THE REPUBLICAN ENERGY COMMITTEE OF THE SR OF SLOVENIALJUBLJANA, YUGOSLAVIA

NUCLEAR SAFETY ACTIVITIESIn

THE SR OF SLOVENIAIn

1 986

Ljubljana, June 1987

Page 1

NUCLEAR SAFETY ACTIVITIES IN THE SR OF SLOVENIA IN 1986

Abstract

Currently Yugoslavia has one 632of PWR design, located at KrSkoof Slovenia. Kr~ko NPP, whichpower operation in 1981.

MWe nuclear power plant (NPP)in the Socialist Republic (SR)is a two-loop plant, started

In general, reactor safety activities in the SR of Slovenia aremostly related to upgrading the safety of our Kr~ko NPP and todeveloping capabilities for use in future units.

This report presentsorganization of theactivities relatedorganizations in the

the nuclear safety related legislation andcorresponding regulatory body, and the

to nuclear safety of the participatingSR of Slovenia in 1986.

Prepared for:

By:

Edited by:

Report number:

The Republican Energy Committeeof the SR of Slovenia,Ljubljana, GregorOiOeva 25

"J. Stefan" Ln s t.L t.ut.eReactor Engineering DepartmentLjubljana, -Jamova 39

Dr.J.Su~nik

IJS-DP-4736June 1987

Contract number: U1-BL-R4/23/87

Page 2

TABLE OF CONTENTS

Page

ABSTRACT 1

TABLE OF CONTENTS 2

A. ORGANIZATIONS AND LEGISLATIONRELATED TO NUCLEAR SAFETY 3

1. Federal organization.................................... 32. Regulatory structure in the SR of Slovenia 43. Activities on the preparation of regulations 74. Activities of the Nuclear Safety Inspectorate 8

B. ACTIVITIES RELATED TO NUCLEAR SAFETY 11

I. Nuclear Power Plants 121. Kr~ko Nuclear Power Plant Operation in 1986 122. Future Nuclear Power Plants 16

11., Systematic Review and Recordingof Safety Related Issues 17

1. Report on Safety Related Issues in 1986 172. Post-Chernobyl Accident Activities 183. Safety Related Library 18

Ill. Probabilistic Safety Analysis (PSA) Programs 20

1. Cooperation with IAEA on PSA projects 202. Computer codes, data base and calculation of risk,

reliability and availability of NPP systems '" 22

IV. Participation in the IAEA Incident Reporting System .... 23

V. Development and Maintenance of Computer Codes forDeterministic Safety Analyses 24

VI. Training 32

VII. Activities of other authorized organizations 32

VIII. International Contacts, Cooperationand Exchange of Information 34

ABBREVIATIONS USED:

EGS Elektrogospodarstvo Slovenije (ElectricityGenerating Board of Slovenia)

EIMV

IAEA

"Milan Vidmar" Electrical Institute

International Atomic Energy Agency

IBE In~enirski biro Elektroprojekt

ICJT Izobra2evalni center za jedrskotehnologijo (Nuclear Training Centre atthe "Jo:::ef St.efan" Institute)

IJS

IJS - RED .

IMK

IRS

" ..Jo z e f Stef an" Institute

IJS Re ao t.o r Engineering Department

Institute for Metal Constructions

Incident Roporting System

JUGEL

NEK

Zajednica jugoslovenske(Yugoslav Community ofGenerating Boards)

Krako Nuclear Power Plant

elektroprivredetho Electricity

NUKLIN NUKLearni INstituti (Managing Communityfor the Research, Development and PeacefulUses of Atomic Energy)

PRA

PSA

REI

Probabilistic Risk Assessment

Probabilistic Safety Analysis

RepubliSki energetski inSpektorat(Republican Energy Inspectorate)

RKE Republican Energy Committee

RUZV Rudnik urana Zirovski vrh(Zirovski vrh Uranium Mine)

RBMK

SKEI

Soviet Design of the Chernobyl NPP

Yugoslav Federal Energy and IndustryCommittee

(US)NRC (United States) Nuclear RegulatoryCommission

2.SHJE group working group preparing the secondSlovene-Croatian nuclear power plant

Page 3

A. ORGANIZATIONS AND LEGISLATION RELATED TO NUCLEAR SAFETY

With the coming into force of the federal "Act on RadiationPro~ection and the Safe Use of Nuclear Energy" (FederalOfficial Gazette No. 62/84, referred to hereinafter as the1984 Act), Yugoslavia has a partly new organizational structureof the regulatory body, competent for nuclear safety. Thiscompetence is divided between the federal and the republic (andautonomous province) authorities.

1) Federal organization

a) Regulations:

Since nuclear safety is a matter of importance for the wholecount,ry, federal authorities regulate this field of activities.Thus, t,he FEDERAL ENERGY AND INDUSTRY COMMITTEE is authorizedto enact four very important regulations for carrying intoeffect the nuclear safety provisions of the above mentioned1984 Act, i.e.:

- Regulation of the conditions for siting, design, construction,commissioning and operation of nuclear facilities;

- Regulation of the format and contents of safety analysisreports for nuclear facilities;

Regulation of qualifications, experience and training ofpersonnel in nuclear facilities;

- Regulation of accounting and control of nuclear materials.

The FEDERAL COMMITTEE FOR LABOUR, HEALTH AND SOCIAL WELFARE isauthorized to adopt several regulations concerning radiationprotection in all fields where radiation sources are beingapplied (e.g. regulations of the national monitoring system forenvironmental radioactivity, of the disposal of radioactivewaste, of the application of ionizing radiation sources formedical purposes, etc.).

b) Licensing:

Responsibility for licensing nuclear facilities in Yugoslavialies with the authorities in the republics or autonomousprovinces where the plant is to be located. However, to assurean assessment and overall control of nuclear safety questionsimportant for the whole country, a federal COMMISSION FOR THESAFETY OF NUCLEAR FACILITIES was established within the FEDERALENERGY AND INDUSTRY COMMITTEE. The competent authority in each

Page 4

republic or province may issue licenses for the site,construction, commissioning and operation of a nuclear facilityonly if the Federal Commission has concurred that all theprescribed safety conditions have been met.

c) Inspections:

Inspections and enforcement of the 1984 Act are carried out bythe competent bodies in each republic or autonomous province.However, in some cases, such as e.g. the implementation ofinternational agreements, the use of standards and qualitynorms etc., the federal body has the right to define bindinginstructions to the competent republic or provincial bodies oreven perform an activity if they failed to carry it out.

2) Regulatory structure in the SR of Slovenia

Regulatory authorities acting on matterssafety in Slovenia are shown below.

related to nuclear

£:ucuU.,. COWK.i1 or tbe

......bl,. of sa Slav.at•

a.public=t... ••publicC~1.t,•• torta""'.....~l'"tee UOD &DdUrbo.. P1UAift4>

a.publlcCo-itt•• orI nc!ua'r'7 a.:iYi,l von.

'.pub11cC~tt.e

tor a•• lthlUId Sc>ct.lW.lt.,..

'ej»Qbl ic$Kretari.ator ••hoD&!De:.D ••

••""bllcCa.aitt••ot lAbour

••publicSecretar1ator IDtenellttair.

Regulatory organizationnuclear safety

in the SR of Slovenia related to

Page 5

At the level of the SRS, the competence to pass regulations forlicensing and for inspection is described below within theseparate presentations on various bodies and organizations.Generally speaking, nuclear safety in the SR of Slovenia isregulated by the republic's (1980) "Act on the Execution ofRadiation Protection and Measures for the Safety of NuclearFacilities" (Republic Official Gazette No. 28/80). Due to thecomprehensive and detailed provisions of the federal 1984 Actand Regulations, passed pursuant to it, there is little roomleft for the Republic's legislative activity. The mostimportant legislative competence of the republic is thedetermination of the regulatory structure for the licensing andinspection activities. Furthermore, in detailing the generalsafety measures, prescribed by the federal 1984 Act, the SR ofSlovenia adopts every 5 years a "Programme of Measures forRadiation Protection' and Nuclear Safety". On this basis thecompetent administrative bodies of the SR of Slovenia, each inits own field of activity, by the end of every year prepare adetailed programme of general activities to be performed in thecoming year. In the field of nuclear safety, this annualpogramme of general measures is financed by a special "Fund fornuclear safety" to which the budget of Slovenia and the 3owners of nuclear facilities in Slovenia contribute on thebasis of a social compact, signed in 1984. In this way generalsafety measures of interest for the whole republic of Sloveniaare assured. Safety measures in each nuclear facility remain,of course, the responsibility of their operators.

The EXECUTIVE COUNCIL of the Assembly of the SR of Slovenia,i.e. the government, has very few direct functions related tonuclear safety. It adopts the already mentioned "Programme ofMeasures for Radiation Protection and Nuclear Safety" for aperiod of 5 years. It is also his direct competence to orderthe evacuation of the population in case of a nuclear accidentor radiological emergency. Otherwise the various republicanadministrative authori. ties are acting within its s t r uc t.u r e .

Before describing the administrative authorities bearingresponsibilities related to nuclear safety, three important.special republican bodies have to be mentioned.

The NUCLEAR ENERGY COMMISSION advises the Executive Council onquestions related to nuclear energy policy, development of thenational nuclear programme and other general matters.

The ADVISORY COMMISSION FOR NUCLEAR SAFETY is the centralexperts' group in Slovenia, dealing with safety relatedquestions and coordination among different governmental organs.It consists 'of representatives of governmental bodies andvarious research institutes. All questions concerningradiation protection and nuclear safety are passed to thiscommission. In the course of a licensing procedure, thecompetent administrative organs have to obtain an opinion fromthe Commission, before their decision is taken.

The REPUBLICAN HEADQUARTERS FOR CIVIL DEFENCE is responsible

Page 6

for planning and executing the civil protective measures incase of national disasters and other significant emergencies,including nuclear accidents and radiation emergencies.

The REPUBLICAN ENERGY COMMITTEE is, within the limits of thefederal regulations, authorized to adopt various regulationsrelated also to nuclear safety (e.g. on regular reports on theoperation of a nuclear facility etc.). Acting within its legalframework the REPUBLIC ENERGY INSPECTORATE is, according to theexisting republic 1980 Act, authorized to issue thecommissioning permits for nuclear facilities. The REPUBLICENERGY INSPECTORATE has a NUCLEAR SAFETY INSPECTION which isresponsible for inspecting the nuclear facility duringconstruction and operation. In discharging theirresponsibilities, this inspection may, among other, discontinuethe operation of a nuclear facility, if not all prescribedconditions have been met.

The REPUBLICAN COMMITTEE FOR ENVIRONMENTAL PROTECTION AND URBANPLANNING is authorized to issue a site license for a nuclearfacility. Through its REPUBLIC WATER WORKS INSPECTORATE andREPUBLICAN URBANISTIC INSPECTORATE, control over this part ofthe administrative procedure is executed.

The REPUBLICAN COMMITTEE FOR INDUSTRY AND CIVIL WORKS iscompetent for the rest of the licensing procedure. It issuesthe licenses for construction and for the operation of anuclear facility, if all the prescribed conditions are met.The REPUBLICAN CIVIL WORKS INSPECTORATE has an authorizationfor inspections during the construction. The REPUBLICANCOMMITTEE OF HEALTH AND SOCIAL WELFARE is competent for thecontrol of environmental radioactivity and the control ofworkers exposed to radiation. These tasks are realized throughthe REPUBLICAN HEALTH INSPECTORATE.

The REPUBLXCA~l COMMXTTRF. OF LABOUR, the P~U~CAN SECRETARIATOF INTERNAL AFFAIRS, and the REPUBLICAN SECRETARIAT OF NATIONALDEFENCE perform actions relating to their competences.

These administrative bodies, in discharging theirresponsibilities, rely on the professional support ofauthorized organizations in technical matters. The AUTHORIZEDORGANIZATIONS which are listed in the Official Gazette performimportant technical tasks related to nuclear safety and reportannually to the competent administrative bodies.

At the beginning of 1987 an important reorganization of theregulatory body in the Socialist Republic of Slovenia was

. initiated. Up to now no specialized, exclusively competent andresponsible regulatory body for nuclear safety existed asdescribed above.

Activities in this field have been carried out by differentcommittees and secretariats, by the Inspectorate for NuclearSafety (in the framework of the Republican Energy Inspectorateunder the Republican Energy Committee) and by the Advisory

Page 7

Commission on Nuclear Safety. Above all the functions ofpromoting energy production and the function of surveillanceover it had to be divided between different bodies. In duetime it was found appropriate to improve this situation forvarious organizational, procedural and functional reasons. Itwas decided therefore to propose the establishment of a newbody, the Republican Administration for Nuclear Safety. InApr~l 1987 the Government of Slovenia approved an amendment tothe 1980 "Act. on the organization and sphere of activity of theRepublic's Administrative Bodies" etc. (Official Gazette ofthe SRS No 50/80, 12/82,9/85, 14/86) and passed it to theAssembly of the SR Slovenia. It is expected that the Assemblywill discuss the issue in June and October 1987.

According to this Bill, the proposed Republican Administrationfor Nuclear Safety' will be an independent, functionallyautonomous body, dealing with all matters concerning nuclearsafety, including legislative competences for RepublicanRegulations, some of the licensing procedures, enforcement andcompliance assurance of the Federal and Republican legislation,inspections etc. It will be directly responsible to theGovernment and to the Assembly of the Socialist Republic ofSlovenia.

If the enactment of the proposed Bill is realized in the way itis planned, a very important step will be taken and an old ideafor the improvement of nuclear safety in Slovenia will bebrought to life. In this way also the Agency's Code ofPractice on Governmental Organization (SS No. 50-C-G), Section3.1 will be implemented in the Socialist Republic of Slovenia.

3) Activities on the preparation of regulations

A , , __

.t'l;:; d.J..L't:ctuy merrtd one d , --_._--... _-~.kJu,1.. .:::U d..I:. L..1 no A A_.....L VV~ .!'ll...... '!... j

Energy and Industry Committee is authorized to adopt thefollowing four regulations important to nuclear safety:

- the regulation of the conditions for siting, construction,commissioning and operat.ion of nuclear facilities;

- the regulation of the contents of safety reports for nuclearfacili t.ies;

- the regulation of professional qualifications, experience andtraining of personnel in nuclear facilities;

- the regulation of accounting for and control of nuclearmaterials.

Drafts of all four regulations are being prepared by workinggroups from the SR of Slovenia. Through coordination by the"Jo~ef Stefan" Institute from Ljubljana, the drafts of the"Regulation of professional qualifications, experience and

Page 8

training of personnel in nuclear facilities" and of the"Regulation of accounting for and control of nuclear materials"were completed and presented to federal authorities forapproval. Also the working drafts of the "Regulation of theconditions for the siting, design, construction, commissioningand operation of nuclear facilities" and of the "Regulation ofthe format and contents of safety analysis reports for nuclearfacrlities" are being prepared in cooperation with experts fromSlovenia.

In the field of radiation protection the Federal Committee forLabour, Health and Social Welfare adopted nine regulations. InSlovenia a working group was set up which contributed manyuseful amendments during the drafting of the mentionedregulations.

In the meantime, a formal procedure for the amendment of theConstitution of the Socialist Federative Republic of Yugoslaviawas initiated. The amendments, which were proposed for otherreasons, among other issues refer also to nuclear energy.Thus, it is proposed to establish an energy and radiationprotection committee. In this way the draft proposal alsoformally entitles the Federal Assembly to adopt the entiresubstantial legislation in this field, a competence which untilnow, from the constitutional point of view, was not so clearlydefined. It remains, however, up to the individual Republicsand Provinces to adopt further legislation, necessary for theexecution of the federal law.

It is expected that amendments to the Constitution, providing aclearer constitutional organization of the Federation, will notinterfere with the 1984 Act.

After adopting several important supplementary Regulations, the1984 Act is being more and more completed, providing asatisfactory legislative basis for all activities concerningnuclear safety and radiation protection. It is important topoint out that it was the constant aim of the legislator tointroduce through the 1984 Act, and especially through theregulations adopted on its basis, the principles and philosophyof the IAEA Safety Standards and Guides.

4) Activities of the Nuclear Safety Inspectorate

Introduction

The Nuclear Safety Inspection operates within the RepublicanEnergy Inspectorate as concerns affairs subject to Republicanauthorities.

The 1984 Act provides a basis for the work of regulatoryinspection. The major activities of inspection are connectedwith the following:

Page 8

training of personnel in nuclear facilities" and of the"Regulation of accounting for and control of nuclear materials"were completed and presented to federal authorities forapproval. Also the working drafts of the "Regulation of theconditions for the siting, design, construction. commissioningand operation of nuclear facilities" and of the "Regulation ofthe format and contents of safety analysis reports for nuclearfacilities" are' being prepared in cooperation with experts fromSlovenia.

In the field of radiation protection the Federal Committee forLabour, Health and Social Welfare adopted nine regulations. InSlovenia a working group was set up which contributed manyuseful amendments during the drafting of the mentionedregulations.

In the meantime, a formal procedure for the amendment of theConstitution of the Socialist Federative Republic of Yugoslaviawas initiated. The amendments, which were proposed for otherreasons, among other issues refer also to nuclear energy.Thus. it. is proposed to establish an energy and radiationprotection committee. In this way the draft proposal alsoformally entitles the Federal Assembly to adopt the entiresubstantial legislation in this field. a competence which untilnow, from the constitutional point of view, was not so clearlydefined. It remains, however, up to the individual Republicsand Provinces to adopt further legislation, necessary for theexecution of the federal law.

It is expected that amendments to the Constitution. providing aclearer constitutional organization of the Federation, will notinterfere with the 1984 Act.

After adopting several important supplementary Regulations, t.he1984 Act is being more and more completed. providing asatisfactory leg~s.lative basis for all acti'Vities conc6rningnuclear safety and radiation protection. It is important topoint out that it was the constant aim of the legislator tointroduce through the 1984 Act, and especially through theregulations adopted on i t.s basis, the principles and philosophyof the IAEA Safety Standards and Guides.

4) Activities of the Nuclear Safety Inspectorate

Introduction

lne Nuclear SafetyEnergy Inspectorateaut.ho r-Lties.

Inspection operates within the Republicanas concerns affairs subject to Republican

The 1984 Act provides a basis for the work of regulatoryinspection. The major activities of inspection are connectedwith the following:

Page 9

Kr~ko NPP reports:

- regular Kr~ko NPP monthly reports- report on radioactive release from Kr~ko NPP- report on changes of nuclear material in Kr~ko NPP- report on changes of nuclear material at Podgorica- report on radiation dose rates in Kr~ko NPP- ahnual Kr~ko NPP reports- reports on exceeded releases of liquid or gaseous effluents

Kr~ko NPP outages:

- plant outage from the electric grid- violation of technical specification limitations- unplanned plant sh~tdowns

Final Safety Analysis Reports:

- revisions of technical specifications- final safety analysis report to Kr~ko NPP- index of operating procedures- examinations of reactor vessel samples

Kr~ko NPP repairs:

Measurements of the Kr~ko NPP environment:

- programme of meteorological measurements- radiological monitoring of the Kr~ko NPP environment- nonradiological monitoring of the Kr~ko NPP environment

Reports from authorized and other organizations:

- annual reports of authorized organizations- preparations for the construction of the 2nd Croatian

Slovene nuclear power plant

Confirmation and renewal of regulations:

- cooperation in elaborating proposals for regulations- proposal for issuing regulations- cooperation in changing regulations

Explanations:

explanations concerning the competence of nuclear safetyinspection

- opinions on regulations and their use in the field of nuclearsafety

Professional examination andstaff:

Page 10

qualification of operational

cooperation in training programmes- cooperation in qualification test commissions

There are a number of other activities that are covered by thefoliowing inspectorates:

- Republican Energy Inspectorate (within which the NuclearSafety Inspectorate operates)

- Republican Sanitary Inspectorate which is connected with theRepublican Health and Welfare Committee (their competence isradiation protection)

Republican Water Inspectorate which is connected with theEnvironmental Protection and Urban Planning Committee (theircompetence is ecological monitoring of the KrSko NPPenvironment, including temperature change of the river Sava,etc. ).

With respect to fire protection, emergency planning andpreparedness etc. there is also a close cooperation with thecompetent authorities at the republican level. The NuclearSafety Inspectorate coordinates the various inspectorates'activities concerning the KrSko NPP.

As the regulatory body is not self-sufficient in all technicalareas relevant to inspection, it supplements its inspectionprogramme through qualified and authorized consultantorganizations. These are normally involved during all yearlyoutages for refuelling, when extensive maintenance is beingdone. Each year they give a written report to the regulatorybody about their findings, safety assessments andrecommendations. Their findings and recommendat-ions then serveas a basis for the inspectors' activities in the future. Inthe case of the occurrence of an unusual event or finding,technical evaluations and studies are done by theseinstitutions. The nuclear safety inspector can at any timerequest an extra meeting of Nuclear Safety Commission in orderto have an urgent safety matter reviewed or to obtainadditional advice. In particular, the Nuclear SafetyInspectorate took part in the following KrSko NPPmodifications:

- review of TMI documentation- problems related to the steam generator- SU-PA-12 test- test operation of the cooling tower system- reactor head deaeration

modernization of the data processing system in KrSko NPP

The Nuclear Safety Inspectorate cooperated in the followingIAEA projects: the IAEA Incident Reporting System, the ASSETmission to Yugoslavia, and the PSA project (INT/09/063).

Page .11

B. ACTIVITIES RELATED TO NUCLEAR SAFETY

Activities in the field of nuclear safety are performed by theRegulatory Body (see Section A of this report). Kr~ko NPPpersonnel and the authorized organizations: IJS. EIMV. IMK. IBEand" others.

Nominated representatives of the authorized institutions havecooperated in work performed by SKJV (Nuclear Safety Committeeof the SR Slovenia) and in examination of NPP Kr~ko operators.

Activities presented in chapters 11 to VII are focused mainlyon the "Jo:2:ef Stefan" Institute. while activities of otherauthorized organizations are described in chapter VII.

Page 12

I. NUCLEAR POWER PLANTS

1. Kr~ko Nuclear Power Plant Operation in 1986

a) In 1986 the plant produced 3824.5 GWh of electric energy,which is 1.2% above the planned production. Generatoron-line operation was 6561 hrs. By May 1987 the NPP Kr~ko

has supplied over 20.000 GWh to the grid.

Figure 1 shows monthly production of the Kr~ko NPP in 1986

b) Thermal energy generated in 1986 was 11 671 379 MWh and theburnup was 9949 MWD/MTU.

c) Cumulative factors for unit service and availability afterJanuary 1,1983, when the startup tests were completed:

Unit Availability FactorUnit Capacity FactorUnit Forced Outage Rate

(%)(%)(%)

1986

74.969.01.3

cumulative

74.569.83.5

Analysis of operating period hours %

Total time availability of operation

Plant operating timeTotal outage time:

- r efue Ll.Lng c\.~tage

- planned shutdowns- unplanned shutdowns

8760

65612199

155117

100

74.925.1

1.81.3

Figure 2 shows Kr~ko NPP monthly time availabilities in 1986.

Visit of IAEA Safety Team

An lAEA Assessment of Safety Significant Events Team (ASSET)visited Yugoslavia's Kr~ko nuclear power plant inNovember/December - the first such mission to' be sent by theAgency to a member state. Yugoslavia had volunteered to makeKr~ko available for the ASSET mission to test the assessmentmethods developed for the IAEA's nuclear safety programme. Theauthorized organizations IJS, EIMV, and IMK cooperated with theASSET mission of IAEA experts.

Page 13

cc

Figure 1 : NPP Krsko Electricity Product(3824.5 GWhr) In 1986

on

2.00 u.co 6.00 8.00T I M E IMONTHI

InFigure

:32: Availability Fo c l or­

of the NPP Kr~ko 1986

12.0010.00~.oo 6.00 8.00T I M E IMONTHI

2.00

c~r--,....--c==.,-,r----r-......,r---r--.....---...,...--r-....,--r----,

Cb.oo

t---"1 .1 i ~! : i=.::J.=. ::=:::=:~ ::~~~~-r~:I=~~:::t=:~~:: .::::::::::= ===~:. ·::::::='1-=~~::: ~~:~=:::r::~:::::~: .--·F· _._+ _+_+ _-_._.. _.__ ,-t--- _+ _.0:1 i '! I!--i-- _- -_.._-+._ _ +.__ _ -.•.- _ - _+.__.._ _-+_ _.

I I i ~:

;::8 :=:==t=:::::::· ::::~:::=r::::~::~ :::::~~J:=::.:~~:: :::~:~:.= :~=:~:::··==~~~t=:=::. :~~~=~~~==::.'0 i 'I i i(Q' , i

w _ J ~............... ········1·············· ...........................•....•.•.•..~ _ .(.:l I !. ! I

§~ :~=~:F::::=:::· ::~=~:::r~:::::=.I:~:~:=::l~:~·::~~ :::~:::~=: ~::::::=~. ·::::::::~:1=:::::: ::::~::::::l::=:~:~:

~;$===$==:t::: ==~: :=:::::~== ::::1=N

Page 14

Table 1: Power reductions and shutdowns of the Kr~ko NPP in1986 more than 20% of the nominal power and for morethan 4 hours

No. Date Type Duration Cause Mode Remarks.. (1) (hours) (2) (3)

---------------------------------------------------------------1) February

22-23 2 44 A manual

2) Feb.24 2 9 A manual

3) Feb.27to Mar.01 1 51 A R-regular

4) March 4 1 21 A R-forced powerreduction

5) March 14 1 9 A R-forced powerreduction

6) May 1-5 2 102 H manual powerreduction

7) July 9 1 18 A R-regular

8) Aug.01to Oct.24 2 2055 B,C R-regular refuelling,

maintenance9) Oct.24 1 28 A automatic

10)Nov.17 1 20 A automatic------------------------------------------------------ - - - - - - - -Legend:

( 1) 1 ........................ Forced,..., ." , (Planned)L. ...................... 0CneaUl.ea

(2) A: Equipment failure (description)B: maintenance or testingC: refuellingD: regulatory body requirementsE: operator training, examsF: administrative action (description)G: operating error (description)H: other (description)

(3) Manual (regular)Manual (forced)AutomaticOther (description)

Page 15

Table 2: DESCRIPTION OF PLANNED AND UNPLANNED SHUTDOWNS ANDPOWER REDUCTIONS BY MORE THAN 20% OF THE NOMINAL VALUEAND FOR MORE THAN 4 HOURS IN 1986

---------------------------------------------------------------No. Date Duration Description

1} Feb.22 44 hrsto Feb.23

The plant was manually shut down due tosteam leakage on moisture separation linesof a high-pressure turbine part. Leakagewas caused by tube erosion. Damaged partswere cut out and replaced.

2} Feb.24

3} Feb.27

4} Mar.4

5} Mar.14

6} May 1-5

9 hrs A repeated leakage on drain lines of ahigh-pressure part of a turbine. The plant·was manually shut down.

51 hrs HD A and B pumps trip caused by BD controlsystem failure and condensate leakage insections D and C resulted in forced plant'shutdown. HD LCV5126 valve repair andplant startup followed.

21 hrs Power reduction to 50% due to loss of flowacross LCV 5126 and both HD pumps trip.

9 hrs Power reduction to 55% due to HD A pumptrip and simultaneous repair of BD B pump.

96 hrs Power reduction to 50% on dispatcher'srequest No.356.

---------------------------------------------------------------7} Jul. 9 18 hrs Plant shutdown due to vacuum loss in a

condenser. Safety pin of a "tapprogefilter" was repaired and B condenser wascleaned.

---------------------------------------------------------------8} Aug.l 2055 hrs Annual refuelling outage, eddy current

test of SG tubes, annealing of shotto Oct.24 pinning parts of SG tubes.

---------------------------------------------------------------9} Oct.24 28 hrs At lockout relay 86U activation for test

purposes, there was no rapid switch overfrom Ml to MD1 bus. DIGl started.Automatic reactor shutdown occurred. Dueto steam leakage on turbine stop valveNo.3 and due to the failure of isolationvalve No.20141, uncontrolled cooling ofthe primary system occurred. Pressure dropin the secondary system activated thesafety injection system. Termination ofsafety injection and event recoveryaccording to the procedure followed.

---------------------------------------------------------------10} Nov.17 20 hrs Feedwater control valve FCY 551 closed,

which caused SIGl level decrease andautomatic plant shutdown.

Page 16

2. Future Nuclear Power Plants

Preparatory work has been going on for the planned series ofnuclear power plants to be built for the Yugoslav electricitygrid up to the year 2000. JUGEL (Zajednica jugoslovenskeelektroprivrede) has ordered a study of safety criteria to beapplied for these nuclear power plants. The ReactorEngineering Division at the "Jo~ef Stefan" Institute hascoordin~ted the effort in which several Yugoslav institutionstook part and the resulting final report was published in1986.

I .•., ,~.~ "J/I

Unpacking of fuel in the Fuel Handling Building

J!

Page 17

11. SYSTEMATIC REVIEW AND RECORDING OF SAFETY RELATED ISSUES--------------------------------------------------------

1) Report on Safety Related Issues in 1986

Based on the "Programme of Measures for Radiation Protectionand Nuclear Safety", the Regulatory Bodies of the SocialistRepublic of Slovenia require a systematic review of selectedsafety related activities and independent evaluation ofoperational events in nuclear plants and facilities abroad andfrom the Kr~ko NPP to be conducted and reported to them. Thiswork is done by the "J.Stefan" Institute, located at theReactor Centre at Podgorica, about 10 km from Ljubljana,assisted by the authorized institutions EIMV (Elektroinstitut"Milan Vidmar") and IMK (Institut za metalne konstrukcije) fromLjubljana.

In the report prepared for 1986 a description is given of thepresent status of regulatory codes, new designs, researchactivities and operating experience as regards nuclear safetyabroad.

In the field of codes and regulations the report describes theUSA Regulation of Advanced Nuclear Power Plants and USA Safetygoals for the operation of nuclear power plants (Statement ofpolicy, 10 CFR 50).

An overview of advanced designs and of reactor safety researchis included. The IAEA index on reactor safety research, as runin member states, is shortly described. So is I NSAG(International Nuclear Safety Advisory Group, IAEA) activityand the situation in the TMI-2 NPP in the USA.

As regards the operational events the following operationalevents were analysed:

loss of on-site power supply and water hammer in the SanOnofre 1 NPP (Nov. 21, 1985),

- loss of DC power supply to the control system and thesubcooling transient in the Rancho Seco NPP (Dec. 26, 1985),

- UF6 release in Sequoyah Fuel Corporation (Jan. 4, 1986),- the accident at the Chernobyl nuclear power station, Unit 4,

(April 26,1986), and- the operational transient in THTR-300 at the Hamm Uentrop NPP

(May 1986)

The annual US NRC report and the lAEA report on nuclear safetyactivities in 1985 are presented in detail. Finally, adiscussion on the authorized organizations and the qualityassurance in nuclear installations with respect to the Yugoslavregulations is given.

Page 18

2) Post Chernobyl Accident Activities

Immediately after the occurrence of the accident in theChernobyl NPP, the division staff have elaborated a safetyanalysis of characteristics of RBMK reactors and estimated theprobable events and consequences .

..With the CRAC-2 code the upper limit of the expected acuteconsequences was assessed for whole body and thyroid doses, thesource term being taken as the steam explosion scenarium in thePWR (lA accident) and assuming a direct wind from the site toour country.

Later, as theChernobyl sitethyroid, totalthe whole bodygreat detail.4 and 5.

question of the radioactive cloud rise at thewas open, its effects on acute irradiation ofbone marrow, lower large intestine, lungs and

were studied, again with the help of CRAC-2, inSome of the results are presented in Figures 3,

From the calculation of partial doses to individual organs, theinfluence of the release height on lung dose is shown in Figure3. At a fixed release height, dose magnitudes as received bythe whole body, bone marrow, lower large intestine, lungs andthyroid, are shown in Figure 4. The thr~e contributions fromthe radioactive cloud, from the contaminated ground and frominhalation of contaminated air to the total marrow dose arepresented in Figure 5.

3) Safety Related Library

All documents collected by local institutions which are relatedt·o nuclear.s.afet.y .. are centrally registered by the help of theIJS DIS program package. Records include the following items:date of publication, language, signature, author, title, placeof publication, publisher, institution, type of document,keywords and remarks. In this way all documents can be foundif only one of the above mentioned items is given to thecomputer. The list of documents is being updated monthly andthe information on the latest documents is distributed to allparties of the Agreement on Exchange of Information. The listof documents presently contains more than 5000 records whichare classified according to the institutions where they arelocated. At present the Safety Documentation Library coverspublications collected by IJS, EIMV, IMK and partially by NEKand RKE.

Page 19

Figure 3: ACUTE EFFECTS FROM EARLY EXPOSURE. LUNG DOSE/In sleverls/, RELEASE FROM HEIGHT H.

~r------...,-------r-----..--------r--------,H = 25mH.. 250mH = SOOmH = 1200m

10" 10so 1ST A NeE CM)

10'

'b-tiD~z:------l":.-----....L..::------L.:------L--------...l

t-'b-

c-

Fi gure 4:: ACUTE EFFECTS FROM EARLY EXPOSURE. D~SE /Sv/TO INDIVIDUAL ORGANS. RELEASE FROM SDOm.

O.-------r--------.-----~-----.-------,

Cl THiRClID(!) Iol Boor... LUNG+ LLI WALLx T MARRClIol

10" 10~o 1ST A NeE CM)10~ .

'l'.... L...- --l.- --I. ...L- ~!!..._ _l

iOz

'b-..c

Figure S: ACUTE EFFECTS FROM EARLi EXPOSURE. CONTRIBUTIONSTO THE T MARROW DOSE/Sv/. RELEASE FROM SDOm.

Cl TOTAL DC! Ee CLClUD... GROUND-t- INHALATI N

lOll 10so 1ST A NeE CM)

~r------r-----==----.-----~-----.-------.,

biO==Z----"'OO:::::'--:-'-:------..L...------L-----L--------...l

..o-

Page 20

Ill. PROBABILISTIC SAFETY ANALYSIS (PSA) PROGRAMS

Probabilistic Safety Analysis (PSA) is defined as theapplication of probabilistic risk analysis to safety decisions.PSA can be of use in various fields of investigationst~dards and regulation development , siting of plants,operator training, risk comParison, design optimization, safetymodifications, operating procedures, test and maintenanceprocedures, safety goals and plant availability.

Probabilistic risk assessments can be performed at differentlevels, depending on the objectives of the study and theavailability of time and manpower. These three discrete levelsare the following:

Level 1: System analysisLevel 2: Systems and containment analysisLevel 3: Systems, containment and consequence analysis.

An analysis of external events may be included in any of theselevels. The external events that are selected for the analysisdepend on the site, but they include such events as plantfires, internal and external floods and earthquakes.

1) Cooperation with IAEA on PSA projects

Yugoslavia has joined the Interregional IAEA project,INT/9/063, Probabilistic Safety Analysis in late 1985. Thisproject, locally coordinated by IJS, is performed jointly bydifferent institutions from the SR of Slovenia and the SR ofCroatia. Six institutions have been engaged altogether. Theanalysis comprise.5--the- evaluation of t.h.e- importance andinteraction of various plant systems and components.identification of accident sequences, deficiencies of design.of operating procedures and of test and maintenance work. Theoverall objective of this programme is to produce aprobabilistic model of the Krsko NPP which can be used by theutility and regulators in both safety and operational analysisof the plant.

The project scope is a level 1 PSA (according to NUREG-2300).Specifically the project envisages:

uncertainties,

the total

sequences,failure modes.of lE category to

- determining the core melt frequency from a comprehensive set ofaccident initiators internal to the plant. including Loss ofOffsite Power.

- reporting dominant accidentimportance ranking of systems and

- reporting specific contributionscore melt frequency.

In parallel. the Reactor Engineering Division at the "J.Stefan"

Page 21

Institute, is also participating in the IAEA coordinatedprogramme on the use of PSA in safety analysis and on thedevelopment of risk criteria for the whole nuclear fuel cycle.The programme of work (Agency research contract No.3941jRB) isthe following:

a) Detailed evaluation and comparison of code results for MainFeedwater System Reliability of the KrSko NPP.

b) Probabilistic estimate of the possibility ofoperation of the NPP after the 105s of theindependent off-site power source introducingimprovements.

furthersecond

certain

The IAEA stimulates exchange of experiences in the area of PSAamong the actively participating member states. Jo~ef StefanInstitute staff regularly participate in IAEA workshops.

Page 22

2) Computer codes, data base and calculation ofrisk, reliability and availability of NPP systems

The current data base uses generic values of component failuresas specified by foreign documentation (like the US ReactorSaf~ty Study WASH 1400), and NREP (National ReliabilityEvaluation Program) NRC documents. It is planned to substitutethese values gradually by the specific operational data fromKr~ko NPP.

Recently, two accident sequences were evaluated in detail,triggered by a steam generator tube rupture and a small leak ofthe reactor coolant. In parallel, analyses on the system levelwere performed for safety and other systems that can mitigateconsequences of the mentioned accidents.

Figure 6 shows the analysed event tree for the SG tube ruptureaccident.

I

I SGTR

i -

RPS SI

SG RVcloses/MSIV

AFW'S PORVs close

PRIMARYCOIl...PNT LONGTERMDEPRESSUR. RECIRC. RECIRC.

II'

~ucr.~'!IIS

cor'! 1'>t!I"t I(CH> •succ.. ss

CM

suec.. ss:

CM

CH

CM

Arv s

6: STEAM GENERATOR TUBE RUPTURE EVENT TREE._-_.. _._-- -----

Page 23

IV. PARTICIPATION IN THE IAEA INCIDENT REPORTING SYSTEM (IRS)AND SAFETY ASSESSMENT OF EVENTS IN NUCLEAR FACILITIES

With the rapidly increasing number of cumulative reactor years,the feedback of experience is becoming a valuable tool forenhancing the safety and reliability of nuclear power plants.Systematic reporting and evaluation of safety-related eventscan lead to the identification of necessary plant modificationsand the development of improved plant procedures. Tofacilitate the exchange of experience, both the Nuclear EnergyAgency of the OECD (OECD/NEA) and the IAEA have establishedIncident Reporting Systems (IRS) to collect and examine eventssubmitted by national organizations. National coordinatorsscreen all events, passing on the most significant. Yugoslaviahas joined IRS, the national coordinator being the RepublicanEnergy Inspectorate of the SR of Slovenia.

In establishing the national reporting system, the RepublicanEnergy Inspectorate is being assisted by the "Jo~ef Stefan"Institute which has developed a computer-aided data base onincidents in nuclear power plants. The data base is organizedon a personal computer. Simple searching and grouping ofcertain types of incidents is possible. The data base wasenlarged by 22 new reports from the NEA/IAEA meeting in Paris,September 1986. Further enlargement of the IRS library isenvisaged as reports on many incidents became available inDecember 1986.

All events are described on forms according to IRS. Inaddition to incident causes, the consequences and correctiveactions are included. Safety assessment and categorization aremade using American National Standards (ANS) and consideringlAEA recommendations. The ANS classification from the FinalSafety Ana Ivs l s Repo r-t havLrig f our c a'te go r i e s c-f ir!l:i,jents j

according to their frequency and probability of radiationexposure to the environment) and the IAEA Guide to a NationalSystem for Collecting, Assessing and Disseminating Informationon Safety Related Events in NPPs which classifies sevencategories of incidents were used. Depending on the categorythe incidents are then selected for reports to regulatorybodies.

Page 24

V. DEVELOPMENT AND MAINTENANCEDETERMINISTIC SAFETY ANALYSES

OF COMPUTER CODES FOR

Reactor Engineering Department staff at the "Jo~ef Stefan"Institute are continuing their research in the field of nuclearenergy with particular attention to the safety of nuclearinstallations and power plants. The basic fields of researchcomprise deterministic and probabilistic safety analysis, heatand mass transfer, two-phase coolant flow, dynamic behaviour ofsystems and plant components during transients, and structuralanalyses of components and constructions.

The work was focused on the analyses of structural, operationaland safety characteristics of nuclear power plants and on theimprovement of computer codes for the performance of theseanalyses. The staff have developed their own codes orinstalled and tested other computer programs used for safetyanalyses and for the reliability and availability assessment ofsystems and equipment. For these purposes, intensive workstarted on the transfer of the RELAP5/MODl code from CDC andIBM environment to VAX, and independently, to transfer testprograms for the performance on the array processor CSPIMAP6420.

Deterministic safety analyses enable the calculation of thermaland hydrodynamic conditions in cases of assumed accidents andtransients. The department staff has performed these analyseson the basis of the models prepared in previous years forassumed accident conditions in the Kr~ko NPP. A large part ofthese efforts was directed towards the analysis of steamgenerator tube plugging impact on the normal and the transientoperation of the Kr~ko NPP..

A large break loss-of-coolant accident was calculated using theconservative evaluation model and the computer codeRELAP4/MOD6. The results of the preliminary analysis showedthe relative rise of the maximum cladding temperature dependingon the plugging rate (Fig. 7). The results also showed whatpeaking factor production is necessary to compensate thecritical conditions caused by plugging (Fig. 8).

Page 25

rFr g. 7: REFLOOD CLRDDING TEMPERATURE OF THE HOT PIN AT

ELEVATION 2.59m (EM DECL 0.4. OF.. 10X l.p •• Fq=2.221

. .1

II

....!I

III

"'1I

..-,.--- -~-- -t-----1-- -- - --~----J200.00 o?~O.OO 2R~.Of) 320.00 36U.00 ~OO.OQ

c;

.. ..: .

. . . . . . . .·······Ir·r··'········· ···:···········1·······;····1 ....·············j·············i·············+············.! j ~ + ···!·············i··············

I ~ ~ i i I I I I :•••••~ •• - •••••.••• :. - ••••••..• - .~_ •• •••••• ..:.. '0 __ - _••.•• _~ ••••••••• _••• : ••••• ••• ~ •••.

! l ' ~ ~

. ... ··f·············!·

NEK-IJS Ft. HOT PIN. oret .4. 0%.10% PLUG•• 95 FQ'...-__-..,... ,..-__-,-__H:..:.., 11

"'"O.I--JL.L_...."b.oo

00

.;0

~

00

.;...~

00

0.. '"~00

.;",ID<n~

",00

.;a..'"::I:~UJ>-

0a: 0

:::>0<no

'"a:0

'"0...

'"'".;'"

Figure 8: REQUIRED PEAKING FRCTOR DECREASEo..,jr--'T""---r----,.----r---,----..__--..__--,

.......,j t...."=:::::::-__

r­e.,j

1.25 2.50 3.75 5.00 6.25PLUGGING LEVEL /7./

7.50 8.75

Page 26

With the help of the RELAP4/MOD6 code a standard problem wasanalysed which is performed under the sponsorship of theInternational Atomic Energy Agency and is based on the PMK-NVHnuclear plant model from Hungary. (An experiment was performedon the PMK NVH facility simulating SB LOCA on the VVER powerplants.) Analysis of the calculated results showed goodagreement with the measured data .

..The division staff has developed two new computer programs:SMUP-05 and MS-01. The former analyses the steady-state modelof the U-tube steam generator with a preheater of theWestinghouse-D4 type, while the latter is used to determine thesteady-state model of the main steamline with turbine controlvalves. The purpose of these models is the analysis anddetermination of new operating conditions in the primary andthe secondary system under various conditions resulting frommodifications or changes to the primary or the secondarysystem. The model was also used to analyse the steam generatortube plugging effects on the parameters of the primary and thesecondary side during normal operation. Fig. 9 shows itseffect on the additional necessary opening of the steam turbinecontrol valves for operation at nominal power.

0.

100

50

o-------- L-- L--.-_....A-~_..l..____ ~

4. 5. 7. 9.4

Ye or PLUGGED TUBES

ng. 91 ADDITIONAL NECESSARY OPENING D'" TURBINE CONTROL VAt.VES No.3 Clnd ..DUE TO PLUGGING or SG TUBES

Page 27

For the purposes of evaluating core capability, the staff hasdeveloped a model for the design calculation of the reactorcore thermal-hydraulics by using the COBRA-III-C comput.er code.Departure from the minimum boiling ratio was analysed dependingon the design power history distributions, and on the type ofcore (KWU,W). KrSko NPP uses Wand KWU fuel elements. Figures10 to 12 show some results of this calculation: mass flow, voidfractions and the minimal DNBR along the different hotsubchannels.

In addition, structural analysis of fuel rods was conductedwith FRAPCON-2 and the thermal-mechanical response studiedduring reactor operation.

Flg~1'e 10: C~RE THERM~HIDRAULIC DESIGN M~DEL,

0 0 0 0 0 COMPARISON ~F DESIGN MASS FLOW.CD CD CD CD ....N N N N N

(\'l (\'l C') (\'l (\'l

lI\ it> it> JIl it>. N N N NN

111 -\I) _lI) NlI) NlI)....",N~ N~

.,.J::I .,.J::I

N' ..... .... ..... N .... N .... N x N x N.... ....... x x .c .c::c .c .c <, <,.c , <, ~ J:J

'co J:JCO ..QCD ..... co ..... CD..c.., ......., ..... (r) ~(") ~(")...... x' x'X N .... N .... N ..-N :x:: N.... Cl UZ ..- :x:: ..- ..-a: Cl u :x:: :x::

~I't..- ..-.LL1 :e-..-. , ::e- I Ir;; :r;; :r::: .

I(r) 1(") w~I • x' x' W.XN UJN UJN :::>N :::>NW 3: 3: 3: 3:

:l<:: :l<::

I"l (r) (r) (r) (r)

N N N N N

N N N N N

co co co co co- - - -N N N N~.oo

1!I (!) • 20.00 1,\0.00 60.00 80.00 100.00 120.00 11,\0.00 160.00+ x AXIAL POSITION (I ne h l

~ WES. model - mean flow in 25 central fuel assembl iesoWES. model - hot thimble subchannelA WES. model - hot typical subchannel+ WES.- KWU. mixed core model - hot thimble subchannelx WES.- KWU. mixed core model - hot typical subchannel

Page 28

"'oo

g g g00 0

I!l C!l •Iqo.oo120.00qo.oo 60.00 80.00 100.00

RXIRL POSITIONl'ncnJ20.00

Figure 11: CORE THERMOHYDRAULIC DESIGN MODEL.COMPARISON OF VOID FRACTIONS.

;;.;

:g0,-----,----.,---.....,----,-----,.----..,..---,..----,

..oo

;;.;

;;o

;;o

..oo

.:11 ...... 0 0Wo Woa: a:0: 0:... ...

..

152.0C

I

II

"!I

..~

r- e-.. .. ...: .:

g g 0 00 0

,; .; .;cb.oO IV.OO 38.00 57.00 76.00 05.00 11'.00 133.00

I!l III . + RXIRL POS1TIONlInchl

Figure 12: CORE THERMOHrDMI:lLIC DES IGill "'ODEL.I g g g C17fU>ARISION OF MINIMAL ONBR.~ ~

.; .;

• ::: :: ..• .... .. .. ..~

.. .. ..J.. .. ...... :z:' "'..;

:z: •"," u .. u ..... ... ... ...X ,I I"'4 .I I , I

Co erO erO Co1D0 "'0 "'0 1D0Z· Z· Z· Z.0" 0" 0'" 0"z: x z: z:I , I I

z: z: z: z:...... ..... ~::: ~:...... VI ..ILl • ... . Jt. Jt.Jt .. ;Z'" x .. x ..

o WL6. model - not thImble subchannelo W[S. model - hot typical subchannel4 wES.- KWU. mIxed core model - hot thImble subchannel+ wlS.- KWU. mIxed core model - hot tYPical subcnannel

Page 29

With RELAP5/MOD1, cycle 19, steam generator tube pluggingeffects were studied for two very important assumed accidents:small-break loss-of-coolant and the rupture of one or moretubes in a steam generator, Some of the results obtained areshown in Figs. 13 to 16.

With this programme the staff has joined the internationalstandard problem ISP-20, which is performed under the auspicesof the OECD and represents the analysis of an actual event inthe Belgian Doel nuclear power plant - a steam generator tuberupture. The effects of 10% plugging were obtained for breaksizes equivalent to 1", 3" and 5" 5G tube pipes.

In the field of transient analysis close cooperation hascontinued with the Elektrotehni~ki fakultet (Faculty ofElectric Engineering.) in Zagreb and with Gesellschaft fuerReaktorsicherheit in Garching. The ALMOD computer code hasbeen improved jointly, so that it is now capable of simulatingnon-symmetric phenomena in multi-loop plants. The modifiedALMOD code was verified with the calculations of startup testsand with the results of measurements in the KrSko NPP.

6"70.LJ620.0n5"70.00

,- 5 tubes break 127 K/h)~- 3 tub~5 break (27 K/h)0- 1 tube break (27 K/h)0- 1 tuh8 break (140 K/h)

-........,.-----,------r------,-----.,1

//

//

//

/,/

././

420.00 470.00 520.00OC'lWNCuMfR T I~I

370.00320.00

ClCl

NPP KRSKO OPERRTIONRL SRFETY DURINGo SGTR RCCIDENT-RELRP5/MODl CRLCULRTION~ r-----.-----,------,..

)fx ~ l'~Cl

~-I_. I

II

r-, Cl I~ClI

a:~ :wr- r

B/~gll0'o~

ClCl I

Page 30

Fig. 14: PARAHETRIC STUDT OF SGTR ACCIDENT DONE WITHftELAPS/HODI CODE

..

1- 5 tubes break (27 K/h)b- 3 tubes break (27 K/h)0- 1 tube break (27 K/h)I!I- 1 tube brellk (140 K/h~

I

t ... n." .... ..... 1ft•• ea.• _._ ....

Fig. 15: ~RR~MElnIC STUDT OF SGTR ACCIDENT DONE W]THREL"lPS/I1ODI CODE

.;

~~~1- 5 tUbes break (27 K/h)~ . A- 3 tubes break (27 K/h).or e- 1 tube break (27 K/h)I CI- 1 tube break (140 K/h) ,

~~ is ,.. 1x ,- I

\_~.. 8w.I.~

'" '.,.. I~:.. <,

! I

~!I

of ........ ."w! 1g:~I . . , . • I . , ~".ac '5.00 so... "'.00 lOCI. 00 lIS. DO ,lto.OO n~.aD 7:10.00 115. oa ......

r I"E ;.1 -ID

Fig. 16: NPP KRSKO RESPONSE ON U-TUBE PLUGGINGFOR SGTR DONE WITH RELRPS/HODl CODE

~,---..- .....-...----r----r---....---""---""----'

g..C1- 5 tubes break (no plugging)0- 5 tubes break (10~ plugging)

!.

.'10.00

.120.00

.'''0.00 160.00

Page 31

The department staff have successfully transferred to VAX theSAP-IV computer program, used for the analyses of various kindsof constructions, components and pipes. It uses the finiteelement method for static and dynamic structural analyses ofelasticity. The program was supplemented by subroutines forspace plotting of the geometry of components and deformations,see Fig.17. First test calculations of the reactor vessel headvent have been run. A test model was made of athree-dimensional, thick-wall pressure vessel of a nuclearreactor.

In cooperation with the University of Erlangen, FRG, theycontinued to develop program for determining the non-steadystate temperatures of fuel pellet axially-symmetric problemswith fractures and melting by a self-adaptive mesh grid usingthe boundary element method.

Figure 11: REACTOR PRESSURE VESSEL, 3-D, SY""lTRICInitial meshDeformed mesh due to Interndl pre5sureDeformations enlarged 200 tlme5

Page 32

VI. TRAINING

In the framework of the Programme of measures for theprotection against ionizing radiation and the programme ofnuclear safety the Reactor Engineering Department at the "Jo~ef

Steian" Institute organized a technical seminar for the membersof the operator licensing board. The seminar was held inPortoro~ from 13 to 15 October 1986.

The Nuclear Training Centre (ICJT) at the "Jo~ef Stefan"Institute organized a training course for professionals workingin the field of nuclear power plant technology, entitled"Safety and Reliability of NPP Operation". The course wasorganized with the assistance of the IAEA and the ArgonneNational Laboratory (USA). Beside foreign lecturers, a numberof domestic experts were invited to give lectures on selectedtopics. The course was conducted in two parts:

- Part 1: Probability Safety Analyses,May 19-30, 1986,

- Part 2: Prevention of Unusual Events,September 15 to October 10, 1986

In 1986, the ICJT of the "J.Stefan" Institute published severaltraining manuals aiming at professional training of operatorsand other staff in a nuclear plant; and the staff in otherorganizations that work in the field of nuclear technology.

VII. ACTIVITIES OF OTHER AUTHORIZED ORGANIZATIONS

1) "MILAN VIDMAR" ELECTRICAL INSTITUTE (EIMV)

The "Milan Vidmar" Electrical Institute has cooperated, asevery year, in the annual refuelling outage of the Kr~ko NPP,where the staff has coordinated the work of other authorizedorganizations and performed QA/QC activities.

Representatives of the institute also participated in sessionsof the technical commission for nuclear safety and cooperatedwith the ASSET mission at analysing events which caused anautomatic reactor trip, and in analysing the problems of planttransformers and auxiliary diesel generators.

The Instituteand to IMK ondocuments.

has quarterlyrelevant new

conveyed information topublications, articles

I,JS, REIand other

Page 33

2) INSTITUTE FOR METAL CONSTRUCTIONS (IMK)

IMK is authorized for the following activities:

QA activities, measurements and inspection of quality andoperational functions including non-destructive analyses and QAof ~supporting metal constructions and metal parts of theequipment, pressure pipes and vessels during construction, testoperation and normal operation of nuclear plants andinstallations.

In 1986, work for the Kr~ko NPP included activities in theframework of refuelling outage, inspection of manufacture andinstallation of the mechanical part of the reactor vessel headvent system, work on Q-list, cooperation in the ASSET projecton leakage of RPV O-ring, and participation in the Portoro~

Meeting (Thermal Shock Issue). The Institute has collecteddocumentation and evidence of safety in nuclear plants andinstallations, which is described in IMK reports. The IMKexpert cooperated in the SKJV commission and cooperated in thegroup for updating regulations concerning nuclear safety.

3) IB ELEKTROPROJEKT (IBE) - Architect/Engineer

IBE is authorized for the following activities:

- preparation of investment and technical documentation forNPPs,

- construction management of NPPs and nuclear installations,inspection during construction, preoperational tests, testoperation, including organization of QA for NPPs andinstallations during construction,

- inspection of investment and technical documentation for NPPsand installations,

- preparation of site documentation.

For the Kr~ko NPP the IB Elektroprojekt participated inmodifying and upgrading different systems and components. Thestaff has cooperated in the study of disposal of low and mediumlevel radioactive wastes.

Page 34

VIII. INTERNATIONAL CONTACTS, COOPERATIONAND EXCHANGE OF INFORMATION

Contacts with the IAEA

..All Slovene organizations working in the nuclear field haveclose contacts with IAEA, especially in the field of nuclearsafety. This cooperation is also emphasized by lAEA technicalassistance in developing and training for independent activityin the field of nuclear safety.

Information on IAEA activities is distributed in Yugoslavia bythe Federal Energy and Industry Committee in Beograd (SKEI) andthrough the Republican Institution for InternationalScientific, Technical and Cultural Cooperation (ZAMTES). At aworking level, the exchange of information is also going onthrough individual Yugoslav participants in various Agencyprojects and programmes.

Contacts with the lAEA include cooperationparticipation in conferences and workshops,expert missions and technical assistance.

Contacts with NRC

in projects,scholarships,

In September 1985 USNRC and SKEI from Belgrade signed an"Agreement on Information Exchange and Cooperation Related toNuclear Safety between the Yugoslav Federal Energy and IndustryCommittee and the US NRC". This agreement extended contactsbetween USNRC and IJS which were previously related mostly tot.he safe startt~p and cpexa:ticn.·----o.f ---t.he:~Kr.Ako .NEP.

Based on the Agreement signed between USNRCsuggested that the "Jo~ef Stefan" Institutethrough NUKLIN association the execution ofall who participate in the Yugoslav nuclearneed information on NPP safety.

and SKEI it wasshould coordinatethe Agreement forprogramme and who

Compilation, ordering, and classification of NRC documents wasfocused on documents related to computer safety analyses,operating events, source terms, PSA, releases into theenvironment, problems concerning steam generators and selectednews.

In 1986 the IJS has continued with a systematic classificationand distribution of the compiled documentation. As a result ofthis work a systematic list of safety related documents at the"J.Stefan" Institute, the "Milan Vidmar" "Electrical Instituteand "The Institute for Metal Constructions" was sent to partiesof the Agreement and to some other interested workorganizations.

Page 35

Professional contacts which have been going on for a number ofyears are indispensible in order to disseminate currentinformation concerning nuclear safety. The present scope ofcooperation, though small, still presents a fair basis forcontinuation, extension and deepening.

Good information is one of the basic conditions for safeoperation of our nuclear power plant, so only an adequateinformation system that will include all participants in thenuclear program will give satisfactory results.

Other international contacts are held with Gesselschaft fuerReaktorsicherheit (Garching, FRG) with whom we cooperate indeveloping computer programs for transient analysis. TheReactor community atIJS maintains permanent contacts with thefollowing foreign software centres: NEA Data Bank in Paris,National Energy Software Center in Argonne (USA), RadiationShielding Information Center in Oak Ridge (USA) and with theIAEA Nuclear Data Section. In the framework of thiscooperation, several programs and data bases have beenexchanged.