Report from the I.W.G.F.R. meeting Bologna, Italy (October 8–10, 1984)

Progress in Nuclear Energy. 1985, Vol. 15, pp. 121-134

(X)7t~6530/85 $(I.(XI + .5(

Printed in Great Britain.

REPORT FROM THE I.W.G.F.R. MEETING BOLOGNA, ITALY (OCTOBER 8-10, 1984) M. MOTrA (EDITOR)

E.N.E.A., Bologna, Italy

INTRODUCTION

The Specialists' Meeting on "Methods and Tools to Detect Thermal Noise in Fast Reactors" was held in Bologna on 8-10 october 1984. The meeting was hosted by th~ ENEA and was sponsored by the IAEA on the recommendation of the International Working Group on Fast Reactors. 17 participants attended the meeting from France, the Federal Republic of Germany, Italy, Japan, the United Kingdom, Joint Research Centre of CEC and from IAEA. The meeting was presided over by Prof. Mario Motta of Italy. The purpose of the meeting was to review and discuss methods and tools for temperature noise detection and related analysis as a potential means for detecting local blockages in fuel and blanket subassemblies

and other faults in LMFBR.

The meeting was divided into four technical sessions as follows: i.

National

review

presentations

on application

purposes

and

research

activities

for

thermal noise detection. 2.

Detection

instruments

and electronic

equipment

for temperature

measurements

in fast

reactors. 3. Physical models. 4. Signal processing techniques. During the meeting, papers were presented by the participants on behalf of their countries and organizations (Ref. /1/-/12/). Each presentation was followed by an open discussion on the subject covered in the paper and general discussion was held at the end of each session. Afver the formal technical sessions were completed s final discussion session was held and general conclusions and recommendations were reached by consensus. Session summaries, general conclusions and recommendations of the official participants (see Appendix i) are given below.

121

22

M. MOTTA

SESSION

I

National review presentations on application purposes and research activities for thermal noise detection

Papers presented by experts from France, the Federal Republic of Germany, Italy, Japan and the United Kingdom indicated that the thermal noise detection and analysis methods in LMFBR are being developed mainly for subassembly surveillance under normal and fault conditions. Detection of coolant flow disturbances and blockages, diagnostics of other malfunctions in subassemblies (due to swelling, deformation, etc.) are the major objectives for application of thermal noise detection in fast reactors. Additional application areas for temperature noise studies include estimates of time constants for instrumentation and transfer functions for reactor phenomena (France and Italy), as well as evaluation of temperature fluctuation impact on mechanical structures

(France).

These areas are also recognized to be important (Federal Republic of Germany, the United Kingdom).

other

by

specialists

of

countries

Instrumentation, physical models and signal processing techniques are being developed for the above purposes and are being tested in out-of-pile experimental facilities used in different countries included subassembly mock-ups (both in sodium and water loops) and unbloeked and blocked electrically heated rod bundles (up to 169 pin bundles). In pile performance tests are carried out in experimental reactors (KNK-II in the Federal Republic of Germany, Joyo in Japan, Phenix in France) and planned for prototype and commercial size plants. French Super-Phenix-I

reactor

is equipped with

which will be able to monitor hourly

temperature

the ANABEL

system for

fluctuations

core surveillance

in the whole core through

eight analogue channels. In addition the use of operational thermocouples for approximately 60 subassemblies is under consideration for temperature fluctuation measurements in SNR300 in Germany. Future investigations are expected to be devoted to the improvement of the sensitivity of methods and sensors. Further theoretical work is envisaged to extend any application of temperature noise detection methods to more realistic conditions. It was agreed by the participants, that two important areas which had not yet been adequately studied were (i) the transport of temperature information between the subassembly outlet and the sensor location, and (2) the optimization of signal processing strategies to obtain reliable discrimination with appropriate response. These problems need to be resolved before the use of temperature noise monitoring can be envisaged in future commercial reactors.

SESSION

Detection reactors.

II

instruments

and

electronic

equipment

Each of the following four countries presented fluctuation monitoring at the S/A outlet.

for

a

temperature

particular

measurements

device

f or

in

fast

temperature

FRANCE emphasized the performance of stainless-steel/sodium thermoelectric junction (used and studied in Japan and FRG too). Developments on mean and fluctuating behaviour were presented. It was shown that a twinned probe (associating a type K and a stainless-steel electrode) could be used for transfer function estimation of the type K sensor.

I.W.G.F.R. meeting

123

JAPAN presented the sensor used in the Joyo experimental reactor and also to be placed at the exit of a few tens of S/As on the MONJU power plant,

It consists

flowmeter used for both temperature and flowrate measurements.

of an eddy current

Sensitivity of this device

vs temperature is shown to be as high as for a standard type K thermocouple. A review of temperature time constants (vs diameter and for different technologies) also presented.

was

F.R.G. has developed a multipurpose probe consisting of a pair of permanent magnetic flowmeters and a pair of 3-wire thermocouples. The sensor is now being operated in KNKII. Standard and transit time analysis of the flowrate meter and thermocouple signals enables the simultaneous determination and on-line comparison of the mean and fluctuating components of flow and temperature. The transfer functions between type-K TC's and SS/Na-junctions have been compared using a simple TC model. In addition the influence of the TC itself on the measurements has been estimated by replacing the TC with sodium. Results, presented for a 0.5 mm diameter type K TC, show very limited frequency response, whereas SS/Na-TC indicates undistorted measurement.

U.K.

presented

an

evaluation

of

a clustered

probe consisting

of 6 mineral

insulated,

coaxial Chromel/Alumel thermocouples. An estimate of the response time of such clusters was obtained and the effect of the presence of gas in the sodium on thermoeouple performance was investigated. The time constant of the clustered thermocouples was found to be better than 50 ms and it was noted that the observed electrical background noise levels would permit the detection of attenuated temperature noise components up to 20 Hz for subassembly fault detection.

Tables 1-5 give an overview of temperature core equipment in the different participating countries.

SESSION III

Physical modelling JAPAN presented

a physical

model which

predicted

RMS

values

of temperature

fluctuation

for 37 and 91 pin bundles. The calculation showed that the RMS temperature fluctuation increases when there are many pins in a bundle, and that there is possibility of detecting the occurence of a blockage in power reactors.

F.R.G. (KfK) made a detailed presentation of physical modelling of the mean and fluctuating temperature fields, and investigated the difference between water and sodium coolant based on eddy diffusivity. Good agreement was observed for axial distance X/d 20. The k-value was introduced as the ratio of RMS noise to axial temperature increase and found to be a sensitive indicator of flow disturbance.

24

M. MOTTA

U.K. has developed the computer code STATEN to predict fluctuation profiles based on a Monte-Carlo technique.

the temperature

and temperature

The effect of heat transfer between fluid particles is considered. Verification of the method was obtained experiments in sodium.

by the use of pipe-flow

and divergent

jet flow

SESSION IV

Signal processing techniques During this Session 3 papers were presented concerned with Signal processing techniques. The first paper, in cooperation between ENEA and Politecnico of Milano potential of a new statistical technique called the Bootstrap method. This technique single sample distributions.

exploited

the

allows the determination of the accuracy of measured quantities from a of independent observations without any assumption of the type of

The method has been used for determination of the accuracy of thermocouple time constants but it can be used also for other quantities, /or example blockage detection values as k-value, skewness and kurtosis. It is proposed that mock-up experiments could be used to validate this method. The Monte-Carlo turbulence and heat transfer model STATEN developed at the Berkeley Nuclear Labs. of the Central Electricity Generating Board, has been used to generate test data to enable the resolution of automatic decision making systems to be determined against different levels of background signals due to temperature tilts across the subassembly. Such data has been supplied as input to a decision making algorithm Learning Network (ALN).

based on an Adaptive

The present evaluation of an ALN has indicated that under the current modelling assumptions, it is possible to automatically identify the presence of blockages ( 6 % ) irrespective of location and temperature tilt (0-50°C) across the subassembly. This has indicated that such a technique has the potential of simplifying core surveillance by enabling the use of a single detection algorithm for all S/A locations. The sensitivity of the blockage detection failure probability to variations in the overall decision time has also been investigated using this approach. The third paper,

from ENEA,

dealt with the use of standard

statistics and functions as

failure indicators in the evaluation of the SILOE-experiments RSI. (One defected preirradiated SPXl-pin). The RMS-value of temperature fluctuations is comparable to the DND method in detecting cladding failure. Additional method.

multi-pin

fuel

element

tests

are

planned

for

further

evaluation

of

this

CONCLUSIONS AND RECOMMENDATIONS

The work that has been performed on rigs, experimental and prototype reactors, physical models and signal processing developments has provided tools which enable the potential usefulness of temperature fluctuation monitoring to be evaluated in experimental situations.

I.W.G.F.R. meeting

125

With the development of commercial breeder reactors the emphasis should now be direct towards the further evaluation of phenomena which must be considered for their safety or operational consequences. This work should develop the phenomenological description of the initiation and evolution of cooling anomalies, as already started. For anomalies which are potentially detectable by temperature fluctuation monitoring there is a requirement to investigate the efficiency, reliability and design consequences of the proposed system and to compare them with the benfeit of other surveillance systems. Additionally, the influence of design and operational constraints (flow mixing at the outlet, power tilts, load following) should be included in the consideration. The

participants

of

the

meeting

recommend

that

further

work

be

carried

out

on

the

following 3 areas: 1 -

2

-

Further developments and justification of current tools to cope with realistic subassembly geometries including transport of temperature information to the sensor and optimisation of signal processing strategies. The

specification

of

realistic

subassembly

phenomena

that

should

and

could

be

monitored by temperature fluctuations. 3 - The efficiency and reliability of temperature noise monitoring for commercial plants.

The status of the work should be discussed at specialists' IWGFR at the appropriate time.

meetings sponsored by the

26

M. MOTrA

REFERENCES

/l/

G. Cantoni, R. Giovannini, M. Piani "Temperature Noise Analysis on a LMFBR defective

fuel pin

irradiated in a sodium

loop"

121 D. Firth and B. O. Wey "Review of temperature noise studies in the UK"

131 R. Giovannini, M. Motta "The activity for the development of the thermal noise detection and analysis at the Italian Committee for Nuclear and Alternative Sources of Energy (ENEA)"

141

J.P. Girard "Temperature-Fluctuation measurements and their use in the french LMFBR program"

151 G. Hughes, R.S. Overton and B.O. Wey "STATEN

Predictions

in

a

CDFR

Subassembly

and

the

Use

of

Simulated

Outlet

Temperature to Test Decision-making Techniques"

161

L. Krebs, G. Weinkotz "Survey on the german

research programme

for blockage

detection within

LMFBR fuel

elements by measurements and analysis of temperature fluctuations" /7/ L. Krebs, K. Bremhorst "Verification of the extended gradient diffusion model by measurements of the mean and fluctuating

temperature fields

in sodium

flow downstream of a multi- Bore jet

block /8/ M. Marseguerra, C.M. Porceddu Cilione "Accuracy evaluation of thermocouple time constants via the bootstrap method"

lel

K. Nakamoto, N. Ohyma, H. Rindo, M. Kamei "Research and Development Activities on Temperature Measurement for LMFBRs"

11Ol R.S. Overton, B.O. Wey, G. Hughes "The temperature Noise Simulation Code STATEN and its Experimental Verification"

1111 T. Sekiya, T. Takeda, K. Nakamoto, K. Kawano, N. Ohyma "A Study

on Detection

of Temperature

Fluctuation Caused by Local Flow Blockage in

37-Pin Bundle" /12/ B.O. Wey, C.J. Brown "CDFR Coaxial Thermocouple Response Measurements at Nigh Reynolds Numbers"

I.W.G.F.R. meeting APPENDIX

127

I

INTERNATIONAL

ATOMIC

ENERGY

AGENCY

- INTERNATIONAL

Organized REACTOR Specialists'

Meeting

-

PHYSICS

WORKING

GROUP OF FAST REACTORS

by the ENEA

AND NOISE

ANALYSIS

LABORATORY

METHODS

AND TOOLS TO DETECT

THERMAL

October

8-10

- Italy

1984 - Bologna

NOISE

IN FAST REACTORS

PARTICIPANTS FEDERAL

REPUBLIC

OF GERMANY

KREBS

L.

T. TAKEDA

Kernoforschungszentrum

Dep.

Institut

fuer R e a k t o r b a u e l m e n t e

OSAKA U N I V E R S I T Y

POSTFACH

3640,D-7500

Yamadaoka

KARLSRUNE

FRANCE J.P.

UNITED

GIRARD

C.E.N.

of Nuclear

Engineering

2-l,Suita,

Osaka

565

KINGDOM

D. FIRTH

- CADARACHE

UKAEA

DRNR/SPCI/LSPC

RISLEY

BP 1 - F-13115

SAIN

PAUL LEZ DURANCE

ITALY

NUCLEAR

WARRINGTON B.O.

LABORATORIES

WAS 6AT

WEY

CEGB A. FEDERICO

Berkeley

ENEA-TERM

BERKELEY,

Str.

Anguillarese,Km

Nuclear

Labs.

GLOS GLIS-9PB

1,300

CASACCIA-ROMA

Commission

of the European

Communities R. GIOVANNINI ENEA

-

TIB/FICS/ANALRUM

Via M a z z i n i , 2

Z. D I A M A N T I D I S

- BOLOGNA

Joint

Research

Centre

Ispra Establ. M.

MARSEGUERRA

Istituto

1-21020

Ingegneria

- ISPRA

Nucleare

Politecnico

di Milano

Via Ponzio,

16 - MILANO

I.A.E.A. V.F.

EFIMENKO

M. MOTTA

International

ENEA

Agency

-

TIB/FICS

Via Mazzini,

2 - BOLOGNA

Wagramerstrasse, A-1400

C.M.

PORCEDDU

ENEA

-

CILIONE

TIB/FICS/ANALRUM

Via Mazzini,

2 - BOLOGNA

R. TAVONI ENEA

-

VEL

Via Dell'Arcoveggio,

56/23

-

BOLOGNA

JAPAN T. SEKIYA Dep.

of Nuclear

Engineering

OSAKA U N I V E R S I T Y Yamadaoka

2-1,

Suita,

Osaka

Atomic

B66

VIENNA

Energy

B PO Box

i00

28

M. MOlTA

OBSERVERS ITALY P. AZZONI ENEA - TIB/FICS/ANALRUM Via Mazzini, 2

M. PIANI ENEA - TIB/FICS/ANALRUM

BOLOGNA

BOLOGNA

B.

-

2

F. CASALI ENEA - TIB/FICS Via Mazzini, 2 BOLOGNA G. CANTONI ENEA - TIB/FICS/ANALRUM Via Mazzini, BOLOGNA

2

V. SANTJUST Istituto Ingegneria Nucleate

BENZI

TIB Via Mazzini, BOLOGNA ENEA

Via Mazzini,

2

Politecnico di Milano Via Ponzio,16 - M I L A N O A. VIGO ENEA-VEL/SIST/PRONOC Str. Anguillarese, km 1,300 CASACCIA - BOMA

COUNTRY FRANCE

NAME OF POWER PLA~IT

TYPE OF PROBE

FREQUENCY CUT-OFF OR TIME CONSTANT

8

8

I

I

I

DISTANCE BETWEEN SENSOR AND THE SUBASSEMBLY EXIT

I

MEAN TEMPERATURE: SAFETY OR CONTRCL~

F

|

!.i X~

g

6~

~u!~om "~I'~l'~'A~'I

TEMPERATURE FLUCTUATIOPI : SAFETY, CONTROL OR EXPERIMENTAL?

TABLE 2

..L

3~

NUMBER OF INSTRUMENTED S/AS

COMMENTS o

o

MEAN TEMPERATURE FLUCTUAT]Or] PART

z

m ul (name o f system)

K N K I[

Probe i n Sodium K

K and SS/Na s p e c i a l instrumentation d e v i c e

% 1 . 5 Hz

%30 mm

Safetys experimen_ tal KASUMOS and MIRA

Experlmental

32

K

32 (operation TC

©

k : ~ 7 HZ SS/Na 20 Hz

1-2 spec.instr.

>

Additional SNR

300

Thimble K

~0.5

Hz

30 ml.

Safety

Experimental

250

Max 60

SS/Na!

instrumentation

a t few S / A - o u t l e t s is under llscussion.

J d

~t is considered

SNR 2

Thimble K

0.8

llz

~ 3 0 mm

Safety

Safety

(?)

to combine the

temperature fluc t u a t i o n method (acoustic, KASUMOS, DND) to Dne conu~on s u r v e i l l a n c e system for SNR2.

ITALY,

COUNTRY

NAME OF POWER PLANT

TYPE OF PROBE

FREQUENCY CUT-OFF OR TIME CONSTANT

DISTANCE BETWEEN SENSOR AND THE SUBASSEMBLY EXIT

MEAN TEMPERATURE: SAFETY OH C~NTRCL?

7

TEMPERATURE FLUCTUAT[O~I: SAFETY, CONTROL OR EXPEEIMENTAL?

ro

Z

o

COUNTRY

JAPAN

NAME OF POWERPLANT

TYPE OF PROBE

P

8

J,,

o

FEEOUENCY CUT-OFF

OR TIME CONSTANT o

8

~

|

|

DISTANCE BETWEEN SENSOR AND THE SUBASSEMBLY EXIT

MEAN TEMPERATURE: SAFETY OR CONTROLq

,7 TEMPERATURE FLUCTUATION: SAFETY, CONTROL OR EXPERIMENTAL?

g.

-7-. g

~

vJ-LoIAI "]AI

~

COUNTRY

U.K.

NAME OF POWER PLANT

~E TYPE OF

PROBE

FREQUENCY CUT-OFF OR TIME CONSTANT

w

DISTANCE BETWEEN SENSOR AND THE SUBASSEMBLY EXIT

MEAN TEMPERATURE: SAFETY CN C~;TRC!. ~

?

Z~ TEMPERATURE FLUCTUAT[O~i: SAFETY, CONTROL OR EXPERIMENTAL?

>

Zg

=

134

M. MOTrA

-DISCUSSION-

BURTON

There is considerable interest in thermal fluctuations not only to detect anomalies in the nuclear core but also because of their possibie e f f e c t on s t r u c t u r a l integrity. Would i t t h e r e f o r e be f i n a l y t o c o n s i der a broadening of the examination ? Particularly to extend the worth of conclusion 1. T h a t i s , t o s t u d y t h e way t h e r m a l f l u c t u a t i o n s are transported to load c a r r y i n g members of t h e r e a c t o r c i r c u i t .

MOTTA

In my personal opinion it should be useful this broadening of examination. Anyway, the general problem of the transport of the thermal signal from the source to the sensor has to be better investigated because of the sensitivity to the distance and structures. I agree that the problem could be considered in the next meeting of I/IEA on this special topic.