Design-Specific Common Position
CP-HPR1000WG-02 FOR PUBLIC USE
Date: August 2022
Validity: until next update or archiving
Version: 1

Multinational Design Evaluation Programme (MDEP)
Design-Specific Common Position
CP-HPR1000WG-02

HPR1000 Working Group

Common Position of the IRWST Strainer
Performance and Downstream Effects ofHPR1000 after LOCA

Participation
Regulators involved in the MDEP working group
discussions:

ARN (Argentina), NNSA(China), NNR (South Africa),
ONR (UK)

Regulators which support the present common
position:

ARN (Argentina), NNSA(China), NNR (South Africa),
ONR (UK)

Regulators with no objection:

noneRegulators which disagree:noneDesign-Specific Common Position
CP-HPR1000WG-02 FOR PUBLIC USE
Date: August 2022
Validity: until next update or archiving
Version: 1

Multinational Design Evaluation Programme
HPR1000 Working GroupCOMMON POSITION OF THE IRWST STRAINER PERFORMANCEAND DOWNSTREAM EFFECTS OF HPR1000 AFTER LOCA
1Purpose

MDEP is a multilateral nuclear safety cooperation mechanism involving thenuclear safety regulatory agencies of major international nuclear energy countries
and aiming at promoting the coordination of safety requirements and regulatorypractices among countries in the design, construction, and commissioning of new
nuclear power plants.
MDEP HPR1000 working group was established in September 2017 at the initiativeof China. The editing of “Common Position of The IRWST Strainer Performance andDownstream Effects of HPR1000 after LOCA”, as a response to the work plan of theSteering Technical Committee (STC) for reaching MDEP consensus, is an importanttask of this working group. The common position aims at:

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Improving the knowledge and understanding of the issues related to IRWSTstrainer among the member states of the MDEP HPR1000 working group(Argentina, China, South Africa and The United Kingdom).

2Determining the regulatory expectations regarding the IRWST strainer
performance and downstream effects of HPR1000 after LOCA.

3

Reducing the risk of excessive blockage of the IRWST strainer and ensuring corecooling.

BackgroundFor some PWR nuclear power plants, the containment sump strainer is speciallydesigned to ensure the safety functions of emergency core cooling and containment
heat removal in the long-term after LOCA. Debris, foreign materials and other debris
generated during the LOCA process or already existing in the containment before theaccident are transported to the containment sump strainer and reactor core.
Debris could also be generated in the main steam line break accident of PWR,
however, it is enveloped by the debris source items of LOCA and thus the debris
source items of LOCA are detailed in this common position.
The following potential safety risks during the long-term recirculation coolingphase of PWR are prevalent, or exist:
1

The debris transported to the containment sump strainer will cause excessive
blockage on the strainer and affect the operability of ECCS and containment
heat removal system, i.e. reduce the net positive suction head (NPSH) at theinlet of pumps.

2

The adverse effects on downstream devices including pumps, valves, andreactor core, such as blockage, wear, or obstruction of heat transfer.
2

Design-Specific Common Position
CP-HPR1000WG-02 FOR PUBLIC USE
Date: August 2022
Validity: until next update or archiving
Version: 1

The early design of the PWR is usually evaluated and analysed based on theassumption that the blockage rate of the sump strainer is 50%. Due to the designers’
insufficient understanding of the potential safety risks in the long-term recirculation
cooling phase after LOCA, the problem of excessive blockage of sump strainer in thedesign of the emergency core cooling system and the containment heat removal
system has been gradually exposed in the operational phase later operation of PWR.
Since the serious consequences of this problem to the safety of nuclear power plants
were realised, the problem of containment sump strainer blockage has become acommon concern in the international nuclear power community.
3. Discussions
Regarding the problem of the internal refuelling water storage tank (IRWST）
strainer blockage, the use of relevant in-containment materials which can generate
the debris are restricted in order to reduce the amount of debris reaching the IRWST
strainer and the reactor core, as well as improving the filtration capacity of the IRWSTstrainer. The performance of the IRWST strainer is evaluated to ensure the safetyfunction of long-term core cooling. This is also the international common practice.
HPR1000 has taken the following measures to reduce the risk of excessive
blockage of the IRWST strainer and loss of long-term core cooling：
1For the aspect of the use of relevant in-containment materials that cangenerate debris source items, HPR1000 restricts the generation and transport ofdebris through the selection of thermal insulation materials in the containment,such as using RMI as thermal insulation material. Certified coatings are used toreduce the amount of debris generated by jet impact and in accident
environmental conditions after LOCA. The generation of chemical deposits is
reduced in the design such as restricting the use of aluminum-containing
materials. A high level of cleanliness in the containment is maintained bymanagement to limit the amount of potential debris. Through the abovemeasures and methods, as well as the intercepting measures on the debris
transport path, the excessive blockage of the IRWST strainer caused by thedebris generated after LOCA can be prevented, and the adverse effect on thelong-term core cooling can be reduced.

2For the aspect of evaluating the performance of the IRWST strainer to fulfil
relevant nuclear safety function, the challenges caused by debris to the IRWST
strainer and long-term core cooling cannot be completely eliminated despite
the above-mentioned control of relevant materials that can produce debris.
The fluid ejected from the breach can wash away the debris, and some debris
will enter the IRWST. The accumulation of the debris and the chemical deposits
on the IRWST strainer will reduce the effective net positive suction head (NPSH)
of the ECCS pump. The debris passing through the strainer will adversely affectthe functions of downstream pumps, valves and other equipment. The
accumulation of the debris in the core active area may adversely affect thelong-term core cooling. The designer of HPR1000 is expected to demonstratethat the performance of equipment and the capacity of core cooling can beensured via experiments and/or analytic methods.
3Design-Specific Common Position
CP-HPR1000WG-02 FOR PUBLIC USE
Date: August 2022
Validity: until next update or archiving
Version: 1

a Upstream Analysis
Based on the failure characteristics of the in-containment debris sources,
combined with the consideration of different positions of breach, the debris iscategorised, counted and analysed. The categories, compositions, characteristics
and total amount of the debris reaching the IRWST strainer are acquired. Theenveloping debris amount is retained as the input for the following analytic
calculations and experiments.
b Head Loss Test of Strainer
The head loss test of strainer should be carried out on the proper scaled prototypeof IRWST strainer. Through the head loss test, combined with the calculation results ofthe flow path resistance of the confluence groove, it is verified whether the head loss
caused by the accumulation of debris on the strainer meets the design limit of thesystem function.
c Chemical Effects Test
The chemical effects test should be carried out to evaluate the impact of new
chemical product generated in the chemical reactions among debris in hightemperature water environment on the head loss of strainer.
d Analysis of Downstream In-vessel Effects
The impact of the blockage at core inlet on the long-term core cooling and therisk of the debris and chemical deposits adhered to the fuel assemblies oraccumulated at the structure interval of fuel assemblies to damage the fuel cladding
integrity should be evaluated via proper experiments and/or theoretic analysis.
e Analysis of Downstream Ex-vessel Effects
It should be evaluated via analytical methods that the malfunction of safetysystem caused by the tiny debris (fibres, particles) and chemical product through theIRWST strainer will not occur, such as the blocking and wearing of downstream pumps,valves, heat exchangers, orifices etc.
4Regulatory positions of member states

Argentina
According to ARN experience, the main safety concerns about long-term
recirculation cooling following a LOCA are LOCA-generated and pre-LOCA debris
materials transported to the emergency core cooling strainers, the containment spraysystem (CSS), and the reactor core, resulting in adverse heat transfer, blockage, orwear effects or some combination of all three effects.
ARN’s expectation in this regard, is that the HPR-1000’s Licensee evaluates debris
generation, debris transport, upstream and downstream effects, and attendant
blockage of emergency core cooling strainers to ensure that they do not jeopardise
the ability of the system to provide long-term, post-LOCA core cooling.
The plant’s potential debris sources must be justified and further evaluated. Thesesources may include, but not limited to, insulation materials (e.g., fibrous, particulate,
4Design-Specific Common Position
CP-HPR1000WG-02 FOR PUBLIC USE
Date: August 2022
Validity: until next update or archiving
Version: 1and metallic), fire barrier materials, filters and other fiber-bearing materials, latentdebris, shielding blankets, corrosion products, chemically reactive materials and theirreaction products, and paints or coatings.
ARN agrees that the practice to replace fibrous thermal insulation materials withRMI in any ZOI (zone of influence) reduce the impact of the debris source upon thestrainer performance. However evaluation of HPR-1000 strainer performance must bebroader demonstrated including break selection, debris characteristics, debris
transport, net positive suction head (NPSH), upstream effects, etc.
China
China's nuclear safety regulations require that in the LOCA, debris generated by
the LOCA impact should be reduced to avoid excessive blockage of debris on thesump strainer, and excessive accumulation of debris passing through the strainer into
the core active area, which could adversely affect the long-term core cooling andto ensure the heat removal capability of the core and containment.
NNSA considers the containment sump strainer as a very important nuclear safetyissue, and it is critical to the control of related materials that can generate incontainment debris source items. RMI should be used as in-containment thermal
insulation materials, only certified coatings are allowed to be used and the use ofaluminum-containing materials is limited. The licensee is also recommended to reducethe in-containment amount of debris that migrates to the strainer and enters the coreby maintaining a high level of in-containment cleanliness to limit the potential debris
amount.
However, NNSA believes that the above measures cannot eliminate thegeneration of in-containment debris and its adverse effects completely.
Therefore, the licensee of HPR1000 are required to demonstrate that the NPSH
margins of the pumps and the capacity of long-term core cooling can be ensured
from the aspects of sump strainer performance, downstream effects and reliable heatremoval from the core via experiments and analytic methods, so as to meet relevant
nuclear safety requirements.
South Africa
NNR considers the selection of materials related to debris generation after LOCA
in-containment as an important consideration in determining the source items ofdebris, for improving the post-LOCA strainer performance and for minimising adverse
downstream effects in-vessel after LOCA.
In addition to controlling materials that can generate debris source items in thecontainment, examples of further measures that could be considered are:
When considering the layout and configuration of the containment, theminimisation of water retention in-containment to facilitate water andcondensates flowing back to the containment sumps.

5Design-Specific Common Position
CP-HPR1000WG-02 FOR PUBLIC USE
Date: August 2022
Validity: until next update or archiving
Version: 1

For a spray system designed to operate in a recirculation mode, the spraynozzles should be designed to prevent clogging by pieces of debris that canreach them through the intake screens and filters.

A cleaning system for the filters should be installed, taking into account the large
uncertainties about the types and amount of debris that could clog the filters.

The reduction of the risk of excessive blockage of the IRWST strainer and of loss oflong-term core cooling must be demonstrated by experiments and analytic methods.
United Kingdom
In the UK there is a legal requirement to reduce risks so far is reasonably
practicable. ONR agrees that to reduce the risks associated with debris in the IRWST
during accidents the focus should be on the selection of in-containment materials.
The UK Requesting Party for GDA has modified the generic UK HPR1000 design toreplace all in-containment fibrous insulation with Reflective Metallic Insulation,
progressing a “zero fibre” philosophy. Although the "zero fibre" approach does notcompletely eliminate the risks associated with blocking the strainer or downstream
effects, ONR considers that the significant safety benefits for a new reactor design areapparent. Further work is required to develop qualification testing associated withcontainment debris and the filtration system and to understand the implications of thedesign choice on other factors (e.g. chemistry effects). Much of this work can only beperformed once detailed design of the insulation and cable tray wrapping iscomplete.
5Common positions

HPR1000 relies on ECCS to maintain emergency core cooling and the incontainment materials that can generate debris (thermal insulation materials,coatings, aluminum-containing materials and potential debris, etc.) have impact on
the design of strainer and core cooling. Based on the high level of regulatory
requirements and the consideration of the design characteristics of HPR1000, theMember States of the HPR1000 Working Group have developed the common
positions on the selection of the in-containment materials and the performancerequirements of the IRWST strainer.
1Based on the regulatory practices of the Member States, it is agreed that theselection of in-containment materials is the primary factor in solving the issue ofthe IRWST strainer blockage, and the amount of debris that transport to thestrainer and vessel should be reduced as much as possible.
a Thermal insulation material. Thermal insulation material debris will begenerated by the impact of the jet fluid in LOCA. Therefore, insulationmaterials that can reduce the generation and transport of debris should
be used as far as possible in the containment. Due to high density, it is noteasy for RMI debris to transport to the strainer. The use of RMI can effectivelyreduce the amount of debris transported to the strainer after LOCA.

6Design-Specific Common Position
CP-HPR1000WG-02 FOR PUBLIC USE
Date: August 2022
Validity: until next update or archiving
Version: 1b Coating materials. Due to impact or accidental conditions after LOCA, thecoating materials may fall off and form debris. Qualified coatings shall be
used in the containment to reduce the generation of coating debris.
c Aluminum-containing materials. After LOCA, the aluminum-containing
materials will be sprayed or immersed by alkaline solution, and thechemical reactions will produce chemical deposits. The use of aluminumcontaining materials in the containment should be limited. It is a goodpractice to replace the aluminum-containing equipment nameplates in
the containment with that aluminum free.
d Potential debris. The potential debris refers to the dust and foreign matters
in-containment. The licensee is recommended to limit the amount ofpotential debris by maintaining a high level of in-containment cleanlinessand removing the foreign matters left in the construction andmaintenance process.
1Although the above requirements can significantly reduce the amount of debris
generated in the containment after LOCA, but the in-containment debris
cannot be eliminated completely.

Therefore, tests and analysis including upstream analysis, head loss tests of strainer,
chemical effects tests and analysis of downstream in-vessel and ex-vessel effects areneeded to demonstrate that the NPSH of ECCS pumps and the capacity of corecooling are ensured.
a Analyse the source items of in-containment debris after LOCA and determine
the amount of debris transported to the strainer conservatively.
b Ensure proper NPSH for ECCS pumps by ensuring adequate filtering area ofstrainer and determining the maximum head loss of strainer by tests.
c Demonstrate that downstream equipment such as ECCS pumps, heatexchangers are still capable of fulfilling their functions under the influence ofbypass debris.
d Perform the head loss analysis of fuel assemblies and evaluate the impact on
the core heat removal because of the accumulation on the fuel assemblies forthe debris passing through the strainers.

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Design-Specific Common Position
CP-HPR1000WG-02 FOR PUBLIC USEDate: August 2022
Validity: until next update or archiving
Version: 1Contributors to drafting and review
Chai Guohan
Yang Peng
Liu Zejun
Li JuanZhao Danni
Robert WhithamMark Drummond
Aidan Parkes
Jean Joubert
Adriana Politi

NNSA, China
NNSA, China
NNSA, China
NNSA, China
NNSA, China
ONR, UK
ONR, UK
ONR, UK
NNR, South Africa
ARN, Argentina

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