Simula ion o an acciden in condi ions o cooling
sys em mal unc ion and en ila ion sys em ailu e in
he spen uel s o age pool o he mul ipu pose as
esea ch eac o *
Ana oly A. Kazan se 1, Olga V. Supo ni skaya1, E geniya A. I ano a1, Na aliya E. As akho a1
1 IPPE JSC, 1 Bonda enko Sq., 249033 Obninsk, Kaluga eg., Russia
Co esponding au ho : Ana oly A. Kazan se ([email p o ec ed])
Academic edi o : Geo gy Tikhomi o ♦ Recei ed 19 June 2025 ♦ Accep ed 24 Sep embe 2025 ♦ Published 9 Oc obe 2025
Ci a ion: Kazan se AA, Supo ni skaya OV, I ano a EA, As akho a NE (2025) Simula ion o an acciden in condi ions o cooling
sys em mal unc ion and en ila ion sys em ailu e in he spen uel s o age pool o he mul ipu pose as esea ch eac o . Nuclea
Ene gy and Technology 11(3): 219–223. h ps://doi.o g/10.3897/nuce .11.173061
Abs ac
The pape p esen s he esul s o he compu a ional analysis o an acciden scena io in he spen uel s o age pool o he
mul ipu pose as esea ch eac o . The simul aneous ailu e o he spen uel cooling sys em and he en ila ion sys-
ems is being conside ed as beyond design basis acciden (BDBA) condi ions. The compu a ional analysis o he BDBA
scena io was pe o med wi h he compu e p og am KUPOL-MT designed o simula e he mohyd aulic p ocesses in
he oom a mosphe e o he eac o acili y con ainmen sys ems. Du ing he compu a ional analysis wi h KUPOL-
MT, a nodaliza ion scheme o he spen uel s o age pool ooms was de eloped. The scheduled loading o spen uel
assemblies in he s o age pool was conside ed in he acciden simula ion, oge he wi h he eme gency unloading o he
en i e eac o co e. I was shown ha he wa e empe a u e in he spen uel s o age pool emained below he boiling
poin and he e was no iola ion o he in eg i y o uel cladding o h ee days a e he s a o he acciden . As he uel
cladding did no collapse, he e we e no adia ion consequences in he conside ed acciden scena io. The calcula ion
esul s demons a ed insigni ican hyd ogen s a i ica ion in he oom abo e he spen uel s o age pool. I was shown
ha hyd ogen con en did no exceed he maximum concen a ion limi o h ee days a e he s a o he BDBA.
Keywo ds
Spen uel s o age pool, spen uel assembly, Mul ipu pose Fas Resea ch Reac o (MBIR), compu e p og am KUPOL-
MT, beyond he design basis acciden (BDBA), uel elemen , hyd ogen
In oduc ion
Nuclea esea ch acili ies (NRF) di e om nuclea
powe plan s (NPP) in ha hey a e in ended no only o
gene a e hea and elec ici y bu also o be used o e-
sea ch ac i i ies. The Mul ipu pose Fas Resea ch Reac o
(MBIR) is designed o es ma e ials and equipmen o
Gene a ion IV eac o s. The design he mal powe o he
MBIR is 150 MW (Technical cha ac e is ics o MBIR).
The cons uc ion o he MBIR eac o a he si e o NIIAR
JSC in Dimi o g ad, he Ulyano sk Region, is expec ed
o ensu e he con inui y o he expe imen al and esea ch
Copy igh Kazan se AA e al. This is an open access a icle dis ibu ed unde he e ms o he C ea i e Commons A ibu ion License (CC-BY 4.0), which pe mi s
un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal au ho and sou ce a e c edi ed.
Nuclea Ene gy and Technology 11(3): 219–223
DOI 10.3897/nuce .11.173061
Resea ch A icle
* Russian ex published: Iz es iya uzo . Yade naya Ene ge ika (ISSN 0204-3327), 2025, n. 2, pp. 142–152.
Kazan se AA e al.: Simula ion o an acciden in condi ions o cooling sys em mal unc ion220
p og ams implemen ed a he BOR-60 esea ch eac o
now in he p ocess o decommissioning.
The spen uel s o age pool (SFSP) is designed o
sa e long- e m s o age and cooling o spen uel. The
SFSP has an impo an ole in ensu ing he eac o
sa e y a he no mal ope a ion (NO), e ueling and u -
he long- e m uel s o age s ages. The egula o y doc-
umen s o he NRF SFSPs a e NP-061-05 (NP-061-
05, 2005) and NP-049-17 (NP-049-17, 2017).
The pape in es iga es he consequences o a beyond
design basis acciden (BDBA), in which a hea emo al
ailu e in he p ocess o he SNF s o age and anspo a-
ion is conside ed an ini ia ing e en (as shown in he Ap-
pendix o NP-061-05 (NP-061-05, 2005). Nonope a ion
o he en ila ion sys em is conside ed a ailu e.
Fuel assembly and spen uel
s o age pool design
The MBIR SFSP comp ises h ee s o age compa men s
in he o m o conc e e boxes wi h a s ainless s eel lining.
Two s o age compa men s a e designed o scheduled FA
s o age. The wo s o age compa men s p o ide edun-
dancy in case one o hem ails. The hi d compa men
is designed o eme gency unloading o he ull eac o
co e. Fig. 1 p esen s he layou o he MBIR SFSP ooms.
Each compa men is sec ionalized o he FA accom-
moda ion. Reliable p o ec ion o pe sonnel agains ioniz-
ing adia ion is p o ided by he wa e le el abo e he FAs
o abou 6.5 m. And he wa e le el om he compa men
bo om is 9.1 m.
The MBIR NRF is in ended o eplace he BOR-60 e-
sea ch eac o and has he same uel elemen design wi h
a diame e o 6 mm and he cladding hickness o 0.3 mm
(Zhemko I.Yu, 2014). P io o he loading, spen uel
is cooled in he in-co e s o age (on he co e pe iphe y)
o wo cycles o 100 days (Technical cha ac e is ics o
MBIR) and 30 days o e ueling. P e-unloading 230-day
SFA cooling in he in-co e s o age leads o a subs an ial de-
c ease in dose loads in he spen uel e ueling and s o age
p ocess and o a dec ease in he SFSP wa e empe a u e.
To emo e esidual hea , he SFSP has a cooling sys-
em which comp ises hea exchange s, pumps, pipelines,
and al es.
The olume o he oom abo e he SFSP is 1507 m3.
The olumes o he wo SFA s o age compa men s a e
384.5 m3, and he olume o he hi d compa men is
370 m3. In he slo ed loo slab o he SFSP compa -
men s he e a e ha ches which a e opened p io o he
FA anspo a ion om he ooms abo e he SFSP. The
conc e e wall lining and he slo ed loo slabs a e made
o s eel.
In he p ocess o no mal ope a ion (NO), he en ila ion
sys em emo es ai om he SFSP space abo e he wa e
(unde he slo ed slab) and om he SFSP gas space ( he
ooms abo e he SFSP). Fo he NO mode, he ollow-
ing ai pa ame e s a e main ained in he oom abo e he
SFSP: a p essu e o 1 a m, a empe a u e o +8 o +30 °C,
and a ela i e ai humidi y o up o 75%.
The oom abo e he SFSP is connec ed wi h he oom
o he SFSP inclined ele a o (IH). The inclined ele a o
is used o anspo FAs. The ai pa ame e s in he NO mode
in he IH oom a e he same as in he oom abo e SFSP.
The SFSP ooms a e p o ided wi h he main and he
s andby en ila ion sys ems.
Acciden wi h he SFSP cooling
ailu e
A beyond-design-basis acciden is conside ed in ol ing he
SNF cooling ailu e in he SFSP compa men s which leads
o he ollowing MBIR sys ems becoming inope a i e:
• en ila ion sys em (SFSP compa men s, oom
abo e he SFSP, IH oom);
• s andby en ila ion sys ems (SFSP compa men s,
oom abo e he SFSP, IH oom).
Figu e 1. Layou o he MBIR SFSP ooms.
Nuclea Ene gy and Technology 11(3): 219–223 221
No en ila ion ai duc s a e shu o in he e en he
en ila ion sys em ails.
To es ima e he maximum haza dous consequences
o an acciden , i is assumed ha ope a ing pe sonnel o
ail o ake measu es o manage he acciden o 72 hou s
( h ee days) as de ined in NP-001-15 (NP-001-15, 2016)
and NP-033-11 (NP-033-11).
In he e en o such acciden , namely, when he SFSP’s
main cooling sys em ails, esidual hea is emo ed om
he SFSP su ace. The wa e in he SFSP compa men s
s a s o hea up, and he wa e le el in he SFSP compa -
men s dec eases due o e apo a ion. O e ime, he wa e
empe a u es in he SFSP and in he gas space abo e he
SFSP su ace equalize.
In no mal ope a ing condi ions o he SFSP, hyd ogen
is o med con inuously in he SFSP compa men s as a
esul o he wa e adiolysis due o pho on abso p ion
om SFAs, SFSPS assemblies and side sc een assemblies
s o ed in he cooling pool wa e . Radioly ic hyd ogen is
eleased in o he gas space abo e he SFSP su ace. In
he e en o an acciden , due o he con inuous elease o
hyd ogen and no o ced en ila ion, he concen a ion o
hyd ogen in he SFSP gas space s a s o inc ease.
Compu a ional acciden
simula ion
The combina ion o he p ocesses aking place in he
MBIR SFSP in he cou se o he acciden unde consid-
e a ion in ol ing he SFSP cooling ailu e is desc ibed
by a se o models implemen ed in he KUPOL-MT con-
ainmen code, e sion 1.0 ( he KUPOL-MT he eina e )
(Kazan se e al. 2019). The KUPOL-MT is designed o
calcula e he pa ame e s wi hin he s eam/ai con ainmen
a mosphe e a he NPP wi h VVER ype eac o . The code
calcula es he ollowing alues (Kazan se e al. 2019):
• p essu e his o y in each oom and p essu e di e -
ences his o y be ween ooms;
• empe a u e his o y in all ooms;
• ansien empe a u e dis ibu ion in s uc u es and
equipmen ins alled in each oom;
• componen concen a ion his o y o in each oom;
• wa e pool le el his o y in ooms.
The calcula ion akes in o accoun he e ec s o an-
sien hea and mass anspo o he gas-d ople mix u e
in he con ainmen ooms, aking in o accoun he e ec s
om na u al con ec ion, olume and su ace condensa-
ion o s eam in he p esence o noncondensable gases,
and hea and mass exchange o he oom a mosphe e wi h
wa e in he sumps.
The KUPOL-MT code uses a lumped pa ame e model.
The design da a o he SFSP compa men s, he ooms
abo e he SFSP and he inclined ele a o oom, which
is connec ed wi h he space o he oom abo e he SFSP
h ough he en ila ion sys em, a e used as inpu da a o
he MBIR SFSP compu a ional model cons uc ion using
he KUPOL-MT code.
The compu a ional model used o he SFSP BDBA
simula ion in he KUPOL-MT code is p esen ed in Fig. 2.
The compu a ional model comp ises en in e nal design
olumes in e connec ed ia wen y wo junc ions. Com-
pu a ional olume 1 simula es he inclined ele a o oom.
Compu a ional olumes 2, 3 and 4 simula e he SFSP
s o age compa men s 1, 2 and 3. The oom abo e he
SFSP is b oken down in o wo axial le els and comp ises
compu a ional olumes 5 h ough 10.
Fuel assemblies in he SFSP compa men s a e sim-
ula ed by cylind ical mul ilaye hea s uc u es (walls).
The loo and walls o he SFSP compa men s a e also
simula ed by la hea s uc u es. The FA a e hea gene -
a ion is assumed o be simila o compa men s 1 and 2
and amoun o 20.7 kW based on he scheduled SFA un-
loading in o he SFSP a e en-yea e ueling mode. The
a e hea gene a ion in compa men 3 is aken as equal o
155 kW and co esponds o 30-day SFA cooling.
The a es o adioly ic hyd ogen gene a ion in each
SFSP compa men a e calcula ed based on he adio-
chemical yield o hyd ogen depending on he FA o al
he mal powe in he compa men . The o al a e o hy-
d ogen gene a ion is 1.87·10-5 kg/s. The empe a u e o
he hyd ogen eleased om he SFSP wa e is aken as
equal o he wa e empe a u e in each SFSP compa -
men . The ini ial wa e empe a u e is 40 °C.
F om he space abo e he SFSP wa e and h ough
b eaks in he slo ed loo slab abo e he SFA ecep acles,
he gas mix u e en e s he space in he oom abo e he
SFSP. The ex en o which he slo ed loo slab is leak-
igh , de e mined as he a io o he slo ed loo slab low
a ea o he o al slo ed loo slab a ea abo e he SFSP
compa men s, is es ima ed as 10%.
Resul s o compu a ional simula ion
using he KUPOL-MT code
The po en ial isk o adioac i i y elease om he cool-
ing pool leads o he need o main ain he SFSP a mo-
sphe e pa ame e s. In he e en o an acciden wi h he
SNF cooling ailu e in he SFSP wa e and he SFSP oom
en ila ion ailu e, he pa ame e s o moni o ing in he
p ocess o compu a ional simula ion a e
Figu e 2. Compu a ional model o he SFSP ooms o he
KUPOL-MT code.
Kazan se AA e al.: Simula ion o an acciden in condi ions o cooling sys em mal unc ion222
• uel cladding empe a u e in he SFSP compa -
men s;
• wa e empe a u e in he SFSP compa men s;
• wa e le el in he SFSP compa men s;
• hyd ogen concen a ion in he space abo e wa e in
he SFSP compa men s and in he SFSP oom.
Figs 3–6 show he esul s o he BDBA compu a ional
simula ion using he KUPOL-MT code (Kazan se e al.
2019). The calcula ion ime is 300000 s (~ 3 days).
The wa e empe a u e in he SFSP compa men s
is shown in Fig. 3. The wa e empe a u e in he SFSP
compa men s 1 and 2 eaches 49 and 51 °С espec i ely.
Compa men 3 wi h eme gency unloading has he wa e
empe a u e eaching 80.6 °C. The e is no wa e boiling in
he SFSP compa men s.
The uel cladding empe a u e in he SFSP compa -
men s 1, 2 and 3 is shown in Fig. 4. The uel cladding
empe a u e in he SFSP compa men 3 eaches a maxi-
mum o 85 °С, and he uel cladding empe a u es each
52 °С (compa men 1) and 49.4 °С (compa men 2)
(Fig. 4), espec i ely.
Fig. 5 shows he a mosphe ic empe a u e in he h ee
SFSP compa men s. The a mosphe ic empe a u e in
compa men 3 eaches 77 °С (see Fig. 5). The a mo-
sphe ic empe a u e in compa men s 1 and 2 (boxes 2
and 3) app oaches 82 and 72 °С espec i ely.
The hyd ogen concen a ion in he SFSP compa men
gas space is shown in Fig. 6. Calcula ions show ha he
hyd ogen concen a ion in he SFSP compa men s does
no exceed 2 ol.%. The maximum hyd ogen concen a-
ions in he SFSP compa men s each 1.22 ol.% in com-
pa men 1, 1.18 ol.% in compa men 2, and 1.03 ol.% in
compa men 3 (see Fig. 6). A e i eaches he maximum
alues, he hyd ogen concen a ion d ops due o dilu ion
wi h sa u a ed s eam, he pa ial p essu e o which on he
sa u a ion line inc eases apidly as he empe a u e g ows.
The maximum hyd ogen concen a ion alues a e less
han 4.1 ol.%, he smalles concen a ion equi ed o he
hyd ogen igni ion in a mix u e wi h ai (Gambu g e al.
1989; Gel and e al. 2008).
The hyd ogen concen a ion change in he oom space
abo e he SFSP is shown in Fig. 6. The a angemen o com-
pu a ional olumes is shown in Fig. 2. I can be seen ha
he e is no no iceable s a i ica ion o hyd ogen in he oom
abo e he SFSP. The maximum concen a ion o hyd ogen in
all compu a ional olumes o he oom abo e he SFSP does
no exceed 1.0 ol.% (see Fig. 6). The hyd ogen concen a-
ion s a s o all hen due o being dilu ed wi h s eam as he
pa ial s eam p essu e g ows wi h he empe a u e g ow in
he oom abo e he SFSP and dec eases o 0.6 ol.%. The
hyd ogen concen a ion in he SFSP compa men is some
0.2 ol.% highe han in he oom abo e he SFSP.
Conclusions
The pape p esen s he esul s o he compu a ional sim-
ula ion using he KUPOL-MT code o an acciden in-
ol ing an i adia ed uel cooling ailu e in he spen uel
s o age pool accompanied by an addi ional ailu e in he
Figu e 3. Wa e empe a u e in h ee SFSP compa men s.
Figu e 4. Fuel cladding empe a u e in he SFSP compa men s.
Figu e 5. Tempe a u e in he SFSP compa men gas space.
Figu e 6. Hyd ogen concen a ion in he SFSP compa men s.
Nuclea Ene gy and Technology 11(3): 219–223 223
MBIR eac o . The addi ional ailu es assumed include
ailu es o he main and s andby en ila ion sys ems in he
SFSP compa men s, and a en ila ion ailu e in he oom
abo e he SFSP and in he SFSP inclined ele a o oom.
The acciden was simula ed o he op ion wi h he SFSP
compa men loading, including scheduled SFA loading
in o compa men s 1 and 2 and eme gency unloading o
he en i e eac o co e in o compa men 3.
The esul s o he compu a ional acciden simula ion
show ha , in he cou se o h ee days (design simula ion
ime), he wa e empe a u e in all SFSP compa men s e-
mains below he boiling poin , and he uel cladding em-
pe a u e does no exceed 85 °С. The e o e, he e is no uel
cladding ailu e. The e a e no adiological consequences
in he conside ed beyond design basis acciden scena io i
he uel cladding emains in ac .
Re e ences
Gambu g DYu, Semeno VP, Dubo kin NF, Smi no a LN (1989)
Hyd ogen. P ope ies, p oduc ion, s o age, anspo a ion, applica-
ion. Handbook. Moscow, Khimiya Publ., 672 pp. [ISBN: 5-7245-
0034-5] [in Russian]
Gel and BE, Popo OE, Chai ano BB (2008) Hyd ogen: pa am-
e e s o combus ion and explosion. Moscow, FIZMATLIT Publ.,
2008, 288 pp. [ISBN: 988-5-9221-0898-0] [in Russian]
Kazan se AA, Popo a TV, Supo ni skaya OV, Se gee VV, Bulynin
VD, Semashko SE, K ylo YuV (2019) Simula ing he Ope a ion
o he Je -Vo ex Condense Used in he VVER-440 Reac o Plan ’s
Con inemen Sys em. The mal Enginee ing 66(6): 433–439. h ps://
doi.o g/10.1134/S0040601519060041
NP-001-15 (2016) Gene al P o isions o Ensu ing Sa e y o Nucle-
a Powe Plan s. Fede al En i onmen al, Indus ial and Nuclea Su-
pe ision Se ice. Moscow, 2016. h ps://docs.secn s. u/documen s/
nps/%D0%9D%D0%9F-001-15/%D0%9D%D0%9F-001-15_OCR.
pd [accessed Dec. 09, 2024] [in Russian]
NP-033-11 (2021) Gene al P o isions o Ensu ing Sa e y o
Nuclea Resea ch Facili ies. Fede al En i onmen al, Indus ial
and Nuclea Supe ision Se ice. h ps://megano m. u/In-
dex2/1/4293842/4293842085.h m [accessed Dec. 09, 2024] [in Russian]
NP-049-17 (2017) Requi emen s o he Con en o he Sa e y Anal-
ysis Repo o Nuclea Resea ch Facili ies. Fede al En i onmen al,
Indus ial and Nuclea Supe ision Se ice. Moscow, 63 pp. h ps://
megano m. u/Da a2/1/4293739/4293739676.pd [accessed Dec. 09,
2024] [in Russian]
NP-061-05 (2005) Sa e y Rules o S o age and T anspo a ion o
Nuclea Fuel a Nuclea Facili ies. Fede al En i onmen al, Indus-
ial and Nuclea Supe ision Se ice. Moscow, 12 pp. h ps://me-
gano m. u/Index2/1/4293850/4293850800.h m [accessed No . 07,
2024] [in Russian]
Technical cha ac e is ics o MBIR (2024) Technical cha ac e is ics
o MBIR. h ps://mbi - osa om. u/ eac o / [accessed No . 07, 2024]
[in Russian]
Zhemko IYu (2014) Scien i ic and me hodological suppo o he
ope a ion o a as neu on esea ch eac o . Synopsis o a hesis o
D . Sci. (Enginee ing) 05.14.03. Dimi o g ad, 41 pp. h p://n cki.
u/ iles/pd /1455530301.pd [accessed Dec. 09, 2024] [in Russian]
