝑡) 𝑑𝑉

wall volume 𝑉

= (∫

𝐿

0

{𝑇 (𝐿, 𝑡) − 𝑇 (0, 𝑡)

𝐿

𝑥 + 𝑇 (0, 𝑡)}

× 2 { (𝑙1− 2𝑥) (𝑙

2− 2𝑥)

+ (𝑙2− 2𝑥) (𝑙

3− 2𝑥)

+ (𝑙3− 2𝑥) (𝑙

1− 2𝑥)} 𝑑𝑥)

× (𝑙1𝑙2𝑙3− (𝑙1− 2𝐿) (𝑙

2− 2𝐿) (𝑙

3− 2𝐿))

−1

= (𝑇 (𝐿, 𝑡) {3𝐿2

−4

3

(𝑙1+ 𝑙2+ 𝑙3) 𝐿 +

1

2

(𝑙1𝑙2+ 𝑙2𝑙3+ 𝑙3𝑙1)}

+𝑇 (0, 𝑡) {𝐿2

−2

3

(𝑙1+ 𝑙2+ 𝑙3) 𝐿+

1

2

(𝑙1𝑙2+ 𝑙2𝑙3+ 𝑙3𝑙1)})

× (4𝐿2

− 2 (𝑙1+ 𝑙2+ 𝑙3) 𝐿 + (𝑙

1𝑙2+ 𝑙2𝑙3+ 𝑙3𝑙1))

−1

= 𝛼𝑇 (0, 𝑡) + 𝛽𝑇 (𝐿, 𝑡) ,

(2)

where

𝛼 =

𝐿2

− (2/3) (𝑙1+ 𝑙2+ 𝑙3) 𝐿 + (1/2) (𝑙

1𝑙2+ 𝑙2𝑙3+ 𝑙3𝑙1)

4𝐿2

− 2 (𝑙1+ 𝑙2+ 𝑙3) 𝐿 + (𝑙

1𝑙2+ 𝑙2𝑙3+ 𝑙3𝑙1)

, (3)

𝛽 =

3𝐿2

− (4/3) (𝑙1+ 𝑙2+ 𝑙3) 𝐿 + (1/2) (𝑙

1𝑙2+ 𝑙2𝑙3+ 𝑙3𝑙1)

4𝐿2

− 2 (𝑙1+ 𝑙2+ 𝑙3) 𝐿 + (𝑙

1𝑙2+ 𝑙2𝑙3+ 𝑙3𝑙1)

.

(4)

𝛼 and 𝛽 are about 0.5 unless wall thickness is too thick.

2.2. Heat Transfer Model. Whether the instrument transmit-ter protection system successfully carries out its intendedfunction or not depends on the inner temperature. That is,the maximum 𝑇

𝑖(𝑡) should remain below 80∘C for the period

of 72 hours.Equation (1) can be revised to (5) under the aforemen-

tioned assumptions and 𝑒1= 2𝑁(𝛼𝐼+𝑘

𝑐𝐺), 𝑒2= 2𝑁𝑘

𝑐𝐺, and

𝑒3= 𝜌𝐼2

𝑁/𝐺.Consider

𝑞𝑐= 𝑒1𝑇𝑖(𝑡) − 𝑒

2𝑇𝑚(𝑡) − 𝑒

3. (5)


The first part of the derivation of inside the inner protector isabout temperature change in the intermediate water:

𝑘1𝐴1

𝐿1

{𝑇𝑖(𝑡) − 𝑇

𝑚(𝑡)} +

𝑘2𝐴2

𝐿2

{𝑇𝑜− 𝑇𝑚(𝑡)} + 𝑞

𝑐

= 𝑐𝑚𝑚𝑚�̇�𝑚+ 𝑐2𝑚2

𝑑

𝑑𝑥

(

∫𝐿2

0

𝑇2,avg (𝑥, 𝑡) 𝑑𝑉

𝑉2

)

= (𝑐𝑚𝑚𝑚+ 𝑐2𝑚2𝛽2) �̇�𝑚,

(6)

where 𝑘 is thermal conductivity, 𝐴 the surface area, and 𝐿the thickness of the protector. 𝑐

𝑚and 𝑚

𝑚are the specific

heat capacity and mass of water, respectively, and �̇�𝑚is time

derivative of water temperature. 𝛽2equals (3𝐿2

2

− (4/3)(𝑙21+

𝑙22+ 𝑙23)𝐿2+ (1/2)(𝑙

21𝑙22+ 𝑙22𝑙23+ 𝑙23𝑙21)) / (4𝐿2

2

− 2(𝑙21+ 𝑙22+

𝑙23)𝐿2+ (𝑙21𝑙22+ 𝑙22𝑙23+ 𝑙23𝑙21)).

If

𝑎1=𝑘1𝐴1

𝐿1

, 𝑎2=𝑘2𝐴2

𝐿2

,

𝑏1=

𝑎1+ 𝑒1

𝑐𝑚𝑚𝑚+ 𝑐2𝑚2𝛽2

, 𝑏2=

𝑎2𝑇𝑜− 𝑒3


,

𝑝 =𝑎1+ 𝑎2+ 𝑒2


,

(7)

from (6), the intermediate water temperature becomes

𝑇𝑚(𝑡) = 𝑒

−𝑝𝑡

[𝑇 (0) + ∫

𝑡

0

𝑒𝑝𝜏

{𝑏1𝑇𝑖(𝜏) + 𝑏

2} 𝑑𝜏] . (8)

The second part of the derivation is about a temperaturechange in the inner protector and the inside temperaturechange, 𝑐

𝑖𝑚𝑖≪ 𝑐1𝑚1:

𝑆 + 𝑎1{𝑇𝑚(𝑡) − 𝑇

𝑖(𝑡)} − 𝑞

𝑐

= 𝑐𝑖𝑚𝑖�̇�𝑖+ 𝑐1𝑚1

𝑑

𝑑𝑥

(

∫𝐿1

0

𝑇1,avg (𝑥, 𝑡) 𝑑𝑉

𝑉1

)

∼ 𝑐1𝑚1(𝛼1�̇�𝑚+ 𝛽1�̇�𝑖) ,

(9)

where

𝛼1

=

𝐿2

1

−(2/3) (𝑙11+𝑙12+𝑙13) 𝐿1+(1/2) (𝑙

11𝑙12+𝑙12𝑙13+𝑙13𝑙11)

4𝐿2

1

− 2 (𝑙11+ 𝑙12+ 𝑙13) 𝐿1+ (𝑙11𝑙12+ 𝑙12𝑙13+ 𝑙13𝑙11)

,

𝛽1

=

3𝐿2

1

−(4/3) (𝑙11+𝑙12+𝑙13) 𝐿1+(1/2) (𝑙

11𝑙12+𝑙12𝑙13+𝑙13𝑙11)

4𝐿2

1

− 2 (𝑙11+ 𝑙12+ 𝑙13) 𝐿1+ (𝑙11𝑙12+ 𝑙12𝑙13+ 𝑙13𝑙11)

.

(10)

Substituting (5) and (8) into (9) results in

𝐴�̈�𝑖+ 𝐵�̇�𝑖+ 𝐶𝑇𝑖= 𝑝 (𝑆 + 𝑒

3) + 𝑏2(𝑎1+ 𝑒2) . (11)

This is a second-order nonhomogeneous differential equa-tion, where

𝐴 = 𝑐𝑖𝑚𝑖+ 𝑐1𝑚1𝛽1∼ 𝑐1𝑚1𝛽1,

𝐵 = 𝑝𝐴 + 𝛼1𝑏1𝑐1𝑚1+ 𝑎1

+ 𝑒1∼

𝑎1+ 𝑎2+ 𝑒2


∗ 𝑐1𝑚1𝛽1

+

𝛼1(𝑎1+ 𝑒1) 𝑐1𝑚1


+ 𝑎1+ 𝑒1,

𝐶 = 𝑎2𝑏1.

(12)

Because 𝐵2 − 4𝐴𝐶 is always positive, its general solution is

𝑇𝑖(𝑡) = 𝑑

1𝑒𝑟1𝑡

+ 𝑑2𝑒𝑟2𝑡

+ 𝑑3. (13)

𝑑1and 𝑑

2are arbitrary constants and 𝑟

1and 𝑟

2are (−𝐵 ∓

√𝐵2

− 4𝐴𝐶)/2𝐴; they are always negative. 𝑑3equals (1/(𝑎

1+

𝑒1)){(𝑎1+ 𝑒2)𝑇𝑜+ 𝑒3} + (𝑎1+ 𝑎2+ 𝑒2)/(𝑎2(𝑎1

+ 𝑒1))𝑆. The first

term can be eliminated as 𝑟1≪ 𝑟2and 𝑑

2equals 𝑇(0) − 𝑑

3

because 𝑇𝑖(𝑡) = 𝑇(0). Equation (13) becomes

𝑇𝑖(𝑡)

= {𝑇 (0) − 𝑑3} 𝑒𝑟2𝑡

+ 𝑑3

= [𝑇 (0) − (1

𝑎1+ 𝑒1

{(𝑎1+ 𝑒2) 𝑇𝑜+ 𝑒3} +

𝑎1+ 𝑎2+ 𝑒2

𝑎2(𝑎1+ 𝑒1)

𝑆)]

× 𝑒((−𝐵+√𝐵2−4𝐴𝐶)/2𝐴)𝑡

+1

𝑎1+ 𝑒1

{(𝑎1+ 𝑒2) 𝑇𝑜+ 𝑒3} +

𝑎1+ 𝑎2+ 𝑒2

𝑎2(𝑎1+ 𝑒1)

𝑆.

(14)

3. Results and Discussion

The temperature inside the inner protector, that is, 𝑇𝑖(𝑡),

continues to increase and converges at 𝑑3.Thus, its maximum

temperature, that is, 𝑇𝑖(72 hr), must be smaller than the

limiting temperature 𝑇lim of 80∘C, as discussed above:

𝑇𝑖(72 hr) ≤ 𝑇lim. (15)

The variables affecting this criterion are the outer protec-tor size/thickness/thermal conductivity, the inner protectorthickness/thermal conductivity/heat capacity, and the num-ber of cooler/current supplies. There are too many variablesto derive the appropriate protector condition. Thus, somevariables such as material properties were fixed in thisanalysis for the sake of computational simplification. Furtheranalyses will be performed with different assumptions asdeemed necessary in the future study.

There arises an issue whether the protection system needsto include a cooler. Regardless of whether to include a cooleror not, it will be good to use small 𝑎

2and large size of outer

protector. If the inner protector is strongly insulated, thesystem will need a cooler to remove heat from the inside of


the inner protector to the water. In this case, the smaller 𝑎1,

the larger the number of TECs, and the higher the current,the better. Equation (16) is a simplified form of (14) applying𝑐𝑚𝑚𝑚+ 𝑐2𝑚2𝛽2≫ 𝑐1𝑚1. Consider

𝑇𝑖(𝑡)

∼ [𝑇 (0) − (1

𝑎1+ 𝑒1

{(𝑎1+ 𝑒2) 𝑇𝑜+ 𝑒3} +

𝑎1+ 𝑎2+ 𝑒2

𝑎2(𝑎1+ 𝑒1)

𝑆)]

× 𝑒((−(𝑎1+𝑒1)+√(𝑎

1+𝑒1)

2−2𝑎1𝑎2(𝑐1𝑚1/(𝑐𝑚𝑚𝑚+𝑐2𝑚2/2)))/𝑐

1𝑚1)𝑡

+1

𝑎1+ 𝑒1

{(𝑎1+ 𝑒2) 𝑇𝑜+ 𝑒3} +

𝑎1+ 𝑎2+ 𝑒2

𝑎2(𝑎1+ 𝑒1)

𝑆.

(16)

In the case where no cooler is used, heat should be welltransferred between the inner air and the water because theheat from the transmitter itself is accumulated inside the air.The outer protector needs a strong insulation in both cases toprotect heat invasion from the environment. Hence, 𝑎

1≫ 𝑎2,

𝑐𝑚𝑚𝑚+𝑐2𝑚2𝛽2≫ 𝑐1𝑚1, and 𝑒

1= 𝑒2= 𝑒3= 0. It is reasonable

to assume that 𝛽1and 𝛽

2are 0.5 each. Equation (14) becomes

𝑇𝑖(𝑡)

∼ [𝑇 (0) − {𝑇𝑜+𝑆

𝑎2

}]

× 𝑒((−𝑎1+√(𝑎1)

2−2𝑎1𝑎2(𝑐1𝑚1/(𝑐𝑚𝑚𝑚+𝑐2𝑚2/2)))/𝑐

1𝑚1)𝑡

+ 𝑇𝑜+𝑆

𝑎2

.

(17)

The inner protector wall material and thickness are much lessinfluential factors than other variables as long as inner protec-tor wall material has high thermal conductivity. A materialthat has 1 J/g/K specific heat, 320 g/m3density, 5W/m/Kthermal conductivity, and 1 cm thickness is applied to theinner protector wall. Outer protector material is one ofthe best insulations whose specific heat, density, and ther-mal conductivity are 0.8 J/g/K, 250 kg/m3, and 0.25W/m/K,respectively [12, 13].

Figure 3 is a top view of 3-dimensional plot of 𝑇𝑖(𝑡)

when 𝑡 is 72 hours in (17). The 𝑦-axis in this figure is thelength difference between the outer protector and the innerprotector. The 𝑥-axis represents the thickness of the outerprotector wall. The area above the line indicates that 𝑇

𝑖(𝑡)

is below 80∘C and the area below the line indicates thatthe temperature is higher than 80∘C. The protector has theminimum size at the minimum point (0.066, 0.278) of theline. Then, the outer protector size becomes 0.578 × 0.578 ×

0.678m3 with 6.6 cm thickness. The lower and right partcalculations of Figure 3 are meaningless because the outerwall and the inner wall are overlapped.

Figure 4 is the temperature distribution at 72 hoursafter the accident simulated by solidworks flow simulation.Figure 5 shows the inner air temperature along time, com-paring equation-based and simulation-based calculations.

0.150.100.05

0.5

0.4

0.3

0.2

Leng

th d

iffer

ence

(m)

Thickness (m)

Figure 3: 𝑇𝑖

(𝑡) along wall thickness and length difference betweenthe inner and outer protectors.

The equation-based result yields a conservative result. Thetemperature reaches 70.99∘C at 72 hours in the case of thesimulation. The temperature profile difference between theequation-based and simulation-based calculations mainlycomes from assumptions (1) and (3) described above. Thetemperature based on heat transfer equations increases morerapidly than the one based on the simulation during the initialphase, because the equation does not consider transient heattransfer and the heat capacity of the wall is underestimated.In assumption (1), it was presumed that there is no convectiveheat transfer and so the heat transfer between the solid sur-face and the fluid was assumed to be perfect. However, thereis a heat transfer lag in real world and the simulation tookinto account this phenomenon. Figure 5 overall indicates thatthe increasing rate of the inner air temperature as predictedby the heat transfer equations quite well corresponds to theone as evaluated by the simulation, although there is a slightdifference.

4. Conclusion

Reliable information through instrumentation systems isessential in mitigating severe accidents such as the one thatoccurred at the Fukushima Daiichi nuclear power plant.Thermal-hydraulic analyses performed for several majoraccident scenarios at a PWR plant, including LOFW, LOCA,and SBO, indicate that compartment temperature reaches600∘C in the worst case, although it decreases to 180∘C inabout 10 minutes. The instrument transmitters cannot per-form their intended functions under such high-temperaturecondition.

In addition to high temperature, the instrumentationsystems may also be required to function in harsh conditioninvolving high pressure, high humidity, high radiation, and


180.00

171.88

163.75

155.63

147.50

139.38

131.25

123.13

115.00

106.88

98.75

90.63

82.50

74.38

66.25

58.13

50.00

Tem

pera

ture

(∘C)

Cut plot 1: contours

xx

yy

zz

Figure 4: The result of simulation and temperature distribution at 𝑡 = 72 hours.

EquationSimulation

20

30

40

50

60

70

80

90

0 50000 100000 150000 200000 250000 300000

Time (s)

Inne

r air

tem

pera

ture

(∘C)

Figure 5: Temperature comparison of the results between equation-based and simulation-based calculations along time.

missiles generated during a severe accident. All those fiveelements pose a potential threat to the reliability of parameterdetection at nuclear power plants. In this study, an analysiswas carried out to design an instrument transmitter protect-ing device that can withstand harsh environment, especiallyhigh-temperature condition. Of the various threats to theinstrumentation system, high temperature apparently posesthe most serious threat, since thin shielding can get rid ofpressure, humidity, radiation (alpha and beta), and missileeffects.

In this study, a novel concept for designing an instrumenttransmitter protecting device was developed and investigatedby analyzing the heat transfer mechanisms. The protectionsystemmay be developed either with or without a cooler, andthe design without a cooler turns out to be more effective.

The thermal properties and geometry of the protector mate-rial also influence the result. Thermal conductivity controlsheat conduction itself; on the other hand, heat capacity ofthe material controls heat spreading by saving heat in thematerial.The inside heat generation has impact on long-termtemperature and heat accumulation. So less heat generatingequipment had better be considered. Our study also pointsout that transient heat transfer and convective heat transfershould be considered to avoid excessively conservatism in theanalysis and as a result, obtain a more accurate solution.

Lastly, note that although transmitters can be easilyprotected from alpha and beta radiations due to the waterincluded in the transmitter protecting device, gamma radi-ation effects ought to be investigated. The gamma ray doserate in a reactor was estimated to be larger than 150Gy/h [14].Verification experiment is necessary to investigate protectorperformance in the gamma radiation environment. Thenext things to do are finding optimized protector structureand material property by developing a more thorough heattransfer model and verifying it through simulation andexperiment.

Nomenclature

𝐴1: Inner protector area (m2)

𝐴2: Outer protector area (m2)

𝑐1: Specific heat of inner protector (J/kg⋅K)

𝑐2: Specific heat of outer protector (J/kg⋅K)

𝑐𝑚: Specific heat of intermediate water (J/kg⋅K)

𝐺: Geometry factor𝐼: Current (amps)𝑘1: Inner protector thermal conductivity(W/m⋅K)

𝑘2: Outer protector thermal conductivity(W/m⋅K)

𝑘𝑐: Thermal conductivity of TEC (W/m⋅K)


𝑙: Length difference between inner and outerprotector edges (m)

𝑙11, 𝑙12, 𝑙13: Inner protector length, width, and height (m)

𝑙21, 𝑙22, 𝑙23: Outer protector length, width, and height(m)

𝐿1: Inner protector thickness (m)

𝐿2: Outer protector thickness (m)

𝑚1: Mass of inner protector (kg)

𝑚2: Mass of outer protector (kg)

𝑚𝑚: Mass of intermediate water (kg)

𝑁: Number of TECs𝑇𝑐: Cold side temperature (∘C)

𝑇ℎ: Hot side temperature (∘C)

𝑇𝑖: Inside air temperature (∘C)

𝑇lim: Limit temperature (∘C)𝑇𝑚: Intermediate water temperature (∘C)

𝑇𝑜: Ambient temperature (∘C)

𝑇(0): Initial temperature (∘C)𝑆: Heat source (W).

Greek Letters

𝛼: Seebeck coefficient (V/K)𝜌: Resistivity (Ω⋅m).

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgments

This work was supported by the International Cooperationof the Korea Institute of Energy Technology Evaluationand Planning (KETEP) under Grant funded by the Koreagovernment Ministry of Trade, Industry and Energy (no.20121610100030).

References

[1] OECD/NEA, The Fukushima Daiichi Nuclear Power PlantAccident: OECD/NEA Nuclear Safety Response and LessonsLearnt, Nuclear Energy Agency, Organization for EconomicCo-operation and Development, 2013.

[2] C. Miller, A. Cubbage, D. Dorman, J. Grobe, G. Holahan, andN. Sanfilippo, Recommendations for Enhancing Reactor Safetyin the 21st Century: The Near-Term Task Force Review of Insightsfrom the Fukushima Dai-Ichi Accident, Nuclear RegulatoryCommission, 2011.

[3] Nuclear Emergency Response Headquarters, Report of JapaneseGovernment to the IAEA Ministerial Conference on NuclearSafety—The Accident at TEPCO’s Fukushima Nuclear PowerStations, Nuclear Emergency Response Headquarters, Govern-ment of Japan, 2011.

[4] The National Diet of Japan, Fukushima Nuclear AccidentIndependent Investigation Commission, The Official Reportof the Fukushima Nuclear Accident Independent InvestigationCommission, The Fukushima Nuclear Accident IndependentInvestigation Commission, Japan, 2012.

[5] KEPCO and KHNP, APR1400 Design Control Document Tier2 Chapter 19: Probabilistic Risk Assessment and Severe AccidentEvaluation, Korea Electric PowerCorporation andKoreaHydro& Nuclear Power Company, 2013.

[6] Emerson Process Management Rosemount Nuclear Instru-ments Inc., “Rosemount 1152 alphaline datasheet—nuclear pres-sure transmitter,” ReferenceManual, Emerson ProcessManage-ment RosemountNuclear Instruments Inc., Chanhassen,Minn,USA, 2007.

[7] US NRC, Final Safety Evaluation Report Related to Certifica-tion of the AP1000 Standard Design, Division of RegulatoryImprovement Programs, Office of Nuclear Reactor Regulation,U.S. Nuclear Regulatory Commission, Washington, DC, USA,2004.

[8] IAEA, “Design measures for prevention and mitigation ofsevere accidents at advanced water cooled reactors,” in Pro-ceedings of the Technical Committee Meeting, Vienna, Austria,October 1996.

[9] TEC Microsystems GmbH, Thermoelectric Cooler Basics, TECMicrosystems GmbH, Berlin, Germany, 2013.

[10] F. J. Disalvo, “Thermoelectric cooling and power generation,”Science, vol. 285, no. 5428, pp. 703–706, 1999.

[11] Laird Technologies,Thermoelectric Handbook, Laird Technolo-gies, St. Louis, Mo, USA, 2010.

[12] Microtherm, “Microtherm standard panel,” Datasheet, 2012.[13] Z. Luo, “A simple method to estimate the physical charac-

teristics of a thermoelectric cooler from vendor datasheets,”Electronics Cooling, vol. 14, no. 3, pp. 22–27, 2008.

[14] J. W. Cho and K. M. Jeong, “A performance evaluation of anotebook PC under a high dose-rate gamma ray irradiationtest,” Science and Technology of Nuclear Installations, vol. 2014,Article ID 362354, 8 pages, 2014.

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