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Author:Vierimaa, Juho
Title:Vakavan reaktorionnettomuuden säteilytasolaskenta APROS-ohjelmistossa
Severe accident radiation calculation in APROS -software
Publication type:Master's thesis
Publication year:2009
Pages:74      Language:   fin
Department/School:Teknillisen fysiikan laitos
Main subject:Ydin- ja energiatekniikka   (Tfy-56)
Supervisor:Salomaa, Rainer
Instructor:Henttonen, Tommi
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark T80     | Archive
Keywords:radiation level calculation
severe accident
nuclear power
simulaattori
säteilytasolaskenta
vakava reaktorionnettomuus
ydinvoima
ydinvoimalaitos
Abstract (eng): Since the end of the 1990's, a considerable amount of development work has been done in order to develope external severe accident calculation models (so called APROS SA calculation) for advanced process simulator APROS.
This development work has come to the point where models describing severe accident phenomena, such as core melting and fission product transport, have been implemented.
In this thesis, a new radiation level calculation model has been added to APROS SA.
With this new model radiation levels in the plant area can be calculated during severe accident simulation.
Radiation level calculation can be divided into two parts, activity calculation and dose rate calculation.

In the activity calculation, the total activities of the most important radioactive nuclides are calculated during the simulation.
For the activity calculation, 20 most important nuclides have been selected and their decay chains have been simplified.
The activities can be calculated from the analytical solutions of the differential equation of these simplified decay chains.

Two APROS calculation modules have been made for the dose rate calculation: Radiation Calculation and Gamma Calculation,.
The function of these modules is to produce data about the activity inside the process components and the containment nodes.
This data is further processed and converted to a dose rate calculated in the point which is defined in the module.
Radiation calculation has been implemented in such a way, that user has to give dose rate coefficients which convert activities in the volume to dose rates in the point where dose rates are calculated.
Gamma Calculation module is developed for dose rate calculations in the simple geometries and the dose rates are computed using gamma constants.

As a test case, a severe accident case was conducted with Loviisa NPP's training simulators containment model.
APROS SA fission product transportation model and Radiation Calculation modules were tested and results were encouraging.
Comparison was made to results calculated by another program, and the results were similar.

The training simulator of Loviisa NPP will be renewed in coming years.
The process models of the simulator will be calculated with APROS simulation software.
The severe accident calculation, APROS SA, including the radiation level calculation developed in this work, will be a part of the new training simulator.
With these models severe accidents can be simulated and radiation levels can be calculated during simulations in e.g. operator training sessions.
Abstract (fin): APROS prosessisimulointiohjelmistolle suunniteltua, vakavien reaktorionnettomuuksien simulointiin tarkoitettua ulkoista laskentaohjelmistoa, APROS SA:ta, on kehitetty Fortumin ja VTT:n toimesta 1990-luvun loppupuolelta lähtien.
Kehitystyössä on päästy siihen pisteeseen, että vakavan onnettomuuden eri ilmiöitä kuvaavat osamallit on pääsääntöisesti saatu valmiiksi.
APROS SA:han on lisätty tässä diplomityössä säteilytasolaskenta, jonka avulla simuloinnin aikana voidaan laskea laitosalueen säteilytasoja.
Säteilytasolaskennan toteutus voidaan jakaa kahteen osaan, eli aktiivisuuslaskentaan ja annosnopeuslaskentaan.

Aktiivisuuslaskennassa lasketaan säteilyn kannalta tärkeiden nuklidien kokonaisaktiivisuuksia koko simuloinnin ajan.
Aktiivisuuslaskentaan on valittu 20 nuklidia, joiden hajoamisketjuja on yksinkertaistettu.
Aktiivisuus saadaan laskettua näiden yksinkertaistettujen hajoamisketjujen differentiaaliyhtälöiden analyyttisista ratkaisuista.
Annosnopeuslaskentaa varten on tehty kaksi moduulia: Radiation Calculation ja Gamma Calculation.
Moduulien tehtävänä on tuottaa tietoa suojarakennuksessa ja prosessikomponenttien sisällä olevasta aktiivisuudesta ja tämän aktiivisuuden aiheuttamasta annosnopeudesta.

Annosnopeusmoduuli Radiation Calculation on toteutettu siten, että käyttäjä joutuu itse laskemaan nuklidikohtaiset annosnopeuskertoimet, joiden avulla tietyn tilavuuden aktiivisuus muutetaan annosnopeudeksi moduulin määrittämässä pisteessä.
Annosnopeusmoduuli Gamma Calculation laskee puolestaan pinta- ja tilavuuslähteen aktiivisuuden aiheuttamaa annosnopeutta.
Laskennan tuloksena saadaan tietoa noodien fissiotuotemassoista ja -massaosuuksista, aktiivisuudesta sekä tärkeimpänä annosnopeus.

Säteilytasolaskennan toimivuuden testaamiseksi ajettiin Loviisan ydinvoimalaitoksen koulutussimulaattorin suojarakennusmallilla vakavan reaktorionnettomuuden simulaatio.
Tässä yhteydessä testattiin APROS SA:n fissiotuotemallin ja Radiation Calculation - moduulin toimimista.
Analyysin tulokset olivat rohkaisevia ja vertailu toisen laskentamallin kanssa antoi yhteneviä ja loogisia tuloksia.
Säteilytasolaskentaa tullaan jatkossa käyttämään Loviisan koulutussimulaattorilla operaattoreiden vakavien onnettomuuksien koulutuksessa ja valmiusharjoitusten yhteydessä.
ED:2009-11-25
INSSI record number: 38616
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